AGL: Of an altitude, above ground level. Traffic pattern altitudes are specified as AGL. In airport weather reports, cloud bases are reported as AGL, whereas in area forecasts, which cover a broad area of varying terrain, cloud bases are forecast as MSL. Obstruction heights are usually given as both, so the pilot can visualize how tall the obstruction is, and can know how big the indication on his altimeter has to be before he's assured of clearing it.
ATC / Air Traffic Control: This is divided into various areas of responsibility: enroute (Center), terminal area (Approach and Departure Control) and local (Tower and Ground Control). Air traffic controllers issue instructions which pilots are required to obey, for the purpose of ensuring an orderly traffic flow and keeping aircraft from colliding. More here.
Aileron: Ready-made definition here. See also flight control surfaces.
Airframe: The structure of an airplane—fuselage, wings, and tail—not including the engine(s) or instrumentation.
Airway: A navigation route through the air. The first airways consisted of rotating beacons in the Northwest of the U.S.A., so the mail could move at night without the pilots blundering into mountains in the dark. A few of those beacons still operate in the passes. Next came the low-frequency four-legged radio ranges, which could be followed even through the clouds. Today, the basic airway structure is provided by VOR's, though that structure is gradually being superseded by airways predicated on area navigation equipment such as GPS.
Altimeter: An instrument which indicates altitude. It's nothing but a sensitive aneroid barometer, really. If you have a "home weather station" hanging on your wall, you need to adjust the barometer for your home's elevation so it shows barometric pressure corrected to sea level. An altimeter is (generally—see FL) adjusted to the current barometric pressure (corrected to sea level) so it shows the actual altitude (with minor variations caused by temperature).
Angle of attack: The angle between the wing and the relative wind. At a given speed, the higher the angle of attack, the more lift is produced, until the airflow breaks down and the wing stalls. But also, the higher the angle of attack, the higher the induced drag, because the lift vector is pointing more and more rearward relative to the airplane's motion. The slower an airplane flies, the greater the angle of attack needed to produce enough lift to support the airplane's weight. The heavier an airplane, the greater the angle of attack needed at any given speed. Clearly, there is a speed below which the airplane can't fly, because the wing will stall before it produces enough lift. That speed is the stall speed, and the heavier an airplane is loaded, the higher that speed will be. This only brushes the surface of this most crucial aspect of aerodynamics. Wikipedia has a more detailed, but still inadequate entry.
Approach Control: Ready-made definition here.
Area navigation: See RNAV.
ATIS / Automatic Terminal Information Service: Rather than have the tower repeat "the numbers" for every arriving and departing aircraft—winds, weather, active runway, approach to be expected, and NOTAMs, e.g. "Taxiway Bravo closed between Taxiways Mike and November for construction; unlighted tower 2 miles south of the airport", etc.—this information is recorded and broadcast repeatedly on a dedicated frequency. As you come within range of your destination, you listen to this frequency on your number-two radio and record or memorize "the numbers". You'll probably have to listen to it several times, because ATC will almost invariably have something to say on #1 and drown out part of the ATIS message. But then when you contact Approach Control or the Tower for the first time, you can say you have, e.g., Information Whiskey. If the numbers have changed in the meantime, Tower might say, "X-Ray's current now, report when you have it." Or she might just say, "Roger", and you're all set.
APU / Auxiliary Power Unit: An onboard device driven by a (relatively) small engine, for supplying electrical power to an aircraft. It can power the aircraft's systems on the ground when the engines aren't running; it can be fired up in flight to replace an engine-driven generator which has failed; it can often be started by the aircraft's battery and then used to start the engine(s), which the battery couldn't handle. This is not something you'd find on a light airplane.
Avgas: Aviation gasoline.
Avionics: Electronic equipment used in an aircraft: radios, transponders, radar, autopilots—the "goodies".
Avionics master switch: There are times, such as when attaching a GPU or when starting an engine, that the voltage in an aircraft's electrical system can fluctuate dramatically. At those times it's safer to have all the avionics switched off. Rather than having to switch them off and then back on individually, it's much more convenient to have one switch to rule them all: the avionics master. Each device can be switched on or off individually, but where an avionics master switch is installed, those individual switches are rarely used—except for the one on the autopilot. (See also Battery master switch.)
Bank: The angle between an airplane's wings and the horizon, as seen from directly ahead or behind.
Battery master switch: Before you can do anything with an airplane which requires electricity, like start an engine, you need to connect the battery to the aircraft's electrical system. In a car, this is the first click of the ignition key. In an airplane, it's the battery master switch. And just as, in a car, that first click of the key powers a few devices which draw current from the battery, so, in an airplane, there'll usually be a gyroscope and maybe a fan or two that come on with the switch. So if you forget to turn off the master switch before you leave the airplane, you'll find your battery dead in the morning. Ask me how I know this. (See also Avionics master switch.)
Beta: Flatter-than-normal propeller pitch. A turbine engine idles at 50 or 60 per cent of maximum RPM, and if you couldn't reduce a turboprop's propeller pitch below the in-flight minimum, you'd wear out your brakes trying to keep from galloping down the taxiway. The beta range is from slightly positive to slightly negative pitch.
Block altitude: A range of altitudes. A clearance to "maintain block 9,000 to 13,000 feet" allows the pilot to fly, protected from other traffic, at 9,000 feet, or at 13,000 feet, or at any altitude in between.
Boundary layer: Ready-made definition here.
Carburetor ice: For those of you too young to be carburetor-literate, I'll mention that, while a fuel-injection system sprays fuel under pressure into the engine's intake air, a carburetor draws fuel into the intake stream using the lowered pressure in its narrow throat, or venturi. When you lower the pressure of air, of course, you cool it, and if the air is saturated, moisture will condense on the carburetor throat. If the air temperature in the venturi is below freezing, the moisture will condense as ice and gradually choke off the air flow. Airplanes with carburetors are provided with a way of directing intake air through a shroud around an exhaust pipe, so it's hot as it enters the carburetor, and still warm enough to melt the ice even after the venturi effect has cooled it. But if the pilot is asleep at the wheel and the ice builds up until the engine is barely running before he applies carburetor heat, the exhaust pipe won't be hot enough to do the job.
Very early in my career as a ferry pilot I was flying, as I recall, a Grumman Tiger across the Atlantic. I was just passing 30° West Longitude—which is to say I was halfway across—when the engine began running rough. I changed fuel tanks, adjusted the mixture, checked the mags—nothing helped. I wondered, "Am I going to die out here?" I was desperately searching the instrument panel for inspiration when I noticed a little black knob labeled "Carburetor Heat". Oh, yeah! Carburetor! I'd been flying turboprops for a dozen-plus years before I started ferrying, and carburetors had drifted away from the center of my consciousness. I pulled that little black knob and the engine started choking and sputtering as if it were going to quit outright. Boy, was I relieved! The sputtering meant the ice was melting, and that meant carburetor ice was the problem. Whew!
I was flying in snow when that happened. We're taught that carburetor ice is most prevalent around 10°C (50°F) because air at that temperature can hold a fair amount of moisture and can be cooled below freezing in the venturi, while colder air is too dry to be much of a problem. But I've had my most notable experiences with carb ice in snow, and I imagine the snowflakes impacted on the air filter have had water molecules torn off of them by the inrushing air until it's saturated.
Cell: In weather, a single thunderstorm process. A thunderstorm is caused by an updraft which accelerates in conditionally unstable air. When raindrops have grown large enough to fall through the updraft, they drag air with them to create a downdraft which continues to build as more rain falls. The interference between the updraft and the downdraft creates the destructive turbulence that makes thunderstorms dangerous. The image we see on weather radar is the reflection of the rain shaft, and when pilots refer to a "cell", that's usually what they're talking about. A large storm can contain several individual cells in various stages of maturity—a multicell cluster. Wikipedia has more.
Ceiling: Relating to weather, this is the height—AGL—of the lowest layer of clouds that are either broken or overcast, or, if the sky is obscured by surface restrictions to visibility (fog, snow, dust, etc.), the height of the obscuration. Practically, the cloud ceiling limits how high you can climb under VFR, and the reported ceiling lets you know at what altitude you will likely be able to transition from flying by instruments to visual references during an instrument approach.
Center: An Air Route Traffic Control Center (ARTCC). (See ATC.)
Circling approach: An instrument approach which does not line up with the landing runway. It might be an approach to the opposite end of the same runway, or to a different runway, or just to the airport and not lined up with any runway at all. In any case, once achieving visual contact with the runway environment at or before the missed approach point, the pilot must maintain that visual contact at or above the minimum descent altitude while maneuvering to line up with the duty runway. The minimums will be higher for a circling approach than for a straight-in, and you might wonder, why bother? But suppose there's only enough money for one approach at an airport. You can put it on the runway that's usually active when the weather's at its worst, and arriving airplanes can circle for the other runways in better weather. Or suppose there's an airport with a minimal budget near a VOR, but the inbound course from the VOR doesn't line up with any runway. You can get a circling approach to that airport—a whole lot better than no approach at all—without installing any additional equipment. These days, of course, with all the necessary equipment for an approach to any point on the earth orbiting overhead, GPS approaches are proliferating and making circling approaches less valuable than they used to be.
Class A airspace: Airspace in which all aircraft must operate under IFR. In the United States and Canada, this is everything above 18,000 feet.
Clean: Of an airplane, with landing gear and flaps retracted, thus in a low-drag configuration.
Cleared: In reference to a flight operation, having received an IFR clearance.
Cloud coverage: There are five levels of reported or forecast cloud coverage. "Clear" means "no clouds" (yes, I know); "few" means clouds cover up to one quarter of the sky; "scattered" clouds cover from 3/8's to half the sky; "broken" means 5/8's to 7/8's coverage; and an "overcast" covers more than 7/8's of the sky. For practical reasons, these coverages are cumulative as viewed from the ground, e.g. if there are two layers that each cover half the sky, the higher layer will probably be reported as broken.
Clouds: Here's a good, brief treatise on cloud types.
Comm radio: Communications radio. There are usually two these in an airplane—"Comm #1" and "Comm #2"—and each usually includes a Nav radio.
Constant-speed propeller: A propeller whose pitch is adjusted in flight by a governor, so that the engine RPM stays constant.
Contact approach: From the Aeronautical Information Manual, Chapter 5, Section 5-4-24: "Pilots operating in accordance with an IFR flight plan, provided they are clear of clouds and have at least 1 mile flight visibility and can reasonably expect to continue to the destination airport in those conditions, may request ATC authorization for a contact approach...." Note that, unlike a visual approach, the weather doesn't have to be VFR; and that ATC can't assign a contact approach—the pilot has to request it. And the airport must have a functioning instrument approach available to the pilot. The contact approach is basically a time-saver: as a pilot is approaching an airport in bad weather—but not too bad—he (or she) breaks out of the clouds and realizes he can safely just proceed to the airport and land, without flying the entire approach procedure; and he asks for clearance to do so, i.e., a contact approach.
Departure Control: Ready-made definition here.
Dirty: Of an airplane, with landing gear and/or flaps extended, thus in a high-drag configuration.
DME / Distance Measuring Equipment: Ready-made definition here.
Deviate: To depart temporarily from a navigation route in order to go around a thunderstorm or a cumulus cloud, for the sake of the safety of the flight and/or passenger comfort.
EFIS / Electronic Flight Instrument System: Display screens which replace conventional instruments. They usually consist of a Primary Flight Display (PFD)—or, in large airplanes, a PFD for each pilot—and one or more Multi-Function Displays (MFD). Attitude, airspeed, altitude, and vertical speed—at a minimum—will be grouped on the PFD. Course and heading are often shown on the PFD as well. The MFD will show either navigation information (course, heading, moving map, radar and/or traffic information overlaid on the moving map, etc.) or engine parameters. The displays are highly configurable. Checklists and trouble-shooting flowcharts are a couple of the options. Redundancy is achieved by the ability to combine PFD and MFD information on one display if the other fails. Pilots who have used EFIS tend to refer to conventional round instruments as "steam gauges". More information here.
Elevator: Ready-made definition here. See also flight control surfaces.
File: As a verb, to file a flight plan. Used this way, "file" generally refers to an IFR flight plan, which constitutes a request for an enroute IFR clearance at a given time, to a given destination.
FAF / Final approach fix: The fix at which the final approach segment of an instrument approach begins. If an airplane has retractable landing gear, it's extended here (if it's not already down); the landing checklist is completed; and the aircraft is stabilized in the configuration it will retain throughout the rest of the approach. On a precision approach, all this happens at glideslope intercept, and though that point isn't commonly referred to as a final approach fix, it serves as one.
Fix: A navigational point. This might be a radio-navigational station such as a VOR, or point defined by bearing and distance from one or more such stations. "Fix" rarely refers to a geographical location.
FBO / Fixed-base Operation: The first commercial operators in aviation were the barnstormers, who would sell rides in their airplanes, flying out of a convenient pasture, only remaining in one place until the interest dwindled as the novelty wore off before moving on to the next likely spot. After actual airports came into being, someone had the startling idea that he might make a living not only offering rides, but selling fuel, giving flight lessons, providing maintenance, renting hangar space, etc., all from a single airport. We still use the name "Fixed-base Operation" for such businesses.
Fixed-pitch propeller: A propeller whose blade angle—"pitch"—is not adjustable. Such a propeller is lighter and less expensive than a constant-speed propeller, but it's not as efficient. During a climb, because of the relatively low airspeed, a fixed-pitch prop will drag the engine below the RPM at which it can produce the most power; whereas at high-speed cruise, the engine will be operating above its ideal RPM.
FL / Flight Level: Indicated altitude with the altimeter set to standard pressure, i.e. 29.92 inches of mercury, or 1013.2 millibars. Altimeters are used primarily for vertical separation, either from the terrain or from other airplanes. If you're interested in how high you are above the hilltops, you want your altimeter set to local pressure (corrected to sea level), and you'll have to update that as you fly along. If you're well above the terrain, and are interested in being well-separated from any airplanes on opposite-direction courses, then it's good to know that all airplanes are using the same altimeter setting. That's what flight levels are all about. In the U.S. and Canada, flight levels begin at 18,000 feet. That is, you don't fly at, say, 19,000 feet, but at FL190. You may be higher or lower than 19,000 feet above mean sea level, but you know you're a thousand feet above any airplanes flying at FL180, and a thousand feet below the ones at FL200. Flight levels begin much lower in Europe, at from 4,000 to 7,000 feet. Airplanes flying at night or in clouds maintain clearance from high terrain by using only the "lowest safe flight level" for the current barometric pressure.
Flap: A portion of the trailing edge of a wing, which can be deflected downward to increase the curvature ("camber") of the airfoil, thus increasing both lift and drag. Many flaps also extend behind the wing as they deflect, increasing wing area as well as camber. They are used during landing and takeoff, where lift is precious, and are retracted for cruise, where the added drag is unacceptable.
FPM / Feet per minute: A measure of vertical speed, i.e. climb or descent.
Flight Service Station: Ready-made definition here.
Float: As a noun: one of two pontoons which a seaplane (a "floatplane") uses to land on the water. Sometimes retractable landing gear is fitted into the floats, which makes the floatplane amphibious. As a verb:
Fog: For a quick summary of fog types, go here. For more details, check out the very interesting Wikipedia entry.
Fuselage: The (roughly) cylindrical body of an airplane, excluding the wings and tail.
G: A multiple of the force of gravity. Sitting on your sofa, you feel one G pressing you into the seat. You'd feel the same 1 G sitting in an airplane in straight and level flight. But in a turn, "centrifugal force" is added in, and in a level turn with a 60-degree bank angle, that force equals the force of gravity, so you'd feel 2 G's. In turbulence you (and the airframe feel more or less than 1 G; just how much more or less depends on the severity of the turbulence.
Gear: Of an airplane, the landing gear.
Glideslope: A radio navigation aid used to provide vertical guidance for instrument approaches. The glideslope provides the "precision" in "precision approaches". It consists of an antenna abeam the touchdown zone of a runway which radiates a narrow beam toward approaching aircraft at an angle of (typically) three degrees to the horizontal. It also radiates unwanted beams at steeper angles, so it's wise to intercept a glideslope from below.
Ground Control: Ready-made definition here.
GPU / Ground Power Unit: A device (sometimes just a battery) for applying external electrical power to an airplane on the ground. It's used to power the airplane's systems when the engines aren't running, or to start the engine(s). Large airplanes generally need a GPU or an APU for every start. Smaller ones only need it when their batteries are weak.
GPS / Global Positioning System: I think most people know what GPS is by now. If you're vague about the meaning, or want to know more, the Wikipedia entry is likely to exhaust your curiosity.
Ground Clearance switch: A switch which turns on the #1 Comm radio, even with the aircraft's battery master switch off. This allows communications on battery power alone, without the battery being run down by the various fans and gyroscopes which are activated by the master switch, and is most often used, as the name suggests, to obtain an IFR clearance before starting the engine(s).
HF / High Frequency: A radio band used in aviation for long-range communications. The Wikipedia entry has the details. Over populated land masses the usual band is VHF, which is much less subject to atmospheric or man-made interference than HF, so communications are relatively clear and easy to understand. But VHF signals aren't typically refracted from the ionosphere, so its propagation is limited to, essentially, "line of sight", and once you've followed the curvature of the earth beyond the horizon from whoever it is you want to talk to, your VHF radios won't help you. Before you pass out of VHF range, on an ocean crossing, you'll be assigned a primary and a back-up HF frequency for your initial contact. Various factors determine which particular HF frequencies will be strongly refracted at a given time, but in practice we expect to use higher frequencies during the day and lower frequencies at night, and we search around among the available frequencies to find the one with the best propagation and the least noise.
Holding fix: A navigational point at which a holding pattern has been established.
Holding pattern: A procedure for interrupting the progress of a flight, most often used because of congestion up ahead. Formally (i.e. under IFR), it consists of a racetrack pattern which begins at a fix which is crossed on a given course. Immediately after crossing the fix, the pilot starts a right-hand standard-rate turn of 180 degrees (a course reversal), after which he flies in a straight line for one minute and then makes another standard-rate course reversal so as to roll out on the inbound course to the fix. The pilot is expected to compensate for wind by adjusting the heading and time of the outbound leg such that he intercepts the inbound course exactly upon completion of the second turn, and crosses the holding fix exactly one minute later. If a pilot expects a lengthy delay he'll usually ask for and receive approval for longer legs. More information can be found at the Wikipedia entry, which is informative and accurate.
Hot mike: The cabins of light airplanes are very noisy in flight, so most airplanes these days have an intercom, and a headset for each occupant. The headsets consist of full-coverage earphones and a boom mike, with "push-to-talk" (PTT) switches for the pilot and copilot. The boom mikes are "hot", meaning they will pick up whatever is said and send it over the intercom, unless the speaker is holding down the PTT switch, in which case what he says will be transmitted instead. It's standard design to be able to change the configuration of the intercom, such that either all occupants can talk to each other, or the pilot and copilot can talk to each other and the passengers can talk among themselves, but the two groups are isolated from each other so passenger chatter won't interfere with the crewmembers' communications with ATC. Usually the pilot can also be isolated from everyone else, for single-pilot operations.
Ice: Ice is a killer. Ice and thunderstorms are the Cthulhu and Balrog of aviation. Sure, pilots fly their airplanes into the ground with depressing frequency, but they have to do that themselves. The terrain won't reach up and get you. Ice and thunderstorms lurk in the very air we breathe and navigate, often hidden in ambush. They are the demons that haunt our nightmares—or, anyhow, our flight planning.
There's such a thing as carburetor ice, but what we're talking about here is airframe ice. Water expands when it freezes. It can't freeze unless it does expand, because the hexagonal ice crystals take up more room than the unorganized mosh of molecules in liquid water. So a droplet of water floating in the air, compressed by surface tension, can be cooled well below the freezing point yet remain a liquid for a long time unless it's disturbed. And a good way to disturb it is to hit it with an airplane.
Clearly, you can avoid airframe ice by never flying in a cloud that's below freezing. But if you do that, you'll cancel flights you could have made safely, because not all such clouds contain super-cooled water droplets: another way for a droplet to freeze is for it to encounter an ice nucleus, in which case it will crystallize on that foundation; once this process begins in a cloud, it will accelerate, so the longer a cloud has been hanging around, the fewer super-cooled liquid droplets it will contain, and the less ice will adhere to an airplane flying through it. (This is why cumulus clouds tend to have more ice than stratus clouds, since cumulus clouds are formed by lifting, and the droplets in them have only recently arrived at their present altitude and temperature.)
Another thing that makes forecasting icing encounters problematic is snow. Snow looks like clouds—it doesn't look exactly like clouds, but it takes a fair amount of experience to tell the difference—but snow won't stick to the airframe. It might clog up a forward-facing opening like a pitot tube or a fuel tank vent, and for that reason, among others, most pitot tubes are heated and most fuel vents are located such that they're not susceptible to clogging—but the most you'll get on the airframe itself is a faint white stripe along the leading edge of the wing, where the airflow divides between the upper and lower surfaces.
There are two kinds of airframe ice: rime ice and clear ice (and mixed, i.e. both). Rime is formed from tiny droplets that freeze instantaneously. It's rough, and opaque because of trapped air. Clear ice is clear and smooth because it's formed from large droplets that flow a bit before they freeze. Ice adds drag and destroys lift, because it distorts the carefully designed shape of the airfoil. If enough ice forms, it will add significant weight. Rime ice is rougher, and sometimes it can build out into odd projections—but clear ice is the more dangerous, because when you pick it up, you usually get a lot in a hurry.
IAS / Indicated airspeed: The first measurement of airspeed was the feel of the wind on the pilot's face. Nowadays we measure the difference between ram air pressure in the forward-facing pitot tube, and static air pressure at one or more static vents located at neutral-pressure points on the airframe. Neither of these is actually a measurement of speed, but they're related to speed, and airspeed indicators are calibrated such that for any given pressure differential, they show the speed at which the airplane would be moving through the International Standard Atmosphere at sea level. At higher altitudes (or temperatures) the pressures are lower, and the indicated airspeed will be lower than the true airspeed. But the airspeed indication is still a direct expression of the pressures working on the airframe, and thus is always useful to the pilot.
Initial approach fix: Ready-made definition here.
IFR / Instrument Flight Rules: These are flight rules under which a pilot can operate an aircraft even if he (or she) can't see where he's going, e.g. in clouds or heavy precipitation. To operate under IFR a pilot must obtain and adhere to a clearance from Air Traffic Control. All airplanes operating under IFR will be kept from running into each other by adherance to their clearances or by following instructions from ATC (which are also clearances, actually). But if the airplane is flying in good weather, the pilot must look out for airplanes operating under VFR, so as to avoid them visually. Pilots flying in Class A airspace (everything above 18,000 feet, in the U.S. and Canada) must all operate under IFR.
IFR clearance: An authorization to fly under IFR. This might be a full enroute clearance which includes, typically, the route to fly, the initial heading and altitude after take-off, the next altitude clearance to be expected and how soon to expect it, and the transponder code; or it might be merely an authorization to climb or descent to a different altitude or to proceed directly to an enroute fix.
ILS / Instrument Landing System: The ILS consists of electronic lateral and vertical guidance to the runway, and runway environment lighting. It's a "precision" approach. by virtue of the vertical guidance, which "non-precision" approaches lack. The electronic ILS signal consists of a localizer radiating from an antenna at the far end of the runway, precise enough to put your nosewheel on the centerline, and a glideslope radiating from an antenna beside the runway, a thousand feet from the threshold, which brings you down at (usually) a three-degree descent angle. The runway environment lighting consists of some or all of: runway edge lights, approach lights, flashing sequential lights (the "rabbit"), centerline lights, and touchdown zone lights. With all those lights available, the electronic signals specially certified, special equipment in the airplane, and special training for the crew, an ILS can be flown coupled (i.e. by the autopilot) all the way through touchdown.
IMC / Instrument meteorological conditions: In the clouds. More generally, those conditions under which, because of restricted visibility, the pilot has insufficient visual references by which to control the aircraft. Now, if you're flying over the ocean at night under an overcast, you can't see the horizon, you can't see the stars, and I guarantee you can't control the airplane by visual references—but, strictly speaking, you're not "IMC" because there's no restriction to visibility.
Instrument approach: An instrument approach is a procedure for letting down through the clouds to land on a given runway, or, in the case of a "circling approach", on any runway at a given airport. These approaches are carefully surveyed by a country's aviation authority (the FAA, for the United States) to guarantee that if you conform to the headings, altitudes, and routes specified in the approach, you won't hit anything on the ground. The types of equipment on the ground and in the aircraft used in the approach (now that GPS approaches have become common, it would be better to say "inside and outside the aircraft") vary in their accuracy, and this variation is reflected in how close you can approach the runway with that vital guarantee intact.
There are two main types of approach—"precision" and "non-precision"—the difference being that a precision approach has vertical guidance to the runway on the final approach segment. A typical non-precision approach will lead you to a missed approach point 400 feet above the runway, with one mile visibility required. Those numbers will be higher—sometimes much higher—in the case of difficult terrain; occasionally, where the terrain is favorable, they'll be a bit lower. The simplest precision approach, a Category I ILS, will have "landing minima" of, typically, 200 feet and one-half mile. Higher category ILS's have lower minima, all the way to zero-zero for a Category IIIc ILS, but they require specialized equipment in the airplane and on the ground, and special training for the crew, and they lie outside the operating environment of a ferry pilot flying alone in little airplanes.
ISA / International Standard Atmosphere: A standardized set of conditions for measuring performance, which, in the troposphere, comprise a barometric pressure of 29.92 inches of mercury (1013.2 millibars), a temperature of 15°C at sea level, and a decrease in temperature ("lapse rate") of 2°C per thousand feet of altitude.
ITT / Interstage Turbine Temperature: In a turbine (jet or turboprop) engine, the temperature between rotors in the "hot section" of the engine. This is watched carefully during engine start, since if the airflow through the engine is too low (low turbine RPM or tailwind), the ITT can quickly exceed the limit.
Jet A: The standard jet fuel in the United States. More information here.
Jet A-1: The standard jet fuel outside the United States. It has a lower freezing point than Jet A: -47°C as opposed to Jet A's -40°C. More information here.
KIAS: Indicated airspeed, expressed in knots.
Knots: Nautical miles per hour. A nautical mile is defined as essentially 1 minute of latitude—the precise definition results in a length of 6067 feet. Thus, 100 knots equals 115 statute miles per hour, or 185 kilometers per hour. The name comes from the earliest method of measuring a ship's speed: a sailor would toss overboard a log (hence "logbook") to which was attached a rope with knots in it. As the ship sailed away from the floating log, the sailor would count the number of knots which passed through his fingers in a fixed period of time. Timing knots spaced fifty feet apart with a half-minute sandglass gives nautical miles per hour. More information here.
KTAS: True airspeed, expressed in knots.
Landing: You might think that when a pilot comes in for a landing, he just drives the airplane smoothly onto the ground. That's approximately what happens, but if he (or she) does that at too high a speed, the wings will still be producing significant lift, which will reduce the traction of the tires and make it difficult to control the airplane—something like driving on an icy road. If, after such a landing, the pilot allows much of the airplane's weight to be concentrated on the nosewheel, the result is something called "wheelbarrowing", the consequences of which tend to be both dismaying and expensive.
Lean: To adjust the mixture control in a piston-engine airplane so that less fuel is mixed with the intake air. The air up high is thinner than the air down low (yes, I know: you knew that). At any altitude above sea level, the pilot needs to lean the mixture to keep the ratio of fuel to air near the optimum for the power setting. The higher he (or she) flies, the leaner he needs the mixture to be.
Localizer: A radio navigation aid used for instrument approaches. It consists of an antenna array at the far end of the runway, and will guide an aircraft not just to the runway but to the centerline. It's a component of the ILS, but where terrain or cost or other considerations prevent the addition of a glideslope, it makes for a relatively precise "non-precision" approach.
Log: To record flight time, or an aspect of a flight, in a record book (the logbook). You might log a flight, or the time spent at night or in IMC during a flight, or the number of landings performed during a training flight, etc. The original "logbook" was, of course, the record of the castings of a ship's log in order to measure its speed.
Magneto: Ready-made definition here.
Manifold pressure: The pressure in a piston engine's intake manifold, downstream of the throttle. If the pitch of an airplane's propeller can be adjusted in flight, then RPM alone isn't a sufficient indication of engine power. The additional information needed is provided for piston engines by a manifold pressure gauge. With the engine running, if the throttle is closed, the manifold pressure will be low, less than ten inches of mercury. If it's wide open, the manifold pressure will be the maximum available, less losses past the throttle valve itself. In a "normally aspirated" engine, this will be the ambient pressure at the airplane's altitude; if the engine is turbocharged, it will be the "deck pressure", that is, the pressure provided by the turbocharger in the intake manifold, upstream of the throttle. It may have caught your attention that RPM plus manifold pressure really only indicate the conditions available to the engine for producing power. If the engine is starved for fuel, or the ignition fails, the RPM and manifold pressure won't change—but the pilot will be alerted by the reduction in engine noise and, before long, a loss of airspeed and/or altitude.
Mesocyclone: A rotating updraft within a severe thunderstorm. If you're a pilot, those few simple words will cause sweat to break out on your forehead, and your hair to stand on end. A mesocyclone is the precursor of a tornado. If you get within twenty miles of one in an airplane, you're way too close. If you're interested in more information, with links to follow for even more, I think the Wikipedia entry is pretty good.
Met: Short for "meteorological".
MDA / Minimum Descent Altitude: Ready-made definition here.
MEA / Minimum Enroute Altitude: The lowest available altitude on an airway. This is generally the lowest altitude which will provide both safe clearance from the terrain and reliable reception of the (earth-based) radio navigation aids—such as VOR's—which define the airway. In Europe and Africa, some MEA's are much higher than would seem to be necessary.
Minimums: Or, more correctly but less commonly, minima. How low you can go on an instrument approach. The minima are expressed in height above touchdown and visibility. Thus, with landing minima of 400 & 1, the pilot can descend to 400 feet above the runway, and must have at least one statue mile visibility, that is, be able to establish visual contact with the runway environment from one mile out. Since the pilot is looking at an altimeter, the descent minimum will be expressed in the instrument approach procedure as an altitude, so a pilot landing at an airport with an elevation of 1200 feet and minima of 400 & 1 will have a minimum descent altitude of 1600 feet.
MAP / Missed approach point: That point in an instrument approach procedure where the pilot must either transition to visual references to complete the approach and landing, or begin the missed approach procedure.
Missed approach: Also called a "go-around", or a "rejected approach"; in the U.K., an "overshoot". An instrument approach guides the pilot to a point relatively near the ground from which he must transition to visual references in order to continue to the runway and land. If visual flight conditions don't prevail at that missed approach point, he must begin the missed approach procedure, which guides him back up and away from hard things he doesn't want to hit with his airplane, and out of the way of other airplanes. The missed approach procedure commonly ends at a holding fix, where the pilot can fly a holding pattern while he figures out what to do next—in case he had failed to decide what to do in the event of a "miss" before he ever began the approach.
Mixture control: In the old days, if you moved from Florida to Colorado, you'd have to take your car to the shop to have the carburetor adjusted for the higher altitude. That's because, in the thinner air, the mixture of gasoline and air would be too "rich" for optimal combustion. Airplanes typically change altitude that much every time they fly, and the ones with piston engines need a way to adjust the mixture to compensate. Some of the newest designs have digital engine controls, like the newest cars; but the mixture in most piston-engine airplanes is manually adjusted by a push-pull knob or a lever.
MSL: Of an altitude, above mean sea level—as opposed to AGL.
Nautical mile: A nautical mile is defined as essentially 1 minute of latitude—the precise definition results in a length of 6067 feet, or 1.15 statute miles.
Nav radio: A navigation radio. In current practice, usually a VOR receiver: even though GPS is the primary navigation technology for modern airplanes, it's commonly included in addition to two VOR receivers—"Nav #1" and "Nav #2"—which are themselves typically coupled with a Comm radio in what's called a NavCom.
NDB / Non-directional beacon: A radio navigation aid which broadcasts an undifferentiated signal in all directions. Equipment aboard the aircraft can determine the relative bearing to or from the beacon (e.g. 30 degrees left of the nose), but only by combining that information with the aircraft's heading can the absolute bearing be determined (the beacon's 30 degrees left of the nose and we're heading due east, so the bearing to the station is 060). NDB's operate at low frequency, so the signal bounces off the ionosphere and can be received even when the station is beyond the earth's curvature. Powerful NDB's, such as the one at Prinz Christiansund at the southern tip of Greenland, or the one at Flores, the westernmost island of the Azores—or even the Droitwich BBC transmitter in Worcestershire (a commercial broadcast station is, after all, a non-directional beacon)—were very important to me before the advent of GPS. But most NDB's these days are low-powered ones used as components of instrument approaches.
Non-precision approach: An instrument approach which has no vertical guidance. The pilot will descend on the inbound course to the minimum descent altitude, hoping to "break out"—i.e. achieve visual contact with the runway environment—before he reaches it. If he doesn't, he can maintain the MDA to the missed approach point, at which, if he still can't see the runway, he must initiate the missed approach. Non-precision approach minima are typically 400 & 1.
NOTAMs / Notices to Airmen: These are notifications of recent or temporary changes to the aviating environment of which the pilot might not otherwise be aware. Many are trivial, such as a change of one degree in the course of an airway. Some are not. I learned this to my sorrow, early in my career, when I carried a plane-load of paying passengers toward an airport which had been closed for a week. (I told them of the closure, and took them to a nearby one which served almost as well. I somehow failed to inform them just how long the airport had been closed.) Check your NOTAMs. You will—eventually—be glad you did.
On top: Flying above the highest significant layer of clouds. If you have a few cirrus clouds above you, you're still on top. This is used mostly in reference to stratus clouds, since their tops are level. If a pilot is flying above the highest cumulus tops, he's more likely to say he's "above the tops" than "on top". Embedded in this phrase is one of the great benefits of being a pilot. Sometimes there'll be a long stretch of gloomy weather: low clouds, rain, cranky people. But if the sun won't come to the pilot, the pilot can go to the sun. To take off in dismal weather, climb through sodden clouds, then suddenly break out into brilliant sunshine, bright blue sky, fleecy cloud tops—that's one the great joys of flying.
OAT / Outside Air Temperature: The temperature displayed on the O.A.T. indicator. In a fast airplane this can be several degrees warmer than the True Air Temperature, because of the heat of compression as the air impacts the sensor.
Occluded front: As the air swirls around a low, frequently two fronts will form: the warm air coming up from the south (in the Northern Hemisphere) overtaking cooler air ahead to form a warm front, and relatively cold air rushing in from the northwest, sliding under that warm air to form a cold front. Since cold fronts typically move much faster over the ground than warm fronts, it's not uncommon for the cold front to catch the warm front and push it aloft. The result is an occluded front, or occlusion, and the weather associated with it is a combination of warm-front and cold-front weather. Wikipedia has a bit more, with links and a nice diagram.
P-factor: Ready-made definition here.
Pattern altitude: The altitude at which the traffic pattern is flown. Unless it's specified by the airport management, it's 1,000 feet above the ground for light aircraft, and 1,500 feet AGL for heavy or turbine-powered aircraft.
POH / Pilot's Operating Handbook: A document which contains a general description of the aircraft, limitations, emergency procedures, normal procedures, performance specifications, weight & balance information, systems descriptions and operational details, etc. It's part of the aircraft's required paperwork, and must be on board for flight.
Pitot tube: A forward-facing tube, positioned so its opening is in air undisturbed by the airframe, and which therefore senses the ram-air pressure caused by the passage of the airplane through the air. The sole purpose of this tube is to provide the source for the indicated airspeed measurement.
Precision approach: An instrument approach which has vertical guidance—the "glide slope"—on the final approach segment. The pilot will intercept the glide slope from beneath and follow both it and the inbound course to the "decision altitude", at which point, if he doesn't have the runway environment in sight, he must initiate a missed approach. The simplest precision approach, a Category I ILS, will have "landing minima" of, typically, 200 feet and one-half mile. Higher category ILS's have lower minima, all the way to zero-zero for a Category IIIc ILS, but they require specialized equipment in the airplane and on the ground, and special training for the crew.
Radio: In the early days of air traffic control, communication was by low frequency radios. That frequency band is very susceptible to interference, and it was a full-time job just to understand pilots and make oneself understood. So the radio operator talked to the pilots, and he passed messages to and from the controller. With the advent of VHF radios with their clarity of transmission, the controller was able to handle both separation of aircraft and communication, and the radio operator became someone you called to open or close a flight plan, or to check the weather. But over the ocean, where we use HF for communication, the radio operator's job is the same as it ever was: he takes position reports from pilots and passes them on to the controller, and if the controller sees a conflict he sends a revised clearance to the radio operator, whose job it is to contact the pilot and make sure he understands the new clearance; he takes requests for revised clearances from pilots (typically for a change of flight level), and he transmits the clearance—or the information that the requested level is not available—to the pilot; and if you find yourself in trouble, he's the one you call to get help.
Relative wind: An airplane flying through the air at 60 knots feels the same forces it would if it were tied down squarely into a 60-knot wind. Different causes, same effects—it's all relative. So we call the movement of air past an airplane the "relative wind".
Roger: In ATC communications, it means "Received and understood." In the American Phonetic Alphabet (which has been replaced in aviation by the ICAO phonetic alphabet, "Roger" stood for "R".
Rudder: Ready-made definition here. See also flight control surfaces.
Runway numbering: Runways are numbered in accordance to their magnetic direction: round off to the nearest ten degrees, then drop the zero. Thus an east-west runway will be Runway 09 if you're landing to the east. If you land in the opposite direction, it's Runway 27. This makes it feasible for pilots to relate what they see on the ground to what they're hearing on the radio.
RVR / Runway Visual Range: Visibility reported at an airport is "prevailing visibility". When it's good, that's all you need to know. But when it's bad, you become very interested in that particular visibility just where you're going to land. They can be quite different. On my first ferry flight, the active runway at my destination, Birmingham, England, was below minimums in fog at 2:00 in the morning. (Yes, 2:00 a.m. I...um...was just beginning to learn this business.) I held for a while, waiting for things to move, but nothing happened. Finally I gave up and landed the wrong way on the same runway in perfectly clear conditions. Halfway down the runway I ran into the fog and had to slow to a crawl and follow the painted markings practically foot by foot to find the parking area. Runway Visual Range is the distance over which a pilot on the centerline of a given runway can identify the visual markings defining that runway. RVR is measured these days by a photosensitive cell at which a light of fixed intensity is shining a narrow beam alongside the runway. According to Wikipedia, it used to be measured by a person standing on a vehicle beside the runway threshold, peering into the murk.
RNAV / Area navigation: A navigation system which, using inertial sensors and/or radio signals from the ground or from satellites, provides the aircraft's position relative to the earth, hence relative to any fix defined in relation to the earth, rather than merely to the navigational facility being used. The most modern and by far the most accurate such system is GPS.
Schengen Agreement: Ready-made definition here.
Scud: Low wisps or fragments of clouds that form in bad weather, often from the moisture added to the air by falling rain—fractostratus and its cousins.
Scud-run: To fly low in bad weather by visual references; i.e., to run through the scud. Real scud-running is done less than a thousand feet AGL and is extremely dangerous—though it can be done successfully by pilots who are knowledgeable about what causes bad weather to get worse, stay very alert to the first signs that the (already bad) weather is worsening, and will abandon the flight the instant their several options start to dwindle away. Pilots who persist in scud-running until they've only got one option left, are those who kill themselves and their trusting passengers. On the other hand, pilots who've gotten used to operating in the flight levels often feel like they're scud-running when they're flying comfortably above all obstacles in fairly decent weather.
SHP / Shaft Horse Power: The output of turboprop engines is measured in Shaft Horse Power, rather than the Brake Horse Power used for piston engines. Brake Horse Power is measured at the crankshaft, before any reduction gearing; Shaft Horse Power is measured at the propeller shaft, after the reduction gearing. In most piston aircraft engines, the prop is bolted directly to the crankshaft; in those few which do have reduction gearing, the ratio isn't very great: for example, in the Pratt & Whitney R-1340 which powers the single-engine DeHavilland Otter, the prop turns at 2/3 the RPM of the engine. But turboprop engines spin at, typically, 30,000 to 40,000 RPM, and that's reduced to 2,000 RPM or less for the propeller, so horsepower losses through the reduction gearing are significant in turboprops, and shp is more meaningful than bhp.
Shoot an approach: To fly a published instrument approach procedure. I don't know why we call it "shooting" the approach, but we do.
Side-tone: What you hear when you transmit. Anything picked up by the microphone of a pilot's headset is sent to his (or her) headphones as well as being sent over the intercom or the airwaves, as appropriate. Knowing how you sound is a great help in refining your microphone technique and adjusting mike gain for clearest communication.
Skywave: Ready-made definition here.
Soup: In aviation slang, clouds, particularly thick stratus clouds. To fly "in the soup" is to fly through unremitting murk, with nary a glimpse of sunshine or terrain. cf. "pea soup" as slang for thick fog.
Speed brake: Ready-made definition here and here.
Squawk: Ready-made definition here.
Standard-rate turn: A turn in which a light aircraft makes a full circle (360 degrees) in exactly two minutes; hence, a course reversal one minute. This standard rate of three degrees per second is a compromise that allows a pilot operating under IMC to change heading expeditiously without making extreme maneuvers and risking loss of control. Making this rate the standard allows pilots and controllers to know what to expect from each other. Because a greater bank angle is required to maintain a given rate of turn at higher airspeeds, heavy airplanes use 1½°/sec as their standard rate.
TAS / True airspeed: The speed at which the airplane is actually moving through the air. This is not indicated by any of the airplane's basic flight instruments, but can be calculated by applying corrections for altitude and temperature to the indicated airspeed.
Threshold: The end of the runway over which an airplane flies just before landing.
Torque: The torque on the propeller shaft is the primary measure of turboprop engine output in flight. A good, brief article on the relationship between torque, propeller RPM, and power, can be found here.
Tower: Ready-made definition here.
Traffic pattern: The flight pattern aircraft follow in order to operate in an orderly fashion in the vicinity of an active runway. The standard pattern is a rectangle with left-hand turns at the corners, and consists of an upwind leg parallel to the runway and in the landing direction, followed by a crosswind leg ninety degrees to the runway and flying away from it, a downwind leg parallel to the runway but opposite the landing direction and flown at a spacing which allows comfortable turns to line up with the runway for landing, a base leg ninety degrees to the runway and approaching it, sufficiently far from the runway threshold to allow a comfortable descent to the runway, and a final approach on the runway centerline. An aircraft which is "staying in the pattern" after takeoff, for an immediate landing, will climb on upwind and crosswind to reach pattern altitude early on downwind, and begin its descent on downwind abeam the intended point of landing, continuing the descent through base and final to the runway. At airports with control towers (which comprise a miniscule percentage of the airports in the United States, but account for most of the aircraft "movements"), pilots are usually instructed to make a straight-in approach to the runway, or to enter on a right- or left-hand base leg, as appropriate. But even here, the full pattern forms the basis on which these instructions are given.
Transponder: An electronic device which, when it receives a certain signal, responds by transmitting another signal. This might just be an amplification of the original signal, but in air traffic control it's used to identify individual targets on a radar screen: rotating along with the radar's primary antenna (which captures echoes) is another antenna—the "beacon radar" antenna—which transmits a signal that triggers an aircraft's transponder to "reply" with a coded message. This message includes, at a minimum, the code which the pilot has set into his transponder (his "squawk code"), frequently the altitude of the aircraft (which gives the air traffic controller third-dimensional information), and, with newer units, other information including the aircraft's registration number. Transponders were originally used in aviation in World War II, as a means to Identify Friend or Foe (IFF): with IFF, a pilot could query another aircraft he could see only as a dot in the sky, and if it were friendly, it would "squawk" the appropriate reply, like a password. More here
Trim: To establish cruising flight, a pilot generally adjusts the engine(s) to a desired power setting, and then controls the angle of attack using the elevator so the airplane neither gains nor loses altitude. In smooth air this will result in a constant cruising speed, and the pilot will find he or she is maintaining a constant elevator deflection by holding a steady pressure on the flight controls. This would be tedious on a long flight, so almost all airplanes have a way of adjusting the elevator trim to reduce that pressure to zero. This is usually done by a trim tab on the control surface, but it can also be accomplished by adjustable springs or bungees attached to the flight controls. Most airplanes have rudder trim, as well, because of P-factor during the climb, and a few light airplanes and most larger ones have aileron trim, to compensate for imbalances in the fuel load in the wing tanks, etc. A pilot's goal in setting the trim is to reduce the constant control pressures to neutral, so the airplane flies "hands off" (this phrase implies "feet off" as well). Then the only control inputs needed are gentle pressures to correct for the inevitable slight disturbances to the flight path.
TIT / Turbine Inlet Temperature: The temperature of the exhaust gases entering a turbocharger. It's very important not to exceed the TIT limit—in other words, it's very expensive if you do. Since, in a turbocharged airplane, this temperature will certainly be displayed to the pilot, it's usually also used as an indication of combustion conditions during leaning.
Turboprop: Ready-made definition here.
Turbulence: Turbulent air is classified into two types and four levels of severity by its effect on the airplanes flying through it—and on their contents, including passengers. The types are "turbulence" and "chop", and the levels are "light", "moderate", "severe", and "extreme". Its persistence is characterized as "occasional", "intermittent", or "continuous". "Turbulence" displaces the whole airplane, like an unimproved road heaves a jeep up and down over its bumps and dips. "Chop" can be annoying, and if it's bad enough it'll rattle your dentures, but it doesn't heave the airplane up and down and sideways. It's like driving over a washboard road. "Light" turbulence can be felt, but it doesn't displace unsecured objects, and passengers aren't pressed against their seatbelts. An airline pilot may turn on the "Fasten Seatbelt" sign, but the flight attendants continue to serve hot liquids. Unsecured objects in "moderate" turbulence will move around, and passengers will feel their seatbelts restraining them. Flight attendants sit down and buckle up. In "severe" turbulence, unsecured objects fly through the air, and passengers are thrown violently against their seatbelts. You'll hear some screams. If the pilots aren't skillful, they can lose control of the airplane, in which case it will inevitably end up with its nose down, and accelerate past Vne and break up. If the pilots are skillful, they'll just have to pay close attention and work hard. Don't try to engage them in idle conversation. "Extreme" turbulence involves all the symptoms of severe turbulence, but it's so bad it's at or beyond the limit at which the airplane is controllable. The flight attendants are screaming, too, and if the pilots can't fly out of it in short order they'll most likely lose the airplane and it will be destroyed. I've experienced severe turbulence often enough, but rarely has it been continuous. Most often it's the occasional hard bump during moderate turbulence, that makes my clipboard fly off my lap. I've never experienced extreme turbulence, and I've only heard of it being reported once or twice. That's the stuff you find in really bad thunderstorms, into which airplanes may fly, but only pieces emerge.
I was flying a Piper Warrior to Hawaii one night (that's not a flight that can be accomplished entirely in daylight) and I heard an Air New Zealand pilot request a change of altitude, because the flight had encountered "moderate to occasionally severe turbulence". Several minutes went by, and I heard him request a return to Los Angeles to arrange medical attention for a passenger who had "suffered a massive coronary". I often think about that. "Moderate to occasionally severe turbulence", with an airline pilot at the controls, is not dangerous. Uncomfortable, yes; annoying, stressful, yes. Clearly, for some people, it's frightening, even terrifying. But it is not dangerous. I have no way of knowing how long it took them to return to Los Angeles, but I think that passenger's odds of survival were practically nil—which means he or she was frightened to death by the equivalent of a bumpy road.
UTC / Coordinated Universal Time: The abbreviation is a compromise between the English ("CUT") and the French ("TUC"). The Wikipedia entry has all the details, but for practical air navigation where we're not concerned about fractions of a second, this is the same as Greenwich Mean Time—and I've long suspected that the shift in usage from GMT to UTC was made largely to placate the French, who are apparently still miffed about the decision in 1884 to select the Greenwich Meridian (established in 1851) as the official Prime Meridian. Well, you can hardly blame them: the Paris Meridian had been in use since the 17th century. In aviation, we more often than not use the military designation Zulu, as in 1800Z.
Vector / Radar Vector: In ATC terminology, a heading assigned by the controller to keep you clear of other targets on his radar screen.
VHF / Very High Frequency: The frequency band commonly used for aircraft communication. It's great advantage is its relative immunity to atmospheric or man-made interference, which results in clear transmissions that are easy to understand. It's disadvantage is that the signal passes through the ionosphere rather than being refracted back to earth, so its propagation is limited to "line of sight". Over the open ocean or sparsely developed terrain (e.g. Africa), it's replaced by HF. Wikipedia has the details.
VNAV / Vertical Navigation: Airplanes often fly at high altitudes, and they typically land at low elevations. It can take a bit of planning to arrange your descent so as to arrive at the airport at an appropriate altitude. VNAV is an onboard computer program which helps you do that. It's typically part of a GPS installation. You tell it where you want to be at what altitude, and the rate or angle of descent you want to use, and it'll tell you when to start down, and it'll keep you advised how well you're conforming to your selected profile. It's just as useful—though less frequently needed—in planning how to climb to cross a fix at given altitude.
VOR / VHF Omnirange: A radio navigation aid, which is the basis of the airways system throughout the world. It first came out in the 1950's, and provided omni-directional navigational capability, as opposed to the old low-frequency four-legged ranges which it replaced. As an analog to the VOR's principle of operation, imagine a lighthouse with a narrow red beam which rotates once every six minutes—one degree per second—and a white omnidirectional light which flashes as the red beam passes north. By patiently timing the delay between the white and red flashes, you could tell your bearing from the station (your "radial"). The VOR, of course, to keep up with aircraft speeds, operates much more quickly than that. VOR's have been surpassed by various forms of area navigation, and greatly surpassed by GPS. In Europe there are now many airways which would be impossible to navigate using VOR alone.
VFR / Visual Flight Rules: Rules under which a pilot can operate an aircraft without an ATC clearance. The ceiling must be at least 1,000 feet AGL and the visibility at least three stature miles. Additionally, pilots must be able to navigate by reference to the ground (though they don't actually have to do that) and to see and avoid other aircraft, and must stay far enough away from clouds that they have time to see and avoid airplanes—operating under IFR—which may emerge from them.
Vne / Never-exceed speed: The red-line on your airspeed indicator. The airplane is not certified to fly faster than this indicated airspeed, because the resultant stresses may be more than the airframe can bear. This doesn't mean the airplane will immediately fall apart if you exceed this speed; but, if you hit some turbulence or pull a little G, it just might break.
Vr / Rotation speed: During takeoff in a light airplane, typically, when the airplane seems light on its wheels the pilot will add slight back pressure to the stick (or control wheel) and the plane will fly off the ground when it's ready. In a transport category airplane or a jet, the takeoff and climb speeds are pre-calculated based on the actual weight of the airplane and its contents. Vr is the speed at which the nosewheel should leave the ground as the pilot rotates to the takeoff pitch attitude.
VSR / Vertical speed required: A VNAV readout. It tells how fast you need to be descending (or climbing), in feet per minute, in order to keep up with your planned descent (or climb) profile.
Visual approach: From the Aeronautical Information Manual, Chapter 5, Section 5-4-22: "A visual approach is conducted on an IFR flight plan and authorizes a pilot to proceed visually and clear of clouds to the airport. The pilot must have either the airport or the preceding identified aircraft in sight. This approach must be authorized and controlled by the appropriate air traffic control facility. Reported weather at the airport must have a ceiling at or above 1,000 feet and visibility 3 miles or greater...." In the United States and Canada, ATC will, in appropriate conditions, assign a visual approach. In Europe, you have to ask for it—the only time I've been assigned a visual approach in Europe was when the instrument landing system for the duty runway was inoperative.
Warm sector: In meteorology, that area of warm air bounded to the east by a warm front and to the west by a cold front. cf. Occluded front.
XM Weather: Ready-made information here.
Z / Zulu time zone: This is the military designation for UTC. It's commonly used in aviation because it's short to write and quick to pronounce. For more details, see this entry at time and date.com.
