Descriptive Glossary

If human beings were intended to fly, The Intelligent Designer would have made their poop white.
     -- Paul Niquette

When in doubt, hold your altitude.  No one has ever collided with the sky.
     -- Old Aviation Saying

In 1980, a friend of mine set one of aviation's lesser known world records: Low-Altitude Endurance, flying at -200 feet MSL (+50 feet AGL) for over five hours, in Death Valley (now her husband plans to set the high-altitude submarine record with a one-man submersible in Peru's Lake Titicaca).

To determine altitude AGL -- the most vital measurement aloft -- the pilot must know: (a) the plane's altitude MSL, (b) the plane's geographical position, and (c) the elevation (MSL) of the ground (the G in AGL) at that location.

Aileron is one of the few pure aviation terms and was derived from the diminutive form of the French aile (wing).  Other French contributions: empennage, fuselage, and longeron.

Distinguished from groundspeed. 'Indicated' airspeed corrected for altitude and temperature becomes 'true' airspeed ('truing out' at 150 knots with a 15-knot tailwind 'makes good' 165 knots 'over the ground').

Use these in casual conversation anywhere in the world and pilots will reveal themselves by asking, "What are you flying?"
 
Never drop the airplane to fly the microphone.
-- Old Aviation Saying

angle-of-attack The angle between the chord of the wing and the relative wind (also called angle-of-incidence).

The chord is simply the straight line that connects the leading edge of the wing with the trailing edge (longest dimension front-to-back). The relative wind, not so simply, is the direction from which the air appears to be coming. In level flight, the relative wind strikes the plane horizontally from straight ahead. During ascent (or descent), the relative wind comes from above (or below) the plane.

Most people are familiar with control towers. The 'tower' operators (also called 'local' controllers) are responsible for planes in the process of landing and taking off. 'Ground control' directs planes on the ground. Movie-makers take note: you never call ground control while in the air. At the radar scopes you have 'departure' controllers, 'enroute' controllers, and 'approach' controllers.

The vast majority of airports do not have control towers. Most use Unicom or CTAF (Common Traffic Advisory Frequency) to exchange information among the pilots flying in the pattern. Works fine, by the way. ("Caldwell traffic, Cardinal Niner One Four, wing-up, turning right base for Runway Three Zero, behind the Cherokee.")

"Torrance Airport, Information Juliet, zero-two-zero-zero Zulu. Weather: sky partially obscured, two thousand scattered, two-five thousand broken. Visibility: five, haze. Wind: two-seven-zero at one-five. ILS Two-Niner Right approach in use, landing and departure: Runways Two-Niner Right and Two-Niner Left. Caution equipment in use on taxiway kilo. Advise on initial contact, you have received Information Juliet."

Attitude is a vital thing for the pilot to know -- which way is up? -- and to control. The task is made easy when you can see the horizon out the window, difficult -- hard! -- when you cannot. Straight and level flight is one of the most common -- 'usual' -- attitudes, as are climbing, descending, and coordinated turns.

So then, what is an 'unusual' attitude? It is any attitude not required for the normal conduct of flight. Unintentional attitude is more to the point.

Airplanes tend to 'overbank' constantly. Here's why. Say a slight disturbance lifts the right wing. Suppose that, through momentary pilot inattention, it is not immediately corrected. A left turn ensues. That might not be especially inconvenient -- if you happen to desire a left turn. Inadvertent, though, and you have an unusual attitude.

Overbanking results from the turn itself. Intended or not, while flying in a curving path the outside wing has farther to go than the inside wing. For the case under consideration, that means the right wing is travelling faster than the left wing, and develops more lift -- rolling your plane more steeply to the left. The motion can be exceedingly subtle. You are not likely to feel it.

Most likely, though, the pilot is the problem. Carelessness in cross-checking the instruments and errors of interpretation, confusion and disorientation, lack of training or being out of practice -- these are among the foibles that beset the person at the controls.

Unusual attitudes are not really so unusual. Safety dictates that you must learn how to recover from them, which often requires dealing with vertigo.

The simplest is called a 'wing leveler,' which is capable merely of 'roll-hold.' You might add 'heading-hold,' 'pitch-hold,' and 'altitude-hold.' Finally, there is the 'coupler' that connects the autopilot to your navigation system. Then you might ask yourself why you took up flying.

The sky, to an even greater extent than the sea, is terribly unforgiving of errors.
      -- Old Aviation Saying

In 'coordinated turns' (neither slipping nor skidding), best to think of your fanny as 'down' and what you see through the plexiglass as a crooked picture on the wall.

bearing An angle measured clockwise relative to some reference, often the longitudinal axis of the airplane (see numbers) or from North (see omni).

blip The spot on the radar screen corresponding to the echo of an airplane, also called 'target' (see transponder). Maybe blip sounds like what a spot looks like.

checklist An ordered set of references to procedures vital to the safe conduct of flight.  Checklists are customarily printed on laminated pages bound into a notebook immediately accessible to the pilot in command.

A given checklist pertains to a specific phase of flight: Pre-Flight-Inspection, Before-Starting-Engine, Pre-Taxi, Pre-Take-Off, Approach-to-Landing,.. Emergencies (by type).  Aviation mnemonics are commonly used as informal checklists (CIGAR, GUMP, CCCC, TTTTT), with varying degrees of effectiveness.  Every item on a checklist has two parts, the first in the form of a noun phrase called the “challenge,” for each of which a “response” is mandated:  "Flaps -- Set"; “Landing Gear – Down and Locked, Three-Greens Showing”;  "Mixture -- Full Rich."  A checklist does not tell the pilot how to perform the procedure.  Technical manuals and flight training are supposed to do that.

A checklist is not a do-list.
      – Old Aviation Saying

ceiling A broken or overcast cloud layer at some measured elevation AGL.

For landing, an aircraft must have some prescribed forward visibility, often a mile, under a ceiling of at least a few hundred feet. These are the so-called 'landing minimums,' and they vary from airport to airport.

The least useful acronyms are those which provide no mnemonic support for sequence: TTTTT (Time, Turn, Throttle, Tune, Talk) for the five things you are supposed to do at the outer marker (which I have replaced with "watchman power and radio chatter"); for emergencies, I replaced the traditional CCCC (Climb, Confess, Communicate, Comply) with my on credo: PADO (Pull-up, Admit that I need help, Describe my predicament, Obey instructions).

Under IFR, a clearance covers a chain of in-flight procedures, which must be taken down by the pilot in "aviation shorthand" from clearance delivery and read back verbatim.  Here is an example: C34914 CLRD TO SFO M3 EXP H IN 5MIN.  MRH TO X SLB R123, RT 270, RV TO LAX VOR.  FPR.  DEP 126.4, SQ3241.  Which sounds like this over the radio…

"ATC Clears Cardinal Three Four Niner One Four to the Santa Francisco Airport. Maintain three thousand. Expect higher five minutes after departure. Maintain runway heading until crossing the Seal Beach one-two-three degree radial, right turn heading two-seven-zero for radar vectors to Los Angeles VOR. Flight plan route. Contact Departure Control, 126.4. Squawk 3241. Proceed with your readback."

As with other terms ('navigate,' 'dead reckoning,' 'rudder'), 'cockpit' came to aviation by way of maritime parlance, there being a lower space near the stern from whence some vessels are steered. Just so there is no misunderstanding, 'cock' derives originally from the fighting bird.

Prepare to learn a whole new collection of TLDs, including FMS, SVS, and PFD.

For safety's sake, headings are invariably given over the radio as three digits.  That's called 'redundancy.'  Thus, North-West is said, "three-zero-zero."  On both compass and heading indicator, the least significant digit is deleted on every printed number, such that North West reads "30."   That's bad enough, but then leading zeroes are also deleted (must be to save paint).  That means North-East, which is said "zero-three-zero," reads just plain "3."  Now, 30 is exactly 270 degrees from 300, making the expression "right angle" a potentially fatal misnomer.  And yes, a high-time pilot I know personally has experienced the indicated inadvertence while aloft on instruments.

crab Angle between course and heading resulting from the influence of a crosswind component.

Crab is especially onerous on landing. The pilot uses an intentional (side) slip to correct it out; otherwise the wheels will not be lined up with the runway at the instant of touchdown.

crosswind leg See pattern.

crosswind take-off Runways are generally designed to be lined up with the wind.  Once the airport is built, though, it doesn't always work out that way.

If a significant component of the wind is blowing across the runway, an airplane taking off tends to skid sideways just as the wheels leave the ground.  For a crosswind take-off, the pilot anticipates this tendency by prepositioning the aileron control for a turn into the wind before releasing the brakes.  Immediately after take-off the plane actually does turn into the wind and then commences to crab along the runway. Best to explain these matters to your passengers before starting the engine(s).

Crosswind landings have the same problem in reverse, but not the same solution.  The preferred approach is to execute an intentional slip by banking into the wind and holding opposite rudder to cancel out the effect of the crosswind and to keep the plane's landing gear lined up with the runway.  Of course, with the plane banked, one wheel will touch-down first, but -- hey, nobody ever said landings have to be pretty.

The procedure is prone to errors, primarily because of winds, but it's anything but dead. The preferred term is 'pilotage.' Likewise, the phrase 'positioning flight' seems to have replaced 'dead-head' in aviation parlance.

There is some controversy about the derivation of the phrase. According to the Oxford English Dictionary, the phrase dates from Elizabethan times (1605-1615).  The popular etymology cited here is not documented in any historical dictionary.  Instead, 'dead reckoning' is navigation without stellar observation. Whereas with stellar observation, you are in some sense -- well, 'live', working with the stars and the movement of the planet; however, with mere compasses and clocks but no sky, you are working 'dead'.

DF Direction Finding, a primitive instrument on the ground that responds to the radio transmission of an aircraft and indicates its bearing, which can be relayed by radio back to the pilot.

Most light planes today have Automatic Direction Finding (ADF) instruments with a needle which continuously points to a selected radio beacon or commercial broadcast station.  ADF dates back to olden times, before neither the VOR nor PC made their way into aviation parlance ("We pause now for station identification, just in case there's some poor sap in the sky who's trying to to use his ADF to figure out where the hell he is.")

drag Force acting to retard the motion of the plane or to keep people from having fun at a party.

All things that move through fluids experience drag. Airplanes are distinguished by the fact that for them, there are two kinds of drag. Common old ordinary drag is called 'parasite' drag, which becomes greater with increasing speed, the same as for barracuda and boats, bikes and blimps, bullets and buses.  Airplanes also experience a pernicious form of drag, which paradoxically increases at low airspeeds. It is called 'induced' drag.

Added together and graphed against airspeed, these two drags form a U-shaped curve. Corresponding to the bottom of the curve is the 'minimum drag speed,' usually about 30% above the airplane's stall speed. In still air, this is the most efficient airspeed, giving the greatest distance for the least fuel consumption.

By the way, since drag is overcome by thrust (or 'power'), an airplane exhibits a U-shaped 'power curve.' Hence the expression that has been so rudely appropriated by management and politicians, "getting behind the power curve." It means flying so slow that no amount of power can prevent a stall.

E6B Computer A circular slide-rule used to perform in-flight calculations, such as time-distance-speed, fuel consumption, and wind-triangle.

Doesn't have batteries. That's neat.  Not only that but, unlike GPS, the E6B is not disabled by solar flares in the daytime.

'Elevator' is a misleading term. Within limits, the throttle controls 'elevation.' The elevator -- through pitch -- controls airspeed.

While it is true that pulling back on the control wheel, which pushes down on the tail, imparts an upward motion to the plane, the long-term effect is to slow your airspeed. Enough of that and you achieve a stall. Old saying: "To go up, pull back. To go down, pull all the way back."

Empennage is one of the few pure aviation terms and was derived from the French word (tail feathers of an arrow). Other French contributions: aileron, fuselage, and longeron.

ETA Estimated time of arrival at a fix or destination. Distinguished from ATA, actual time of arrival.

FADEC Full authority digital engine control.

Just the thing for 21st centry flying, especially in light aircraft with diesel engines that burn jet fuel.  FADECs monitor and simplifies engine operation (throttle, propeller, mixture), enable single lever power control, support improved engine starting , reduce fuel consumption through parameter optimization, and perform real-time data logging.

A fail-safe system incorporates redundancy ('back-up'), so that an isolated failure (‘single-point-of-failure’) shall not result in catastrophe. Moreover, a single-point-of-failure must not go undetected (‘unrevealed’ is my term for it).   That would take away the redundancy.  Thus the popular juxtaposition ‘safety-and-reliability’ has meaning only by virtue of systematic measures that assure the joint unlikelihood of simultaneous multiple failures.

Piston engines have dual ignition systems independent of the plane's electrical system, with two spark plugs in each cylinder energized by separate magnetos that are individually tested before take-off.  Planes also have two wings; however,...

Some FBOs run charter services and sell or rent airplanes. The etymology of FBO is unknown to this author. I like to suppose that it was originally a term of distinction: the early 'barnstormers,' always on the move, would not have qualified for any term with 'fixed' in it. {Egg Plant on Wheels}

Strictly speaking, flaps do not increase lift, which in steady flight equals the weight of the aircraft. With the flaps extended, stall speed is lessened, permitting slower flight for landing. (Cowl flaps are a different thing; they control the cooling of the engine. Marital flaps are cockpit discussions resulting from both partners holding pilots' licenses.)

There are three simple rules for making a smooth landing.  Unfortunately no one knows what they are.
    -- Old Aviation Saying

Sitting in the right seat of a Skylane, I watched with admiration while the pilot executed a perfect approach in a stiff but steady wind at Flagstaff, Arizona, flaring just right so that, with the plane nearly stopped, the wheels might 'smooch' the pavement without even squealing -- except for one thing: I could see the shadow of the right main gear wheel on the runway four feet below the right main gear wheel. The pilot peered over the instrument panel and grinned, preparing to taxi off the runway and accept my applause. Then all at once: ka-thunk. Glad I was there.

flight, perfect That perfect flight repays the requisite diligence deserves an artful treatment.

Flight Service Part of the services offered to all pilots by the FAA. Briefers at hundreds of locations reply to pilot requests for weather information by telephone and radio. They operate a network over which flight planning information is communicated.  Also see DUAT. 

flight plan A document prepared by the pilot and submitted to Flight Service (in person, by phone, or by radio).

Under VFR, filing a flight plan is optional. The pilot 'opens' the flight plan shortly after take-off and 'closes' it just prior to landing (or by telephone after landing). An overdue flight triggers search-and-rescue operations along the flight plan route. Under IFR, a flight plan is required and forms the basis of a clearance.

FMS Flight Management System, subset of glass cockpit, flat-screen depicting an ensemble of flight and navigation instruments plus other panel gauges.

fugoid See phugoid.

fuselage The central body portion of an aircraft designed to accommodate the crew and the passengers or cargo.

Fuselage is one of the few pure aviation terms and was derived from the French word (spindle-shaped). Other French contributions: aileron, empennage, and longeron.

The requisite airborne equipment is nil. All you need is a two-way radio. Thus, GCA can be considered a last resort for getting one's backside on the ground when everything airborne has run amuck.

The special GCA radar facilities are rare -- most have been de-commissioned. Unless there's an emergency, you have to make an appointment to get some practice.

Along with Beech and other companies, Piper manufactures many fine General Aviation aircraft today -- always with their wings on the bottom, by the way.  Piper Cubs are history.  The most popular private planes are made by Cessna.  Like the venerable Cubs, their planes have wings (and petrol tanks) on the top, which means no fuel pumps to fail, no interferences with spectacular views out the windows for passengers, and no ungraceful entries for ladies in miniskirts.

All low-wing birds must be extinct. 
     -- Old Cessna Pilot

Private flying is a scarce privilege, almost uniquely American. Nobody, though -- not even an aviation enthusiast -- would say that private flying is the most pleasurable activity in the world. That terminology, by convention, is reserved for something else. For many persons, a trip in the sky aboard a light airplane ranks as a close second. {Not everybody agrees.}

GPS Global Positioning System, precise, feature-rich navigation system using signals received from a fleet of low-orbiting satellites.  Also see FMS.

ground effect Increased pressure underneath the wings produced by flying close to the ground. An overloaded airplane taking off on a hot humid day may not be able to fly without it. Upon reaching the airport boundary, such a hapless airplane can experience another kind of ground effect.

groundspeed The speed (in knots usually) at which the airplane moves ('makes good') over the ground. Distinguished from airspeed. With a 'tailwind,' the groundspeed is faster than the airspeed. With a 'headwind,' the groundspeed is, alas, slower.

GUMP An abbreviated pre-landing checklist: Gas (fuel selector on the fullest tank), Undercarriage (landing gear, Old Chap), Mixture (full rich), Propeller (highest RPM).

On an instrument approach, the pilot has plenty of things to do. I concocted "Check freak killers and Miss High Time's Speed" for pre-landing checklist, set up frequencies, study approach chart for obstacles and terrain hazards (killers), recite the missed approach procedure, review decision altitude (high), set timer for missed approach limit, and slow to approach speed. After that, GUMP.

For a typical light plane, gliding at 65 knots, the descent rate is 600 feet per minute (about 6 knots in the downward direction).

The 'artificial horizon' or 'attitude indicator' is the primary gyro instrument. Because of the idiosyncratic behavior of the magnetic compass, the pilot relies instead on the 'direction gyro' or 'heading indicator.' Finally, there's the old 'needle-and-ball' or the new 'turn coordinator' that tells the pilot the rate at which the plane is turning and whether the turn is 'coordinated' (yaw in balance with roll).

heading The direction the plane is pointed. Because of wind, it does not necessarily correspond to the intended course, the latter achieved by a 'cross-track correction' (see crab).

HIRL High-Intensity Runway Lights, a row of lights located at the approach to a runway that flash in rapid succession to provide a visual reference at the conclusion of an ILS approach.

For the story of its invention, see "Flash in the Sky."

The holding pattern is shaped like a race track in the sky. Actually a stack of them, each separated by a thousand feet. One plane at a time can occupy any particular level. Think of a half dozen Indianapolis 500's piled up over a navigational fix

The holding pattern comprises four parts, each requiring one minute: upon reaching the assigned fix, you make a 180-degree turn at three degrees per second, next you fly outbound for one minute, make a 180-degree turn back inbound at three degrees per second which takes a minute, finally, you "home in" on the fix, like cruising along the straight-away at Indianapolis.

The IFR instructor acts as a safety pilot to watch for other airplanes. The weather might be perfectly clear, but the student 'under the hood' must conduct the whole flight by reference only to instruments. {Under the Hood}

One requirement is called a 'clearance,' which constitutes a contract between the pilot and flight controllers that sets forth the de-fault procedures to be followed if a break-down occurs in air-to-ground communications.

The informal expressions "flying on instruments" or "flying IFR" mean controlling the plane by reference only to gauges on the panel, especially those that incorporate gyros, a mode of flight necessitated by "IFR conditions," which is a phrase now generally replaced by "IMC" for "Instrument Meteorogical Conditions."

Two of its subsystems, 'localizer' and 'glide slope,' are radio transmitters on the ground which define respectively the straight-in course over the ground and the vertically slanting path to the touch-down point. The pilot uses a pair of needles on the panel for the requisite guidance. On my approaches, it looks like a sword fight.

intersection A fix or waypoint defined by the crossing of radials from two omni stations.

A number of years ago, the FAA changed all intersection names to five-letter words, ostensibly pronounceable. Computers again, folks. Back when I started flying, there were no such constraints. Intersections were named for what underlay them, usually a city. Thus, Anaheim became AHEIM; Tustin, TUSTI; El Monte, ELMOO. Out in the ocean, we had Albacore, which became ALBAS, and Mermaid, which is now, alas, MERMA.

lift The upward force of the air upon the wings.

In level flight, lift acts vertically (opposing weight) and produces -- well, level flight. When you bank the plane, part of the lift acts horizontally to cause a turn.

Longeron is one of the few pure aviation terms and was derived from the French word (to pass along). Other French contributions: aileron, empennage, and fuselage.

mayday internationally recognized distress signal via radiotelephone (from the French m'aider), shortening of venez m'aider "come help me!"

mile Two sizes: nautical mile (6,080 feet) and statute mile (5,280 feet). You can get from one to the other by either dividing or multiplying by 1.1515, but there's never enough time for that. The nautical mile corresponds to one minute of latitude.

MSL (Above) Mean Sea Level, the measurement of altitude provided by the airplane's altimeter. Compare to AGL, Above Ground Level.

navigation Determining one's location and guiding the control of heading to achieve a desired course.

Appropriated by aviation from nautical parlance, the term is gradually being replaced by avigation.

Thus, 12,500 is said "One-two tousand, fife hundred." You do hear pilots taking shortcuts ("twelve point five") but never controllers. By the way 'point' is supposed to be said "day-see-mal."

The numbers ten, eleven, and twelve appear only preceding o'clock to designate the relative bearing of traffic or landmarks. 'Twelve o'clock' means straight ahead, 'eleven o'clock' means 30 degrees to the left of straight ahead, 'one o'clock' means 30 degrees to the right, and so forth. Pity pilots who have grown up with digital watches.

In the expression, 'inbound with your numbers," the term is used to summarize the current operating conditions and procedures at an airport to save repeated instructions from the controllers (see ATIS).

"Landing on the numbers" means touching down on the painted numerals -- hey, at the beginning of the runway.

There are hundreds of omni-range stations in the United States and elsewhere. Each defines a set of 360 invisible 'radials,' each resembling the spokes of a wheel and corresponding to the magnetic bearing of the plane's position (not the airplane's heading). Certain radials are shown on charts connected together forming the 'Victor' airway system.

The pilot first tunes his or her omni receiver to the frequency of a nearby station. Then, by centering a needle, the magnetic course to or from the station can be determined.

pattern A rectangular flight path associated with each runway, one side of which is the runway. It forms the conventional framework for controlling the orderly flow of aircraft to and from an airport.

There are five legs: upwind (straight ahead immediately after take-off), crosswind (a ninety degree turn at the departure end of the runway either left or right depending on the published pattern for that runway), downwind (parallel and to the side of the runway), base (perpendicular to the runway at the approach end), and final (lined up with the runway, descending for touch-down).

Generally, you depart on a 45 degree angle from the upwind leg and enter the pattern on a 45 degree angle to the downwind leg ("on the forty-five"). At controlled airports, you may request such alternative procedures as a "straight-out" departure or a "straight-in" approach. And sometimes you will get cleared for a mouthful: "mid-field crossing downwind entry." Listen up.  (In Canada, by the way, MFCDE is the standard procedure for pattern entry.)

P-factor A tendency for a single-engine aircraft to yaw to the left at high angle-of-attack, most pronounced immediately following take-off and during climb-out.  In a twin, the P-factor defines the 'critical engine'.

As the wheels lift off the ground at the beginning of your first flying lesson, it will feel like your plane has hit a patch of ice.  Your instinct will be to turn the "steering wheel" to the right; however, that will only make matters worse (see adverse yaw).  At that moment -- and often thereafter -- your instructor smirks and hollers over the sound of the engine, "Get on that right rudder pedal!"

The propeller customarily rotates clockwise as viewed from the rear. Drag in "air screw"  might be expected to bank the aircraft counterclockwise; however, the aelerons have much greater mechanical advantage in the roll axis than the propeller tips, making any banking effects negligible.  So why does the P-factor show up in yaw?

Several explanations are offered in aviation literature. One suggests that the empennage is rigged in the factory to match airflow forces passing along the fuselage and optimized for cruise speed.  Those forces are not exactly balanced in a climbing maneuver.  At full climb power and with reductions in airspeed toward a stall, that effect would decrease not increase.  Another explanation has it that the vertical stabilizer gets pushed to the side by clockwise spiraling propwash.  However, that would also decrease with speed, as more time will be allowed for the spiraling component of airflow to dissipate before the rear of the plane can catch up to it.  Gyroscopic 'precession' of the engine and propeller may contribute to the P-factor, but that will manifest itself only as a transient torque during pitch rotation not as a steady-state condition while climbing.  Oh right, the gyroscopic torque acts in the opposite direction to the P-factor, yawing the aircraft to the right not the left.

The best explanation is based on the observation that in a climb the upward inclination of the fuselage tilts the plane-of- rotation of the propeller away from its normal orientation -- perpendicular to the flight path.  Accordingly, the downward-moving blade on the righthand side of the aircraft is advancing at an angle into the relative wind and thus developing more thrust than the upward-moving blade on the lefthand side, which is retreating out of the relative wind.

The propeller is just a big fan in front of the plane used to keep the pilot cool. When it stops, you can actually watch the pilot start sweating. 
     -- Old Aviation Saying

Named for its inventor, Henri Pitot (1695–1771) a French hydraulic engineer, the pitot tube has an external opening perpendicular to the airflow that registers "stagnation pressure," also called "ram pressure," and a parallel port that registers "static pressure."  The difference between these two pressures is used to indicate airspeed.  The altimeter is an aneroid barometer.  It uses the static pressure, which is not static, of course, but varies with altitude.  A third instrument, the "vertical speed indicator," measures the rate of change in static pressure.

A small atmospheric disturbance, might cause a plane, which has been trimmed for level flight hands off, to pitch nose downward, say.  Airspeed increases, which increases lift, raising the nose back up again.  With no corrections by the pilot, inertia produces an overshoot into a nose upward attitude.  Airspeed now decreases, which decreases lift, lowering the nose back down again.  For a light aircraft the period of oscillation might be as long as 30 seconds.

A pregnant pilot who is a parent of an only child would describe her condition as "one in the hangar, one on the ramp."

One of the most useless things for a pilot is one second ago.
     -- Old Aviation Saying

roger Spoken on the radio, it means "I understand and will comply." 'Affirmative' -- not roger -- means 'yes.' Etymology: from Roger, circa 1941 communications code word for the letter r (now replaced by Romeo) -- used especially in radio and signaling to indicate that a message has been received and understood.

The term is seldom used except to offer commiserations for delays or turbulance.

"Gettin' a lot of chop up here at 7,000."

"Roger that."
 

Unlike in the movies, pilots repeat back instructions, often in abbr. form.
 
"Cardinal Niner One Four, two miles north of MAGIC, turn right to One Five Zero, maintain three thousand five hundred until established on the localizer; cleared for the ILS Runway Two-One approach, contact Watkins tower 121.1 at the outer marker."

"Niner One Four, right, One Five Zero the heading, three point five 'til established, cleared for the approach, tower at the marker."
 

Listen in on such conversations on Channel 9 next time you're bored in an airliner.

"Rolling" is also an atavistic expression used by old pilots like me (pronounced "Rollin'") to acknowledge "Cleared for take-off," referring with joy to the action of the wheels along the runway.

RPM Revolutions per Minute, the speed at which an airplane engine swings those paddles around, measured by the tachometer.

rudder The movable surface on the trailing edge of the vertical fin. Operated by the action of the pilot's feet upon the rudder pedals, the rudder controls yaw. The fixed part is called the 'vertical stabilizer.'

runway Numbered at each end according to the magnetic course of an airplane taking off or landing on it.

The last digit of the course, of course, is rounded. Thus, Runway One Niner has a magnetic direction between 186 and 195 degrees. Movie-makers take note: there are no runways with numbers greater than 36.

skid An uncoordinated maneuver which results from too much rudder (or not enough aileron, your choice) in a turn. Compare to slip.

An airplane might also skid on the ground, much as any wheeled vehicle.

Intentional slips are useful for making 'crosswind' landings (see crab) or for rapid loss of altitude ('forward slip').

For some pilots, a thousand hours of flying experience really means only one hour of flying experience over and over again a thousand times.
      -- Old Aviation Saying

Maneuvering speed must be placarded on the instrument panel, indicating its dependence on gross weight.  For safety, heavier means faster.  That irony is explained by the fact that increasing weight increases the aircraft's stall speed.   In stalling, the wings are politely released from what I call the "Grasp of Bernoulli."  With an unloaded airplane, you must slow down, so that a sudden gust of turbulence will intentionally cause a stall.  You may loose some altitude, which you can spare, but not your wings, of which you need both.

Flying is not dangerous.  Crashing is what is dangerous.
     -- Old Aviation Saying

squawk Post-flight complaint about malfunctioning aircraft equipment, obviously not quite fatal. Also see transponder.

stack (see holding pattern)

stall An aerodynamic condition that develops when the angle-of-attack reaches a high value. The air flowing over the top of the wing separates into turbulent eddies, and the wing becomes exceptionally inefficient.

Push the controls forward and the houses get bigger; pull back and they get smaller -- that is, unless you keep pulling all the way back, then the houses get bigger again. 
     -- Old Aviation Saying

One way a stall can occur is flying too slow ("unable to obtain/maintain flying speed," the accident report will say). During training, the student goes aloft to practice stalls -- rather recovery from stalls. Two basic kinds: with power (departure stalls) and without power (approach-to-landing stalls).  The remedy for either is counter-intuitive: immediately push forward on the controls.

For the airframe, ironically, a stall is the least stressful maneuver except for taxiing (see maneuvering speed).

A 'full stall landing' is an intentional maneuver resulting in the cessation of flight at zero altitude (AGL) and the lowest possible airspeed.

After more than a century of aviation, 'stall' is still one of the most poorly understood terms. Stall has nothing to do with the engine.  Almost nothing.  FOD (foreign object damage) can result in a turbine stall, as the air flow is disturbed by the ingestion of snow, sludge or, ugh, a bird in a jet engine.  The remedy is counter-intuitive: immediately pull back on the thrust lever for the affected engine.

The definition is easy; the maneuver is not.  In apparent contradiction to Newton's Third Law of Motion, every action (of the pilot) does not produce an equal and opposite reaction (of the airplane).  Flight controls impose forces that are interconnected to each other in counter-intuitive ways.  You will get some idea about that by regarding straight-and-level as a coordinated turn with an infinite radius.

The regs forbid flying less than eight hours after drinking ("Eight hours from bottle to throttle," the saying goes) or when 'hung-over,' whatever that means. Objective experiments have shown that, depending upon all the familiar variables, alcohol can adversely affect the pilot's performance of functions essential to flight safety up to -- now get this -- 36 hours following its consumption.

Old-time pilots will doubtless complain that SVS effectively reduces your aviation experiences to nothing more than flight simulator sessions on a laptop.

TCA Terminal Control Area, positive controlled airspace surrounding the busiest airports, in the shape of an invisible inverted wedding cake -- intended to exclude all aircraft not under the radar control.

The concept is incomplete. Airplanes are considered outside the TCA even when they are inside the borders of a TCA. All they have to do is fly above the ceiling or below the floor of the TCA. Flying is a three-dimensional activity. Radars surveillance is not. Without reliable altitude information (see transponder) for all aircraft, there is no way for ATC to assure protection for any aircraft, inside -- or outside -- a TCA.

throttle Controls the flow of fuel into the engine and therefore the amount of power delivered by the engine.

Within limits, the throttle determines the vertical movement of the plane (see elevator). For a given airspeed (the elevator held in a fixed position), one will cause the plane to ascend or descend by changing the throttle setting. Closing the throttle produces a glide -- at an airspeed determined by the elevator. Confusing, huh?

TLD Triple-Letter Designator, "They talk in TLDs / 'space-speak' if you please."

ADF, AGL, ATA, ATC, CUT, E6B, ETA, FAA, FBO, FMS, GCA, GMT, GPS, IFR, ILS, IMC, MSL, PFD, SVS, TCA, TLD, VFR, VOR

Many of the instruments in an airplane (airspeed indicator, engine instruments) have green arcs which mark their safe operating ranges. Some also have yellow arcs or a redline that signify dangerous operating regimes or absolute limits.

To non-flyers, the term connotes motor vehicles in close proximity, all at the same altitude, of course, accompanied by frustrating delays. Except in formation flying, air traffic is typically separated by miles and thousands of feet. There can be delays, but the popular expression "crowded skies" is nevertheless misleading.

Imagine vehicular traffic without signals. Or visit Shanghai. There, you will find a white-gloved 'traffic controller' on every corner. Throughout the U.S., traffic control has been automated. Except in the sky.

All transponders transmit an assigned ("squawk") code, which identifies the airplane to radar controllers. Only 'Mode C' (altitude encoding) transponders provide a measurement of the aircraft's altitude MSL. Both are displayed on the radar screen in a box near the plane's blip, also called 'primary echo.'

To assure interoperability, two frequencies are used worldwide: 1,030 MHz for interrogation and 1,090 MHz for reply.  The flight crew sets the assigned squawk code into the instrument using four thumbwheel switches displaying octal digits, (limited to cyphers 0, 1, 2...7), capable of supporting no more than 4,096 codes.  Nota bene: code "0000" is not used.  Moreover, for declaring emergencies aloft, the pilot will use any of 64 codes starting with "77"; likewise "76" signals a radio failure to radar operators on the ground, "75" declares a skyjacking in progress, and "12" means the aircraft is operating under VFR.  Thus, a net of only 3,839 discrete codes are available for routine use under IFR..

For background on the altitude-reporting transponder and its impact on ATC, see the Internet Version of Squawk 1200: A history of the next midair collision.

All aircraft have elevator trim. Some also have rudder trim. A few have aileron trim. A perfectly trimmed airplane in smooth air can be flown 'hands-off.'

Say you want to make a left turn in level flight.  You use what looks like a steering wheel in front of you to apply left aileron, and the plane begins banking to the left.  At that moment, the right wing is developing more lift than the left wing and therefore more drag.  The unbalance causes your plane to yaw to the right -- opposite to your intended maneuver. That would be adverse yaw; however, you prevent it by simultaneously applying left rudder.  By the way, the plane has not yet started to turn.  For a few seconds, you continue to fly straight ahead with your wings going steadily more crooked in the sky. Eventually, you will have the 'angle-of-bank' that you intend to use for your turn.  You neutralize the ailerons to stop the roll.  At last, the plane starts its turn.

With the heading changing toward the left, the outside wing (the one on the right) is now moving through the air faster than the inside wing and developing more lift.  The result is, the plane will continue rolling to the left, increasing your angle-of-bank ("over-banking," it's called).  Naturally, you prevent that by applying opposite (right) aileron. In resisting that tendency for the plane to continue rolling toward the inside of the turn, you have intentionally increased the lift on the inside wing and unintentionally increased its drag, yawing the plane to the left.  That, too, would be regarded as adverse yaw, except it is acting in the same direction as the turn.  Still, to avoid over-banking you must apply right rudder.  The plane keeps turning steadily toward the left at a fixed angle-of-bank as you wanted.

Meanwhile, with the wings at an angle to the horizon, some of their lift is being taken away from holding your plane aloft and used instead to produce the turn.  If you don't do something about that, your airplane will begin to pitch downward, losing altitude.  You prevent that by pulling back on the control wheel which operates the elevator to increase lift on both wings in unison.  By the way, that increases drag in both wings, slightly slowing the airspeed. The plane stays at the same altitude nice as you please; however, part of that extra lift is directed toward the left simultaneously increasing your rate-of-turn and the tendency for the airplane to over-bank. To prevent that, you crank in more right aileron, which you must balance with more right rudder.  And so it goes.

There you are, all crossed up in the cockpit: banked left, applying right aileron and rudder, watching your heading change to the left while pulling back on the elevator to hold altitude.  Quite counter-intuitive and hardly 'coordinated' when you think about it -- which you soon learn not to do.  Nothing like driving a car, is it.  Oh right, and to stop the left turn, you must go back to the top of this exercise and reverse each action as if you want to make a right turn.

Almost.

Reminder: The purpose of a turn is to take up a new direction of flight, often on an assigned heading.  That imposes a timing requirement for stopping the turn -- a requirement you don't have when you're starting a turn.  Your car-driving intuition will suggest that you should start gradually rolling out level before reaching that new heading so as not ro turn too much.  But watch out.

All during your left turn, you are holding right aeleron and rudder.  To stop the turn, you must increase right aileron so that the inside (left) wing develops more lift.  Its increased drag toward the left will resist your effort in stopping the turn, so you must apply more right rudder at the same time.  But how much more?  Too much right rudder will cause you to stop the turn short of the desired heading; too little and you can expect to overshoot it.  That's what you think, anyway.  In reality, the tendency will be to use too much right rudder -- rather to be tardy in reducing it. Here's why: In your perceptions, angle-of-bank is far more obvious than rate-of-turn.  While reducing angle-of-bank, you will unsuspectingly stop the turn almost immediately.  The effect is similar to the way overcoming adverse yaw delays the start of a turn.  Although you won't find this advice in any flight manual, you will discover that the most practical stratagem is to continue the turn until you just about arrive at the heading you want, then rack the plane level with plenty of aileron and rudder while holding that heading nearly constant.

With the turn abruptly stopped, the plane still takes a few seconds to finish rolling out. As the wings become level, their combined lift will no longer act in the direction of the turn but instead become fully devoted to holding the plane aloft.  While that is taking place, you must remind yourself to stop pulling back on the elevator, otherwise that extra lift you needed in the turn will cause the plane to nose up into a climb. Whoa!  Simply relaxing the elevator control will not be enough, however.  To regain the airspeed lost during the turn, you will need to push the control wheel forward for awhile.

unstable air A condition of the atmosphere in which small vertical perturbations of the air produce runaway drafts. Two separate properties of the air collaborate to produce this atmospheric phenomenon.

First, thermodynamics will mandate a change in temperature whenever a parcel of air is moved vertically. Air blowing up the side of a mountain, say, experiences a decrease in pressure and consequently cools to a lower temperature ('lapse rate,' meteorologists call it).

Second, the temperature of non-moving air generally decreases with altitude ('temperature gradient'). It simply gets colder outside when you go higher up.

Consider what might happen when a parcel of air gets lifted slightly. Its temperature goes down. The surrounding air at the higher elevation is also cooler -- but probably not cooler by exactly the same amount, since there are two phenomena involved. 
 

• Suppose that the lifted parcel cools off to a temperature lower than the surrounding air. The parcel will be slightly more dense and tend to sink back toward the elevation from which it was lifted. That's stable air.
• Suppose, on the other hand, that the lifted parcel remains slightly warmer than the surrounding air higher up. Well, the lifted parcel would be less dense and, instead of going back down, it will be lifted still higher. The cause of the initial lifting (the upslope breeze, perhaps) has been reinforced by the thermodynamics of the situation, and up goes our parcel of air like a bubble.

On a clear, summer afternoon. the sun shines through the atmosphere and warms the surface. The air aloft is affected hardly at all. It stays cool. The air adjacent to the ground, though, is warmed. The greater temperature difference -- you should excuse the expression -- gives rise to unstable air and the ascending currents of air called 'thermals.'

Best to avoid such convective frenzies. Fly in the morning.

VASI Visual Approach Slope Indicators.  Two sets of stationary lights adjacent to the beginning of the runway.  With lenses and masks, the lights form beams, such that viewing them from above a specific angle (the glide slope for that runway) shows white lights and below that angle red lights. If the pilot can see red on the set farther down the runway and white on the closer set then he or she is on the glide slope. White-over-white means the plane is approaching too high and red-over-red too low.

Red-over-white, you're all right. White-over-white, you're high as a kite. Red-over-red, you're gonna be dead.
     -- Old Aviation Saying

During instrument flight training, the student spends many hours flying around 'under the hood.' The instructor periodically takes over the controls and asks the student to cover his or her eyes. Then the instructor puts the plane through a sequence of maneuvers -- some gradual, some not so gradual -- designed to obliterate or confuse sensory inputs. After establishing the plane in an unusual attitude, the instructor traditionally calls out, "Your airplane!" Hah, then the fun begins.

The student sits up, blinks, and analyzes the instruments, some of which might have been concealed by jar-lids. Everything goes askew. The plane is either twirling toward earth or clamoring for height. The task is to re-establish straight and level flight as quickly as possible.

That may not be the end of the exercise, however. Sometimes, after curing an unusual attitude on behalf of the aeroplane, the pilot becomes afflicted with a malady of his or her own, vertigo. The student feels like the plane is not level, even though it is, and must consciously struggle not to tilt the controls in obedience to counterfeit stimuli.

Stay out of clouds.  The silver lining everyone keeps talking about might be another airplane.  Reliable sources also report that mountains have been known to hide out in clouds.
     -- Old Aviation Saying

Generally, to operate VFR, in-flight visibility is required to be greater than three miles. For landing and taking off, cloud 'ceilings' have to be higher than 1,000 feet AGL.

In the past, 'VFR' was informally used to denote the conditions that permit operating under VFR (replaced by VMC, Visual Meteorological Conditions).

WAAS Wide Area Augmentation System, a system of satellites and ground stations that provide GPS signal corrections, giving the pilot a position accuracy of three meters 95 percent of the time. 

weight-'n'-balance, pronounced as one word, although two decidedly different flight parameters are involved.

The load-carrying capacity of an aircraft is limited ultimately by the lift of its wings at take-off and the strength of its undercarriage during landing. It is incumbent upon the pilot to tally up the weight of passengers and luggage, fuel and -- oh yes -- airframe to assure that certified 'gross weight' not be exceeded.

The controllability of the aircraft is limited by the 'pitch-authority' of its elevatorwhich depends on how weight is distributed.

An aircraft is obviously heaviest at the moment of take-off and gets steadily lighter throughout the flight (the only exception is when icing is encountered, but -- hey, it's the pernicious effects of ice on the airfoil not its weight that can bring down a plane).

Not so obvious is the location of an aircraft's center-of-gravity, which can change during flight. 'Nose-heavy' any hope of 'up' gets to be out of the question. 'Tail-heavy' and -- well, stall happens, but recovery won't be physically possible.

Yaw is just one of the three axes about which an airplane can be rotated (the other two: pitch and roll). Incidentally, yaw is the only control axis you have for an automobile or a boat. How dull.

zero-zero Ceiling zero and visibility zero, the extreme opposite of CAVU. Inside a cloud, visibility is zero. At some non-zero elevation AGL, clouds can form a real ceiling, so 'zero-zero' is somewhat redundant, but the condition deserves to be emphasized.

Equipped with modern gyro instruments, private aviators can indeed take off safely in a ground fog. At this writing, airliners cannot.

After lining up with the runway by reference to a couple of runway lights, looking through the windshield is a bad idea. Everything depends on the instruments. The most essential information on the take-off roll is the heading. Best to tweak the direction gyro slightly to one side so as not to confuse any of its degree markings with the reference line ('lubber,' in nautical terms). It's an exciting experience, I can tell you...

Bring the power up smoothly while releasing the brakes. Apply slight back pressure on the elevator.  Hold right rudder against the P-factor. Check engine instruments for full power. Feel the acceleration. Adjust heading with rudders. Check airspeed. Heading again. Airspeed for rotation. Refer to artificial horizon and lift nose wheel. Feel lift-off. Vibration in the spinning wheels can be a source of distraction: tap brakes. Wings level. Check heading. Now altitude. Trim for best rate-of-climb. Reach for microphone. "Airborne."

Take-offs are optional.  Landings are mandatory.
     -- Old Aviation Saying