Wednesday, December 2, 2009


This Glossary is intended to provide some idea of the meanings of abbreviations, acronyms, jargon and terms of art that may find their way into posts without adequate definition. It will be maintained in the sidebar and will always be a work in progress, as I will add to it and refine the definitions as allowed by improved understanding and corrective inputs.

These are not definitions that I've looked up. They represent my understanding of the meanings of the terms, and that may evolve. If you think I've got something wrong, please let me know via the comment field or by e-mail (the address is in my profile).



AD - Airworthiness Directive. An order from the FAA specifying actions that must be taken to maintain the airworthiness of subject aircraft. In practical effect, an AD is a modification to the aircraft's Type Certificate.

AIRMET - AIRman's METeorological Information. A notification of reported or forecast widespread conditions that may affect aircraft operations, not rising to the level that would justify a SIGMET. AIRMET's come in three flavors - AIRMET SIERRA for IFR and mountain obscuration conditions; AIRMET TANGO for turbulence; and AIRMET ZULU for icing conditions. If any of these are extant, the nice weather briefer from Lockheed-Martin will be sure to tell you. Colloquially referred to as "Scare-MET's" because they are invoked at the slightest hint of adverse conditions, seemingly in a CYA mode, by the weather people. SIGMET's are an entirely different kettle of fish.

AMTRAK - The ultimate "Plan B". Transportation mode usable for travel from Connecticut to DC (and back) in zero/zero conditions at 0 feet AGL. Usually averages about 55 knots ground speed.

ATC - The FAA's Air Traffic Control organization, encompassing Air Route Traffic Control Centers (ARTCC), Terminal Radar Control facilities (TRACON - aka "Approach" and "Departure") and Air Traffic Control Towers (ATCT). ATC is the source of all clearances and the employer of all those wonderful controllers.

AVGAS - Aviation Gasoline, as distinct from MoGas (which is the stuff you put in your car). Also referred to as 100LL (pronounced "one-hundred low-lead"). Normally fed to reciprocating aircraft engines, it's the last fuel containing tetra-ethyl lead (an anti-detonation additive) commonly sold in the US. A dinosaur among petroleum products, its demise has been predicted for years but to date no successful substitute has been developed. That may be changing.

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BDR - The FAA identifier for KBDR.

Broken - Refers to a cloud layer that covers from 5/8 to 7/8 of the sky.

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Ceiling - The height above ground level of the lowest layer of clouds reported as either broken or overcast.

Clag - Jargon. Generic gusty, wet, low, opaque weather. Probably absorbed from UK railway terminology during WW2. According to Wikipedia, the term formerly referred to the exhaust of steam locomotives - "clag" is a term describing "the often spectacular (particularly blackened, as in Class 37, or whitesmoked, as in Class 55) exhaust emissions of many older British diesel locomotives, especially, Classes 52 and 55." See also, schmoo.

Class B Airspace - The airspace surrounding major air-carrier airports like JFK and O'Hare. The canonical Class B airspace geometry is an "upside-down wedding cake" form centered on the airport and extending up to 10,000 feet MSL and out to 20 miles at its greatest extent. (Individual Class B designs may vary substantially.) All aircraft require a specific ATC clearance to enter the Class B, and all aircraft therein are under positive control.

Clearance Delivery - A discrete radio frequency available at fairly active airports that's reserved for the issuance and readback of IFR clearances. Avoids cluttering up the local control frequencies, tower and ground.

CTAF - Common Traffic Advisory Frequency, a radio frequency assigned for the use of pilots in the vicinity of non-towered fields to exchange information on location and intentions so that conflicts between aircraft are avoided.

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DA - Decision Altitude, the altitude at which a pilot flying an ILS approach must decide whether to continue the approach to the runway or execute the missed approach procedure. Formerly known as "Decision Height", the new terminology was adopted because "heights" normally reference the ground and DA is referenced to MSL.

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FBO - Fixed Base Operator, in essence an Aviation Full-Service Gas Station (with affiliated Driving School). Nearly every airport hosts one or more FBO's. They provide ramp services, sell fuel, offer crew facilities, accomplish repairs, and give flight training. FBO owners are the unsung heroes of General Aviation - without them our entire system would grind to a halt. Usually, these businesses are so pathetically unprofitable that only a crazy person or an addict would own one. Fortunately, aviation is very addictive.

FRZ - Flight Restricted Zone, the "inner core" of the Washington SFRA, essentially the airspace within 15 nm of the DCA VOR (located on the field at Washington National Airport (KDCA)), from the surface up to but not including 18,000 feet MSL. Additional security requirements (over and above those applicable in the SFRA) are imposed on operations in the FRZ. Positive identification procedures are in place and all pilots must be vetted and cleared. The FRZ may be the only airspace in the US where the security provisions extend beyond pointless "security theater" in their effectiveness.

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George - Venerable jargon term for the aircraft's autopilot. Dates back at least to WW2, when the most junior member of a unit was referred to as George, regardless of his actual name. Common usage, relative to any boring or undesirable task was, "Let George do it."

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ICAO - International Civil Aviation Organization, a supra-national body charged with the naming of names and the homogenization of standards for all things related to air transport.

IFR - Instrument Flight Rules, the regulatory regime governing operations in IMC, where the airplane is controlled by reference to instruments rather than external visual references. For IFR operations, the airplane must be properly equipped and the pilot must be instrument rated and current.

ILS - Instrument Landing System, for decades the gold standard for bad-weather landing aids. The system consists of two precisely calibrated ground-based radio transmitters that provide both horizontal (Localizer) and vertical (Glideslope) guidance to the approaching aircraft. The receiver on the aircraft uses the signals to provide a visual display to the pilot in the form of vertical and horizontal needles that should be kept centered. The ILS system is normally effective down to visibilities of less than a mile and ceiling heights of 250 feet. In emergencies, pilots have been known to follow the ILS signals all the way down to the runway.

IMC - Instrument Meteorological Conditions, i.e., conditions where either the ceiling or the flight visibility does not meet minimum requirements for flight by visual references.

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KBDR - The ICAO identifier for Igor Sikorsky Memorial Airport, located in Stratford, CT. The airport is owned and operated by the nearby City of Bridgeport even though it lies entirely within Stratford's boundaries. This odd circumstance has caused substantial ill will and controversy over the years.

knots - Nautical miles per hour. The modern definition of a nautical mile is exactly 1,852 meters, which equals 6,076.115 feet. Therefore, 1 NM = 1.1508 statute miles and 1 knot = 1.1508 mph. The historical definition of the nautical mile was the length of one minute (i.e., 1/60th of one degree) of latitude which is quite close enough for most purposes.

KVKX - The ICAO identifier for Potomac Airfield in Friendly, MD. It is, along with Hyde Field and College Park, one of the "DC-3" airports that lie within the Washington, DC Flight Restricted Zone.

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MDA - Minimum Descent Altitude, the lowest altitude to which a pilot flying a non-precision instrument approach may descend without having the runway environment in sight.

METAR - The acronym for the (usually) hourly report of weather conditions at an airport. From the expression for "Aviation Routine Weather Report" in French (MÉTéorologique Aviation Régulière). Typically provides winds, visibility, source of any obscuration, sky condition (i.e., clouds), temperature, dew point, and barometric altimeter setting. Other interesting information is often added in the RMK section. Before the adoption of ICAO acronyms in the interest of international amity and harmonization, this was known as the SA report and provided input to the Surface Analysis chart.

MSL - Indicates an altitude above the datum defined by Mean Sea Level. This is the altitude reported by a barometric altimeter adjusted to the correct local altimeter setting.

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NOTAM - A contraction of "Notice to Airmen". The NOTAM system is an obsolete and archaic mechanism intended for the timely distribution of late information of current importance to pilots operating in the National Airspace System. If a pilot is fortunate, he may be able to obtain NOTAM's pertinent to an intended flight from several sources. Or not.

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OAT - Outside Air Temperature. This is a very interesting number for pilots flying in visible moisture (rain or clouds) during cold weather.

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PIC - Pilot-in-Command, the person who, according to the FAA, "is directly responsible for, and is the final authority as to, the operation of [the] aircraft." Further, in "an in-flight emergency requiring immediate action, the pilot in command may deviate from any rule ... to the extent required to meet that emergency." In other words, for good or ill, "it's your baby, Captain."

pirep - Pilot Report, a description of flight conditions filed by radio, in a specified format and sequence, with Flight Service. One good pirep is worth a hundred forecasts.

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SAIB - Special Airworthiness Information Bulletin - An FAA document that promulgates important safety-related information throughout the aviation community. The content is considered urgent but not so critical as to warrant issuance of an Airworthiness Directive (AD).

Scattered - Refers to a cloud layer that covers between 3/8 and 4/8 of the sky.

Schmoo - Jargon. Generic gusty, wet, low, opaque weather. See also, clag.

Sectional Chart - An aeronautical chart used for navigation on flights under VFR conditions. The continental US is covered by 38 of these charts. They are usually referred to simply as "sectionals". The scale of a sectional is 1:500,000 which is about 6.85 nautical miles per inch. The charts can be ordered on-line from the National Aeronautical Charting Office (NACO).

SFRA - Special Flight Rules Area, an area where the FAA has determined that additional requirements need to be imposed permanently on aircraft operations, in contrast to a TFR, which is promulgated by NOTAM and is by definition temporary. These requirements are codified as a sub-part of 14 CFR 93. Among the SFRA's are the airspace over Niagara Falls, the Hudson and East River Exclusions from the New York Class B Airspace, the Grand Canyon and the airspace surrounding Washington, DC.

SIGMET - SIGnificant METeorological Information. Notifications of Really Serious Weather that will affect flight operations. In contrast to AIRMET's, a SIGMET is as serious as a heart attack. Comes in two flavors: SIGMET for SEVERE icing, turbulence, and other met phenomena, and Convective SIGMET for severe thunderstorms, lines of thunderstorms and tornadoes. Before the advent of in-cockpit weather displays, the prudent pilot looked at SIGMET's as No-Fly Zones. Today, with much better information on what is happening within the SIGMET boundaries, it can be prudent to trim the edges or cut the corners. Finally, an active SIGMET can be a useful stick to beat ATC over the head with to get them to modify an undesirable IFR clearance into something more sensible.

Situational Awareness - Sometimes abbreviated 'SA', the cognitive state vital to any aviator, wherein he or she knows with adequate accuracy and precision where the airplane is, where it is going, what it's doing now, what will happen next, and what is out there that could hurt. Loss of Situational Awareness (a.k.a. LOSA, or "getting behind the airplane") figures into many accidents and incidents.

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TAC - Terminal Area Chart, pronounced "tack". A VFR aeronautical chart prepared at twice the scale of a sectional, i.e., 1:250,000 or 3.43 nautical miles per inch. TAC's are centered on the primary airport(s) of Class B Airspaces. There are 27 of them in the continental US. TAC's can be ordered on-line from the National Aeronautical Charting Office (NACO).

TAF - Terminal Area Forecast, a prediction of weather conditions expected to prevail within about a 5 statute mile radius of an airport over a 24 hour period (or 30 hours for major international airports). TAF's are issued four times daily, at 00Z, 06Z, 12Z and 18Z. They are usually available 15 to 30 minutes prior to the official time of issue. The TAF will include forecasted winds, visibility, type of obscuration if any, and sky condition (i.e., clouds).

TFR - Temporary Flight Restriction, a limitation on aircraft operations, promulgated by NOTAM, and typically short term. Reasons for TFR's include emergency operations (fire, disaster relief or law enforcement), VIP movements, or adverse meteorological conditions.

Transponder - A radio transceiver installed in nearly all aircraft that receives an interrogating signal from an FAA radar facility and responds with an answering signal that includes a pilot-assignable four-digit code and usually the altitude of the aircraft. The radar derives azimuth and range from the response and appends the received code and altitude for display on the controller's screen. If the transponder fails or is turned off, only the much weaker "primary" radar return is available for ATC use.

Type Certificate - A document approved by the FAA that describes in detail the characteristics of a Certificated aircraft. To be regarded as Airworthy, an aircraft must be maintained at all times in conformance with its Type Certificate (as properly modified).
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VFR - Visual Flight Rules, the regulatory regime that governs flight controlled by external visual references. VFR flight must be conducted in VMC.

VKX - The FAA identifier for KVKX.

VMC - Visual Meteorological Conditions, where clouds and visibility are good enough to permit VFR operations. Specific conditions vary with time and location, but basic day VFR requires at least 3 statute miles visibility and a sky condition that will permit the pilot to remain at least 500 feet below or 1,000 feet above or 2,000 feet away horizontally from any cloud or similar obscuration.

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XM Weather - A service that provides nearly-real-time weather data in the cockpit via satellite broadcast. Aboard N631S this is displayed on a Garmin GPSmap 396 portable GPS receiver. The service provides NEXRAD weather radar, cloud cover, winds, echo tops, lightning, storm cells, METAR's, TAF's, AIRMET's, SIGMET's and forecasts.

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Z - Indicator for "Zulu" time. Outside of aviation and military communities, this is known as UTC (which abbreviates, more or less, "Coordinated Universal Time"). We all used to use Greenwich Mean Time (GMT) but that standard is now officially out of favor because GMT is an astronomical time whereas UTC is an atomic-clock-based standard. On the East coast of the USA, Z is 5 hours ahead of the local clock during Standard Time (i.e., 7 AM EST = 12Z), and 4 hours ahead during Daylight Saving Time (8 AM EDT = 12Z). Incidentally, back in the 1970's when the International Telecommunications Union set all this up, the English-speakers wanted to use CUT to abbreviate Coordinated Universal Time but the French, bless their hearts, wanted to use TUC (for "Temps Universel Coordonné"). UTC was used as a compromise.

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