Glossary of Terms

Glossary of Terms

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1 in 60 Rule

The 1 in 60 rule is a rule of thumb used in air navigation, and states that if a pilot has travelled sixty miles then an error in track of 1 nm is approximately a 1° error. It is based on the small-angle approximation. In reality the error is 0.96° but this difference is trivial in air navigation.

You can also use the 1 in 60 rule to approximate your distance from a VOR by flying 90 degrees to a radial and timing how long it takes to fly 10 degrees. The time in seconds divided by 10 is roughly equal to the time in minutes from the station at your current speed.

Entry link: 1 in 60 Rule



Aircraft-based augmentation system

An augmentation system which augments and/or integrates the information obtained from the other GNSS elements with information available on board the aircraft.

Entry link: ABAS

Abortive Start

‘Abortive Start’ (turbine engines) means an attempt to start, in which the engine lights up, but fails to accelerate.

Entry link: Abortive Start

Absolute Humidity

Absolute Humidity - Absolute humidity is the total mass of water vapour present in a given volume of air. It does not take temperature into consideration. Absolute humidity in the atmosphere ranges from near zero to roughly 30 grams per cubic meter when the air is saturated at 30 °C (86 °F)

Entry link: Absolute Humidity

Accessory drives

‘Accessory drives’ means any drive shaft or utility mounting pad, furnished as a part of the auxiliary power unit, that is used for the extraction of power to drive accessories, components, or controls essential to the operation of the auxiliary power unit or any of its associated systems.

Entry link: Accessory drives


Accident. An occurrence associated with the operation of an aircraft which, in the case of a manned aircraft, takes place
between the time any person boards the aircraft with the intention of flight until such time as all such persons have
disembarked, or in the case of an unmanned aircraft, takes place between the time the aircraft is ready to move with the
purpose of flight until such time as it comes to rest at the end of the flight and the primary propulsion system is shut down,
in which:

a) a person is fatally or seriously injured as a result of:
— being in the aircraft, or
— direct contact with any part of the aircraft, including parts which have become detached from the aircraft, or
— direct exposure to jet blast,
except when the injuries are from natural causes, self-inflicted or inflicted by other persons, or when the injuries are to
stowaways hiding outside the areas normally available to the passengers and crew; or

b) the aircraft sustains damage or structural failure which:
— adversely affects the structural strength, performance or flight characteristics of the aircraft, and
— would normally require major repair or replacement of the affected component,
except for engine failure or damage, when the damage is limited to a single engine, (including its cowlings or
accessories), to propellers, wing tips, antennas, probes, vanes, tires, brakes, wheels, fairings, panels, landing gear
doors, windscreens, the aircraft skin (such as small dents or puncture holes), or for minor damages to main rotor
blades, tail rotor blades, landing gear, and those resulting from hail or bird strike (including holes in the radome); or

c) the aircraft is missing or is completely inaccessible

Note 1.— For statistical uniformity only, an injury resulting in death within thirty days of the date of the accident is
classified, by ICAO, as a fatal injury.

Note 2.— An aircraft is considered to be missing when the official search has been terminated and the wreckage has not
been located.

Note 3.— The type of unmanned aircraft system to be investigated is addressed in ICAO Annex 13, 5.1.

Note 4.— Guidance for the determination of aircraft damage can be found in ICAO Annex 13, Attachment G.

Entry link: Accident

Accredited representative

Accredited representative. A person designated by a State, on the basis of his or her qualifications, for the purpose of
participating in an investigation conducted by another State. Where the State has established an accident investigation
authority, the designated accredited representative would normally be from that authority.

Entry link: Accredited representative


A.C.D. - Additional Control Device

Entry link: ACD


Aircraft classification number (ACN). A number expressing the relative effect of an aircraft on a pavement for a specified
standard subgrade category.
Note.C The aircraft classification number is calculated with respect to the center of gravity (CG) position which yields the
critical loading on the critical gear. Normally the aftmost CG position appropriate to the maximum gross apron (ramp) mass
is used to calculate the ACN. In exceptional cases the forwardmost CG position may result in the nose gear loading being
more critical.

Entry link: ACN

Acrobatic flight

“acrobatic flight” means manoeuvres intentionally performed by an aircraft involving an
abrupt change in its attitude, an abnormal attitude, or an abnormal variation in speed

Entry link: Acrobatic flight

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