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Glossary

Every term, in plain language

Each definition is written in plain English, cites the FAA source it comes from, and names the volume and chapter where the term is taught in full.

Showing 16 of 2,368 terms. Search, pick a letter or show all.

0–9
0.55 pound threshold
The weight at or below which registration is not required, counting everything on board or attached to the aircraft. It is also the Category 1 weight limit.
Source: 14 CFR 48.15(b).
0–9
100-hour inspection
An inspection required every 100 hours of time in service for aircraft carrying people for hire or used for flight instruction for hire.
Source: 14 CFR 91.409(b). Taught in: AMT Vol. 1, Ch. 11
100-hour overfly allowance
A 100-hour inspection may be exceeded by up to ten hours, and only while flying to the place where the inspection will be done. The hours used count against the next interval rather than being forgiven.
Source: 14 CFR 91.409(b).
0–9
3P model
A three-step loop run continuously through a flight: Perceive the hazards, Process the risk they carry, and Perform the mitigation.
Source: FAA-H-8083-9 Ch. 1.
0–9
400 feet AGL limit
The maximum height above the ground for a small unmanned aircraft operation, absent a waiver or the structure exception.
Source: 14 CFR 107.51(b).
400-foot structure exception
An aircraft may climb above 400 feet above ground level while within a 400-foot radius of a structure, but no more than 400 feet above that structure's uppermost limit.
Source: 14 CFR 107.51(b)(2).
0–9
87 knots groundspeed limit
The maximum groundspeed for a small unmanned aircraft, equal to 100 miles per hour.
Source: 14 CFR 107.51(a).
0–9
9900
A winds aloft code meaning light and variable: either calm or less than five knots.
Source: PHAK FAA-H-8083-25C Ch.13.
A
Abbreviated briefing
A briefing used to update one already received, to fill in around mass-disseminated information, or to get one or two specific items. Say what you already have so the briefer can work from it.
Source: AIM 7-1-5.
Abeam
A position roughly 90 degrees off the left or right of the aircraft's track. It fixes a general position, not a precise one.
Source: FAA Pilot/Controller Glossary, eff. 7/9/2026.
Aborted takeoff
A takeoff stopped before it is completed because something has been found that makes continuing dangerous. It is a decision made against criteria set before the roll begins, not judged in the moment.
Source: AMT Airframe FAA-H-8083-31B.
Abradable strip
A soft liner in the compressor housing of some axial flow turbine engines. The blade tips cut their own groove into it on the first runs, so each blade ends up with the tightest clearance it can have without binding.
Source: AMT Powerplant FAA-H-8083-32B.
Abradable tip (compressor blade tip)
A compressor blade tip made to wear away rather than resist when it touches the housing. Sacrificing a little of the blade is what holds tip clearance to a minimum, and tip clearance is what keeps compressed air from leaking backward past the blade.
Source: AMT Powerplant FAA-H-8083-32B.
Absolute humidity
The actual quantity of water vapor present in a mixture of air and water. It is an amount rather than a proportion, which is what distinguishes it from relative humidity.
Source: AMT General FAA-H-8083-30B.
Absolute pressure
Pressure counted up from a perfect vacuum rather than from the air around you. It is written psia, and it is the only way to express pressure when the surrounding air pressure is itself changing, as it does with altitude.
Source: AMT Powerplant FAA-H-8083-32B; AMT Airframe FAA-H-8083-31B; AMT General FAA-H-8083-30B.
Absolute pressure regulator
A valve at the inlet of a pneumatic system compressor that controls inlet air pressure. Holding inlet pressure steady keeps the compressor from varying in speed or overspeeding as altitude changes.
Source: AMT Airframe FAA-H-8083-31B.

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