FTDT Definitions — USA (FAR Part 117)

Updated: 2026-06-26 · Audited: 2026-06-26

Definitions marked [§117.3] are defined verbatim (or substantially verbatim) under 14 CFR § 117.3. Terms marked [App-specific] are ALPA FTDT application conventions and are not defined terms under 14 CFR § 117.3.

§117.3 Defined Terms

[§117.3] Flight Duty Period (FDP)

A period that begins when a flightcrew member is required to report for duty with the intention of conducting a flight, a series of flights, or positioning or ferrying flights, and ends when the aircraft is parked after the last flight and there is no intention for further aircraft movement by the same flightcrew member. A flight duty period includes the duties performed by the flightcrew member on behalf of the certificate holder that occur before a flight segment or between flight segments without a required intervening rest period. Examples of tasks that are part of the flight duty period include deadhead transportation, training conducted in an aircraft or flight simulator, and airport/standby reserve, if the above tasks occur before a flight segment or between flight segments without an intervening required rest period.

[§117.3] Theater

A geographical area in which the distance between the flightcrew member's FDP departure point and arrival point differs by no more than 60 degrees longitude.

[§117.3] Acclimated

A condition in which a flightcrew member has been in a theater for 72 hours or has been given at least 36 consecutive hours free from duty.

[§117.3] Deadhead Transportation

Transportation of a flightcrew member as a passenger or non-operating flightcrew member, by any mode of transportation, as required by a certificate holder, excluding transportation to or from a suitable accommodation. All time spent in deadhead transportation is duty and is not rest. For purposes of determining the maximum flight duty period in Table B, deadhead transportation is not considered a flight segment.

[§117.3] Duty

Any task that a flightcrew member performs as required by the certificate holder, including but not limited to flight duty period, flight duty, pre- and post-flight duties, administrative work, training, deadhead transportation, aircraft positioning on the ground, aircraft loading, and aircraft servicing.

[§117.3] Fatigue

A physiological state of reduced mental or physical performance capability resulting from lack of sleep or increased physical activity that can reduce a flightcrew member's alertness and ability to safely operate an aircraft or perform safety-related duties.

[§117.3] Home Base

The location designated by a certificate holder where a flightcrew member normally begins and ends his or her duty periods. Home base is used in § 117.25(d) to determine eligibility for the 56-hour trans-theater rest requirement and to define physiological night's rest.

[§117.3] Physiological Night's Rest

10 hours of rest that encompass the hours of 0100 and 0700 at the flightcrew member's home base, unless the individual has acclimated to a different theater. If the flightcrew member has acclimated to a different theater, the rest must encompass the hours of 0100 and 0700 at the acclimated location.

[§117.3] Reserve Flightcrew Member

A flightcrew member who a certificate holder requires to be available to receive an assignment for duty.

[§117.3] Rest Period

A continuous period determined prospectively during which the flightcrew member is free from all restraint by the certificate holder, including freedom from present responsibility for work should the occasion arise.

[§117.3] Short-Call Reserve

A period of time in which a flightcrew member is assigned to a reserve availability period.

[§117.3] Long-Call Reserve

Prior to beginning the rest period required by § 117.25, the flightcrew member is notified by the certificate holder to report for a flight duty period following the completion of the rest period. The flightcrew member must receive at least 10 hours' notice before the start of the FDP.

[§117.3] Unforeseen Operational Circumstance

An unplanned event of insufficient duration to allow for adjustments to schedules, including unforecast weather, equipment malfunction, or air traffic delay that is not reasonably expected. This is the prerequisite condition for any FDP extension under § 117.19.

[§117.3] Window of Circadian Low (WOCL)

A period of maximum sleepiness that occurs between 0200 and 0559 during a physiological night. The WOCL is relevant to § 117.17 cumulative limitations and to FDP extension restrictions under § 117.19.

[§117.3] Rest Facility Classes

Rest facility class determines the maximum augmented FDP under Table C to Part 117:

Reserve Duty

Reserve duty is divided into three categories:

App-Specific Terms

The following terms are used within the ALPA FTDT application for calculation and display purposes. They are not defined terms under 14 CFR § 117.3.
[App-specific] Extension

An FDP that has been extended beyond its Table B maximum due to an unforeseen operational circumstance, as governed by § 117.19. Extension is not a standalone defined term under § 117.3; the regulatory framework for extensions is found in § 117.19.

[App-specific] Rest Availability Period (RAP)

This application's shorthand for the reserve availability period during which a certificate holder requires a flightcrew member on short-call reserve to be available to receive an assignment for a FDP. The terms "RAP" and "Rest Availability Period" are not defined in § 117.3; the regulation uses "reserve availability period" as part of the Short-call reserve definition. For calculation purposes, RAP time counts as FDP hours.

[App-specific] Rest Opportunity (RO)

This application's shorthand for the sleep opportunity afforded to a flightcrew member during a split-duty FDP, as governed by § 117.15. The terms "Rest Opportunity" and "RO" are not defined in § 117.3. A valid RO effectively splits the FDP for legality purposes. For calculation purposes, RO time does not count as FDP hours.

FDP Types

A Flight Duty Period is categorized by operation type: