Introductory Overview

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Definitions to be applied to FAR part 117

FAR 117.1 Applicability:

FAR part 117, applies to all certificate holders conducting passenger operations under FAR part 121 subparts Q, R or S. The regulation also applies to part 91 operations should those operations be conducted without the required rest period before as stipulated within 117.25.

General Concepts:

The FAA introduced several new concepts as well as a re-definition / clarification of several existing concepts.
Most of the concepts are defined in the definitions section (117.3), while many concepts are not new to the industry, the exact definition in FAR 117, should be compared to pre-existing definitions contained in contract agreements and/or operations manuals.


  • new concept – a state of a crewmember, used in conjunction with Acclimatization and Theater.


  • new concept – a process, used in conjunction with Acclimated and Theater.

Calendar Day:

  • re-defined – impacts accumulated flight time limitations in 365 calendar days.

Duty Break

  • new concept – impacts Split Duty and Night Duty.

Flight Duty Period (FDP):

  • new concept

Night Duty:

  • new concept – impacts Split Duty.

Physiological Night Rest

  • new concept – impacts rest requirements.
  • known by other names such as Overnight Rest Period, Local Night’s Rest, etc.

Rest Facility:

  • clarification – impacts Crew schemes.

Rest Opportunity:

  • new concept – impacts Rest Period.

Rest Period

  • re-defined – impacted by Rest Opportunity.

Split Duty:

  • new concept – impacted by Night Duty and Duty Break.
  • known by other names such as Continuous Duty Overnight (CDO), High speed, Night Turns etc.


  • new concept – based upon Longitude, used in conjunction with Acclimatization and Acclimated.

Window of Circadian Low (WOCL):

  • new concept – impacts Night Duty.
  1. Rest is required before a Flight Duty Period (FDP), a Flightcrew member (FCM) must be given a rest period in order to report for an assigned FDP.
  2. A diurnal component is used to limit both Flight Time and FDP with higher and lower limitations coinciding, respectfully, with peak and low alertness.
  3. Daily FDP is also limited by the number of take-offs and landings, with fewer landings allowing for higher flight time.
  4. It is NOT permitted to extend the Daily Flight Time Limitations before takeoff.
  5. It IS permitted to extend a FDP above scheduled limitations by upto 2 hours due to unforeseen circumstances.
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    Definitions to be applied to FAR part 117


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