What is the difference between flight time and flight duty period under Part 117?

Flight time is the period from an aircraft's first movement under its own power until it comes to rest at the end of a flight, and it counts toward the 100-hour and 1,000-hour cumulative limits. The flight duty period (FDP) is broader — it begins the moment a crewmember is required to report for duty and ends when the aircraft parks at the conclusion of the last flight, so all ground time before departure and between legs is included. A crewmember can exhaust FDP hours without accumulating equivalent flight time simply by sitting through lengthy ground delays.

How does the time of day affect the maximum flight duty period under 14 CFR Part 117?

Part 117 uses a physiologically based table that reduces the maximum FDP for FDPs starting during the crewmember's early morning hours — roughly 0200 to 0559 acclimated time — because human alertness and cognitive performance are at their lowest near the circadian nadir. A two-pilot crew starting an FDP at that time may be limited to as few as 9 hours, while the same crew starting mid-afternoon could be permitted up to 13 hours for a comparable number of segments. The applicable time is keyed to the crewmember's acclimated time zone, not simply the local time at the departure city.

Does Part 117 apply to Part 135 charter operations?

No. Part 117 applies exclusively to flightcrew members conducting operations under 14 CFR Part 121 — that is, scheduled domestic, flag, and supplemental air carrier operations. Pilots flying under Part 135 on-demand or commuter operations are subject to a separate and distinct set of flight and duty time rules found in 14 CFR Part 135, Subpart F. Applying Part 117 limits to a Part 135 scenario on the ATP knowledge test or in actual operations would be incorrect.

Flight and Duty Time Limitations Under Part 117

Pilot fatigue has been identified repeatedly by the National Transportation Safety Board as a causal or contributing factor in air carrier accidents. In response, the FAA overhauled its flight and duty time rules with 14 CFR Part 117, which took effect in January 2014 and applies to all flightcrew members operating under 14 CFR Part 121 — that is, domestic, flag, and supplemental scheduled air carrier operations. For any pilot pursuing an Airline Transport Pilot certificate, Part 117 is not just a knowledge-test topic; it is the regulatory backbone of every line schedule worked throughout a career. What follows is a thorough, operationally grounded breakdown of how these rules work, why they are structured the way they are, and where the most common misunderstandings arise.

The Three Foundational Definitions

Before touching a single number, you must have three definitions locked in, because Part 117 is built entirely on the precise relationship among them.

Flight time: The interval from the moment an aircraft first moves under its own power for the purpose of flight until it comes to rest at the end of that flight. This is the classic "block time" concept and is what accumulates toward the 100-hour and 1,000-hour cumulative ceilings.
Flight duty period (FDP): The period that begins when a crewmember is required to report for duty and ends when the aircraft is parked following the last flight of that duty period. Ground time before departure, time between legs, and taxi time all count inside the FDP even though none of it is "flight time." This is the most frequently misunderstood relationship on the knowledge test.
Rest period: A continuous, uninterrupted period free from all duty, including deadhead transportation when the carrier requires it. The rest period is measured differently from simple "time off," and quality — specifically the opportunity for uninterrupted sleep — matters as much as quantity.

Cumulative Flight Time Limits

Part 117 sets two hard ceilings on the total flight time a flightcrew member may accumulate, regardless of rest received:

100 flight hours in any 672 consecutive hours (equivalent to 28 days, not a calendar month).
1,000 flight hours in any 365 consecutive calendar days.

The 672-hour window is a rolling look-back, not a reset that occurs at the start of each month. A pilot who flew 90 hours in the last 27 days can fly only 10 more hours in the next 24 hours before hitting the ceiling — regardless of where those hours fall on a calendar page. This rolling nature is one of the most reliable distractor techniques used on ATP knowledge test questions.

Maximum Flight Duty Period: The Table-Based System

Unlike the older Part 121 Subpart Q rules, which used fixed duty-time limits independent of when the duty started, Part 117 uses a physiologically driven table that adjusts the maximum allowable FDP based on two variables: the time of day at which the FDP begins (measured against the crewmember's acclimated time zone) and the number of flight segments to be flown during that FDP.

The underlying science is circadian biology. Human alertness follows a roughly 24-hour cycle driven by the suprachiasmatic nucleus, and performance degrades most severely during the early morning hours — roughly 0200 to 0559 local acclimated time — when core body temperature is at its nadir. Part 117 accounts for this by compressing the maximum FDP at those hours and allowing longer FDPs during the middle of the biological day.

For a standard two-pilot crew, the maximum FDP for a single-segment operation started during the most permissive window (roughly 1300–1659 acclimated time) is 13 hours. That same crew starting their FDP between 0200 and 0459 may be limited to as few as 9 hours. As the number of flight segments increases, the maximum FDP is further reduced — each additional segment adds to mental workload and the potential for cumulative error. By the time a crew is flying five or more segments, the FDP ceiling drops further still, even during daytime starts.

An important nuance: Part 117 uses the crewmember's acclimated time zone, defined as the time zone the crewmember has been in for the preceding 72 hours or more. A pilot who just flew from New York to Los Angeles is not immediately operating on Pacific time for regulatory purposes — the body's clock takes time to shift, and the regulation acknowledges that physiological lag.

Rest Requirements Before and After an FDP

Before beginning any FDP, a flightcrew member must have received a minimum 10 consecutive hours of rest. Critically, that 10-hour rest period must include an opportunity for at least 8 hours of uninterrupted sleep. If commuting, eating, or any other activity consumes time during the rest window and reduces the sleep opportunity below 8 hours, the carrier is obligated to extend the rest period until the full 8-hour sleep opportunity has been available — even if that delays the next departure.

After an FDP that exceeds a certain length or occurs during particularly fatiguing hours, a 30-hour rest period may be required before the next FDP. This longer rest window is designed to allow full physiological recovery from a severely fatiguing duty period and represents one of the more operationally significant limits planners must accommodate.

Augmented Crews and Rest Facility Classes

For long-haul operations — transoceanic routes or other extended-range flights — carriers may use an augmented crew of three or more pilots. With an augmented crew, one pilot at a time can be relieved of active flying duties and rest in an onboard rest facility, which allows the FDP itself to be extended beyond the two-pilot maximums. However, the amount of extension permitted depends directly on the quality of the onboard rest facility, which Part 117 categorizes into three classes:

Class 1 rest facility: A bunk or seat that reclines to a flat, horizontal position, separated from the flightdeck and passenger cabin, with access to individual lighting and temperature controls. This is the highest-quality facility and permits the greatest FDP extension.
Class 2 rest facility: A seat that reclines at least 40 degrees, with leg and foot rests, located in a separate compartment from passengers (typically separated by a curtain or partition). Permits a moderate extension — less than Class 1, more than Class 3.
Class 3 rest facility: A standard passenger seat or crew seat in the passenger cabin — the minimum acceptable facility. Permits the smallest extension of the three classes.

The practical implication is that airlines operating long-haul routes have a direct operational and economic incentive to equip aircraft with Class 1 rest facilities, since better facilities unlock longer legally permitted FDPs and reduce the need to carry an additional crew member.

Fatigue Reporting and FRMS

Part 117 also mandates that covered carriers establish procedures under which any flightcrew member who believes they are too fatigued to fly safely must report that condition without fear of reprisal. Carriers operating under an approved Fatigue Risk Management System (FRMS) may apply for authorization to use alternative compliance methods based on data-driven fatigue modeling, subject to FAA approval and ongoing monitoring. The FRMS pathway underscores the regulation's intent: the tables are a floor, not a ceiling for safety decision-making.

Key Numbers and Rules Summary

Minimum pre-FDP rest: 10 consecutive hours, including an 8-hour sleep opportunity.
Cumulative flight time limits: 100 hours / 672 consecutive hours and 1,000 hours / 365 consecutive calendar days.
Maximum FDP for a two-pilot crew ranges from roughly 9 hours to 13 hours, depending on start time and segment count.
Augmented crew FDP extensions depend on Class 1, 2, or 3 rest facility quality.
Part 117 applies only to Part 121 operations — not Part 135 or Part 91.
The acclimated time zone governs which column of the FDP table applies — not local departure-city time.

Common Test Traps

FDP begins at report time, not pushback: Every minute of pre-departure ground time counts. A crewmember who reports at 0600 and departs at 0800 has already consumed two hours of FDP before leaving the gate.
28 days ≠ calendar month: The 100-hour limit uses any rolling 672-hour window, not a fixed monthly reset. A month has 28, 29, 30, or 31 days; the regulation does not care — it always looks back exactly 672 hours.
Rest opportunity vs. rest period: The regulation demands that 8 hours of sleep be possible, not just that 10 hours of rest be scheduled. If anything eats into those 10 hours, more rest is required.
Acclimated time, not local time: A pilot who landed in Frankfurt yesterday is still operating on their home-base biological clock for up to 72 hours. Using local Frankfurt time to determine which FDP table row applies would be an error.
Part 117 is not Part 135: On-demand charter pilots operating under Part 135 follow an entirely separate set of flight and duty rules found in 14 CFR Part 135, Subpart F. Never mix these on an exam scenario.

Memory Aid

Anchor the cumulative limits with "10 — 100 — 1,000": 10 hours minimum rest before each FDP, 100 flight hours in any 28-day (672-hour) window, 1,000 flight hours in any 365-day window. This three-number chain will not substitute for knowing the FDP tables, but it reliably prevents the most common errors on cumulative-limit questions.