Almost every fatigue rule is built from four ideas: flight time, the flight duty period, duty, and rest. Getting them straight, and understanding how the flight duty period is worked out, is the foundation for reading any flight time limitation scheme. This goes a level deeper than our overview of flight time limitations.
This is general educational information, not operational, legal, or regulatory advice. Rules differ by authority and change over time. Always verify against current official sources and follow your operator's approved procedures.
The four terms
The EASA definitions in ORO.FTL.105 and the FAA Part 117 definitions in 14 CFR 117.3 describe the same four ideas in close, but not identical, terms. The one that looks most identical, flight time, is where they actually part.
- Flight time is block time, and each authority measures the block differently. Under EASA (ORO.FTL.105) it is the time from the aircraft first moving from its parking place for the purpose of taking off until it comes to rest on the designated parking position and all engines or propellers are shut down. There is no "under its own power" limb, so a pushback counts, and the clock does not stop until the engines do. Under the FAA, Part 117 does not define flight time at all: the definition lives in 14 CFR 1.1, and it runs from when the aircraft moves under its own power for the purpose of flight until it comes to rest after landing. Close enough to feel like one rule, different enough to give you different minutes.
- Flight duty period (FDP) runs from the moment you are required to report for a flight or a series of flights until the aircraft finally comes to rest and the engines are shut down at the end of the last sector. It is flight time plus the ground time between and around the sectors.
- Duty is broader again: any task the operator requires you to carry out, including the FDP, positioning, training, and administrative duties.
- Rest is a continuous, protected period during which you are free of all duties and can sleep.
Picture them nested: flight time sits inside the flight duty period, which sits inside duty, with rest as the counterweight that has to come before the next duty begins.
How the maximum FDP is built
The flight duty period is the one that drives the working day, and its maximum is not a single number. It is built from two main inputs.
Report time. Both systems recognise that a duty starting in the small hours, when the body expects to be asleep, is more fatiguing. EASA reduces the maximum FDP for reports that fall in or touch the window of circadian low (WOCL), roughly 0200 to 0559 in the time zone you are acclimatised to. The FAA's Table B in 14 CFR 117.13 sets the maximum FDP directly against the local report time.
Number of sectors. More take-offs and landings mean more workload, so both systems cut the maximum FDP as the count rises. This is worth saying plainly, because it is routinely taught as an EASA-only idea and it is not. EASA's ORO.FTL.205 table steps down sector by sector: at the most favourable report times it gives 13 hours for one or two sectors and falls to 9 hours by ten. The FAA's Table B does the same job under the name flight segments, and the step is not trivial: the 0700 to 1159 row runs 14, 14, 13, 13, 12.5, 12 and 11.5 hours for one through seven or more segments, a two-and-a-half-hour reduction across the range.
As an illustration with the source attached: under EASA, the basic maximum daily FDP for an acclimatised crew starting at the most favourable time is 13 hours, reduced from there for unfavourable report times and for additional sectors (EASA ORO.FTL.205). Under the FAA, the unaugmented maximum FDP runs up to 14 hours at the most favourable report times and reduces from there for both an unfavourable report and additional segments (FAA 14 CFR 117.13, Table B). These are not the same number for the same situation, which is the whole point: read the table for your authority and your day.
Extensions and commander's discretion
The maximum FDP can be stretched, but only within defined bounds:
- Planned extension. EASA allows the maximum daily FDP to be extended by up to one hour a limited number of times within a period, under conditions set in ORO.FTL.205.
- Commander's discretion. Once the FDP has begun and unforeseen circumstances arise, the commander may extend it further within limits, and the FAA gives the pilot in command an equivalent power to extend in unforeseen operational circumstances under 14 CFR 117.19, within a capped amount.
Both kinds of extension are bounded and must be reported, so they are a safety valve for the unexpected, not a routine way to beat the limit.
Why the distinctions matter
Because flight time, FDP, and duty are different, a long day can hit a limit on one while leaving room on another. You can be inside your flight time limit but out of FDP because of a long ground delay between sectors, or inside your FDP but bumping a cumulative duty limit across the week. Knowing which clock is closest to its limit is what lets you plan a roster realistically rather than discovering the problem on the day.
Augmented crews and in-flight rest
The maximum flight duty period for a normal, unaugmented crew is a hard constraint, but long-haul flying gets around it in a controlled way: by carrying extra pilots and giving them a chance to sleep in flight. This is the augmented crew.
The idea is that if a pilot can take genuine rest during the cruise, handing the aircraft to another qualified pilot, then the crew as a whole can be on duty longer without the same fatigue. Both systems allow it, and both tie the allowance to the quality of the rest facility:
- Under the FAA, 14 CFR 117.17 sets the maximum FDP for an augmented crew in a table that depends on the report time, the number of pilots (three or four), and the class of onboard rest facility. A Class 1 facility is a proper bunk that lets a pilot lie flat, a Class 2 is a lie-flat or near-flat seat separated from the passengers, and a Class 3 is a reclining seat. A better facility buys a longer maximum FDP, because it allows better sleep.
- Under EASA, ORO.FTL.205 and the associated certification specifications (CS-FTL.1) extend the basic maximum FDP when the crew is augmented and in-flight rest is provided, again graded by the class of rest facility.
Split duty, where a long break on the ground during the duty buys back some of the working day, sounds like the same idea in both systems. It is not. The two schemes are inverted, and this is a genuine trap:
- Under EASA (ORO.FTL.220 and its certification specifications), the break on the ground counts in full as FDP, so the clock keeps running through it. In exchange, the maximum FDP may be increased by up to 50 per cent of the break, for a break of at least 3 consecutive hours with accommodation provided (and suitable accommodation for a break of 6 hours or more, or one that encroaches the window of circadian low). The ceiling rises; the clock does not stop.
- Under the FAA (14 CFR 117.15), it is the other way round. For an unaugmented operation, a scheduled rest opportunity of at least 3 hours in suitable accommodation, provided between 2200 and 0500 local and after the first segment, is not part of the flight duty period at all, while the Table B maximum stays exactly where it was. The clock stops; the ceiling does not move. The flight duty period and the rest opportunity together may not exceed 14 hours.
Same name, opposite mechanics. It is precisely the kind of rule that cannot be carried from one authority to the other, and reading it under the wrong one gives you an answer that is wrong in both directions.
The practical point for anyone reading a roster is that a flight duty period well beyond the unaugmented maximum is not necessarily a mistake: it may be a planned augmented operation with a third or fourth pilot and a rest facility, or an EASA split duty. The allowance is still bounded by a table, still tied to the facility class, and still set by the regulation, so it is read from the rule, not assumed.
A worked maximum FDP
An illustrative example shows how report time and sectors combine, with the firm caution that the binding figures come from the regulation and the operator's scheme, not from this example.
Under EASA, an acclimatised crew reporting at the most favourable time of day for a single sector has a basic maximum flight duty period of 13 hours (ORO.FTL.205). Now change the day. The crew reports at 0500, which falls within the window of circadian low (the WOCL, 02:00 to 05:59), and flies four sectors. Both factors cut the maximum: the unfavourable early report reduces it, and each sector beyond the first reduces it further. The result, read from the regulation's table, is a maximum FDP materially shorter than 13 hours, perhaps in the region of 11 hours, with the exact figure set by the table rather than estimated.
Under the FAA, the same kind of reasoning uses Table B in 14 CFR 117.13: you read the maximum FDP straight off against the local report time and the number of flight segments, and an early report with several segments lands well below the most favourable figure.
The lesson is not the precise number, which differs by authority and is always read from the table, but the shape of it: the same crew and aircraft can have a very different maximum FDP depending on when they start and how many sectors they fly, which is why you check the table for the specific day rather than carrying one figure around.
Common pitfalls
- Confusing flight time with duty. Flight time is just block time; the working day is the FDP, and duty is broader still.
- Assuming both authorities define flight time the same way. EASA's starts when the aircraft first moves from its parking place, so a pushback counts, and ends at engine shutdown. The FAA's, in 14 CFR 1.1, starts under the aircraft's own power and ends when it comes to rest.
- Treating the maximum FDP as fixed. It depends on report time and sectors, read from a table, and both authorities step it down as sectors rise.
- Forgetting the WOCL. An early-hours report cuts the maximum FDP because of the body clock.
- Assuming split duty works the same way. EASA counts the break as FDP and raises the maximum; the FAA excludes the break from the FDP and leaves the maximum alone.
- Relying on extensions. Planned extensions and commander's discretion are bounded and reportable, not routine.
- Carrying one authority's number across. The EASA 13-hour basic maximum and the FAA Table B values are different schemes.
In Pilot EFB
Pilot EFB can import your roster from a CSV file and work out your flight time and duty across a day and across the rolling periods, so you can see how a planned series of sectors sits against the limits, and run a quick what-if for an added sector. It is a planning and awareness aid, not a compliance system: the binding limits are those in your operator's approved scheme and the current regulation, and Pilot EFB is not a certified Electronic Flight Bag. Saved roster data stays available offline; pulling a fresh roster needs a connection.