Part 91 Duty Time Limits: What Applies and a Sample Policy

There are no Part 91 duty time limits for flight crews outside subpart K. The general operating rules in 14 CFR Part 91 set no maximum duty period, no maximum flight time and no minimum rest for the pilots of a corporate or privately operated aircraft. Prescriptive limits exist only for fractional programs under subpart K (91.1059), for Part 135 operators (135.267) and for Part 121 carriers (Part 117). What a Part 91 crew does have is the pilot in command’s authority, the ban on careless or reckless operation, the medical deficiency rule, and whatever duty policy its own company writes. There is a sample at the end of this article to start from.

Does Part 91 have duty time limits?

Not in the general rules. The only Part 91 sections whose titles mention flight time, duty or rest are in subpart K: 91.1057, 91.1059 and 91.1062. The rest of the part covers flight rules, equipment, maintenance, noise and waivers, with nothing that limits how long a crew member may be on duty. Subpart F, which adds rules for large and turbine-powered multiengine airplanes, covers equipment, briefings, cargo, icing and crew complement (91.501 and the sections after it), but no flight or duty time.

The limits start when a flight moves into a different set of rules:

Part 117 reaches into Part 91 in one case only. Section 117.1(b) applies it to “operations directed by part 121 certificate holders under part 91, other than subpart K,” when any segment is a domestic, flag or supplemental passenger operation. A corporate flight department is not a Part 121 certificate holder, so this doesn’t reach it.

The Part 135 limits count more than Part 135 flying. Section 135.267(b) limits “the total flight time of the assigned flight when added to any other commercial flying by that flight crewmember.” If your pilots also fly charter for a certificate holder, ask that operator how it counts the flying they do for you. Our guides to Part 135 duty time limits and Part 91K duty and rest cover those rules in full, and Part 91 vs Part 135 vs Part 91K explains which part a given flight falls under.

What rules apply to Part 91 crew rest?

No rule names crew rest, but four things bear on whether a tired crew should fly.

91.3: the pilot in command decides

Section 91.3(a) says: “The pilot in command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft.” With no hour limits in the regulations, this is the rule that lets a captain refuse a trip because the crew is too tired to fly it. A company duty policy can’t take that authority away, and a good one says so in writing so nobody has to argue the point at 0500.

91.13: careless or reckless operation

Section 91.13(a) says: “No person may operate an aircraft in a careless or reckless manner so as to endanger the life or property of another.” It mentions neither fatigue nor hours. It is a general rule that applies to every flight, including one flown by a crew that has been awake for 20 hours.

61.53: medical deficiency

Section 61.53(a) bars a pilot who holds a medical certificate from acting as pilot in command, or as a required pilot flight crewmember, while the pilot “knows or has reason to know of any medical condition that would make the person unable to meet the requirements for the medical certificate,” or while taking medication or treatment that has the same result. For operations that don’t need a medical certificate, 61.53(b) uses a broader test: a medical condition that “would make the person unable to operate the aircraft in a safe manner.”

The rule doesn’t mention fatigue. It is about medical conditions and medication, so don’t build a fatigue policy on 61.53 alone.

The AIM on fatigue

The FAA’s guidance on fatigue sits in the Aeronautical Information Manual, 8-1-1, “Fitness For Flight”. It calls fatigue “one of the most treacherous hazards to flight safety, as it may not be apparent to a pilot until serious errors are made,” and separates acute fatigue, which “is prevented by adequate rest and sleep,” from chronic fatigue, where “there is not enough time for full recovery between episodes of acute fatigue.” The same section ends with a personal checklist whose initials spell IMSAFE: illness, medication, stress, alcohol, fatigue, emotion. The AIM is guidance, not regulation.

Why flight departments write their own duty policy

Without a regulation, the duty limit at a Part 91 department is whatever the principal, the scheduler and the crew agree to on the day, with the passengers waiting. A written policy decides the limits in advance, when nobody is waiting at the FBO.

A policy also does things the regulations can’t:

• It protects the captain’s no-go call. 91.3 gives the authority. A policy that says a fatigue call is never held against a crew member makes it easier to use.
• It gives schedulers a number. “Is this legal?” needs an answer before the trip is booked. With a policy, the scheduler can check a proposed week against it instead of asking the chief pilot every time.
• It answers the boss’s request in advance. When an executive wants a same-day return after a 13-hour duty day, “our policy is 14 hours, and this would be 17” lands better than a captain’s opinion.
• It meets a voluntary standard’s expectations. The International Standard for Business Aircraft Operations (IS-BAO) is a voluntary standard run by IBAC. IBAC says it delivers a safety management system and that it “does not dictate the method to be used to achieve conformity.” Its full requirements are sold as a document suite, so check them there rather than relying on a summary.

What do the NBAA and FSF duty and rest guidelines recommend?

NBAA’s published guidance is the Duty/Rest Guidelines for Business Aviation, published in April 2014 by NBAA and Flight Safety Foundation. NBAA’s fatigue page presents them as “science-based guidelines for duty and rest scheduling” and says they “are not intended as an exclusive ‘one-size-fits-all’ solution.” They are written for crews of two or more pilots.

Table 1 of the guidelines, for non-augmented crews in a 24-hour period:

The guidelines define the window of circadian low (WOCL) as roughly 0200 to 0600 for someone on a normal day-wake, night-sleep schedule. A WOCL operation is one where landing occurs in that window, the flight passes through both sides of it, or the duty period starts at 0400 or earlier.

Other recommendations from the same document that belong in a policy:

• The 10-hour off-duty period is meant to include an eight-hour sleep opportunity, a wind-down period, and time for travel to the hotel, meals and the rest.
• After a duty period that crosses four or more time zones and involves 48 hours or more away from the home time zone, schedule at least 48 hours off on return.
• The 14-hour duty period should be extended only with an augmented crew. Table 2 sets a maximum of 18 hours of duty with a reclining rest seat and up to 20 with a bunk, each separated and screened from the flight deck and passengers.
• Extensions of flight time should not fall on consecutive days, and after one the next off-duty period goes from 10 to 12 hours.
• For long-term limits the guidelines say “the current industry standard is 100 cumulative flight hours per month and 1,000 cumulative flight hours per year,” while noting that cumulative limits vary among operators.
• Duty includes more than flying: the guidelines list flight duty, aircraft maintenance, administrative work, training, positioning, and standby “when it is likely to induce fatigue.”

The guidelines also recommend a fatigue reporting system and list a flight risk assessment tool that includes fatigue factors among the tools a department can use.

A sample company duty policy

What follows is an example to adapt, not a standard and not a recommendation for your operation. Its numbers mirror the NBAA and FSF table above. Change them to fit your aircraft, your crews and your trips, and have your chief pilot and safety lead sign off on the result.

Example: flight crew duty and rest policy

1. Scope. This policy applies to every flight crew member flying the company’s aircraft under Part 91. It does not replace the pilot in command’s authority under 14 CFR 91.3.
2. Definitions.
   • Duty: any task the company requires, including flying, positioning, training, office work and standby.
   • Duty period: from the report time to release from all duties. Report time is 60 minutes before the first scheduled block out; release is 30 minutes after the last block in.
   • Flight time: block out to block in.
   • Rest: a continuous period free of all duties, including calls and messages that require a response.
   • WOCL: 0200 to 0600 in the home time zone, or local time after 48 hours away.
3. Daily limits. In any 24 consecutive hours: no more than 14 hours of duty and 10 hours of flight time, with at least 10 consecutive hours of rest before each duty period.
4. WOCL trips. If a landing falls in the WOCL, a flight crosses it, or duty starts at 0400 or earlier, the duty limit is 12 hours and the rest before the next duty period is at least 12 hours.
5. Days off. At least 36 consecutive hours off, including two consecutive nights, in any seven days.
6. Long trips. After a trip that crosses four or more time zones and keeps the crew away 48 hours or more, at least 48 hours off on return.
7. Extensions. The chief pilot may approve a flight time extension of up to 2 hours, no more than twice in seven days and never on consecutive days, for two-pilot crews only. The rest after an extension is at least 12 hours. Each extension is recorded with the reason.
8. Duty extensions beyond 14 hours. Only with an augmented crew and an approved rest facility on board.
9. Cumulative limits. No more than 100 hours of flight time in a calendar month or 1,000 in a calendar year.
10. Standby. Standby counts as duty. The scheduler sets the start and end time of each standby period in advance.
11. Fatigue calls. Any crew member may remove themselves from a trip for fatigue. The call is reported to the chief pilot and is never held against the crew member.
12. Records and review. The scheduler checks each trip against this policy before it is confirmed and again whenever it changes. The safety lead reviews every exceedance and every fatigue call, and the policy is reviewed once a year.

Checking a week against the policy: a worked example

Every time and trip below is illustrative, all times are in the home time zone, and report and release use the 60 and 30 minutes from the sample policy.

Against the sample policy:

1. Monday is at the duty limit exactly: 14:00 with 6:10 of flight time. It passes, with no room for a delay. A late passenger turns it into an exceedance.
2. Tuesday fails. A long afternoon wait for the passengers and an evening leg home make a 15:15 duty day, over the 14-hour limit. The options are to move the last leg to Wednesday morning, add an augmented crew (item 8), or swap in a crew that started later.
3. Wednesday releases at 1600 and Thursday reports at 0030, which is 8:30 of rest. That fails item 3, which needs 10. It also breaks item 3’s 14 hours of duty in any 24 consecutive hours: from 0800 Wednesday to 0800 Thursday the crew is on duty 8:00 + 6:30 = 14:30.
4. Thursday is a WOCL trip: duty starts at 0030 and the flight crosses 0200 to 0600. Its duty limit is 12 hours, so 6:30 passes. The rest after it must be at least 12 hours (item 4).
5. The week: the crew needs 36 consecutive hours off, including two nights, somewhere in the seven days (item 5). With Thursday ending at 0700, Friday and Saturday off would meet it.

Done by hand, this means four days of arithmetic for each pilot, redone every time a passenger moves a departure. In a spreadsheet it means formulas that break when a trip crosses midnight or a time zone.

Common mistakes in Part 91 duty policies

• Counting flight time and forgetting duty. A day with three hours of flight time and a long wait between legs can still be a 15-hour duty day.
• Leaving out report and release. If the policy doesn’t say when duty starts and ends, duty tends to get measured from block out, and the duty day looks an hour or more shorter than it was.
• Counting rest that isn’t rest. Time at the FBO between legs, or a “rest” night with an 0400 hotel pickup, rarely gives the eight-hour sleep opportunity the NBAA and FSF guidelines build their 10 hours around.
• No rule for standby. The NBAA and FSF guidelines count standby as duty “when it is likely to induce fatigue.” A pilot on call all day who then flies an evening trip is the case to decide in advance.
• Extensions with no limit. If the policy allows extensions but doesn’t cap how many or who approves them, the limit becomes a suggestion.
• A policy nobody checks. Limits that live in the operations manual but not in the scheduling process get checked after the trip, if at all.

Part 91 duty policy in Avion Desk

In Avion Desk, duty and rest are checked whenever the schedule moves, and Part 91 trips are checked against a company duty policy you can edit to match your own.

Seating a pilot who isn’t qualified on the aircraft is flagged too.

If you also fly charter, the plan for charter operators adds Part 135 and Part 91K duty and rest; see crew, duty and rest and pricing.

To try it, start a free trial, enter your duty policy and see this week’s trips checked against it, or request a demo.

Frequently asked questions

Are there duty time limits for Part 91 pilots?

Not in the regulations, unless the flight is part of a fractional ownership program under subpart K (91.1059). Corporate and private Part 91 operations set their own limits in a company policy.

Does Part 117 apply to Part 91 flights?

Only to Part 91 operations directed by a Part 121 certificate holder when any segment is a domestic, flag or supplemental passenger operation (117.1(b)). It doesn’t apply to a corporate flight department.

What rest do the NBAA and FSF guidelines recommend?

At least 10 hours off duty in each 24-hour period for standard operations, including an eight-hour sleep opportunity, and at least 36 continuous hours off, including two consecutive nights, in seven days (Duty/Rest Guidelines for Business Aviation).

Can a Part 91 pilot refuse a trip for fatigue?

The pilot in command “is directly responsible for, and is the final authority as to, the operation of that aircraft” (91.3(a)). Whether a refusal has employment consequences is up to the company, which is why a duty policy can say a fatigue call is never held against a crew member.

Does 61.53 cover pilot fatigue?

It doesn’t name fatigue. Section 61.53 covers medical conditions and medication. The FAA’s fatigue guidance is in AIM 8-1-1.

This article explains the rules in plain language and isn’t legal advice; the regulation text governs.

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