Part 117 Calculator

FAA Flight Duty Period (FDP) & Rest Limitation Tool

Formula: Max FDP is determined by Table B of 14 CFR Part 117 based on start time and segments. Max Flight Time is determined by Table A.

What is the Part 117 Calculator?

The Part 117 calculator is an essential tool for airline pilots and flight schedulers operating under 14 CFR Part 117 regulations. These rules, established by the Federal Aviation Administration (FAA), govern the flight and duty time limitations for all Part 121 commercial operations in the United States. The primary purpose of the Part 117 calculator is to mitigate pilot fatigue by ensuring that duty periods do not exceed scientifically derived safety limits.

Who should use it? Commercial pilots, dispatchers, crew schedulers, and aviation safety officers. A common misconception is that duty time and flight time are the same; in reality, “Flight Duty Period” (FDP) includes the time from reporting for a flight with the intent to fly until the aircraft is parked after the last segment, whereas “Flight Time” is strictly block-to-block time.

Part 117 Calculator Formula and Mathematical Explanation

The calculation is not a single linear formula but a lookup logic based on two primary FAA tables. The Part 117 calculator looks up values based on the “Time of Report” and the “Number of Flight Segments.”

Variable Explanation Table

Variable	Meaning	Unit	Typical Range
Report Time	Local time at base or acclimatized location	HH:MM	00:00 – 23:59
Segments	Number of flight legs in a single FDP	Count	1 – 7+
Acclimatization	Status regarding circadian rhythm sync	Boolean	Yes / No
Table B Value	Raw FDP limit from FAA regulations	Hours	9 – 14 Hours

The logic follows: Limit = TableValue(ReportTime, Segments) – AcclimatizationPenalty. If a pilot is not acclimatized, the limit is typically reduced by 30 minutes to account for the increased fatigue risk of “Window of Circadian Low” (WOCL) operations.

Practical Examples (Real-World Use Cases)

Example 1: Morning Short-Haul

A pilot reports at 07:00 for a 3-segment day. Using the Part 117 calculator, we look at Table B. For a 07:00 report with 3 segments, the Max FDP is 13.5 hours. The Max Flight Time (Table A) is 9 hours. This means the pilot must finish their last flight segment within 13.5 hours of reporting, and their total air time cannot exceed 9 hours.

Example 2: Midnight Operations

A pilot reports at 02:00 (during the WOCL) for 1 segment. The Part 117 calculator identifies this as a high-fatigue window. The Max FDP is restricted to 9 hours, even with only one segment. If the pilot is not acclimatized, this would be further reduced to 8.5 hours.

How to Use This Part 117 Calculator

1. Enter Report Time: Input the exact local time you report for duty at your base or the location where you are acclimatized.
2. Select Segments: Choose the number of scheduled flight legs. Note that “7+” covers all instances of seven or more takeoffs.
3. Check Acclimatization: If you have had 36 hours of rest or have been in the new theater for 72 hours, select “Yes.” Otherwise, select “No.”
4. Review Results: The tool will instantly display your Maximum Flight Duty Period and your Maximum Flight Time limit.
5. Plan Rest: Ensure you have at least 10 hours of rest (with 8 hours of sleep opportunity) before the next FDP.

Key Factors That Affect Part 117 Calculator Results

• Time of Day: Reporting during the Window of Circadian Low (02:00-05:59) significantly reduces allowed duty time.
• Number of Segments: Each additional takeoff and landing adds a “task saturation” penalty, reducing the total allowed FDP.
• Acclimatization: Being “out of theater” or unacclimatized reduces your legal limits due to the body’s internal clock mismatch.
• Augmented Crews: If extra pilots are on board and there are onboard rest facilities, FDP limits can increase significantly (beyond the scope of this basic unaugmented tool).
• Extensions: Under specific circumstances, a pilot can extend an FDP by up to 2 hours, but this requires specific reporting and cannot be used for scheduling.
• Cumulative Limits: Regardless of daily limits, pilots must not exceed 100 flight hours in 672 consecutive hours or 1,000 hours in 365 days.

Frequently Asked Questions (FAQ)

1. What is the maximum flight time in a 24-hour period?

Under Part 117, the flight time limit is either 8 or 9 hours for unaugmented crews, depending on the report time.

2. How much rest is required after a duty period?

A pilot must have at least 10 hours of rest, including 8 hours of uninterrupted sleep opportunity, immediately before beginning any FDP.

3. What happens if I have a flight delay?

If a delay occurs before takeoff, you must re-calculate your FDP using the Part 117 calculator to ensure the new expected arrival time falls within the legal window.

4. Does deadheading count toward FDP?

Deadheading does not count as a “segment,” but if you deadhead to a flight, the time spent deadheading counts as part of your Flight Duty Period.

5. What is the “Window of Circadian Low”?

It is generally between 02:00 and 05:59. This is when the human body is most programmed to sleep and fatigue risk is highest.

6. Can I fly more than 60 hours of duty in a week?

No. Part 117 limits duty to 60 hours in any 168 consecutive hours (7 days).

7. How does the Part 117 calculator handle split duty?

Split duty (rest in a hotel during a duty day) can extend the FDP, provided the rest is at least 3 hours and occurs between 22:00 and 05:00 local time.

8. What if my report time is at 04:59 vs 05:00?

The Part 117 calculator shows a significant jump; at 04:59, you are in the WOCL (9-hour limit), but at 05:00, your limit increases (to 12 hours for 1 segment).

Related Tools and Internal Resources

• FAA Duty Limit Guide – A comprehensive breakdown of all Part 121 regulations.
• Pilot Rest Calculator – Determine exactly when you need to be in bed for your 8-hour sleep opportunity.
• Flight Crew Scheduling – Software solutions for managing large-scale airline operations.
• Aviation Compliance Tools – A suite of calculators for fuel, weight and balance, and duty.
• Crew Rest Rules – Specifics on bunk requirements for augmented long-haul flights.
• Part 121 Regulations – The full legal text of the FAA commercial aviation handbook.