8.3 Cumulative Duty/Flight Limits & Fatigue Risk Management
Key Takeaways
- 14 CFR § 117.23 establishes hard cumulative FDP caps: a maximum of 60 FDP hours in any 168 consecutive hours (rolling 7-day window) and 190 FDP hours in any 672 consecutive hours (rolling 28-day window).
- Cumulative flight time under § 117.23 is restricted to 100 block hours in any 672 consecutive hours (28 days) and 1,000 block hours in any 365 consecutive calendar days.
- Under § 117.19, unforeseen operational circumstances before takeoff permit the PIC and certificate holder to jointly extend Table B or Table C FDP limits by up to 2 hours; an extension exceeding 30 minutes may occur only once before the pilot receives the rest described in § 117.25(b), and the carrier must report it to the FAA within 10 days.
- For unforeseen operational circumstances arising after takeoff, the PIC and certificate holder may extend the FDP only as necessary to land safely at the next destination or alternate; an extension over 30 minutes is subject to the once-before-rest rule and specified FAA reporting requirements.
- A Fatigue Risk Management System (FRMS) under § 117.7 is an FAA-approved, data-driven safety methodology that allows certificate holders to deviate from prescriptive limits while maintaining an equivalent or higher level of safety.
Last updated: August 2026
Cumulative Duty/Flight Limits & Fatigue Risk Management
Core Airline Transport Principle: While single-duty limits (Tables A, B, and C) protect against acute sleep deprivation, chronic fatigue is governed by strict rolling cumulative limitations under 14 CFR § 117.23. Furthermore, Part 117 integrates dynamic real-time operational flexibility via strictly controlled FDP extensions (§ 117.19) and scientific Fatigue Risk Management Systems (FRMS, § 117.7).
1. Cumulative Flight Time and FDP Limitations (§ 117.23)
Part 117 replaces old calendar-month tracking with continuous rolling hourly lookback windows (168 consecutive hours and 672 consecutive hours) to prevent duty stacking and cumulative fatigue accumulation.
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| PART 117 CUMULATIVE LIMITATIONS SUMMARY |
| |
| [ CUMULATIVE FLIGHT DUTY PERIOD (FDP) LIMITS ] |
| --------------------------------------------------------------------------------------------- |
| * 60 FDP Hours in any 168 Consecutive Hours --> Rolling 7-day lookback window |
| * 190 FDP Hours in any 672 Consecutive Hours --> Rolling 28-day lookback window |
| |
| [ CUMULATIVE FLIGHT TIME (BLOCK TIME) LIMITS ] |
| --------------------------------------------------------------------------------------------- |
| * 100 Flight Hours in any 672 Consecutive Hours --> Rolling 28-day lookback window |
| * 1,000 Flight Hours in any 365 Consecutive Days --> Rolling 365-day calendar window |
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The Rolling Window Lookback Mechanism
- Continuous Lookback: Compliance is not evaluated on a fixed weekly or monthly reset (e.g., Sunday night or end of month). At every single moment of a proposed duty period, dispatch systems and flightcrews must look back over the preceding 168 hours (7 × 24) and 672 hours (28 × 24).
- Prospective Legality: An assignment is illegal if the scheduled flight time or FDP will cause the pilot to exceed any cumulative limit at the scheduled completion of the trip.
| Regulatory Metric | Timeframe | Limit | Operational Purpose |
|---|---|---|---|
| Cumulative FDP | 168 Consecutive Hours (7 days) | 60 Hours | Prevents excessive weekly duty accumulation |
| Cumulative FDP | 672 Consecutive Hours (28 days) | 190 Hours | Prevents medium-term chronic duty exhaustion |
| Cumulative Flight Time | 672 Consecutive Hours (28 days) | 100 Hours | Caps total monthly block flight exposure |
| Cumulative Flight Time | 365 Calendar Days (1 year) | 1,000 Hours | Caps total annual flight exposure |
2. Flight Duty Period Extensions for Unforeseen Operational Circumstances (§ 117.19)
Airline operations are subject to severe weather, ATC ground stops, mechanical delays, and diversions. 14 CFR § 117.19 provides legal mechanisms to extend FDP limits, with sharp distinctions between delays occurring before takeoff versus after takeoff.
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| FDP EXTENSION RULES FOR UNFORESEEN DELAYS (§ 117.19) |
| |
| [ DELAY OCCURS BEFORE TAKEOFF ] |
| - Must be an UNFORESEEN operational circumstance. |
| - Requires MUTUAL CONCURRENCE of both the Pilot-in-Command (PIC) and Certificate Holder. |
| - MAXIMUM EXTENSION: Up to 2.0 Hours beyond Table B or Table C limit. |
| - CUMULATIVE CAPS CANNOT BE EXCEEDED (60-hr / 190-hr FDP limits remain absolute hard stops!). |
| - An extension > 30 minutes may occur only ONCE before the pilot receives the |
| § 117.25(b) rest: at least 30 consecutive hours free from duty in the prior 168 hours. |
| - Carrier must submit a WRITTEN REPORT to FAA within 10 DAYS for an extension > 30 minutes. |
| |
| [ DELAY OCCURS AFTER TAKEOFF ] |
| - Airborne hold, diversion, or unexpected headwinds. |
| - PIC and certificate holder may extend only as necessary to land safely at the next |
| destination or alternate; the extension may exceed the § 117.23(c) cumulative FDP limits. |
| - The once-before-§ 117.25(b)-rest rule applies to extensions > 30 minutes. |
| - Carrier reports within 10 days if the extension exceeds Table B/C by > 30 minutes or causes |
| an exceedance of the cumulative FDP limits. |
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Unforeseen Operational Circumstances Defined
- Qualifying Events: Unforecast enroute convective weather, sudden ATC ground delay programs, runway closures, bird strikes, or late-developing aircraft maintenance anomalies.
- Disqualifying Events: Inadequate crew scheduling, predictable late turnarounds, routine seasonal weather, or known airline staffing shortages. Using § 117.19 extensions for routine scheduling failures violates federal law.
3. Reserve Duty Limitations (§ 117.21)
Reserve pilots are on standby to cover sick calls, trip disruptions, and charter requirements. Part 117 classifies reserve into three distinct categories:
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| PART 117 RESERVE CLASSIFICATIONS |
| |
| 1. AIRPORT / STANDBY RESERVE (On-call at the airport): |
| * ALL time spent in airport/standby reserve is part of the FDP (§ 117.21(b)). |
| * Total FDP (including standby time) may not exceed the applicable Table B limit. |
| |
| 2. SHORT-CALL RESERVE (On-call at home/hotel with short response time): |
| * Reserve Availability Period (RAP) capped at 14 CONSECUTIVE HOURS. |
| * FDP + RAP combined: lesser of Table B + 4 hrs or 16 hrs (augmented: Table C + 4 hrs). |
| * Must receive 10 consecutive hours rest immediately prior to starting the RAP. |
| |
| 3. LONG-CALL RESERVE (Default reserve category, § 117.21(a)): |
| * Any reserve not designated airport/standby or short-call is long-call reserve. |
| * Assignment starting before & operating into WOCL requires 12-HOUR notice of report time. |
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4. Fatigue Risk Management System (FRMS, § 117.7)
A Fatigue Risk Management System (FRMS) is a comprehensive, data-driven, science-based safety methodology that allows an airline to establish customized duty, flight, and rest schedules alternative to the prescriptive rules of Part 117, provided an equivalent level of safety is demonstrated.
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| THE FOUR PILLARS OF AN FAA-APPROVED FRMS (§ 117.7) |
| |
| +-------------------------------------------------------------------------------------------+ |
| | 1. FRMS POLICY & DOCUMENTATION: Executive commitment, clear roles, non-punitive reporting. | |
| +-------------------------------------------------------------------------------------------+ |
| | 2. FATIGUE RISK ASSESSMENT: Biomodels (SAFTE/FAST), actigraphy sleep studies, PVT testing. | |
| +-------------------------------------------------------------------------------------------+ |
| | 3. FATIGUE SAFETY ASSURANCE: Trend monitoring, line audits, safety KPIs, incident analysis. | |
| +-------------------------------------------------------------------------------------------+ |
| | 4. FATIGUE PROMOTION & TRAINING: Crew fatigue education, sleep hygiene, circadian science. | |
| +-------------------------------------------------------------------------------------------+ |
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FRMS Certification Process
- FAA Approval: The airline must obtain specific FAA approval through its principal operations inspector (POI) and the Air Transportation Division before operating any pairing under an FRMS.
- Biomathematical Modeling: Operators utilize bio-mathematical fatigue models (such as SAFTE/FAST or CAS) combined with crew actigraphy data (wearable sleep monitors) to validate that predicted alertness levels on proposed pairings exceed established safety baselines.
- Continuous Monitoring: An FRMS requires continuous collection and analysis of flight operational quality assurance (FOQA) data, sleep logs, and fatigue reports to maintain regulatory approval.
5. Mandatory Fatigue Reporting & Fitness for Duty (§ 117.5)
Under 14 CFR § 117.5, fatigue management is an active joint legal responsibility between the air carrier and the individual airman.
Affirmation of Fitness for Duty
- Prior to beginning each and every Flight Duty Period, each flightcrew member must affirm in writing (or electronically on the dispatch release) that they are rested and fit for duty.
- If a pilot feels fatigued to the extent that cognitive or psychomotor performance is impaired, they are legally prohibited from accepting the assignment.
Non-Punitive Fatigue Call Policy
- Under FAA Advisory Circular AC 120-103A and § 117.5, airlines must maintain a non-punitive fatigue reporting policy.
- If a crewmember declares themselves fatigued ("fatigue call"), the airline must immediately remove the pilot from duty without threat of termination, disciplinary action, or financial penalty.
- A formal fatigue event report is filed within a specified window (typically 24 to 72 hours), which is reviewed by a joint Fatigue Safety Action Group (FSAG) comprising union and management safety representatives to identify root causes and optimize future crew scheduling.
6. Worked Cumulative Tracking Calculation
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| WORKED CUMULATIVE LOOKBACK AUDIT |
| |
| SCENARIO: First Officer Martinez is scheduled for a 4-leg trip starting Monday at 07:00. |
| - Scheduled FDP for Monday trip = 11.5 Hours. |
| - Scheduled Flight Time for Monday trip = 7.5 Hours. |
| |
| STEP 1: Audit 168-Hour Cumulative FDP Lookback: |
| - FDP accumulated across preceding 6 days = 49.0 Hours. |
| - Proposed new FDP = 11.5 Hours. |
| - Projected 168-hr FDP Total = 49.0 + 11.5 = 60.5 Hours. |
| --> RESULT: ILLEGAL! (Exceeds 60.0 FDP hour limit in 168 consecutive hours). |
| --> Corrective Action: Dispatch must drop the last leg or reassign trip to another FO. |
| |
| STEP 2: Audit 672-Hour Cumulative Flight Time Lookback: |
| - Block flight time accumulated in preceding 27 days = 88.0 Hours. |
| - Proposed flight time = 7.5 Hours. |
| - Projected 672-hr Flight Time = 88.0 + 7.5 = 95.5 Hours. |
| --> RESULT: LEGAL! (Under 100.0 block hour limit in 672 consecutive hours). |
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Test Your Knowledge
Under 14 CFR § 117.23, what are the maximum allowable cumulative Flight Duty Period (FDP) limits for a flightcrew member across 168 consecutive hours and 672 consecutive hours?
A
B
C
D
Test Your Knowledge
A flight is delayed at the departure gate due to an unforeseen ground stop. The flight has not yet taken off. Under 14 CFR § 117.19, what are the legal constraints regarding an FDP extension?
A
B
C
D
Test Your Knowledge
If an FDP is extended by 45 minutes prior to takeoff due to unforeseen operational circumstances, what post-flight actions are required under 14 CFR § 117.19?
A
B
C
D