10 in 24 Calculator

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Regulation Overview: 14 CFR 135.267(b)

The 10 in 24 rule is one of the fundamental flight time limitations for Part 135 operations. It exists to prevent crew fatigue by limiting the amount of flying that can be conducted within any consecutive 24-hour period.

Key Points

• Rolling 24-Hour Window: The limitation applies to any consecutive 24-hour period, not just calendar days
• Flight Time Definition: Only actual flight time (block-to-block) counts toward the limit
• Scheduling vs. Actual: The rule applies to both scheduled flight time and actual flight time
• All Commercial Flying: The limit counts the assigned flight "when added to any other commercial flying" — Part 91 positioning and ferry legs flown for the certificate holder count, and so does flying for hire for anyone else
• Single pilot: 8 hours. The 10-hour figure is for a two-pilot crew; § 135.267(b)(1) sets 8 hours for one pilot
• Two Reliefs Only: § 135.267(c) lets earlier flight time drop out of the rolling count when the day is a regularly assigned duty period of no more than 14 hours, bracketed by 10 hours of rest on each side, with no more than 10 hours of flight time inside it; and § 135.267(g) says an assignment that normally terminates within the limit, but runs over because of circumstances beyond the control of the certificate holder or crewmember, is not an assignment in excess of it. Neither is an extension the calculator models

How the Calculator Works

Our 10 in 24 Calculator uses a rolling window analysis to check compliance at every moment throughout your flight schedule. Here's how it works:

Calculation Method

1. Create Timeline: The calculator creates a continuous timeline of all scheduled flights
2. Rolling Window Analysis: For every minute of the schedule, it looks backward 24 hours
3. Sum Flight Time: It calculates the total flight time within each 24-hour window
4. Identify Violations: Any window exceeding 10 hours is flagged as a violation
5. Visual Representation: Results are displayed on an interactive timeline

Input Requirements

• Crew Configuration: Select standard 2-pilot, 3-pilot, or 4-pilot augmented crew
• Flight Legs: Add each flight segment with:
  • Departure airport and departure time (entered as local clock time)
  • Arrival airport — the arrival time is calculated for you and shown read-only
  • Aircraft, which sets the cruise speed behind the flight time estimate. This is required: a leg with no aircraft (and no manually entered cruise speed) is flagged as "missing: aircraft" and is dropped from the compliance check
• One Time Base: The calculator performs no time zone conversion — every departure time you enter is read on a single clock. Convert the whole schedule to one time base before entering it

Output & Visualization

The calculator provides:

• Interactive Timeline: Visual representation of all flights and flight time accumulation
• Violation Indicators: Clear red markers showing where the 10-hour limit is exceeded
• Summary Cards: Total Flights, Total Flight Time, Schedule Span, 24h Limit, and Peak Load. Note that Peak Load is the longest single leg, not the peak of the rolling 24-hour window
• Rolling 24-Hour Peak: Reported as "Peak 24h Flight Time" inside the Compare Crew Configurations comparison, not on the main results screen
• Compliance Status: Overall pass/fail indication
• Detailed Report: Exportable HTML report with all calculations

Crew Configurations

The calculator supports three crew configurations commonly used in Part 135 operations. The configuration affects how the regulation is applied:

Standard 2-Pilot Crew

10 in 24 Application: Standard 10-hour limit applies to each pilot individually.

Typical Aircraft: Light jets, turboprops, piston twins

Example Operations: Short-haul charters, air ambulance, cargo operations

3-Pilot Crew

10 in 24 Application: § 135.267 does not apply to a three-pilot crew. § 135.269(b) governs: no more than 12 hours aloft for the crew during the 24 duty hours, no more than 8 hours of flight deck duty per pilot in any 24 consecutive hours, an 18-hour duty limit, adequate sleeping facilities for the relief pilot, 10 hours of rest before the assignment and 12 hours after it.

Typical Aircraft: Midsize to large cabin jets with crew rest facilities

Example Operations: Long-range charters, international flights

4-Pilot Augmented Crew

10 in 24 Application: § 135.269(b)(4) allows no more than 16 hours aloft for a four-pilot crew during the 24 duty hours, with a 20-hour duty limit ((b)(3)), 8 hours of flight deck duty per pilot ((b)(2)), sleeping facilities ((b)(5)), 10 hours of rest before and 12 after, and the two-PIC, two-SIC composition of (b)(8).

Typical Aircraft: Large cabin, long-range business jets

Example Operations: Ultra-long-range international charters (e.g., US to Asia non-stop)

Examples & Use Cases

Example 1: Simple Day Trip (Compliant)

Example 2: Multi-Leg Charter (Borderline)

Example 3: Back-to-Back Days (Violation Risk)

Example 4: Multi-Day Operation (Compliant)

Best Practices & Tips

For Flight Operations

1. Build in Buffer Time

   Never schedule right up to the 10-hour limit. Weather delays, ATC delays, and headwinds can all extend flight times. Aim for a maximum of 8-9 hours scheduled flight time to provide a safety margin.

2. Consider Time Zones Carefully

   When operating across multiple time zones, the rolling 24-hour window can create unexpected violations. The calculator does not convert between airport time zones, so convert every leg to Zulu yourself and enter the whole schedule in that one time base. The Local/UTC buttons on the results timeline only re-label the display; they do not change how your entered times were read.

3. Monitor Actual vs. Scheduled

   The regulation applies to both scheduled and actual flight time. If actual flight time will exceed scheduled time, you must stop and reassess before accepting additional legs.

4. Account for ALL Flight Time

   Remember to include any Part 91 positioning flights, ferry flights, or other non-revenue operations. All flight time counts toward the limit, regardless of the operation type.

For Schedulers & Dispatchers

1. Use Conservative Flight Time Estimates

   When planning schedules, use realistic flight time estimates that account for:

   • Typical winds for the season and route
   • ATC routing (not just great circle distance)
   • Aircraft performance characteristics
   • Terminal area delays

2. Pre-Flight Planning

   Run every proposed schedule through the calculator during the planning phase, not just before departure. This allows time to make adjustments without disappointing customers.

3. Document Everything

   Keep records of scheduled flight times, actual flight times, and compliance checks. Export the calculator's HTML reports for your records.

4. Have Backup Plans

   For complex multi-leg operations, have contingency plans ready:

   • Alternate routing that stays within limits
   • Reserve crew members who could be called in
   • Hotels identified for unplanned layovers

For Pilots

1. Know Your Limits

   Always be aware of how much flight time you've accumulated in the past 24 hours. Don't rely solely on schedulers or dispatchers - it's your certificate on the line.

2. Speak Up Early

   If you see a schedule that might push limits, raise concerns during the planning phase, not at the aircraft. Early communication allows for better solutions.

3. Log Everything

   Maintain accurate flight time logs. The regulation requires proving compliance, which means detailed records of all flight time.

4. When in Doubt, Calculate

   If you're ever unsure whether a proposed flight would exceed limits, use the calculator. It takes 2 minutes and could save your certificate.

Using the Calculator Effectively

1. Input accurate times: Use actual scheduled times, not approximate times
2. Select correct crew configuration: This sets the 24-hour flight time limit the check runs against — 10 hours Standard, 12 hours Augmented (3 Pilots), 16 hours Augmented (4 Pilots)
3. Review the timeline: Don't just look at the pass/fail - examine the entire timeline
4. Export reports: Keep HTML reports as part of your flight planning documentation
5. Run multiple scenarios: Check with delays or extended flight times to see margins

Additional Resources

Regulatory References

• 14 CFR § 135.267 - Flight time limitations
• 14 CFR § 135.269 - Flight time limitations and rest requirements: Unscheduled three- and four-pilot crews
• FAA Advisory Circulars

Related Tools

• Flight & Duty Time Calculator - For comprehensive duty time analysis
• Fatigue Quick Score - For fatigue risk assessment
• Fleet Schedule Optimizer - For optimizing aircraft schedules

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