Part 135 / HEMS Duty Time Calculator
Quick compliance check against the 14 CFR Part 135 duty and rest limits for rotorcraft operators. The calculator covers the three most common Part 135 configurations: unscheduled (on-demand / charter) under 135.267, helicopter air ambulance (HEMS) under 135.271, and scheduled commuter under 135.265. Tracks duty period elapsed, flight time accumulated, and rest period compliance.
Calculator inputs and results
Operation type
Rotorcraft single-pilot or two-pilot crew. 14-hour rest available if assigned 14+ hours.
Today's duty period
Flight time accumulators
Source: 14 CFR 135.265 (scheduled), 135.267 (unscheduled / on-demand), 135.271 (HEMS), 135.273 (rest in HEMS). This tracker is a quick compliance check only. Operators with augmented crews, rest-period overrides, or special FAA-approved fatigue risk management systems (FRMS) under their OpSpec may operate to different limits. Always confirm against the operator's General Operations Manual (GOM) and FAA OpSpec.
How this calculator works
Unscheduled rotorcraft ops (14 CFR 135.267): pilots may not fly more than 8 hours of flight time in any 24-hour period, or 35 hours in any 7 consecutive days. A 10-hour continuous rest period is required in the 24 hours preceding a flight assignment. Duty period limited to 14 hours.
HEMS (14 CFR 135.271): helicopter air ambulance pilots cannot exceed 8 hours flight time in any 24-hour period (extended to 10 hours with two pilots), with 10 hours of continuous rest. Specific HEMS Subpart L additional rules apply for risk assessment, weather minima, and operational control center (OCC).
Scheduled commuter (14 CFR 135.265): 8 hours flight time in 24, 30 hours in 7 days, 9 hours rest. Longer per-month (100 h) and per-quarter (300 h) limits also apply.
All times are measured against either the duty period start (clock time) or the rolling 24-hour / 7-day window. The calculator uses a single-day model - rolling-window analysis requires the operator's flight time log.
Default assumptions & sources
Every default value the calculator starts with, the realistic range you'd see in the field, and the source we used to set it.
| Input | Default | Typical range | Source |
|---|---|---|---|
| Unscheduled flight time/day | 8 hr | fixed by FAA | 14 CFR 135.267(b)(1) |
| Unscheduled rest minimum | 10 hr | fixed by FAA | 14 CFR 135.267(c)(1) |
| Unscheduled duty period | 14 hr | varies | 14 CFR 135.267 + OpSpec |
| HEMS flight time/day | 8 hr (single pilot) | 10 hr w/ two pilots | 14 CFR 135.271(c) |
| HEMS rest minimum | 10 hr | fixed by FAA | 14 CFR 135.271(d) |
| Scheduled commuter 7-day max | 30 hr | fixed by FAA | 14 CFR 135.265(a)(2) |
What's not modeled
The calculator covers the major cost and time line items. These additional factors apply in some cases but aren't included in the estimate:
- Augmented crew (two pilots) extensions under 14 CFR 135.271(d)(2)
- FAA-approved Fatigue Risk Management System (FRMS) deviations under operator OpSpec
- Rolling 7-day and 30-day flight time totals (calculator handles 24-h + manual 7-day entry only)
- Standby duty vs flight duty distinction (some operators have different OpSpec definitions)
- Reserve / on-call duty time treatment - varies by operator's General Operations Manual (GOM)
- Cross-rated duty (mixed Part 91 personal flying and Part 135 commercial - both count toward the 35-hour limit in 7 days)
Frequently asked questions
What is the difference between 135.265, 135.267, and 135.271?
Three different Part 135 operations categories with different duty/rest rules. 135.265 covers scheduled passenger commuter ops (shortest day, longest rest planning). 135.267 covers unscheduled / on-demand / charter (helicopter air taxi, utility ops). 135.271 covers helicopter air ambulance (HEMS) specifically - it was added in 2014 as part of an FAA HEMS safety rulemaking and overlays additional risk assessment and OCC requirements on top of 135.267 fundamentals.
#Can a HEMS pilot fly 10 hours in a day?
Yes, but only with two pilots and the specific OpSpec approval per 14 CFR 135.271(d)(2). Single-pilot HEMS operations are capped at 8 hours of flight time in any 24-hour period. The 10-hour two-pilot extension also requires augmented crew rest provisions on the operator's certificate.
#Does training time count toward the 8-hour flight time limit?
Depends on context. Training conducted under Part 135 (for the operator's currency and operating certificate requirements) counts. Personal Part 61 training conducted off-duty does NOT count against Part 135 duty/rest limits. However, total flight time under any operation in a 7-day window counts against the 35-hour 7-day limit per 14 CFR 135.267(b)(2).
#How does the 14-hour duty period work?
Per 14 CFR 135.267(c), a pilot may be on duty for up to 14 hours within any 24-hour period. Duty includes flight time, ground duty (briefing, dispatch, maintenance), and standby that the operator requires the pilot to be in a specified location. Pure on-call time at home where the pilot can rest does not typically count, but operator GOM definitions vary.
#What about the FAA-approved FRMS provisions?
Some operators have FAA-approved Fatigue Risk Management Systems (FRMS) in their OpSpec that allow deviations from the standard 135.267/271 limits in exchange for additional fatigue mitigation (scheduling rules, biomathematical models, OCC fatigue scoring). FRMS approvals are uncommon and operator-specific. Always check the OpSpec, not just the regulation text.
#Related guides & tools
This calculator provides estimates only. Actual aircraft performance and regulatory compliance vary by specific aircraft serial number, density altitude, gross weight, equipment installations, and operator's FAA-approved General Operations Manual / OpSpec. Always verify with primary sources: the FAA (faa.gov), 14 CFR (eCFR at ecfr.gov), your aircraft Rotorcraft Flight Manual (RFM) or Pilot Operating Handbook (POH), the relevant FAA Advisory Circular, and NTSB safety studies for the operational profile.