Pilot Duty Time Limits: Part 91 vs Part 135 Explained

Pilot duty time limits are one of the areas of aviation regulation where the specific rules differ significantly between operational categories, and where confusion about which rules apply to which operations creates real compliance risk. A pilot who flies for a Part 91 corporate flight department and then accepts a Part 135 charter trip operates under two fundamentally different sets of duty time requirements, even though the flying activity may look identical from the outside.

This article covers the specific duty time rules under Part 91 versus Part 135 in 2026, how the differences affect crew scheduling, and what both operators and pilots need to understand to remain compliant across both operational contexts. For operators sourcing contract crew across both operational categories, the CrewBlast platform allows requests to specify Part 91 or Part 135 requirements so responding pilots can confirm their recent duty status before accepting the assignment.

THE CORE DIFFERENCE IN ONE PARAGRAPH

Part 91 has no specific duty time or flight time limits. Part 135 has detailed rules including 8 hours between rest periods, 10 hours per 24 hours, and 10 hour rest requirements. When crew move between Part 91 and Part 135 in the same period, the Part 135 rules apply to the Part 135 trip regardless of what happened before.

Part 91 Duty Time: The General Framework

Part 91 governs non commercial operations, aircraft flown for the owner's own use rather than for hire. Part 91 has no specific duty time or flight time limits in the sense that Part 135 does. There is no maximum daily flight time, no maximum duty period, and no specific rest requirement before returning to duty.

This does not mean Part 91 crew can fly indefinitely. Under FAR 91.13, the pilot in command is responsible for the safe operation of the aircraft, and operating with fatigue that impairs judgment or performance violates this general regulation. The FAA has taken enforcement action against Part 91 crew who operated in obviously fatigued conditions even without specific duty time rules being violated.

In practice, most professional Part 91 operators adopt informal duty time practices that mirror Part 135 requirements for consistency and safety, even though they are not legally required to do so. Insurance carriers and safety audit programs (WYVERN, ARGUS) increasingly evaluate Part 91 operators on the discipline of their voluntary duty time practices.

Part 135 Duty Time: The Specific Requirements

Part 135 governs commercial charter operations, aircraft flown for compensation or hire. Part 135 includes specific enforceable rules covering flight time limits, duty period limits, and rest requirements that must be followed for every operation under the certificate.

Flight Time Limits Under Part 135

For unaugmented crew (two pilots) on Part 135 operations, the general flight time limits are 8 hours between required rest periods for two pilot operations, 10 hours in any 24 consecutive hours, 34 hours in any 7 consecutive days (this varies by specific operation type), and 1,200 hours in any calendar year.

For augmented crew operations (three or four pilots), the flight time limits extend significantly to allow ultra long range operations. The specific limits depend on crew composition and rest facility availability during the flight.

Duty Period Limits

Duty period is the total time from when the pilot reports for duty until they are released. Under Part 135, the maximum duty period for two pilot unaugmented operations is generally 14 hours. Augmented crew arrangements extend this.

Required Rest Periods

Before beginning a duty period, pilots must have received the required rest, generally 10 consecutive hours preceded by the completion of the previous duty period. Specific requirements vary based on the length of the upcoming duty period and other factors.

The Key Practical Differences

The practical impact of these differences shows up in several specific scheduling situations.

Long Domestic Trips

A Part 91 corporate operator can schedule a trip that involves 12 hours of flight time in a single day if their crew can safely complete it. A Part 135 charter operator cannot. The 10 hour flight time limit for two pilot operations applies, and augmented crew would be required for longer operations.

Back to Back Operations

A Part 91 operator can potentially schedule a pilot for a trip that ends late in the evening and begins another trip early the next morning. A Part 135 operator must observe the required rest period between operations, which effectively enforces minimum time off between duty periods.

International Long Range Operations

Ultra long range international operations on Gulfstream GVI (G650), GVII (G500/G600), and Global 7500 aircraft frequently require augmented crew under Part 135 due to the flight time limits on unaugmented operations. Part 91 operators have more flexibility to complete these operations with two pilot crew if the specific flight time allows.

Crew Movement Between Part 91 and Part 135

Many business aviation pilots (both full time employed and contract) work across both Part 91 and Part 135 operations. When a pilot completes a Part 91 trip and then accepts a Part 135 trip within the same period, the Part 135 rest requirements apply to their eligibility for the Part 135 trip regardless of what the Part 91 trip looked like.

This creates real scheduling implications. A contract pilot who accepts a Part 91 trip that involves 12 hours of flying and then a short overnight before a scheduled Part 135 charter may find themselves not legally qualified for the Part 135 trip due to insufficient rest between operations. Operators sourcing contract crew for Part 135 operations should specifically confirm the crew's recent duty history when tight sequencing is involved.

The CrewBlast platform allows operators to specify Part 91 or Part 135 requirements in crew requests, and pilots responding to Part 135 requests can indicate their recent duty status. This transparency helps prevent scheduling that would violate Part 135 rest requirements before the crew arrives at the aircraft. For a complete walkthrough of how requests, responses, and confirmations work through the platform, the how it works page covers the full workflow.

Contract Crew Approval Requirements Under Part 135

Beyond duty time, Part 135 adds another compliance layer that Part 91 does not. Contract crew must be approved under the operator's specific training program before flying revenue passengers. A pilot who holds the correct type rating and meets all other qualifications cannot simply be dropped into a Part 135 operation without completing the operator's training program requirements.

This is why most Part 135 operators maintain approved contract crew pools that they have proactively worked with rather than sourcing new contractors for each urgent need. The approval process for a new contract pilot on a Part 135 certificate takes time and cannot typically be completed under emergency time pressure.

THE PROACTIVE PART 135 APPROACH

Building a preferred approved contract crew roster during normal operations is significantly easier than sourcing under emergency time pressure. For Part 135 operators, this proactive approach is not optional. It is the difference between reliable coverage and last minute compliance risk.

For Part 135 operators, CrewBlast OS supports the preferred contractor workflow that makes proactive contract crew management practical. Building your approved contract pool during normal operations rather than during emergencies. Every pilot in the network has completed CertiFly verification including CLEAR biometric identity confirmation, which supports the vetting portion of your certificate holder approval process.

How Duty Time Compliance Affects Insurance and Safety Ratings

Insurance underwriters and safety audit programs increasingly evaluate operators on the systematic discipline of their duty time management, not just on regulatory compliance minimums. Operators who maintain conservative voluntary duty time practices even under Part 91 receive better renewal outcomes than those who consistently operate at the edge of what regulation allows.

Both WYVERN and ARGUS audits evaluate duty time policies and their consistent application. Operators who cannot demonstrate systematic policies, or whose actual practice diverges from their documented policies, score less favorably in these audits than operators with consistent, documented, and observed duty time discipline.