FAR 117 Table B Explained: Part 117 vs. Part 135 Flight and Duty Time Rules for Pilots

Why FAR 117 Table B Matters: From Colgan Air to Circadian Science

A pilot reporting for duty at 02:00 with seven or more flight segments is legally limited to just 9 hours of flight duty — while a colleague starting at 08:00 with two segments can legally fly for 14 hours. That 56% difference in allowable duty time is not arbitrary. It is driven entirely by circadian science, and it is encoded in one of commercial aviation’s most critical compliance tools: FAR 117 Table B. Defined under 14 CFR §117.13, this table establishes maximum flight duty period limits for unaugmented Part 121 operations based on a pilot’s acclimated start time and planned segment count. Understanding FAR Part 117 Table B is essential for every Part 121 pilot, dispatcher, and safety officer — and confusing it with Part 135’s fixed-cap rules is one of the most common and consequential errors in aviation compliance.

FAR 117 Table B exists because of a tragedy. On February 12, 2009, Colgan Air Flight 3407 crashed on approach to Buffalo-Niagara International Airport, killing all 49 people aboard and one person on the ground. The NTSB investigation identified crew fatigue as a contributing factor. The legislative response — the Airline Safety and FAA Extension Act of 2010 (P.L. 111-216) — mandated a complete overhaul of flight and duty time rules for Part 121 carriers. The result was 14 CFR Part 117, which became effective January 4, 2014, replacing legacy duty rules built on arbitrary flat caps with a framework grounded in circadian rhythm fatigue science.

Part 117 applies exclusively to Part 121 scheduled airline operations. It recognizes what fatigue science has long demonstrated: the time of day a pilot begins work, and the number of segments flown, directly affect fatigue risk. In this article, we will walk through Table B itself, show how to read it, compare it to Part 135 limits, address common compliance mistakes, and provide worked scenarios.

Understanding FAR Part 117 Table B: Flight Duty Period Limits for Unaugmented Operations

Table B to Part 117 is the core operational tool for determining Part 117 flight duty period limits in unaugmented flight operations — meaning a standard two-pilot crew with no in-flight rest facility. The table cross-references two variables: the pilot’s acclimated start time and the number of planned flight segments. Below is the complete 14 CFR §117.13 Table B maximum flight duty period table, reproduced for reference.

Three variables determine the FDP limit: (1) the pilot’s acclimated start time, (2) the number of planned flight segments, and (3) whether the operation is augmented or unaugmented. This table covers unaugmented operations only — augmented crew limits appear in Table C under §117.17. Notice the 5-hour range from 9 to 14 hours. That spread reflects circadian science: duties beginning during the Window of Circadian Low (roughly 0200–0600) carry the highest fatigue risk, and the table imposes the strictest limits accordingly.

A critical distinction: Table B governs Flight Duty Period — the time from report to engine shutdown after the final segment. It does not govern flight time. That metric is controlled by Table A (§117.11). Confusing flight time with flight duty period is one of the most frequent compliance errors in the industry.

Table A vs. Table B: Which Limits What?

Table A (§117.11) caps maximum flight time — the period from block-out to block-in, or more precisely, the time an aircraft first moves under its own power for the purpose of flight until it comes to rest at the next point of landing. Table B (§117.13) caps the flight duty period, which includes pre-flight briefings, taxi, all flight segments, and post-flight duties through engine shutdown.

Both limits apply simultaneously. A pilot must comply with whichever limit is reached first. For example, a pilot starting at 0800 acclimated time with 2 segments has a 14-hour FDP limit under Table B — but Table A’s flight time cap may be reached well before that 14-hour window closes. Tracking both concurrently is a regulatory requirement, not optional good practice.

How to Read FAR 117 Table B: Acclimated Time and Segment Count

Reading FAR 117 Table B correctly requires three steps — and getting any one of them wrong can result in an illegal schedule. The following FAR Part 117 Table B FDP calculation process applies to all unaugmented Part 121 operations.

1. Step 1: Determine acclimated time. Per §117.3, acclimated time is the local time at the location where the pilot spent the prior 72 consecutive hours. If the pilot has been at the current location for fewer than 72 hours, acclimated time defaults to the prior location’s time zone. This matters enormously in cross-country operations. Consider a pilot based in New York (EST) who has been operating in Los Angeles (PST) for only 48 hours. That pilot is still acclimated to EST. A 0600 PST report time is 0900 EST for Table B purposes — placing the pilot in the 0700–1159 row rather than the 0600–0659 row. The difference could mean additional available FDP. Using local departure time instead of acclimated time is a documented and consequential error.
2. Step 2: Count the planned flight segments for the entire FDP. Every takeoff and landing counts as one segment.
3. Step 3: Cross-reference the row (acclimated start time) with the column (segment count) to find the maximum FDP in hours.

Worked scenario: A pilot reports at 0500 acclimated time with 4 segments planned. Looking at the 0500–0559 row and the 4-segment column, the maximum FDP is 11.5 hours. Now suppose a 5th segment is added due to a schedule change. The FDP limit drops to 11 hours. That half-hour reduction may seem modest, but if the crew is already 11 hours into the duty, it turns a legal operation into an illegal one. A pilot starting at 0500 with 1–3 segments gets 12 hours, while 7+ segments yields only 10 hours. Ignoring segment count leads to illegal scheduling.

FAR 117 vs. Part 135 Duty Limits: A Side-by-Side Comparison

Pilots transitioning between Part 121 and Part 135 environments frequently encounter confusion about which rules apply. This FAR 117 vs. Part 135 duty limits comparison clarifies the fundamental differences between the two regulatory frameworks governing pilot flight and duty time limits.

The philosophical difference is stark. Part 117 treats fatigue as a variable influenced by time of day, workload intensity, and cumulative exposure. Part 135 treats it as a function of hours flown — a single flat cap regardless of whether a pilot starts at 0200 or 1400. Note that Part 135’s 8- and 10-hour limits are flight time limits, not flight duty period limits; they measure different metrics. A Part 135 operator cannot use FAR Part 117 Table B limits. Part 117 is strictly Part 121. For in-depth Part 135 regulatory training, see CTS’s Part 135 Training program.

Cumulative Limits and Rest Requirements Under Part 117

Table B governs a single duty period, but Part 117 also imposes cumulative caps under §117.23 that operate as rolling windows — not calendar-based resets. These require continuous tracking:

• 60 FDP hours in any 168 consecutive hours (rolling 7-day window)
• 190 FDP hours in any 672 consecutive hours (rolling 28-day window)
• 100 flight time hours in any 672 consecutive hours
• 1,000 flight time hours in any 365 consecutive days

Rest requirements are equally specific. Part 117 mandates a minimum of 10 consecutive hours of rest before an FDP, which must include an opportunity for at least 8 hours of uninterrupted sleep. The distinction between rest and sleep is critical. Ten hours of rest does not equal 10 hours of sleep. Commute time, meal preparation, and personal hygiene all consume a portion of that rest window. The 8-hour sleep opportunity is a distinct requirement within the 10-hour period — a deliberate design grounded in fatigue science, not administrative convenience.

FDP Extensions, Short-Call Reserve, and FRMS

Three advanced compliance topics consistently generate questions from pilots and dispatchers alike. Each addresses what happens when standard Part 117 flight duty period limits intersect with real-world operations.

FDP Extensions (§117.19): The PIC and certificate holder may extend the maximum FDP by up to 2 hours due to unforeseen operational circumstances — weather delays, maintenance issues, or ATC holds that could not have been anticipated. This is not a pre-planned scheduling tool. The PIC must determine the flight can be completed safely, and the extension must be reported to the certificate holder. If circumstances were foreseeable at the time of scheduling, the extension authority does not apply.

Short-Call Reserve (§117.21): For pilots on short-call reserve, the combined Reserve Availability Period (RAP) plus the subsequent FDP cannot exceed the lesser of Table B + 4 hours or 16 hours total. A worked example: a pilot’s acclimated start time falls in the 0700–1159 range with 3 planned segments, giving a Table B limit of 13 hours. The combined RAP + FDP cap is the lesser of 13 + 4 = 17 hours or 16 hours — so 16 hours is the operative limit. Dispatchers must calculate this before assigning reserve pilots to prevent scheduling violations.

FRMS (§117.7): Part 117 permits operators to implement a Fatigue Risk Management System as an FAA-approved alternative compliance pathway. Under FRMS, an operator may deviate from specific Part 117 limits — including Table B — provided safety analysis demonstrates equivalent or better fatigue mitigation outcomes. This is data-driven, scientifically validated, and subject to ongoing FAA oversight. It is not a regulatory workaround.

Common Mistakes Pilots and Dispatchers Make With FAR 117 Table B

1. Confusing flight time (Table A) with FDP (Table B). FDP runs from report time to engine shutdown after the final segment. Flight time runs block-to-block. They are distinct metrics governed by separate tables, and both apply simultaneously.
2. Assuming 10 hours of rest equals 10 hours of sleep. The regulation requires a rest period of at least 10 consecutive hours containing an opportunity for at least 8 hours of uninterrupted sleep. Commuting, eating, and personal time reduce actual sleep availability. The 8-hour sleep opportunity requirement exists precisely because the FAA recognized this gap.
3. Ignoring segment count. A pilot starting at 0500 acclimated time gets 12 hours FDP for 1–3 segments but only 10 hours for 7+ segments. That 2-hour reduction can convert a legal schedule into a violation if segments are added without recalculating the FDP limit.
4. Part 135 pilots assuming Part 117 applies to them. Part 117 is strictly for Part 121 operations. Part 135 operators follow §135.267, which uses fixed flight time caps without circadian-based adjustments. The two frameworks are not interchangeable.
5. Using local departure time instead of acclimated time. The FAR 117 Table B lookup requires the pilot’s acclimated time zone — the local time where the pilot spent the prior 72 consecutive hours. A pilot who recently crossed time zones may have a significantly different acclimated start time than the local clock shows.

Frequently Asked Questions About FAR 117 Table B

Strengthening Your Part 117 Compliance: Next Steps for Pilots and Operators

FAR 117 Table B is not a static lookup chart to be memorized and forgotten. It requires an active understanding of acclimated time zone calculations, segment count effects, the distinction between FDP and flight time, and the interplay between single-duty limits and cumulative rolling windows. More than a decade after Part 117 became effective on January 4, 2014, compliance errors still occur — often because training treats the regulation as a reference document rather than a decision-making framework. Pilots, dispatchers, and safety officers who internalize why FAR Part 117 Table B limits are structured the way they are will be best equipped to apply them correctly under real-world operational pressure.

Scenario-based training remains the most effective path to internalizing these pilot flight and duty time limits. Rote memorization of the table is insufficient. Pilots, dispatchers, and safety officers benefit from structured programs that simulate real-world scheduling decisions — cross-country acclimation scenarios, segment additions mid-duty, and reserve callout calculations. As FRMS adoption grows and fatigue science continues to evolve, the professionals who understand why the rules exist will be best positioned to apply them correctly.

CTS offers structured aviation training programs — including Part 135 Training and IS-BAO/Part 91 Training — that build the regulatory fluency pilots and operators need across all certificate types. Whether you are reinforcing your understanding of flightcrew fatigue and rest regulations or building a compliance culture from the ground up, structured training is an investment in safety.