Time-Zone-Aware Duty Period Calculator
Cross-timezone Part 135 duty math — DST-aware UTC conversions, 135.267 duty limit check, and next legal show time. Free, nothing stored.
UTC conversions use your browser's Intl API — DST-aware for each IANA zone. Advisory decision support; validate against your OpSpecs and GOM.
Frequently asked
Why does time zone matter for Part 135 duty calculations?
14 CFR 135.267 duty and rest limits operate on absolute time (UTC). When a crew shows in one time zone and is released in another — a common scenario for transcontinental or international trips — mentally adding or subtracting UTC offsets is error-prone, especially across Daylight Saving Time boundaries. One wrong UTC conversion can flip a CLEAR/UNABLE finding. This tool converts local show and release times to UTC using DST-aware IANA timezone tables.
When does rest start: at the gate, at the hotel, or at release from duty?
135.267(d) requires the rest to be available during a 24-hour period preceding the planned completion of the assignment. Rest generally begins at release from duty — when the crewmember is no longer subject to the operator's control. A crew van wait or debrief that keeps a pilot under the operator's authority delays the rest start.
Does this calculator account for Daylight Saving Time?
Yes. The tool uses your browser's built-in Intl API, which applies the correct DST rules for each IANA timezone at the specific date you enter. A November flight from New York to London gets the correct UTC offset for both EST and GMT — not a static offset that would be wrong during the summer months.
Clearspar handles all of this automatically on every quote
Airport coordinates → IANA timezone → DST-correct UTC duty window → 135.267 gate. A cross-timezone dispatch never gets the offsets wrong.