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This might be a silly question but my thinking was the following:

There has to be a definition of time in an airplane for the logging of data and so on, but what definition would that be assuming a flight goes across timezones?

Would it be the local time at the airport of departure? Or at that of arrival? or maybe even a third, commonly agreed upon time (e.g., GMT)?


The idea came from a story of a friend that was traveling with the ship from Italy (GMT+1) to Greece (GMT+2). The cafeteria on board had a sign saying that it opens at 14:00, but on 14:20 local Italy time, while the ship was anchored in Italy, he was denied service by the crew saying that the sign was referring to Greece local time; where the ship "belongs".

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    $\begingroup$ Related, maybe a dupe? $\endgroup$ – Pondlife Jun 27 '18 at 12:35
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    $\begingroup$ @Pondlife Nice find. My googling did not bring it up; my title is catchier. $\endgroup$ – Ev. Kounis Jun 27 '18 at 12:41
  • $\begingroup$ Certainly related. This question asks "what", that one asks "why". The question of dupe/no dupe could go either way. $\endgroup$ – Steve V. Jun 27 '18 at 16:53
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    $\begingroup$ Some years ago I had the actual unfortunate (or fortunate depending on perspective) experience of a flight that had a stopover prior to arrival at my location. All THREE times were for 2:00 AM local - but the FUN part was it was on the day where daylight savings time changed so no-one knew the actual UTC time because of everything being listed in local times. They just gave me a 4 hour window as best they could do. $\endgroup$ – Mark Schultheiss Jun 27 '18 at 21:21
  • $\begingroup$ There's a huge difference between what's used internally in the computers and what's displayed to customers - what are you asking about? $\endgroup$ – pipe Jun 28 '18 at 8:24
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The pilot (and the ATC) use the UTC (Coordinated Universal Time). The flight's departure and arrival are in terms of the local times at the respective airports.

As for data logging, the FDR/CVR usually records in UTC (preferred) or the relative time count (usually count increments each 4 seconds of system operation). See Appendix M to Part 121 - Airplane Flight Recorder Specifications, for example.

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ICAO SARPs Annex 2 (Rules of the Air) states:

3.5 Time

3.5.1 Coordinated Universal Time (UTC) shall be used and shall be expressed in hours and minutes and, when required, seconds of the 24-hour day beginning at midnight.

3.5.2 A time check shall be obtained prior to operating a controlled flight and at such other times during the flight as may be necessary.

Note.— Such time check is normally obtained from an air traffic services unit unless other arrangements have been made by the operator or by the appropriate ATS authority.

3.5.3 Wherever time is utilized in the application of data link communications, it shall be accurate to within 1 second of UTC.

The above should apply to almost every country when it comes to international civil aviation. Militaries and uncontrolled flights are not covered by the above.

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The planes use UTC time. The same as ATC.

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    $\begingroup$ Thanks for the answer! A link to UTC would be great too (e.g., this) $\endgroup$ – Ev. Kounis Jun 27 '18 at 12:20
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Let me add that pilots, ATC, and others use UTC, (not GMT) but it's common for customer-facing times to be in the time zone of the event. For example, a Flight from Florida to Alabama may land before it departs on the ticket.

Usually, ticket times are listed in local time. So Departing 1:00 pm Arriving 12:48 pm could actually appear on a ticket.

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  • $\begingroup$ Well, GMT might mean the same thing as UTC. It is, however, ambiguous. $\endgroup$ – Jan Hudec Jun 28 '18 at 21:12

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