Time Conversion and ETA Across a Zone Boundary
An aircraft departs an airfield at 47°30'N 008°30'E at 0640 UTC. The destination is at 33°50'N 070°20'W. The planned groundspeed is 145 KT and the great-circle distance is 3,480 NM. The destination airfield operates on local mean time for its published opening hours, which are 0800 to 1800 LMT. The pilot must file an ETA in UTC and also confirm whether the aircraft will arrive within the destination's opening hours. Sunrise at the destination on the day is 0642 LMT. The aircraft has 26 hours of fuel endurance but the crew duty limit is 14 hours from 0500 UTC.
1. Calculate the flight time and the ETA in UTC.
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Flight time is distance divided by groundspeed: 3,480 ÷ 145 = 24.0 hours exactly.
Departure is 0640 UTC. Adding 24 hours gives an ETA of 0640 UTC on the following day.
The calculation is sensitive to groundspeed. At 150 KT the time would be 23.2 hours, an ETA of 0552 UTC next day. At 140 KT it would be 24.86 hours, an ETA of 0712 UTC next day. The pilot should therefore file the ETA with a note that it is based on 145 KT and update it in flight.
2. Convert the ETA to destination LMT and determine whether the aircraft arrives within opening hours.
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The destination longitude is 070°20'W. LMT is later than UTC by the longitude expressed in time for west longitudes. 70°20' = 70.333°, and 70.333 × 4 minutes = 281.3 minutes, or 4 h 41 min. So LMT = UTC − 4 h 41 min.
ETA in UTC is 0640 next day. Subtracting 4 h 41 min gives 0159 LMT next day.
The airfield opens at 0800 LMT, so the aircraft arrives about 6 hours before opening. The flight is therefore not acceptable as planned: the crew would arrive in the middle of the local night with the airfield closed.
Options are to delay departure so that arrival is after 0800 LMT, which means departing after about 1319 UTC, or to plan a diversion to an airfield with night opening. The pilot should also check the sunrise time of 0642 LMT: arrival at 0159 LMT is well before sunrise, so a night arrival is unavoidable unless departure is delayed.
3. Check the crew duty limit and comment on the practicality of the plan.
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Crew duty started at 0500 UTC. The limit is 14 hours, which expires at 1900 UTC on the departure day.
The flight time alone is 24 hours, so the ETA of 0640 UTC the next day is 25 h 40 min after duty start. That exceeds the 14-hour duty limit by more than 11 hours.
The plan is therefore not practical as a single crew duty. It would require augmented crew, in-flight rest, or a technical stop with a crew change. The pilot should replan with a stop, recalculate the ETA for each sector, and recheck the destination opening hours and sunrise for the revised arrival time. The fuel endurance of 26 hours is not the limiting factor; crew duty is.