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View Full Version : What´s the time, please ?


captainmorgan888
13th Dec 2009, 16:32
hi all,

maybe i´m the only pilot who does not know....but we are using UTC, right ?
i always ajusted the airplanes clock´s with the GPS time from the FMS, now i read that GPS time is 15sec ahead of UTC, did you consider this ? does the FMS ?

...

STBYRUD
13th Dec 2009, 16:47
Yep, GPS receivers use the UTC Offset message to correct for the 15 second difference automatically to compute UTC (which itself is 34 seconds behind the International Atomic Time). I don't know what kind of FMC you're using, but on the 737NG the clock can display UTC time derived from the GPS directly. (In the end 15 seconds aren't really a big problem anyway, the ICAO only prescribes that clocks should be accurate to the nearest minute) :ok:

mm43
13th Dec 2009, 20:28
STBYRUD
GPS receivers use the UTC Offset message to correct for the 15 second difference automatically to compute UTC (which itself is 4 seconds behind the International Atomic Time)

I suspect it was a 'typo', but UTC is currently 34 seconds behind TAI.

mm43

STBYRUD
14th Dec 2009, 05:31
Indeed it is, good catch! :ok:

PantLoad
15th Dec 2009, 12:27
On the Airbus, the GPS clocks are within 1 second......using WWV/WWVH as the standard. (2.5 MHZ, 5.0 MHz, 10.0 MHz, 15 MHz, and 20 MHz.)
Tune it in on your HF.......

Fly safe,


PantLoad

Busserday
15th Dec 2009, 16:28
The time displayed by most GPSs is adjusted by the time correction transmitted in the GPS data stream to correct the GPS time to UTC (15 seconds presently, due to leap seconds not accounted for by the GPS clocks). Some GPSs will initially display "GPS time" for several minutes on start up until the data is received and the calculation is done.
BD