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OutOfRunWay
26th Jan 2008, 21:42
Are there aircraft types out there where the clocks are automatically adjusted via GPS?

AFAIK, the time on aircraft clocks need to be manually set by crew :confused:

This thought came up while reading an incident report which stated that the timeline of the incident could not be perfectly adjusted, as clocks on the aircraft involved were showing different times..

Cheers
OORW

PantLoad
26th Jan 2008, 22:32
What does your company's SOP say about this?

PantLoad

Spooky 2
26th Jan 2008, 23:02
Boeing offers a clock for all their various models that is GPS calibrated. Big $$. I thought that the standard B777 clock was GPS driven but after looking at the FCOM. I'm not so sure?

Capt Chambo
27th Jan 2008, 01:58
The 737NG has clocks that can be set either manually or off the GPS. It is normal to have them set to UTC which is then updated via the GPS, any failure of your GPS reception is indicated by your clock going blank!

SuperRanger
27th Jan 2008, 02:54
on our 777, the clocks are usually set to UTC (displays AIMS generated UTC time and date which comes from GPS). however, they can be set to MAN (if so required).

what is more interesting is how the FMC uses the time for ETO? boeing's FMC always round-down the time to the nearest minute i.e. 22:34.9 =>22:34. 'Apparently', it isnt so on the airbuses (can someone confirm!).

Dan Winterland
27th Jan 2008, 04:19
On the A320, it's an option. Our fleet, some do - some don't depending when they were orderd and which clock they have. They all display seconds rather than decimals.

Also, on the newer aircraft with Pegasus, the display does actually show UTC (GMT if you're British!) wheras from what I remember of the Boeing FMCs which dispalyed GPS time. There is a difference! This is because when the first GPS satellite was launched, it was set to UTC and since then, every satellite has had to follow the set time. However, UTC has undergone several corrections since to allow for variations in the Earth's rotation rate. I don't know what the difference is, but is now a few seconds. The Airbus FMGC software has a correction factor.

Lord Lucan
27th Jan 2008, 10:17
Our clock (F27) is a wind-up job and it is set to UTC by reference to the GPS. But the GPS time is always there if you want to look...

OutOfRunWay
27th Jan 2008, 10:36
Thanks all for your prompt replies!

OORW

IRRenewal
27th Jan 2008, 15:30
source: http://www.leapsecond.com

# UTC, Coordinated Universal Time, popularly known as GMT (Greenwich Mean Time), or Zulu time. Local time differs from UTC by the number of hours of your timezone.

# GPS, Global Positioning System time, is the atomic time scale implemented by the atomic clocks in the GPS ground control stations and the GPS satellites themselves. GPS time was zero at 0h 6-Jan-1980 and since it is not perturbed by leap seconds GPS is now ahead of UTC by 14 seconds.

Lord Lucan
27th Jan 2008, 15:39
I have no expert knowledge of GPS time. I assume what IRRrenewal says is true for the internal workings of GPS navigation.

But the GPS in my airplane displays UTC.

I'm sure I would have noticed a 14 sec difference as I check my own watch from more than one source.

Slasher
28th Jan 2008, 09:08
Yeh me too. Ive double-checked the on-board GPS clock and
its a spot-on match with WWVH and volmet broadcast times.

OutOfRunWay
28th Jan 2008, 12:07
The "Errors" in the GPS based clock are well understood (Obviously they have to be, since otherwise GPS wouldnt work at all) so its easy for a computer to correct the RAW GPS time data and display a very accurate ZULU time.
Even most Handheld GPS will do this.

Fly gentle! OORW

ITCZ
28th Jan 2008, 13:04
on our 777, the clocks are usually set to UTC (displays AIMS generated UTC time and date which comes from GPS). however, they can be set to MAN (if so required).

Same on the little B717. System time is updated by GPS. Same Honeywell VIA avionics suite as MD-11.

Charles Darwin
29th Jan 2008, 08:26
...what is more interesting is how the FMC uses the time for ETO? boeing's FMC always round-down the time to the nearest minute i.e. 22:34.9 =>22:34. 'Apparently', it isnt so on the airbuses (can someone confirm!).

The same goes for some of some of our older 757 FMC's, but the more recent aircraft always give the right estimate (although manually adjusted).
I find this interesting because I always believe the time to be i.e. 08:11 until it's 08:12, it's not "considered" to be 08:12 when it's really 08:11 and 45 seconds.
When I compared the clock display on the old planes to the FMC time display I found the input to be "staggered" about 35 seconds to fool the FMC into interpolation of time. Totally wrong approach, if you ask me, but like I said I'ts been corrected on the newer planes. The older probably was designed by computer geeks..:zzz:

j_swift
29th Jan 2008, 09:33
The A380 uses either GPS generated time signal or a manually adjusted clock called INT or internal clock. The latter signal is derived from GPS or it is manually set by the pilot. There is a MEMO message that reminds to set it back to GPS.:ok: