737 APU fire warning horn
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Joined: Apr 2003
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From: Sutton
737 APU fire warning horn
With battery power only does the APU fire warning horn sound? Had a sim with total power failure and seem to remember a simulated faint horn. What is the rationale behind this?
Joined: Jun 2010
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From: Brisbane, Australia
OK..my take on this one is...
The APU fire detection system is powered by the battery bus, and the APU fire extinguishing system is powered by the hot battery bus.
Therefore my answer to you is yes.
EW73
The APU fire detection system is powered by the battery bus, and the APU fire extinguishing system is powered by the hot battery bus.
Therefore my answer to you is yes.
EW73
Thread Starter
Joined: Apr 2003
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From: Sutton
Thanks for the answers so far...so are we saying Boeing went to the trouble of utilising an APU fire warning horn....in the wheel well to let us know we can't align the IRS.
It obviously does the job.....also tells the entire airport that the guy doing the cockpit checks has got his check sequence wrong
Just curious as to why they wouldn't consider the on DC light enough of a warning.
Is EW73 onto something? The "Therefore my answer to you is yes" has thrown me
It obviously does the job.....also tells the entire airport that the guy doing the cockpit checks has got his check sequence wrong
Just curious as to why they wouldn't consider the on DC light enough of a warning.
Is EW73 onto something? The "Therefore my answer to you is yes" has thrown me
Joined: Jan 2005
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From: MAN
The APU fire warning horn has got nothing to do with all of this. It is in the MAIN wheel well. The ground crew horn in the nose wheel well is the one you heard. It sounds automatically if the ADIRU's are left on battery power i.e when you had power failure and you were on the ground, the horn comes on after 20 seconds.
Loss of equipment cooling on the ground also brings the warning horn on.
Loss of equipment cooling on the ground also brings the warning horn on.
Last edited by J31 MAN; 29th September 2010 at 09:58.
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From: Australia
RMC,
The info is in the previous posts combined.
There are two seperate horns. The APU fire warning horn in the R/H MLG wheel well, and the ground crew call horn in the NLG wheel well.
The APU fire warning comes off the battery bus. This is why when you start a cold ship you can carry out an APU fire test with the battery switch selected on (the APU fire warning horn in the R/H MLG wheel well will sound during this test).
I believe the warning you are referring to during your sim session came from the ground crew warning horn in the NLG wheel well, or you would have had the associated fire anunciator and master caution lights come on in the cockpit as well as having heard the horn.
A power failure with the IRS's aligned will cause the warning horn in the NLG wheel well to sound after a time delay.
Hope this clarifies for you.
GB
Oops, sorry J31 posted as I was typing....he pretty much sums it up.
The info is in the previous posts combined.
There are two seperate horns. The APU fire warning horn in the R/H MLG wheel well, and the ground crew call horn in the NLG wheel well.
The APU fire warning comes off the battery bus. This is why when you start a cold ship you can carry out an APU fire test with the battery switch selected on (the APU fire warning horn in the R/H MLG wheel well will sound during this test).
I believe the warning you are referring to during your sim session came from the ground crew warning horn in the NLG wheel well, or you would have had the associated fire anunciator and master caution lights come on in the cockpit as well as having heard the horn.
A power failure with the IRS's aligned will cause the warning horn in the NLG wheel well to sound after a time delay.
Hope this clarifies for you.
GB
Oops, sorry J31 posted as I was typing....he pretty much sums it up.
Last edited by Gas Bags; 29th September 2010 at 09:55. Reason: Pipped at the post
Per Ardua ad Astraeus
Joined: Mar 2000
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From: UK
AH! Those fun days of waiting until F/O was in the stbd wheel-well and .....................
- indeed it is to those awake, but the warning is to let anyone outside know the AC or cooling has dropped off line. It is not very obvious inside the cockpit.
Originally Posted by RMC
Just curious as to why they wouldn't consider the on DC light enough of a warning.
Per Ardua ad Astraeus
Joined: Mar 2000
Posts: 18,575
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From: UK
Originally Posted by fb
leaving the FO down there for a sector to find out if it does actually come on at FL360
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From: The Brickyard
RMC,
Had the same the other day in the aircraft. We were sans APU and the GPU just died. The horn sounds immediately. It isn't anything to do with the APU. I often hear that alarm when doing a walk around and an adjacent aircraft is doing a fire test and is a completely different noise from the wheel well.
The faint beeping you can hear from the flight deck is am external warning to the ground engineer that the aircraft is on battery power and that the battery is being depleted. I don't even think there is any specific relation to the IRS.
Had the same the other day in the aircraft. We were sans APU and the GPU just died. The horn sounds immediately. It isn't anything to do with the APU. I often hear that alarm when doing a walk around and an adjacent aircraft is doing a fire test and is a completely different noise from the wheel well.
The faint beeping you can hear from the flight deck is am external warning to the ground engineer that the aircraft is on battery power and that the battery is being depleted. I don't even think there is any specific relation to the IRS.
Joined: Apr 2004
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From: near EDDF
Originally Posted by Spendid Cruiser
...We were sans APU and the GPU just died. The horn sounds immediately. ...
The horn (in conjunction with ADIRUs on DC) have a time delay of 20 seconds.
