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.
Last edited by Gas Bags; 29th Sep 2010 at 09:55.
Reason: Pipped at the post