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A37575
16th Sep 2005, 14:31
During a training session involving the B737-300 flight simulator, it was noticed that when No 2 engine was failed at VR, the first officer's ASI needle immediately winds up to around 300 knots then slowly winds back again to expected speed. This takes 10 seconds to occur. The technicians advise this is normal due operation of transfer bus and that it replicates the same happening on the real aircraft.

While the possibility of EFIS display blanking on engine failure is mentioned in Volume 1, I am unaware of the airspeed indicator being affected. Any idea if this happens to all 737-300 simulators?

LEM
17th Sep 2005, 06:13
That's a common glitch on the real airplane, just did two sectors and everytime I put the APU on line over the GPU the CM2 ASI behaved as you described.

Never seen this happen in a sim.

BOAC
17th Sep 2005, 08:46
Yes - I have seen it many times on power change-over before start, but never in the sim or the a/c airborne. I have always assumed it was some sort of 'black magic' in the ADC. It is accompanied by what appears to be a 'self-test' on the ASI (and sometimes altimeter) including VMO/MMO flags etc. It certainly would not help with an engine failure.

Asfkap - there would have been many 'snagged' a/c and many delays.......

Old Smokey
18th Sep 2005, 01:51
A37575,

I think that you might have provided a significant clue in your initial post when you stated "when No 2 engine was failed at VR", the aircraft is still on the ground. The 3 subsequent respondants (ASFKAP, LEM, and BOAC), presumably current B737 operators, have correctly indicated that this is a normal event after a power supply change on the ground.

I last flew the B737-300 some 16 years ago, and well remember this "quirk", but it is supposed to be inhibited after the aircraft has commenced taxy. Regretably, 16 years has dulled my memory of the other logical operand within the system which inhibits this self test after the aircraft has begun moving under it's own power. It would appear that the personnel programming the simulator have skipped this "gate", and it could be well worthwhile to investigate it further with the technicians responsible for the simulator's operating system.

Be assured, it will not happen in the real aircraft after it has begun moving under it's own power.

Regards,

Old Smokey

A37575
18th Sep 2005, 08:12
Thanks for the replies. Friend of mine at Boeing, Seattle, said no way would the 737-300 aircraft be certified if the first officer's ASI went ape even momentarily on an engine failure on take off. Meanwhile, it still does it in the simulator so the techs are trying to nut this one out. Watch this space!

LEM
18th Sep 2005, 10:08
Hi Old Smokey, I rather think that's a glitch and not a normal self test of the ASI...

We operate 30 classics, and only a few of them present this anomaly.

I can't tell if this always happens on the same airplane, or if the 400 has maybe a different design :confused:

However, that's not every day we see this happening.

LEM

BOAC
18th Sep 2005, 17:34
Snap! The 200 used to go all the way to 'clackers', and as you say sometimes required the CB to sort it out, but I have not seen a classic go that far.