Power down 737 buzzer/sound
 

Hi there,

when you power down the 737, just before you turn off the battery, the 737 gives a distinct sound.

Is it harmfull to turn off the battery while this sound is still on or has Boeing a special purpose with this sound?

I have been told that if you turn off the battery while the sound is still on , the next crew might have a failure/alert upon powering up, because some sort of internal check has not been completed.

Anybody any comment on this.

Thanks

That sound is usually the gyro in the standby instruments spooling down, so its ok to turn it all off.

If the aircraft is on Battery power alone the sound could be the IRS horn in the Nose wheel bay, stating the IRS are powered by DC power only.

For the latter, the IRS would have to be on still. My guess is the first suggestion and its the gyros spoiling down.

That buzzer is a warning that the right IRS will loose power in 5 mins.

Which variant are we talking about?

If no external AC source the buzzer is the BAT discharge warning. It is associated with the R IRS on DC, but it is BAT discharge. On the ground, the R IRS on DC is not too important. The BAT discharge is significant, as when you come out in the morning and try to crank the APU. Whoops!

I don't think it's the IRS horn the question is about since if it's a power down we are talking about, you probably turned off the IRS anyway. The sound is when you for example turn off the ground power, a second later it comes a sound that last for a second and then you turn off the battery.

There is no noise on our NGs during the Electrical Power Down regardless if the battery is discharging. Try setting the STANDBY POWER switch to OFF on the ground prior to the secure procedure, this isolates the standby system and causes a battery discharge with no alarm. The noise on our NGs is only present if the IRS is on.

You might be hearing the altitude alerting chime when you flick off the battery, thats the MCP losing power...

There is actually another aural warning that hasn't been mentioned. It starts after a specific time on battery power and it's NOT the IRS warning. I recently learnt about it in our annual tech. exam but I cannot for the life of me remember anything more specific.

I'll see if I can dig it up.

It's the baggage handlers moaning that another plonker pilot has powered down and left them in the dark :}

That's what the Ground service switch is for mate. Power down is a two man job....

Mind you if the baggage handlers were a bit quicker.....

My company treats it like a missile launch where you have to move two keys in unison. "On mark in 3..2..1..LAUNCH!"

Why? Why can't you just hit the ground service switch on the way out the door?

That is correct, that's the sound I am refering to.

Okay, thanks. I will try to search the internet for this. Maybe you are correct. But does it matter if you turn the battery off, during this sound? Does it affect any systems?

Otto Throttle,
I'm replying as a "plonker pilot". The company I work for has S.O.P's. You may be aware of these.
I have a great admiration and respect for our engineers, a fanatastic bunch of men and women, who, also understand S.O.P's.
When our procedures call for the de-powering of the aeroplane, we do so. The before said engineers, who understand our procedures, when required, ask if we could not do so on this occasion so as to facilitate certain other requirements...