B737 - Loss of GRD PWR
 

Chaps, can we discuss the precautions of losing ground power (whilst on the ground) on the 737.

Obviously yaw damper switches off, voice recorder to auto and autobrake disarm light illuminates.

What other considerations are there? The ground horn warning will sound after a certain time?
Is there a time frame where the power needs to be restored before losing all of the FMC data input?
If ground power cannot be restored, it's best to start the APU.

FMC User’s Guide
 

The version I have shows: pg. 42 “if pwr lost for 10 seconds or more on the ground, all preflight procedures and entries must be done again when power is restored.” Page dated May 98. May be different now.

will look some more and come back if more is found.

I think I remember it lasting more than that in the 800s.

What “precautions” do you want to take? If the GND pwr does not hang in there, just start the APU. Unless…

The NGs and onwards have automatic activation of standby power on the ground, which will keep the left FMC powered for as long as the battery power is available, so it's not an issue, unless the battery is dead.

Which would be a no-go anyway.

Nothing you can prepare for. When you get power back on, just start again. In the worst case scenario, you may have to start an engine when all the ground handling is complete.

On the Classic is was a mad scramble to try and get the APU started if it wasn’t already, and if not then a case of rebuilding the FMC. Perhaps the best precaution is to “re brief the glass” once it’s been rebuilt.

Thankfully, one of those small threats..
 

more in the nuisance category.
I suppose today, more and more time is spent on ground power rather than on the APU. If the APU is inop, it is a proper nuisance.

“If AC electrical power is removed from the aircraft, the switched hot battery bus continues to supply electrical
power to the IRS. The ON DC light illuminates, and the ground-call horn in the nose wheel well sounds to alert Maintenance
Personnel that the IRS is on battery power.”