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willywonka

ISFD power

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Yesterday during the powering down sequence the ISFD did not turn off after all power has been removed, including the APU and battery. There was no external power connected.

 

isfd1.PNG

 

Note that the Brake Source light is off indicating that all power has been removed. The ISFD was functional: I was able to change the altimeter settings.

 

I did manually deploy the RAT earlier as this was a functional test flight. However, the airplane is parked, the RAT is not spinning and should not be generating any power.

 

rat1.PNG

 

Thoughts?

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Think it has it's own dedicated battery/charger arrangement

Hmm, I don't think so. " The left FCDC bus powers the ISFD. The left FCDC is powered when the main ac busses are powered." Also:

 

777-elec.png

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Certainly doesn't seem right. Are you able to recreate the problem? I just tried, shutting down to cold and dark, and the ISFD turned off no problem.

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Certainly doesn't seem right. Are you able to recreate the problem? I just tried, shutting down to cold and dark, and the ISFD turned off no problem.

I haven't got a chance to recreate it yet. Have you also tried shutting down with the RAT deployed? I think that's the key.

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...ever stop to think that the ISFD is still powered because it's your last possible lifeline to get yourself on the ground if everything else fails?

 

Independent system:

 

As an example, Acme Aerospace’s DBC for Boeing’s Integrated Standby Flight Display (ISFD) is a self-contained backup power system designed specifically to protect today’s state-of-the-art integrated standby flight systems. The built-in charger/monitor fully conditions and maintains the high power capability of the sealed lead acid battery.

http://acme-aero.com/battery-back-up-systems.html

 

The ISFD backup power system kicked on because it recognized you were in need of backup power.  That standalone system will continue to operate until it runs out of battery power.  I'm sure that if you make it to the ground while it's still powered, maintenance would be able to switch it off, but to be honest, I'm sure that's the last of their worries if you had to get on the ground in that kind of situation.

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...ever stop to think that the ISFD is still powered because it's your last possible lifeline to get yourself on the ground if everything else fails?

 

Independent system:

http://acme-aero.com/battery-back-up-systems.html

 

The ISFD backup power system kicked on because it recognized you were in need of backup power. That standalone system will continue to operate until it runs out of battery power. I'm sure that if you make it to the ground while it's still powered, maintenance would be able to switch it off, but to be honest, I'm sure that's the last of their worries if you had to get on the ground in that kind of situation.

Yea, I thought about it but couldn't find anything to confirm it. Odd that the FCOM wouldn't mention that the ISFD would continue to operate without airplane power.

 

I notice that the passage you quoted specifically say ISFD. Their brochure also say the same that it supplies power to ISFD. I wonder if the separated standby instruments have a dedicated backup power as well?

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So I tried operating the RAT before landing and shutting down the aircraft. I ended up with a dead ISFD but strangely, the L and R Gen bus breaker fault lights and brake source light were illuminated. :wacko:

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So I tried operating the RAT before landing and shutting down the aircraft. I ended up with a dead ISFD but strangely, the L and R Gen bus breaker fault lights and brake source light were illuminated. :wacko:

Not sure why your ISFD was dead if there's supposed to be a dedicated power now.

 

But your Gen and Brake Source lights will continue to shine for a few minutes after shutdown. That's normal.

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Not sure why your ISFD was dead if there's supposed to be a dedicated power now.

 

But your Gen and Brake Source lights will continue to shine for a few minutes after shutdown. That's normal.

Thanks for the info!

 

A bit off topic, but what's the logic behind that one?

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Thanks for the info!

 

A bit off topic, but what's the logic behind that one?

Good question. In short, the airplane has a powering down sequence that it goes through even after switching off the battery, kinda like your computer when you click "shut down", so it takes a moment to really shut down. There's a technical explanation here: http://www.pprune.org/engineers-technicians/378933-powering-down-777-a.html#post5019701

 

Interestingly, all the FCOM have to say about it is "when swtiched off, a few lights remain illuminated". I guess it's too technical for the pilot to know why :)

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According to the Airplane Flight Manual,

 

The Integrated Standby Flight Display (ISFD) System (if installed)
includes a dedicated battery that provides an additional 150 minutes
minimum of ISFD operation following the loss of standby power (main
battery depletion).

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I was wondering how to trigger the dedicated power to the ISFD. I think it's only possible while the airplane is in flight.

 

I think the GENs and the backup GENs must fail or be disconnected. Then, the auto-APU will kick in a few minutes. Disconnect that too. This might be enough to trigger the dedicated battery, but the RAT may also be producing power at this point, if it doesn't need to load shed to drive the hydraulics. Anyway, turn off the main battery too via the overhead switch.

 

So, Jordan, if you don't fail or disconnect all available power sources, the dedicated battery probably won't kick in, and the ISFD will power down with the rest of the plane as usual. 

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