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oscarbcn78

Displays off if I forget to turn APU off

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Hi!

I am writing to this forum because I don´t understand why displays go off (PFD, ND and EICAS) when flying if I forget to turn APU off (APU START and APU GEN 1-2 OFF) once engines are started on ground. In fact, to have APU on wouldn´t mean that displays have to lose energy because engines are generating energy...

Apart from unknowing the reason, I don´t find any solution for this problem when flying en route. I try to change STAND-BY POWER and/or BUS TRANSFER states but this doesn´t help. So without displays my flight is spoiled...

Thank you so much.

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First this forum requires users to put both first and last name on every post. 

To anwer your problem. You forgot to turn the generator to eng. I highly recommend you to go through the tutorial as it explains all the basic systems in detail.

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No, as I said, sometimes I forgot to turn APU and APU GEN off, so displays go off some time later (when flying).

I have read a lot about 737NGX but no tutorial explains the reason why displays go off when APU remains on. If somebody could explain it to me and how to solve if it happens...

Thanks again.

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If this happens in flight, the first thing you need to do immediately is turn the engine generator switches on. That’s the only way to get the displays re-powered.

The tutorial doesn’t cover this, because it’s an abnormal situation. You are supposed to transfer to the engine generators (from the APU) before takeoff.

I’m not sure which specific APU is modeled in the PMDG NG There are many different models of APU that potentially could be found in a real 737. All of them can be run in flight, but some models have altitude limits. If you climb high enough, the APU might shutdown, and if you forgot to transfer to the engine generators before takeoff. you will be left with very limited electrical supply when that happens. 

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Interestingly, there's exactly one time the engine driven gens will be automatically connected to the busses in a real 73, and it's just this scenario - taking off with the APU accidentally still powering the buses, and then shutting down the APU.  The engine driven gens will automatically come online.   Never thought to try it in the NGX and see if it's modeled. 

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Yes, I turn eng gen on immediately but it desn't work.

Although I don't understand the reason for this issue, there's no another way to repower the system in this situation?

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33 minutes ago, oscarbcn78 said:

Yes, I turn eng gen on immediately but it desn't work.

Although I don't understand the reason for this issue, there's no another way to repower the system in this situation?

There may be something wrong with the way the aircraft initialized if bringing the engine generators online manually doesn’t work. Are you using one of the standard PMDG panel states to start your flight, or one you saved yourself? Sometimes corrupt panel state files can cause a variety of problems with aircraft systems.

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StearmanDriver is indeed correct. It's a feature to save the LCD...Lowest Common Denominator, commonly the worst pilot in any given company!

Without trying to waggle my finger at you, it does show that SOP training has it's place. Please do try to stick to a regular flow pattern and use the supplied checklist to prepare your NGX for takeoff. 

There are Supplementary Procedures  for No Engine Bleed and pressurised take offs too. Well worth using them.

 Put simply You would always select Engine Generators on after start. There really isn't any circumstance where you shouldn't, save for a MEL limited departure with a faulty generator where you would typically leave the APU on and get it to supply the failed side. There is only one model of APU used on all NGs, and it's a very reliable and powerful unit- far better than previous 737s. It very rarely goes wrong, even then it's normally a fouled plug. The NG runs cooler on the ground with 2 packs on rather than 1, clearly the APU is more than man enough for the job! I've sat in 52' heat in South Eastern Turkey with no complaints about the air conditioning....

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I use a saved panel by myself, not a standard pmdg panel.

But do you think it's a panel failure? Or it's a normal behaviour of the airplane if you forget to turn APU off??

Edited by oscarbcn78

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