Hi folks, 

Larry Vance mentions in his book 'Mystery solved' on MH370 that the APU starts automatically in case the engine run out of fuel. 

It seems not to be simulated. 

Cannot find in FCOMs the information. 

Unless I'm grossly mistaken, the engines and APU pull fuel from the same place... the fuel tanks.  So if you're out of fuel, you're out of fuel.

Maybe you're thinking of the Ram Air Turbine (RAT)?

 

The APU autostart logic isn’t tied to the engine state, it’s tied to the power state of the AC transfer buses.  If power is removed from the left and right transfer buses an APU autostart will be initiated. The RAT is also deployed as part of the process. As Dave mentions though if fuel starvation is the reason the generators dropped offline the APU isn’t going to help for very long.

I’m pretty sure I’ve tried it on the PMDG version in the past and it works.  You should be able to just turn your generators off to test it, no engine shutdown required.

6 hours ago, DaveCT2003 said:

Unless I'm grossly mistaken, the engines and APU pull fuel from the same place... the fuel tanks.  So if you're out of fuel, you're out of fuel.

Maybe you're thinking of the Ram Air Turbine (RAT)?

 

Yeah, I’m confused, too...

Hi folks, 

without copyright, for the sake of the discussion I quote from the book: Larry Vance, MH370 Mystery solved, ISBN 978-1-7752834-2-3, p.109. 

"A quick reminder here: the B777 has an auxiliary pwer unit (APU), which is a small jet engine located at the tail end of the fuselage. In the air it is normally not running. It is used only as a backup, but when it is in use it can supply power to (among other things) the airplane's electrical and hydraulic systems. 

The official investigation believes that when the engines stopped from fuel exhaustion, the APU automatically started. It is designed to do that. The APU uses the same fuel as the engines, but it has access to the last bit of fuel in the tanks -- fuel that is not available to the engines. The official investigation contends that the start-up of the APU restored electrical power to the communications unit, and when the communciations unit rebooted it sent a log-on request, and that is why handshake #7 happened."

Larry Vance denies the unpiloted flight theory and claims that the pilot started the APU himself: 

p.111

"There is a logic for why the pilot might start the APU for a controlled ditching. Perhaps he wanted to make sure he would still have electrics and hydraulics. ... He would know that the plumbing inside the airplane's fuel tanks would allow the APU to have access to teh last bit of residual fuel in the tanks; fuel that the engines cannot access." 

 

8 hours ago, BrianW said:

I’m pretty sure I’ve tried it on the PMDG version in the past and it works.  You should be able to just turn your generators off to test it, no engine shutdown required.

Ok, will check again. Thanks, Brian. 

Edited June 30, 20187 yr by 19AB67
editorial

Hi folks, 

I repeated the test with GENs off, but to no avail: The APU does not kick in. 

Actually I don't see a reason for having that automated (with the knob in the off position): 

The pilots should be able to turn it on in case of double GEN failure and/or deploy the RAT. 

So, is Larry Vance mistaken here? (I am going to scan the FCOMs again.) 

There we are: 

FCOMv2 page 6.20.2

"In flight, when both transfer busses are unpowered, the APU starts automatically, regardless of APU selector position."

Edited June 30, 20187 yr by 19AB67

... and it works nicely: 

GENs off, Backup GENs off, and the transfer busses are unpowered. 

APU kicks in, RAT deployed. 

All fine, and Larry Vance is of course also right. 

BTW: The engines run out of fuel with 158kgs total. 

Edited June 30, 20187 yr by 19AB67

Very good to know.  Thanks for sharing this!

 

On 6/30/2018 at 6:38 AM, scandinavian13 said:

Yeah, I’m confused, too...

 

On 6/30/2018 at 2:07 PM, DaveCT2003 said:

Very good to know.  Thanks for sharing this!

 

Yoh, also I am happy to learn bit by bit; still there are new things to discover!