View Full Version : Detection fire APU on B777-300
nikos642002
31st Jul 2017, 17:54
Dear all,
I would like to ask you about an exercise I have in a sim . After takeoff we loose one engine(severe damage) , EO SID then DET FIRE APU, then radar vectors for an approach, go around, second approach and landing. According to QRH DET FIRE APU , Plan to shut down the APU as soon as practical. According to your professional opinion when I have to shut down the APU and why.
Thank you in advance for your help.
westhawk
1st Aug 2017, 04:28
Shut down the APU immediately to prevent the fire spreading and burning the tail off? Okay, I don't know the triple at all. That's just an initial reaction!
Edited to add:
Condition:
Fire is detected in the APU.
APU FIRE switch . . . . . . . . . . . . . . . . . . . Pull, rotate, and hold
Rotate to the stop and hold for 1 second.
If the FIRE APU message remains displayed:
Plan to land at the nearest suitable airport.
Or are you referring to a failure of the APU fire detection system message? In that case, you have to assume your APU fire detection system is inoperative and therefore the APU is being operated without any fire detection capability. If the APU is running, shut it down as soon as you can get by without it. If it's off, don't start it. If it's running and still needed, run it until shutting it down is the safer option. It's a case of weighing the risks between the possibility of an undetected APU fire (remote) and any risks associated with not having the electrical or pneumatic power the APU can provide available. Captain's hat time!
That's just what I gather reading the Delta QRH. Hopefully a qualified 777 pilot will be along shortly to comment.
nikos642002
1st Aug 2017, 08:05
Thank you for your response. I am referring to Loss of APU Detection of a fire . As i sed after we depart we have an engine fail ( severe damage) so according to QRH if APU is working we should start it. After that and before starting another approach we loose the fire detection of our APU and according to QRH we have to ( plant to shut down the APU as soon as practical ) means to me that LEGALLY i can keep it , otherwise it will state ( Shut down the APU ) . So I believe its a tricky item. Also according to Electrical redundancy of B777-300 we have two engine generators, two back up generators, one APU generator and one RAT.
Roj approved
1st Aug 2017, 08:09
Hi Nickos,
Its just the detection system that is U/S, not the APU on fire. But in saying that, why is it U/S and do you want to run the risk?
Follow the QRH, and shut it down as soon as possible is my opinion. (787 pilot, not flown the 777)
Do you have enough electrical power from 1 engine?
do the flaps/slats run at normal speed?
do the flight controls still operate in Normal mode?
If so, shut it down.
if not, you may need to keep it running until landing then shut it down on the roll out.
just my opinion
These are typical scenarios that have a systems gotcha somewhere hidden like an Easter egg.
I've never flown the 777 and therefore have no systems knowledge but they're trying to get you to shut something down that you need.
Is the battery charger or emergency bus involved somewhere?
Not sure about Airbus but on Boeing be careful about following the non-normal checklists blindly when you have multiple failures. The notes in the back of the QRH say the checklists address single failures. Multiple failures require a bit of thought/judgement.
Also a lot of simulator sessions are quite contrived, ie. multiple failures just after take off (hence very close to an adequate airport) therefore most of the time the decision to return will be the correct. The decisions on how to address the failures may be different three or four hours away from landing!
If you shut the APU down OEI you've still got a main generator and the back up generator. Sufficient for immediate landing? Sufficient to hold and jettison? vs the risk of an APU fire.
Fursty Ferret
1st Aug 2017, 17:40
I'd keep it running. If the battery in your smoke alarm goes flat your house doesn't catch fire*.
*OK, bad analogy. But APU fires are extremely rare.
stilton
2nd Aug 2017, 03:15
Knowing the way simulations are run I can almost guarantee you'll
have an undetectable APU fire causing significant damage if you don't
shut it down.
The instructor wants to see you evaluate that there is more than
sufficient redundancy remaining without the APU, if you decide
to keep it running with no fire detection a fire will be next almost
certainly !
westhawk
2nd Aug 2017, 03:57
Thank you for your response.A pleasure sir, I'm gratified to see that several other contributors found your query interesting enough to respond to as well!
As briefly mentioned above, a sim scenario like this is surely designed to put you in the decision-making pressure cooker, forcing you to weigh the relative risks of taking different possible courses of action in a time critical situation. As an instructor utilizing both FTDs and airplanes (smaller, less complex airplanes) for training, I look at such scenarios as learning exercises more than skills tests. I hope that's the intent of your instructors too!
flyhardmo
2nd Aug 2017, 07:42
Shutting down the APU straight away should not affect anything unless you have other faults present (Eng failure not included). There are a quite a few faults listed in the DDG under Det FIRE APU. For your scenario shutting it down when the checklist asks you to is ok. At that point in the Checklist I would probably refer to the DDG and have a discussion ablut further affects or ground contingencies.. There is a note that you can still use the APU once parked at the gate/stand with a fire guard near the tail of the aeroplane to monitor the APU.
Lots of good advice from other posters especially about not blindly following a checklist.
etudiant
2nd Aug 2017, 10:40
Knowing the way simulations are run I can almost guarantee you'll
have an undetectable APU fire causing significant damage if you don't
shut it down.
The instructor wants to see you evaluate that there is more than
sufficient redundancy remaining without the APU, if you decide
to keep it running with no fire detection a fire will be next almost
certainly !
I(f the fire detection circuit is inoperative, how does the student then find out he has a fire?Loss of rudder control?
Roj approved
2nd Aug 2017, 10:59
"Tower reports fire coming from your tail"
The APU fire detection and the APU fire protection are ( should be) on two different busses.
Loosing detection wouldn't rob you of fire protection.
nikos642002
3rd Aug 2017, 13:48
Dear colleagues I would like to thank you all for your valuable advice . The SIM was OK and the instructor wanted to shut down the APU after we finished the ENG severe damage NNC and the After Take off Normal CL. But as flyhardmo wrote above its not as easy as its looks. Yes we have a lot of redundancy on B777 but it depends where we are , how long we have fly to our destination, items affecting our problem and of course we can check the operation of APU from the Lower Display Unit (EGT,RPM,OIL TEMP,OIL PRESS,OIL QTY) so any time we know what is going on . I am not saying to leave it open or close it immediately but I am saying to think very carefully our action. Best regards and always safe flights to everyone .