Procedural Question: Fire at rotation

[Freight Dog]

I was referring to door light, electrical problems, hydraulic problems, fire detection probs etc. because most places teach V1 cuts and aborts for blatantly obvious things. But I think in addition to that, it makes it good to have a side distraction where an item may be important, but do you abort the takeoff? Sure, here we can debate abort items and techniques all day long, but in the sim or in actual conditions, the results can vary.

 

[SLOTH]

Although an APU fire on takeoff may not necessarily be real world in some cases, I think it'll drive home the point of prioritizing of what gets done and when it needs to get done. It is a good way to get people to embrace CRM techniques when they wouldn't otherwise... just my .02 worth.

Sloth

 

[80/20]

The question we are asking here is if an actual APU fire on take-off is likely to occur?
This can be split into at least two questions:
a) Are there situations where the APU should be on during take-offs in the 737?
b) How likely is it to get an APU fire?

WHY WOULD THE APU RUN DURING 737 TAKEOFF?
1) The APU is often used on 737 performance-restricted takeoffs. Boeing calls this a "no engine bleed takeoff" which uses the APU bleed air for cabin pressurization saving all engine bleed for thrust, which can increase the takeoff weight with more than 3000 lbs.
2) The Master 737 MEL will allow you to substitute one inoperative engine driven generator with an operating APU generator
3) ETOPS require the APU to be operating before entering ETOPS phase of flight. In such cases I prefer to leave the APU running from departure, because it can be hard to start the APU at max altitudes. I also leave it on for long flights in remote areas without enroute alternates such as in the Arctic.

HOW REALISTIC IS AN APU FIRE IN-FLIGHT?
Not very realistic - chances are low. This is also the case for many other emergencies that we train for. Just think of how few airliners that has actually had an engine failure at V1.
There have however been problems with APU fires in-flight.
Another issue is false fire warnings - not totally uncommon. As an example one carrier has had more than 4 false wheel-well in-flight fire warnings on the 737-700 during one year.

CONCLUSION:
In my opinion, FlyChicaga's training scenario is as realistic as many other things we train for and it is also a good way to achieve the other goals that he/she has listed.

 

[flyinhard]

I am just curious as to why you would leave the APU on during takeoff. Someone said that if its low out then you do in case of a generator failure. Obdviously, load sharing would take place and the other generator would kick on. Is it left on just in case this doesn't happen and your not in the soup with a full electrical failure? Thanks-

 

[atldc9]

As far as leaving the APU on for those really low takeoff's, it is strictly as an elctrical backup in the 717. If you lost an engine right there on T/O, then obviously the remaining generator would pick up the load, but that might be a lot of load to drop immediately on the only remaining generator. The engineers say the remaining gen can carry it, but they didn't think the engine would quit either. In the 717, the APU has priority over opposite generator in the event of gen failures, so if it is running, the apu will get the load that the hypothetically failed engine's gen just dropped. That way your good engine's gen doesn't get tested to its max.

 

[SLOTH]

As everyone already has said, the APU would help out in some rare instances when you may potentially have a problem... It is ultimately up to the crew to determine their need for an extra generator, bleed, etc. All that FlyChicaga is tring to teach in his program is the use of CRM techniques and prioritizing the workload at a critical phase of flight. We are taught many things in the sim... most of it we will use on a regular basis, and others we will never see again in our flying careers. Remember, the sim is a tool to teach not only to fly an airplane, but to also teach the mental aspects of dealing with problems. Any of you remember reading about a short circuit in a part of the electrical system in your systems manual? Well, how often have you come across that as well?? That doesn't mean it'll never happen, but it isn't a daily/weekly or even a yearly occurence.

Sloth

 

[KC-10 Driver]

It is common practice on some aircraft to leave the APU running for takeoff under certain circumstances. I will grant, however, that I am not all that familiar with the 737 (my type rating notwithstanding).

For example, on the A320, the APU will be left running for a heavy weight and/or short field takeoff where performance is marginal. The APU would be used to provide pneumatics for the air conditioning packs, thus eliminating some bleed from the engines.

It is a technique some use (note, technique only) on the KC-10 to leave the APU running during a marginal weather takeoff to provide backup in case of an electrical problem. This is a similar rationale to the 717 procedures mentioned previously in this thread.

 

[LJDRVR]

Regarding the earlier advice concerning not becoming too involved with ATC, I once got scolded with some great advice from a sim instructor. Take NO action until:

-The AC is under completely under control

-Obstacles have been cleared (at least 400')

-BOTH pilots are situationaly aware of what is occuring.

In other words, don't drop the aiplane to fly the microphone.

Safe Skies!