737NG OEI Landing Checklist - Additional GA Thrust Required
 

Additional go-around thrust is needed:

Do not open the APU bleed air valve if the engine fire switch is illuminated.

What has the APU bleed air valve got to do with the engine Fire Switch Light illuminated ? Also does this refer to the only Engine No 1?

It refers to either engine.

If you think what happens if you have the APU and engine bleeds on at the same time you'll be able to work out why you won't want that configuration when an engine is on fire.

Thanks Spander,

What I seem to understand, is it back pressures the 9th Stage Valve and unlocks. The Bleed air then flows into the engine.

My take would be that if you have the engine fire light on, then half the bleed ducting may well be full of smoke and fumes. If you continue the checklist it has you turning the left pack on and potentially putting all that dodgy air through the pack and into the cabin. The only time I can think of when it would be a problem with a number two engine fire is if you have needed WAI earlier and selected the isolation valve to Auto and opened the isolation valve thus filling the entire bleed ducting with contaminated air. Standing by to be corrected by those much smarter than me.

So far having gone through the checklists, you would have attempted to resolve the situation by shutting down the engine, firing both bottles and the resultant would be operating the aircraft with a with single pack, having started the APU for electrics only.

Configuring for additional thrust would enable you more performance, this now requires you to pressurize the aircraft in a different manner, using APU Bleed Air, or remain unpressurized for the remainder of the flight.

Note: With the engine unable to get extinguished having used both suppressant bottles, the location of fire may be in such location as to be unable to get extinguished, but additional O2 into the area of fire may be very harmful.

My guess thus:
Opening the APU Bleed Air Switch may feed the fire with additional O2 forced into the ducts near the blaze location.
In addition I would tend to agree with framer that opening the APU Bleed Air Switch may feed contaminated and very hot air into the Cabin area which is not designed to withstand these very hot temperatures and may cause serious additional problems.

What did your systems instructor tell you about this?

Systems Instructors? Was that the guy who showed us how to load the CBT onto the computer?

framer, I think you'll find that he is the extremely boring and monotonous American from the early 1990s!

Oh him, didn't they replace him with a CD ?
On topic again, I think it is a good question.
Is the reason cabin air contamination or to prevent an influx of O2 that feeds the fire. That had never even crossed my mind.

If the reason is cabin air contamination , the question highlights the potential for people to continue with the checklist but to omitt the step of turning the APU bleed air on in the case of a fire light remaining on. This would result in the left pack being turned on and the problem arising anyway. I would have thought that the little black boxes ending the checklist might be in order?

Thanks to all of you for your responses. What happens if I have a fire on No 1 Engine, which hasn't extinguished.

There is no way, now i can configure additional GA Thrust. Can I?

If you we're ever unfortunate enough to find yourself with marginal climb performance relative to the terrain in the missed approach area ( it'll probably do about 4% on one at 5 tonnes over MLW) , then the question you'll be asking yourself is " what is more important to me, clearing the hills/obstacles if we go around, or having the cabin pressurised while we are less than 10,000ft?" If you would rather clear the hills then simply turn the bleeds off.

Actually, if I was still on fire I wouldn't be going around.

Yeah I agree.

There is no way, now i can configure additional GA Thrust. Can I?

I sometimes wonder about this philosophy. Different airlines have different ideas about it. Some said, "if above max landing weight, then use bleeds off." others said, "captain's discretion." others, "always go bleeds off." They can't all be correct. Consider the bleeds off takeoff case: how much extra weight does it give you? Not a lot; and that's off the ground , not at MDA. So is it really so critical. I suspect it's there, and for Boeing at Captain's discretion, because it's possible to configure thus, and to protect against any comeback should there be a problem caused allegedly by lack of thrust.

You don't need the APU. The checklist starts with "When below 10,000 feet", hence, if you don't set the APU bleed switch to ON (because you still have a fire switch illuminated), you will continue the points in the list and do an unpressurized landing.

In the unlikely event that your go-around procedure will have you climb back over 10.000 feet you would have to reconfigure again. I guess that would be an extremely rare combination and as most said, you would probably do your best to land with an unextinguishable fire.

About when additional go-around thrust is needed. Need is for me = "won't survive without". Otherwise it is just "nice to have". If you need it or not would depend on your performance calculations. At my company we calculate, in general, with the standard missed approach as our engine out missed approach too. If the calculations showed a need for no bleeds, additional go-around thrust is required. If we can't meet the standard standard missed approach gradient with one engine inoperative, we use an engine failure procedure, that comes from the same database as our takeoff calculations, in those cases additional go-around thrust would almost never be needed, because we would have considerable more height at the departure end of runway. But it could be cross checked with the take-off performance if in doubt or the missed approach altitude is very high.

"Above max landing weight" seems quite arbitrary. Why would I need additional go-around thrust, even if doing a return at almost max takeoff weight in, say, Amsterdam (flat like a pancake, for our friends overseas). It would maybe be nice to have, because you could get off work earlier, since a go around wouldn't take that long to accomplish. :p But in that case shouldn't it be left a commanders discretion?

...but about the question of the original poster. I am curious too.

When both engine bleeds closed, why can't we use the APU?

It can't be because of contaminants, because the checklist doesn't end, like framer pointed out. Also the contaminated air would already have entered the cabin, and it would probably only be a few seconds to blow the ducts clear.

Hence, it must be because we don't want bleedair ducts pressurized? But if the engine bleeds are closed, why would it matter? Also the starter valves are closed so bleed air would enter the engine area through this way.

Or maybe it is just written that way to avoid any mess up, that would complicate the situation further? I am leaning towards that option.

YES YOU CAN...

Before this step in the checklist you have configured for single Pack operations using only the RIGHT Pack as the #2 Engine is OPERATIVE and thus providing air conditioning.

Additional GA Thrust is created by removing the BLEED requirement from the operative engine to ensure all power from the operating engine is available for flight performance, not for pressurization plus flight.

So DO the checklist and when you get to item APU BLEED air switch - do not open it, but continue the checklist...

It continues to turn BLEED 2 air switch - OFF

Resultant:

1. An unpressurized Left duct with Left Pack AUTO (thus not doing anything)
2. An unpressurized Right duct with Right Pack OFF (thus not doing anything)
3. An unpressurized aircraft with additional GA Thrust

If additional go-around thrust is needed:
When the airplane is below 10,000 feet, and the use
of wing anti-ice is not anticipated, configure the
pressurization system for a no engine bleed landing:
WING ANTI-ICE . . . . . . . . . . . . . . . . . . . OFF
ISOLATION VALVE switch . . . . . . . . . . CLOSE
BLEED 1 air switch . . . . . . . . . . . . . . . . . OFF
CAUTION: Do not open the APU bleed air valve if the
engine fire switch is illuminated.
* APU BLEED air switch . . . . . . . . . . . . . . ON
Left PACK switch . . . . . . . . . . . . . . . . . AUTO
BLEED 2 air switch . . . . . . . . . . . . . . . . . OFF

That is what I am interested in as well.
On a different note, looking at this closely as we have it seems likely that there will be a rather terrified call from the cabin informing you of smoke in the cabin and a burning smell etc. This is to be expected until the reference items of the engine fire checklist have been completed past the point where the pack is turned off on the side with the burning engine. That call from the cabin will add stress and urgency to the pilots as they proceed with securing the engine. That is common sense stuff but I imagine it would be easy to forget that it will most likely happen if your simulator training is anything like mine has been. When we get engine fires in the sim our shutdown procedures are never interrupted by the check Captain pretending to be cabin crew saying " there's smoke and a burning smell in the cabin!" , yet I imagine it's very likely if the fire is in the right place.
The biggest learning point for me from this thread is that I will be expecting that and will respond with " that's understood, call me back in two minutes if the smoke hasn't started dissipating" or something like that, and I won't be tooooo worried about it as I will expect it to dissipate as soon as the pack is switched off.
Again, I know that's common sense stuff but an increased expectancy of it will help the pilots maintain a feeling of ' no problem....that's what I expected' and continue in a controlled manner rather than start worrying that the fire is going to incapacitate the pax.
Edit: Cosmo makes a good point about this post directly below, don't let me lead you astray.

Framer, you have a lot of funny ideas. :)

An engine fire is taking place somewhere inside the engine cowling (this is where the fire loops are located.. How would smoke get out of the cowl and in front of the engine (going at 180+ knots forward), then be sucked into the engine and through the compressor get into the bleed system? :hmm:

What passengers will smell is a severe damage or engine surge/stall. Where the airflow is no longer normal in the engine, allowing exhaust to go back to the compressor and thereby going into the bleed system.

P.S.
The engine itself is always on fire as long as it is running. "Engine fire" is when there is a fire outside the engine.