Nick Dobda

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Finally got a failure, and I just couldn't figure out how to diagnose. I had to open the failure menu to see "APU BLEED VALVE"

The Symptom - before taxi checklist - RECALL

AIR COND annunciation, warning will not clear.
Nothing anywhere else, no lights, nothing misbehaving. 

There has got to be a procedure - but obviously I don't know it.

What is the proper way to diagnose... what steps would you have done to diagnose the problem?

Go easy on me, I have no experience with the QRH. Also, only solve the problem with what you have in the cockpit - I was pushed back ready to taxi (If I hadn't gotten this problem)

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See which light is illuminated on your overhead panel, and remember the text written on it. Then go to QRH, look up the text between page 1 to 10. Go to the corresponding section of the manual. Follow the steps and you should be good.

 

 

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There was nothing lit or unusual that I could see on the overhead. Just the master caution and air cond in the recall box.

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This annunciation in the air is usually not a failure, unless accompanied by other indications, but rather your aircraft didn't reach the altitude you had set for cruise and it's saying that it is operating off-schedule.

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It happened after pushback On the before taxi check of recalls, not in the air. I just didn't know where to begin, the qrh didn't have "air cond" in the index anywhere. I had no idea if it was a failure, a warning, or what to do. Totally clueless.

can anyone describe the process to get from the "air cond" master caution to a diagnosis knowing the end should be apu bleed valve failure.

 

Apu was was off at the time, everything configured for taxi with engine bleeds on.

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Not every annunciation needs a QRH entry.  This one for example, you should first look to make sure you don't have actual alarms like pack failure, duct temperature, etc.  If there are no other lights you can reset this by switching between auto and altn and back to auto control modes.

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14 minutes ago, downscc said:

If there are no other lights you can reset this by switching between auto and altn and back to auto control modes.

this may be the case, but how would I know this? All I knew was there was a master caution and "air cond" .

how did you know what to do? Is it just something that you are taught in training somewhere? 

Is that proper procedure? To reset and move on? I'd think you would need to diagnose and be sure what exactly the failure is before knowing it's safe for resetting and continuing. 

What at are the consequences of a bleed valve failure? How did you know it was a bleed valve failure when all you had was a master caution and warning?

It may be rw pilots would be able to diagnose in the cockpit with a cabin full of passengers as you are just getting ready to taxi, but I didn't have extensive training on the 737... And maybe it is just that it's a fact of sim life that there's no quick reference to diagnose this problem. I d just like to know if this is the case or maybe I'm not using the qrh properly

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Just thinking out loud (no RW experience whatsoever).

FCOM2 15.20.4 indicate the eight amber lights that are related to AIR COND on the system annunciator panel. Amber lights indicate conditions which require the timely attention of the flight crew (according to FCOM2 15.20.1). If there are no amber lights accompanying the indication on the system annuciator panel, I'd think it wouldn't be an issue that requires any action by the flight crew but that it would be just a maintenaince issue.

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15 minutes ago, voske said:

Just thinking out loud (no RW experience whatsoever).

FCOM2 15.20.4 indicate the eight amber lights that are related to AIR COND on the system annunciator panel. Amber lights indicate conditions which require the timely attention of the flight crew (according to FCOM2 15.20.1). If there are no amber lights accompanying the indication on the system annuciator panel, I'd think it wouldn't be an issue that requires any action by the flight crew but that it would be just a maintenaince issue.

That's a great reference. Q for rw pilots, would you continue the flight with that caution and no Amber lights? Would you be able to even diagnose it as apu bleed valve issue?

Is there a copy of the fcom2 in the cockpit or would your training be sufficient? 

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Yes... there is training and the books are in the cockpit. Your issue seems to be how come there wasn't a checklist to tell you what to do with an indication of something not otherwise in the QRH.  The answer is experience. The answer is also always studying the books including FCOM and FCTM. Learn the systems. The pilots on these aircraft have to know the systems at least the same detail that is in the FCOM.

Yes, I'd continue the flight because the annunciation turned off when I recycled the controllers. It happens. Add this to your experience.

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Sounds good thanks for advice. If anyone has similar stories or advise please share

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23 hours ago, Nick Dobda said:

Finally got a failure, and I just couldn't figure out how to diagnose. I had to open the failure menu to see "APU BLEED VALVE"

The Symptom - before taxi checklist - RECALL

AIR COND annunciation, warning will not clear.
Nothing anywhere else, no lights, nothing misbehaving.
There has got to be a procedure - but obviously I don't know it.

What is the proper way to diagnose... what steps would you have done to diagnose the problem?

Go easy on me, I have no experience with the QRH. Also, only solve the problem with what you have in the cockpit - I was pushed back ready to taxi (If I hadn't gotten this problem)

I fly the 737, RW and AIR COND is one of the more common problems. It's usually a pack controller fail. Nothing big.

I don't think you can get an AIR COND light without a light on on the AIR COND panel. It sounds like maybe you got a DUAL BLEED problem, if the APU BLEED VALVE didn't close.

It should be a simple matter of look at the "6-pack," see which system/panel to look at and action that light in the QRH. There really isn't that much detective work. The trickiest checklists are the ones dealing with flaps.

 

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8 hours ago, Spin737 said:

It sounds like maybe you got a DUAL BLEED problem, if the APU BLEED VALVE didn't close.

It should be a simple matter of look at the "6-pack," see which system/panel to look at and action that light in the QRH. There really isn't that much detective work. The trickiest checklists are the ones dealing with flaps.

 

You know what... come to think of it you could be right - the dual bleed may have been illuminated... and it should have made sense that that could have been used to diagnose since I close the APU bleed valve and turn off the APU prior to taxi. If the APU bleed valve is off, its impossible to have dual bleed, no?

I may have just been so used to seeing dual bleed lit up all the time during the preflight, that I overlooked it... 

This is what I suspect happened, it could have been staring at me right in the face. 
 

OK system experts... logical question, if the APU bleed valve is stuck open, but the APU is turned off, is there a negative check valve so that engine bleed air doesn't get lost through the APU bleed valve?

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1 hour ago, Nick Dobda said:

OK system experts... logical question, if the APU bleed valve is stuck open, but the APU is turned off, is there a negative check valve so that engine bleed air doesn't get lost through the APU bleed valve?

Yes, there is a check valve, but it can get "coked" so it stays open when it shouldn't.

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23 minutes ago, Spin737 said:

Yes, there is a check valve, but it can get "coked" so it stays open when it shouldn't.

I've been dinking around with this subject - it seems that the fail was the apu bleed valve was stuck open... hence the AIR COND master caution and the DUAL BLEED light on the overhead (with the APU bleed switch set to off. 

There is a blurb in the QRH, and a clue in the FCOM, but its comes down to familiarity with the system to be able to figure out what happened. I couldn't do that at the time, but live and learn. 

But even if I would have been able to piece it together at the time, what should I have done?

As Matt said, there is a check valve, but it can get stuck open too. So in a worst case scenario, the APU bleed valve is stuck open, the APU is off, and the check valve is stuck open... there would be serious back pressure running backward though the APU and turning the compressor blades of the APU - not sure what can happen from there but it can't be good.

So sitting on the tarmac with a cabin full of passengers that just boarded, you see the problem on the before taxi checklist - identify that the APU bleed air valve is stuck open. Do you pull it back in, or do you continue with the flight? Is this a judgement call... or addressed in some sort of SOP... or do you make a call to maintenance to do some sort of quick visual check... or is there some other check  you can do to verify that the back pressure check valve is functioning?

And isn't this so much fun from a simulator? Great job PMDG

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