failures

[wain]

with failures in XP off how does that effect the 737? I had a duct overheat, though not a failure I had to google your blog to work out what to do, was quite simple in the end, what I am wondering is does the 737 remember how I may have mishandled it last flight and fail accordingly or is up to me to set failures? or are they random if on and what takes priority your failures or XP?

[Litjan]

Hi, with failures in XP off you won´t have any failures in the 737, either. Unless you bring them about by not handling the systems correctly, like overrevving the engines will get you a EGT overheat, running out of fuel will trigger a low-pressure light for the fuel pumps, etc.

Your duct overheat is a good example of that - it is a failure we encountered in the real 737 quite often. There is a small crossfeed from one duct to the other (to augment cockpit heating), and when running one pack the other duct often "overheats" even though it´s respective pack is off. Once you turn it on, the failure triggers.

Its also easy to overheat the ducts in manual pack temperature control (no automatic governing) and in situations where it is very cold (and the duct temperature overshoots the limit before the pack valve can react).

But as you found out, handling that is not a big deal - and to tell you the truth, most of the time the pilots will not even pull out the abnormal list for these "nuisance" warnings.

Cheers, Jan

 

[wain]

thanks Jan, helpful as ever, always good to gain some of your knowledge....

 

Wayne

[Fesi]

I was using this search function to figure out how to clear this duct overheat alarm which happens quite often during flight. I don't understand how I get this alarm and how to clear it. I just read the info above but don't know how to clear it. I normally have both packs in auto but can't figure out why this alarm happens. If there is already an explanation can someone point me to it. Thanks

[Litjan]

Hi Fesi,

to avoid this happening:

1. Don´t load the aircraft in a setting with really cold ambient temperature or really cold temperature in the cabin - the AUTO mode may overshoot the temperature limit.
2. If you get the warning, set the temperature controller to full cold (auto), then press the trip reset switch
3. If you get the warning again, set the pack mix valves to full cold (manual mode), then press the trip reset switch. Now set the temp indicator to DUCT, then slowly feed in more warm air (to avoid overheating the duct again). Check PASS temperature from time to time and once the temp is >5C you can go back to AUTO

For what its worth, I never get the pack trip warning when flying - so there may be something unusual about the way you operate the pack controls.

Cheers, Jan

 

[Fesi]

This system seems complicated. I will reference this info on my next flight. Thanks for response.