Hi,

Short after take off, I got a PACK L failure message. I followed the non normal checklist but the failure remained. As my cruise alt was fl 380, I searched the forums because I know that this limits the max alt in many airliners.

I read however that one 777 engine can supply both packs and that a reduced cruise alt wasn't necessary. Others stated that their company policy did prescribe a reduced cruise alt. 

I reached 38000 feet with normal cabin pressure and normal cabin temps. So, what is the correct procedure?

Jos Denis

15 minutes ago, beep747 said:

So, what is the correct procedure?

If it isn't in the QRH, then it's likely something that's part of a company-written and FAA-approved (/overseeing body-approved) procedure. Not everything is left to the FAA (/oversight authority), or the manufacturer. Aviation seems formulaic and rigid - black and white - to many, but in reality, it's actually very grey. Company policies are allowed to be more restrictive (and occasionally, where approved in specific cases, sometimes more permissive) than the generic regulation/AFM-set-limit. As such, hearing that a company says "if you lose a pack, your max alt is X" isn't too surprising, even if the AFM says "doesn't matter."

So...the "correct" answer, if the QRH,/ECL/AFM don't specify is "whatever you decided to do."

Pack failure is an interesting one in this regard.

The QRH is ultimately the document to follow after dispatch (the exact definition of which varies but broadly -- doors closed/pushing back). Before this point, the MEL applies...

...and you may well find in some instances that the MEL limits cruise altitude, whereas the QRH does not! In other words -- if you get a PACK L failure message before pushback, the MEL applies and your max alt may be limited. Get it a minute later after pushback, the QRH applies and there is no limitation...

Someone with more technical knowledge of Boeing's thinking in writing the manuals than I may be able to offer some greater insight as to why this could be. I might theorise that this could be because the QRH assumption is that for the duration of a single flight there will be no adverse effects, whereas operating for perhaps multiple sectors with a pack MEL'd might place excessive stress on the remaining operating pack and thus lead to a greater chance of failure. Just a guess, however.

Thanks for the explanation. I followed the steps on the non normal checklist and there was no mention of a restriction. Just set PACK L to off.

Jos Denis

The MEL is something missing from our sim world, and I'd like to see one for a B77LR/F/W.  I suspect that because the packs are in themselves redundant (dual controllers in each pack) that you're not looking at a single point failure potential even with one pack out of service and this brings me to the original event of a pack failure.  Was that something programmed with service based failures, random failures or did you program the failure in any way to occur?  Did you try the A/C reset?

It was a random failure. I tried resetting the A/C as the non normal checklist  suggested. 

Jos Denis