Hi All,I was reading about the Air Conditioning system and found out that "One pack may be inoperative provided maximum altitude is limited to: FL250"Why cant the 737-NG fly above FL250 if one pack fails?Also, "If you dispatch with one pack inop, then max alt FL250. If a pack fails when above this level, then you may continue at the higher level. "I don't understand this statment neither. How can a pack fail ABOVE FL250 if you cant fly above that altitude if 1 Pack Inop? :-roll Besides, If both pack fails why can the 737-NG then climb to , let's say, FL310 and not without 1 pack? Why this limitation?I think i messed up everything in my mind. x(Bruno Francescoli.

Hi Bruno,I believe the reasoning behind this is that the amount of airlflow available from a single pack would make it hard to increase the cabin pressure above FL250 to maintain an acceptable cabin altitude. It would still increase above FL250, but the rate would require a horribly slow rate of climb to avoid a cabin altitude above 10000 (deploying the rubber jungle). If the cabin is already pressurized, a single pack can maintain the cabin altitude without to much trouble, just won't increase the cabin altitude. RegardsPaul Gollnick :-coolTechnical Operations/Customer Operational SupportPrecision Manuals Development Groupwww.precisionmanuals.com

Hi Paul,Thanks for the answer. It seems logical to me, but yet, one thing I don't understand.Since with only 1 pack working it would be much more difficult to climb above FL250 (Due to the high risk of Cabin ALT) that it would require an extreme slow rate of climb that it wouldn't even be worth it. Seems very logical to me but..Why can then the 737-NG Climb above FL250 withouth any Pack working? I mean, you would get a CABIN ALT right away...Best,Bruno Francescoli.

"Why can then the 737-NG Climb above FL250 withouth any Pack working? I mean, you would get a CABIN ALT right away..."Hi, Bruno.I'm sure the statement which mentions a pack failing above 25,000, is there for pilot reference only (not part of the MEL/DDG, which, in most cases, would be applied by the engineer (i.e. on the ground)).If one pack fails on the previous flight or on the ground before the next flight, then the MEL is applied, restricting the aircraft below 25,000'. If both packs are ok on takeoff, but one fails above 25,000', then it's ok to continue at that height.If one pack has already been MEL-ed and another fails in flight, the crew would most certainly have to make a descent to 10,000' or lower. It would only be a matter of time before the aircraft lost pressurization.... there are too many holes/leaks in your average 737 to keep the aircraft pressurized... and even if there wasn't.... there is only so long you can survive on recycled air ;-)Hope this helps.Cheers.Ian.

Hi Ian.Thanks for the explanation too.You're gonna kill me, I stil have another question. :-hah>If both packs are ok on takeoff, but one fails above 25,000', then it's ok to continue at that height.

You would need a very good reason to send a aircraft up with such a major item failed. Being stuck under FL250 will result in a fuel cost that will pay for the repairs a couple of times over by the time you got to the other end ;)Ray

Indeed.Bruno Francescoli.

All:Part of the problem with a single pack failure is the ability

Sorry ... still new to posting images ... this is the MEL referencechttp://forums.avsim.net/user_files/34698.jpgSean

Hey!Thanks all of you guys, got it now, very clear.Again, Thanks a lot! Appreciate...Bruno Francescoli.