The 31,500' applies to my current airline and my last airline. Could this be a UK restriction, I appreciate that airlines are able to make further restrictions on the original MMEL but for two airlines to do it, makes me think that there may well be a reason for it. A copy of the exact wording is below:
a) Except for ER operations, one may be
inoperative provided:
1) Flight altitude is limited to 31,500
ft (9,600 m), and
2) COND ZONE REGUL FAULT
caution is not displayed on ECAM
E/WD, and
3) Affected PACK 1(2) pb sw is
selected OFF, and
4) Affected pack flow control valve is
checked closed on ECAM BLEED
page.
Note: Above condition 4) does not
apply if pack valve has been
secured closed as per item 21–51–
01.
Naturally, I know that the MEL is not limiting when airborne but I would adhere to it's guidance, especially in the circumstances where you are doing something non-standard.
Is this 31,500' in any other airlines MEL? Seems strange why it is as exact as to the 500' when other airlines don't have it at all in their MELs.