Penko - You are correct. My reply was probably a little harsh. Pacinolove I applogise. May I suggest the answer is that with a demand from two packs, somewhere above 15,000 the ECAM message as described by cinocav will be displayed. With a single pack the same message will be generated above 22,500'. Why? As the aircraft climbs the APU, like most other engines, suffers from a loss of power associated with reduced air density. Once the bleed air is lost, the next message to be expected will be EXCESS CABIN ALTITUDE. But exactly where and when this message will be displayed can not be precisely determined.