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Chapter 15. Pneumatic

Table of Contents

15.1. Dual bleed failure

15.1. Dual bleed failure

The historical failure case where supplying two packs from one bleed would overload it and cause it to fail appears to have been resolved. Furthermore, recent airframes have four new ECAM procedures associated with dual bleed failure, the variants based on whether neither, either or both bleeds have failed due to a wing or pylon leak on its respective side. The ECAMs all hand off to a new QRH paper procedure if no successful reset is achieved. Older airframes make do with just the QRH procedure.

Whilst the procedures look complex, the underlying philosophy is fairly simple:

  • A depressurisation will be underway. It should be relatively slow, but unless a successful reset is achieved immediately, a prompt descent to FL100/MFA needs to be initiated.

  • A bleed lost to a wing or pylon leak is lost for good, whereas a simple bleed fault or bleed low pressure may be recoverable. The cross bleed should be shut and the wing anti-ice should be off before an attempt is made to recover a bleed.

  • A leak on the left side precludes the use of the APU bleed for pressurisation, but otherwise the APU bleed can be used to supply pack 1 when below 22500ft. If pack 1 is unavailable, the APU bleed can supply pack 2 via the cross bleed provided the whole pneumatic system is available.

In line with this philosophy, both the ECAM and QRH procedures start by shutting the cross bleed and turning off the wing anti-ice. The ECAM procedures each then attempt an immediate recovery of any recoverable bleed by cycling the bleed off then on. The QRH attempts an immediate recovery only in the case that both bleeds are potentially recoverable.

If no bleeds are recovered, the bleeds are all turned off and a descent to FL100/MFA is initiated. At this point, the ECAM procedures join the QRH procedure.

During the descent the APU is started. If the left hand side of the pneumatic system is available, at attempt to use the APU bleed for pressurisation is made at FL200. If this is successful, the descent is stopped at FL200 and a further attempt is made to reset the engine bleeds; if unsuccessful, the flight can be continued at FL200 using the APU bleed for pressurisation.

If APU cannot be used for pressurisation descent must be continued. When level at FL100/MFA, a final attempt is made to restore any available engine bleeds. If unsuccessful, the flight is completed with ram air.