Multiple Issues - One Cause

You open the log book..... read.... and say "WTF"!!!
  
     
  
So we have a cabin dump, equipment overheat, bleed fault, and a pressurization fault warning.

Sometimes you need to step back..... get other opinions..... and put the story together. Here's "this" write-up's story.

The crew is flying a 25+ year old 767 at 41K. The ceiling on this aircraft is 42.5.
They're flying on ONE BLEED and ONE PACK @ 41k. They pull back on the throttles to begin descent and the bleed system doesn't shift to HP (from LP) bleed with the engine now at flight idle. Result..... not enough air for pack operation.

What happens? Well..... the pressurization controller goes ape-shit because the outflow valve is fully closed and the cabin pressure is going down. The equipment overheat trips because is has no flow across one of its sensors....
  
     
  
..... the Air System Controller senses no air flow and trips the "Bleed Fault" and the crew knows the cabin is dumping because they feel it in their ears. Was it bad enough to at least pull the masks out of the boxes??? I guess not, because they didn't. (Just ask Payne Stewart how a cabin dump worked out for him.)

Seriously.....  41K on one pack. I just can't see it as being a smart move.

Anyway, we verified a wiring issue on the HP Bleed controller and changed it.
  
     
  
I hate flying now (and have for a while), maybe there's a reason why!!

Bleed shift on PW4000.

Look at duct pressure around 80% N2 while accelerating and decelerating. 

As the engine slows down LP pressure drops off up to a point when HP air kicks in and drives the pressure back up again.
  
     
  
For the write-up above..... that bleed shift did not happen in a timely manner. It finally shifted, but for a few seconds I'm sure there was some serious ass-puckering going on.