Hi BOAC,
Decreases from 5,400 to 8,500? I just realised when typing that why that is. The aircraft is at FL350, and the differential is usually 35,000 - 5,400 but now it's 'decreased' following the 'increase' from 35,000 - 8,500. Logical, really.
But I think I should go and read up on pressures affection oxygen supplies to fuel fires since I have no knowledge of that.
Thanks for the heads-up.
TP