Originally Posted by
NSEU
Mick, are you asking this question from the point of view of Maintenance Control with only one aircraft in your fleet?
Is the aircraft currently flying? You say that 1850 is the normal pressure, but the aircraft has gone for 50 days without servicing back to this pressure? Do your regulations allow the bottle/s to be topped up in-situ? Or do the bottles have to be removed? I'm sure your local major airline would be willing to do a service for you and check for leaks in typical spots (bottles, regulator, masks). My former airline didn't have any 777's, but we routinely topped up the bottles for other operators (some didn't let the O2 levels drop to this level, though). We had adaptors for left and right hand threaded connections on refill points and we also did bottle top-ups in-situ.
NSEU, I'm asking the question because I am looking at an investigation report that says "
the decay in pressure from the nominal value of 1850 psi [to 1120 psi over 75 flights]
was not unusual.". However, it strikes me as highly unusual. By my calculations, pre-flight mask testing and bleed on engine start up should have accounted for no more than a 200-250 psi drop in pressure over 75 flights, nowhere near the 730 psi drop recorded.
I don't have access to the maintenance records so I was hoping someone familiar with the B777 crew oxy system, a driver or maintainer, could say yea or nay, not unusual or unusual.