Read all the MEL details

[pelmet]

It might prevent an embarrassing situation....

"G-VBEL a Boeing 787-9 aircraft operated by Virgin Atlantic, was conducting flight VIR20 from San
Francisco Intl (KSFO), CA to London/Heathrow (EGLL), UK. During cruise flight, the flight crew
initiated a climb from FL390 to FL410. The flight crew noted that the cabin altitude started to rise at
a rate of 600 feet per minute, deviating from the normal 6000 feet. Manual cabin pressure control
was selected, and a PAN PAN was declared. The flight crew elected to descend back down to
FL390. The aircraft had been dispatched under Minimum Equipment List (MEL) provision for an
inoperative Cabin Air Compressor (CAC) on the left air conditioning pack. Section 2 of the B787
MEL notes that the cabin altitude, which is normally 6000 feet, may rise to 8000 feet with an
inoperative pack or CAC in degraded operations. After review of this section of the MEL, the flight
crew continued to destination without further incident."

[complexintentions]

There's never any embarrassment in immediately embracing the safest option, which in this and pretty much any pressurization event is to descend.

According to the report the remaining CAC's were able to maintain a 6,000ft cabin altitude to FL390. This only changed when they attempted to climb another 2,000 ft. Yes, the MEL does mention the possibility of higher cabin altitudes. But there is zero guidance given on precisely when this may happen - no tables for expected cabin altitude versus altitude, approximate pressure delta, nothing. Given that there is MEL relief for more than one CAC inoperative, as usual Boeing is being pretty economical with system information. Where has that gotten them lately?

If I saw normal cabin altitude up to FL390, then a 600 ft climb rate for only a 2,000 ft level change, I'd be concerned too and head back down, no matter what I read in the MEL. Reassess and decide what to do next. I personally don't completely trust those electrically-driven CAC's anyway, wailing away at 30,000 RPM.

Seems properly-handled to me.

[pelmet]

There's never any embarrassment in immediately embracing the safest option, which in this and pretty much any pressurization event is to descend.

According to the report the remaining CAC's were able to maintain a 6,000ft cabin altitude to FL390. This only changed when they attempted to climb another 2,000 ft. Yes, the MEL does mention the possibility of higher cabin altitudes. But there is zero guidance given on precisely when this may happen - no tables for expected cabin altitude versus altitude, approximate pressure delta, nothing. Given that there is MEL relief for more than one CAC inoperative, as usual Boeing is being pretty economical with system information. Where has that gotten them lately?

If I saw normal cabin altitude up to FL390, then a 600 ft climb rate for only a 2,000 ft level change, I'd be concerned too and head back down, no matter what I read in the MEL. Reassess and decide what to do next. I personally don't completely trust those electrically-driven CAC's anyway, wailing away at 30,000 RPM.

Thanks for the reply.

It is difficult to know if more detail was not put into the MEL because someone(or group) felt that it was unnecessary or if there happens to be too many variable situations/possibilities and is therefore left as just a blanket statement with the crew expected to keep in mind the statement of what can happen to cabin altitude but not know how and in what manner.

Anyways, it is an interesting anecdote and now more people of aware of how such a condition may be experienced/present itself. It seems that after reading the MEL again(as stated in the report), they felt comfortable with the system operation and continued. It is unknown if any further step climbs were made.

[Victory]

Can 787 pilots even handle a 8000' cabin?

[leftoftrack]

no

[Darkwing Duck]

I'm not discrediting the crew for what they did. I'm not at the pointy end of the airplane and am not questioning their decision. I am also not familiar with the 787 MEL so all of this is a question to learn. Could the crew not remain at FL410 with a 8000' cabin pressure as most aircraft have that set anyway? I understand that the increase was erroneous and unexpected(?) but is it a major issue if they stayed at FL410. And why call PAN if they would continue ENRT?