Two aircon systems down?

[jolihokistix]

This article was published by Kyodo News on 5 June, but I cannot yet find an English language page. My quick translation, for which apologies.
https://this.kiji.is/508672031161779297?c=39546741839462401

国土交通省は5日未明、米サンノゼを離陸し成田空港に向かっていた全日空171便ボーイング787が1日午後2時ごろ、二つある 空調系統が相次いで不具合となり、緊急事態宣言を出し、高度約1万3千メートルから約3千メートルまで降下していたと発表した。 その後、宣言を取り消し、約1時間後に成田空港に着陸、乗客乗員163人にけがはなかった。
国交省は事故につながりかねない重大インシデントに認定。運輸安全委員会が5日、航空事故調査官4人を成田空港に派 遣する。
Essentially what it is describing is a failure of two air conditioning systems aboard ANA 171 from San Jose to Narita, Boeing 787. (Around 2 pm on 1 June.) For this reason the aircraft declared an emergency and dropped from 13,000 meters to 3,000 meters and, canceling the alert continued to Narita, landing one hour later. No-one of the 163 pax was hurt but a team has been formed to investigate. Being called a ‘serious incident’.

PS Now being reported on the main TV news channels in Japan.

[jolihokistix]

Roll the news out before it gets buried, I thought to myself.

But the original questions remain. In the absence of any further explanation, what, if anything, is the nature of this event and why has it been called a serious incident?

[pattern_is_full]

"Air conditioning" is closely related (one might even say integral) to the cabin pressurization system. The fact they descended to 3000m (10000 feet) also indicates they had lost control of cabin pressure.

The emergency descent means 1) they were abandoning the filed flight plan and passing through altitudes possibly occupied by other aircraft, and 2) would end up at an altitude where their fuel burn rate would increase significantly, perhaps requiring a diversion (no longer enough fuel to reach Narita).

Fortunately they were relatively close to destination, so once they reached 3000m where pressurization was not necessary to support life, the crew determined they could cancel the alert and continue safely to Narita on the remaining fuel.

A dual air-conditioning/pressurization "pack" failure is an emergency worthy of investigation. Both systems should not fail at the same time (that is why there are two). If it had happened a thousand miles further out over the Pacific, it could have ended up in a mid-ocean ditching.

See report of similar incident, coincidentally released June 4: Incident: Vueling A320 near Alicante on Feb 21st 2017, both air conditioning systems failed (http://avherald.com/h?article=4a601a69&opt=0)

[Fanatic]

If it had happened a thousand miles further out over the Pacific, it could have ended up in a mid-ocean ditching.
I think you need to re do your ETOPS course.

But I agree it is a incident worthy of investigation.

I had a similar one dispatching on a single pack which unsurprisingly overheated at FL330. We were lucky to be able to descend rapidly enough to avoid the rubber jungle and were close enough to destination to make it there. The pack cooled down and lower demand at FL100 meant it worked fine to landing. In fact we kept it from the pax too as cabin alt was kept below 10000'. Nobody mentioned it until de-boarding when one, just one, pax questioned why we did an unusually early descent!! That was investigated as a serious incident.

[derjodel]

With any duplicated system, the probability of both systems failing at the same time is much lower as with a single system, but it‘s not zero.

Many people falsely assume low probability means „it never happens“. But on the contrary, the right notion is „it is expected to happen in 1 in 10^n cases“.

You might think „1 in 10 millions“ is low, but the FAA alone handles more than 15 million flights per year... If your odds are 1 in 10m, you‘d expext at least one such event per year.

Even for ETOPS flights, dual engine out is not impossible... just excpected very rarely. But, it is expected.

[jolihokistix]

Thank you kindly for the explanations which make sense even to my feeble brain. :ok:

[bill fly]

I hope they were vmc as 3000m is below Fuji...

[WingNut60]

I hope they were vmc as 3000m is below Fuji...

If they were worried about Fuji on a flight from San Jose to Narita then altitude would be the least of their problems.

[bill fly]

If they were worried about Fuji on a flight from San Jose to Narita then altitude would be the least of their problems.

Try an emergency descent to below 100 at NRT on your next sim check and see what the JCAB think about that...