Alvorlig luftfartshendelse - Tap av begge A/C pakkene - ASN

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Date:	27-MAY-2016
Time:	08:22 LT
Type:	Boeing 737-881
Owner/operator:	All Nippon Airways - ANA
Registration:	JA85AN
C/n / msn:	62640/5766
Fatalities:	Fatalities: 0 / Occupants: 170
Other fatalities:	0
Aircraft damage:	Minor
Category:	Serious incident
Location:	over Miura peninunsla, Kanagawa prefecture -    Japan
Phase:	Initial climb
Nature:	Domestic Scheduled Passenger
Departure airport:	Tokyo International Airport/Haneda (HND/RJTT)
Destination airport:	Kochi Airport (KCZ/RJOK)
Investigating agency:	JTSB

Narrative:
A Boeing 737-800, registered JA85AN, operated by All Nippon Airways took off from Tokyo International Airport at 08:22 as scheduled flight NH561 but, as it was climbing, turned back at 08:27 because there was a warning indicating a drop in cabin pressurization. The flight landed back at 09:11. Upon a detailed inspection of the same aircraft, no damage to the aircraft was observed; however, it was found that both valves for the intake of bleed air from the left and right engines into the respective air conditioning packs had temporarily malfunctioned and were closed. 
There were 170 people on board the aircraft, consisting of a Captain, five other crewmembers, and 164 passengers. One passenger suffered minor injuries. 

Probable Causes: 
It is highly probable that this serious incident occurred when, as the aircraft was being continuously operated without a malfunction involving temporary shutdowns of the left air conditioning pack being perceived by the flight crewmembers or mechanics, the left air conditioning pack shut down at the time of the flight’s take off and then the right air conditioning pack, which had the same service hours and service environment, also shut down, and as a result pressurization was not maintained. 
It is probable that the left and right air conditioning packs shut down because, in both cases, the reference regulators inside the valves that control airflow to the air conditioning packs (eFCV) were stuck, and as a result the eFCVs closed from the rising bleed pressure and air was not supplied to the air conditioning packs.