ANA B738 near Tokyo on May 27th 2016, cabin pressure problems

Last Update: October 19, 2018 / 16:17:43 GMT/Zulu time

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Incident Facts

Date of incident
May 27, 2016

Classification
Accident

Flight number
NH-561

Destination
Kochi, Japan

Aircraft Registration
JA85AN

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

An ANA All Nippon Airways Boeing 737-800, registration JA85AN performing flight NH-561 from Tokyo Haneda to Kochi (Japan), was climbing out of Tokyo's Haneda Airport when the crew stopped the climb at FL160 due to problems with the cabin pressure and descended the aircraft to FL130, later to FL100. The aircraft returned to Tokyo's Haneda Airport for a safe landing on runway 34R about 45 minutes after departure. One passenger needed to be taken to a hospital with ear injuries.

Japan's TSB reported on Jun 1st 2016, the crew received indication of the loss of cabin pressure while climbing out of Tokyo and returned to Tokyo. One passenger received injuries to the left ear, the rupture of the ear drum (left tympanic membrane perforation). The JTSB have opened an investigation.

The airline posted an apology for the malfunction of the cabin pressurization system.

On Oct 19th 2018 the JTSB released their final report concluding the probable cause of the serious incident was:

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 during takeoff 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, electronic Flow Control Valve) were stuck, and as a result the eFCVs closed from the rising Bleed Pressure and air was not supplied to the air conditioning packs.

The JTSB reported the left hand air conditioning pack shut down during acceleration for takeoff, about 15 seconds after takeoff commenced. The right hand air conditioning system shut down 53 seconds after takeoff commenced and about 13 seconds after the aircraft had become airborne. About 5 minutes later, when the aircraft climbed through FL141 the cabin altitude climbed through 10100 feet and the cabin altitude warning activated. About 2:20 after the cabin altiude warning activated both air conditioning systems restarted, the outflow valve, which had closed fully during the takeoff run, opened partially but again closed fully as the left hand air conditioning systems shut down again. The crew requested to descend to FL140 and was cleared to descend to FL130. The crew selected the air conditioning from AUTO to MAN. The left hand air conditioning system started again and the cabin altitude descended to 9000 feet, the cabin altitude warning ceased. When the aircraft levelled off at 13,000 feet the cabin altitude had decreased to 6900 feet but began to rise again slowly. The left air conditioning system again shut down, the crew decided to return to Tokyo. The left pack was again started, the cabin altitude now dropped to below -8000 feet (negative altitude) equivalent to a pressure differential between inside and ambient pressure of 8.79 psi. The outflow valve began to open when the crew selected the cabin pressurization from MAN to AUTO again, while outflow valve opened to about 76% the cabin altitude stabilized at about 2000 feet (positive altitude). The outflow valve closed fully again, the cabin pressure control issued a fail code, the crew received an AUTO FAIL and ALTN light.

One passenger received minor injuries.

The JTSB analysed:

it is probable that the following factors contributed to the shutdown of both air conditioning packs at the time of takeoff.

(1) Grime and abrasions similarly existed inside the reference regulators of both eFCVs. It is probable that this was because both eFCVs had been installed in the Aircraft since its manufacture and had been in operation in the same environment, and that as a result the reference regulators of both eFCVs were similarly prone to becoming stuck open.

(2) It is probable that both air conditioning packs shut down during takeoff on the day of the serious incident because, under conditions in which the reference regulators of both eFCVs were similarly prone to becoming stuck open, the reference regulators became stuck due to high humidity resulting from weather conditions marked by showers and mist while the Aircraft was parked on the two previous days, said stuck condition continued until the first flight of the following day (specifically, the flight of the serious incident), and both engines power increased when the Aircraft was taking off with the reference regulators in a stuck condition, resulting in a situation in which the air conditioning packs shut down simultaneously for the reason described in 3.5 (2).
(3) instances in which the left air conditioning pack had shut down
were frequently recorded in the FDR in the time leading up to the serious incident in which both air conditioning packs shut down. The FDR contained a record for the most recent period of approximately ten days, and it is somewhat likely that the air conditioning pack had been repeatedly shutting down even before that period. However, it is probable that because, as was mentioned in 2.9.2, the Aircraft was not equipped with a function that notifies flight crewmembers or mechanics even if an eFCV closes and an air conditioning pack shuts down, the frequent failure of the left air conditioning pack was not noticed and the pack remained in operation without repair, and this led to the situation in which the two systems, left and right, malfunctioned simultaneously during the flight of the serious incident.
Incident Facts

Date of incident
May 27, 2016

Classification
Accident

Flight number
NH-561

Destination
Kochi, Japan

Aircraft Registration
JA85AN

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

This article is published under license from Avherald.com. © of text by Avherald.com.
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