Titan B763 near Amsterdam on Mar 19th 2017, loss of cabin pressure

Last Update: February 8, 2018 / 17:32:02 GMT/Zulu time

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Photo of Titan Airways G-POWD, Boeing 767-300 — Titan Airways G-POWD, Boeing 767-300 (Photo credit: oliver.holzbauer / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Mar 19, 2017

Classification
Incident

Cause
Loss of cabin pressure

Airline
Titan Airways

Departure
London Stansted, United Kingdom

Destination
Rzeszow, Poland

Aircraft Registration
G-POWD

Aircraft Type
Boeing 767-300

ICAO Type Designator
B763

A Titan Airways Boeing 767-300, registration G-POWD performing charter flight ZT-1941 (callsign AWC-941) from London Stansted,EN (UK) to Rzeszow (Poland) with 262 passengers and 9 crew, was enroute at FL370 about 25nm southwest of Amsterdam (Netherlands) when the crew initiated an emergency descent to FL100 due to the loss of cabin pressure, the passenger oxygen masks deployed. The crew requested medical assistance available at the gate, emergency services received a major alert, a rescue helicopter was dispatched to the aerodrome, all other arriving flights were sent into holds. The aircraft landed safely on Amsterdam's runway 27 about 25 minutes after leaving FL370. There were no injuries, the alert level of emergency services was downgraded after the aircraft had landed.

The remainder of the flight was cancelled, a number of passengers took other flights to Poland, a number returned to the UK.

The occurrence aircraft is still on the ground in Amsterdam about 7 hours after landing.

On May 15th 2017 the Dutch Onderzoeksraad (DSB) reported the crew received a cabin altitude warning which resulted in the automatic release of the passenger oxygen masks. The crew declared emergency, descended the aircraft and diverted to Amsterdam. The United Kingdom's AAIB is investigating the occurrence with the assistance by the DSB.

On Feb 8th 2018 the AAIB released their Bulletin concluding the probable cause of the serious incident was:

The failure of the cabin to pressurise correctly resulted from a faulty PPRV which was installed during recent maintenance. The maintenance checks of the replacement valves did not identify the defect with the faulty PPRV.

The event was a failure to pressurise correctly, rather than a sudden depressurisation and the crew’s timely actions in identifying the problem and carrying out the appropriate emergency procedure ensured a safe outcome.

The AAIB reported the aircraft had been in heavy maintenance during which both positive pressure relief valves (PPRV) were replaced. A post maintenance test flight of one hour had been performed, which climbed to FL350, no pressurization problems were noticed during the test flight.

The aircraft subsequently was to perform the rotation from Stansted to Rzeszow, the maintenance engineer supervising the test flight the previous day complemented the crew. The aircraft was enroute at FL370 when the fasten seat belt signs illuminated unexpectedly shortly followed by the cabin altitude alert. The captain and the engineer donned their oxygen masks, the first officer needed to be assisted donning his oxygen masks - the AAIB reported the first officer believed he was suffering from some degree of hypoxia already -, transmitted Mayday and initiated an emergency descent. The passenger oxygen masks were released. The aircraft diverted to Amsterdam.

The AAIB wrote: "External inspection of the aircraft revealed that the indicator flag on the upper PPRV upper door flap was visible, indicating that the valve had operated in flight, allowing cabin air to leak overboard."

The AAIB reported regarding the failed PPRV:

It was removed from a Boeing 757 after being described as “inoperative”. The valve had completed 25,270 hours and 16,162 cycles in service. The date of removal was not disclosed, but it was received at the manufacturer’s UK facility on 3 January 2012, where it failed a bench test. Following an overhaul, it received its final inspection stamp on 26 January 2012, with its associated EASA Form 1, dated 27 January 2012. A note in the Component Maintenance Manual (CMM) for the PPRV stated that the unit should be re‑tested if it was not fitted to an aircraft within twelve months. However, this instruction was not reproduced on the EASA Form 1 (which formed part of the release documentation), so maintenance personnel installing the valve on the aircraft would not have been aware of it. Until its fitment to G-POWD, the valve had not been fitted to an aircraft since being overhauled in 2012.

The AAIB reported regarding testing of the PPRV:

The defective PPRV assembly was taken to the manufacturer’s UK overhaul facility where it was tested and disassembled with the AAIB. The valve was installed in a test chamber that included a representation of an aircraft fuselage. A negative pressure was then applied to the ‘outside’, to simulate the aircraft climbing. With a correctly functioning unit there should be no flow through it until a pressure differential of at least 8.95 psi is reached. However, it was found that a flow became established at a pressure differential as low as 3.36 psi. This would result in cabin air being able to leak from the aircraft during a normal climb.

The tests pointed to a fundamental problem with the valve and a strip examination was performed. This proved inconclusive, with no obvious evidence found to explain the valve malfunction.

Whilst the reason for the PPRV’s failure was not found, the manufacturer calculated that the valve would have opened at around 3.5 psi differential pressure if a piece of debris as small as 0.0033 inches in diameter had become trapped underneath the ball valve in either the primary or secondary metering section.

The AAIB analysed:

The valve had remained in storage for approximately five years before being fitted to G-POWD. The CMM states that the PPRV should be re-tested if it was not fitted to an aircraft within 12 months, but this information was not available outside the manufacturing organisation nor was it stated on the EASA Form 1.

During the recent maintenance and, in the absence of serviceable test equipment, the maintenance organisation had removed both PPRVs from the aircraft, replacing them with overhauled units. The AMM test of the replacement valves failed to detect any defect and it is likely that the aircraft departed for its first flight with the faulty valve leaking cabin air as soon as the cabin differential pressure exceeded approximately 3.4 psi. This would have led to a gradual loss of cabin pressure and the cabin altitude to climb to the level that triggered the cabin altitude warning.

It is not clear why the cabin pressurisation problem did not manifest itself during the post‑maintenance check flight, during which the aircraft climbed to FL350 without any cabin pressure warning. However, it is possible that the leak rate may not have been enough for the cabin altitude to climb to a level that would have triggered the warning during this flight.