Singapore A333 near Mandalay on Feb 7th 2018, engine shut down in flight

Last Update: September 30, 2019 / 14:16:06 GMT/Zulu time

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Incident Facts

Date of incident
Feb 7, 2018

Classification
Incident

Cause
Engine shut down in flight

Airline
Singapore Airlines

Flight number
SQ-449

Departure
Dhaka, Bangladesh

Destination
Singapore, Singapore

Aircraft Registration
9V-SSE

Aircraft Type
Airbus A330-300

ICAO Type Designator
A333

A Singapore Airlines Airbus A330-300, registration 9V-SSE performing flight SQ-449 from Dhaka (Bangladesh) to Singapore (Singapore) with 190 people on board, was climbing through FL320 out of Dhaka when the left hand engine (Trent 772) failed and developed high vibrations prompting the crew to shut the engine down and divert to Mandalay (Myanmar) where the aircraft landed safely. The aircraft leaked hydraulic fluid.

On Feb 15th 2018 Singapore's AIB reported the aircraft was climbing from FL290 to FL370 in Myanmar Airspace when the crew heard a sudden loud bang and noticed severe vibration of the entire airframe. The crew declared PAN and received vectors to Mandalay, the nearest suitable aerodrome, where the aircraft landed without further incident. The occurrence was rated an incident, an investigation has been opened.

On Feb 27th 2019 Singapore's AIB reported in an (annual) interim statement, that the left hand fan blades and fan case were found damaged. The investigation team is currently drafting the final report.

On Sep 30th 2019 Singapore's AIB released their final report concluding the probable causes of the incident were:

- The failure of the fan blade with more than 75% missing material originated from a fatigue crack that initiated at the acute corner of the inner convex surface bond.

- The fuse system in the engine front bearing housing operated fully and separated completely as designed for a Fan Blade Off event, although the second fuse had activated slower than expected due to the release of a partial fan blade section.

- Despite the complete functioning of the two fuses in the engine front bearing housing, significant airframe vibrations persisted due to shaft bending coupled with the engine windmilling effect.

- The C-Scan ultrasonic inspection detected the defect in the event fan blade, but the defect was accepted because the defect feature was below the rejection threshold size.

- Though the inlet and outlet LP fuel pump pipes had been redesigned, cracking in those pipes still occurred. The presence of fuel released from the cracked inlet and outlet fuel pipes of the LP fuel pump could be a safety hazard.

The SAIB described the sequence of events:

While the aircraft was climbing through 30,000 feet at 1630 hours, the flight crew heard a loud bang and felt airframe vibrations. In accordance with the operator’s standard operating procedures, the PIC immediately took over control of the aircraft and assumed the role of PF, and the SFO assumed the role of PM. The PIC instructed the SFO to carry out remedy actions for the Electronic Centralised Aircraft Monitoring (ECAM)2 messages. The ECAM remedy actions entailed the shutting down of the No.1 engine (i.e. the left engine). However, even after the remedy actions were completed and the No.1 engine was shut down, the airframe vibrations continued to be felt.

The aircraft was flying in Myanmar airspace at that time. The flight crew made a PAN call to Yangon Air Traffic Control (ATC) and requested clearance to descend to 25,000 feet. Subsequently, the aircraft diverted to and landed in Mandalay International Airport at 1702 hours without further incident.

Immediately after landing, the airport’s rescue and firefighting service conducted an inspection of the aircraft and reported an oil leak from the No.1 engine. The aircraft was towed to a remote bay where passengers were disembarked. There was no injury to any person.

The SAIB analysed:

Fan blade failure

The failure of the fan blade could be attributed to a fatigue crack which compromised the strength of the fan blade. This crack originated from an initiation site at the acute corner of the inner convex surface bond.

Rubbing between LP shaft and OP shaft

As mentioned in paragraph 1.3.5, the LP shaft showed evidence of heavy rubbing with the IP shaft which resulted in deformation and bending of the LP shaft, with cracking extending approximately half the circumference of the shaft. The rubbing was a result of the second fuse in the engine front bearing housing having operated slower than intended.

The two fuses in the engine front bearing housing would operate, as intended by design, to counter the unbalancing effect caused by a fan blade failure. This would allow the fan rotor system to rotate about its new mass centre, and minsimise the chances of contact between the LP shaft and IP shaft. The fuses were designed to operate following a release of a full length fan blade length. In this incident, a shorter length of fan blade was released and there was less force to operate the engine fuses. The resulted in a delay in the operation of the second fuse.

With a delay in the second fuse’s operation, there would be a period of time, albeit a very short one, during which the LP shaft and IP shaft could be in contact, the result of which would be damages to the LP shaft and IP shaft.

...

Cracking of LP fuel pump inlet and outlet pipes

As a result of the fan blade failure, both the inlet and outlet fuel pipes of the engine LP fuel pump were cracked. The cracking of the fuel pipes was due to the vibration that followed the fan blade release.