Tiger A320 at Singapore on Oct 16th 2015, engine access door separated in flight

Last Update: August 25, 2017 / 15:42:48 GMT/Zulu time

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Photo of Tiger Airways 9V-TRH, Airbus A320 — Tiger Airways 9V-TRH, Airbus A320 (Photo credit: byeangel / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Oct 16, 2015

Classification
Incident

Airline
Tiger Airways

Flight number
TR-2638

Departure
Singapore, Singapore

Destination
Chennai, India

Aircraft Registration
9V-TRH

Aircraft Type
Airbus A320

ICAO Type Designator
A320

A Tigerair Airbus A320-200, registration 9V-TRH performing flight TR-2638 from Singapore (Singapore) to Chennai (India) with 183 people on board, was climbing out of Singapore's runway 02C in night conditions when passengers informed cabin crew, that parts of cowling of the left hand engine (V2527) had disappeared, cabin crew informed the flight crew, the flight crew stopped the climb at FL100 and decided to return to Singapore advising ATC that both engines were fully operative. The aircraft entered a hold at 4000 feet for about 10 minutes while the crew worked the related checklists. While on approach to runway 02C the crew reported an unsafe gear indication, climbed back to 4000 feet, declared Mayday and entered another hold to work the checklists, then performed a low approach to Singapore Changi Airport's runway 02C about 105 minutes after aborting the first approach, ground personnel reported all gear struts were down and appeared to be in position. The aircraft positioned for another approach to runway 02C and landed safely about 12 minutes after the low approach.

The airline reported the aircraft returned to Changi as a precaution, the airline is cooperating with authorities to determine the causes of the occurrence.

A replacement A320-200 registration 9V-TRK reached Chennai with a delay of about 5:15 hours.

On Oct 28th 2015 the French BEA reported in their weekly bulletin that the engine cowlings liberated from the left hand engine and impacted the left main gear strut door as well as a hydraulic line causing the loss of hydraulic fluid.

Singapore's AIB released their final report dated Aug 11th 2017 without formal conclusions.

The AIB reported that the night before the flight a Base Layover Maintenance Check (BLO) was scheduled requiring the licensed aircraft maintenance engineer (LAME) to check the oil levels of both left and right hand integrated drive generators (IDG). The LAME checked the right hand engine first openeing the engine cowl, verifying the oil level was matching requirement and closed the cowl again, then went over to the left hand engine and again opened the cowl and checked the oil quantity and closed the cowl again. The LAME stated he was not interrupted during that work.

The maintenance supervisor (LAE) subsequently performed a walk around before signing the work off. The AIB wrote: "As part of the walkaround, the LAE looked at the sides of the fan cowl, he checked that there were no gaps between the surfaces of the fan cowl and the engine nacelle which, from his experience, would indicate an unfastened fan cowl condition. He mentioned that he would normally also squat down and extend his hand to reach under the fan cowl to feel if the latches were secured. However, he did not do so this time."

The following day the aircraft was towed to the gate, a departure LAE again performed a walk around and again did not notice any anomaly.

Prior to departure the first officer also performed a walk around. The AIB summarized the first officer's testimony: "He visually inspected the engines from two positions (from the main landing gear1 and from the outboard side of the engine). Accordingly to the FO, he stood at these positions and looked downwards at the fan cowls but he did not bend down or squat to check2. He did not notice any latch protrusions. Looking at the sides of the engine, the FO also checked that the fan cowl surfaces were flush with that of the engine nacelle and that there was no gap."

The captain also performed a walk around however only checked the front cargo doors and aft cargo hold areas.

A video tape taken 4 hours before departure showed at least 3 of 4 latches on the left engine cowl had not been secured.

During takeoff a passenger alerted cabin crew that the left engine cowl had separated from the engine. The flight attendant visually confirmed the passenger's observation and informed the flight deck.

The flight crew had no abnormal indication, all engine parameters had remained normal, the crew however had received a landing gear control interface unit #2 fault message during takeoff. The captain asked the flight attendant to confirm what she saw, she confirmed seeing the interior of the engine.

The flight crew levelled the aircraft off at 8000 feet MSL, the captain left the cockpit to check the engine himself. After observing that parts of the left hand engine cowl were missing with no damage to the surrounding areas including wing area the captain decided to return the aircraft to Singapore.

When the crew selected the gear down for landing the crew received a master warning and an indication that the left main gear had not been locked in the down position. The crew went around and performed the according checklist, cycling the landing gear up and down again and performing the manual extension, however, the indication of the left main gear not having been locked in the down position persisted. The crew declared emergency, and remained in the holding to burn off fuel.

The crew subsequently performed a low approach to have the landing gear checked from the ground, ground observers reported the landing gear appeared to be fully down. The crew subsequently landed the aircraft, which went without further incident.

A ship recovered the missing cowl doors, so that all 4 latches as well as latch keepers were available to the investigation. None of the latches and latch keepers showed any damage.

Fan cowl debris had lodged into the left main gear door and damaged the proximity sensor on the left main gear.

The AIB analysed:

Evidence shows that at least three of the four latches of the fan cowl of the left engine were not fastened four hours before the incident aircraft took off. Detailed inspection on the recovered latches (inboard fan cowl hooks and outboard fan cowl keepers) showed no damage on the connecting surfaces, and the damage was solely on the fan cowl structure. This would indicate that there was no mechanical failure or structural damage on the latch hooks and keepers, and would suggest that all latches were likely to be unfastened at the time of take-off.

With fan cowl latches not fastened, the airflow generated during the aircraft’s flight would tear off the fan cowls.

As mentioned in paragraph 1.1.2, the BLO LAE “checked that there were no gaps between the surfaces of the fan cowl and the engine nacelle which, from his experience, would indicate an unfastened fan cowl condition.” And as mentioned in paragraph 1.1.6, “the FO also checked that the fan cowl surfaces were flush with that of the engine nacelle and that there was no gap.” It is not known how such flushness assessment has become an acceptable way of ascertaining that the fan cowl latches are fastened, in lieu of bending down or crouching to bring eye level low enough to confirm latches are fastened. The simulation test (paragraph 1.6.3) showed that a fan cowl with unfastened latches could still appear flush with the engine nacelle. Such a flushness assessment is not a method recommended by the aircraft manufacturer.

The BLO technician was not aware of the key actions to be performed in the aircraft manufacturer’s instructions for opening and closing fan cowls. The walkaround procedure adopted by the BLO LAE, the Departure LAE and the FO differed from the procedure provided by the aircraft manufacturer.

It is also found from the simulation test that, at a distance away from the engine, the unfastened latches could be difficult to detect as the curvature of the engine nacelle could obscure the view of the latches.

It is not a reliable method to determine if the fan cowl’s latches had been fastened properly by trying to judge from a distance whether there are protrusions of the latches. The lighting condition and the angle of view may make the judging difficult. The silhouette of the engine drain mast may also obscure the outline of protruding latches.

In short, a better way to ascertain whether the fan cowl latches are fastened is to squat down low enough to sight the latches.

It is noted that, although the aircraft manufacturer has emphasised the need to bend down or crouch to check that latches are fastened in its Safety First Magazine, this requirement is not mentioned in the aircraft manufacturer’s FCOM for exterior walkaround check.