An Airbus A320-232 was scheduled to operate an evening flight from Singapore to Chennai (India) with a crew of six and 172 passengers. The aircraft arrived in Singapore on the 15th of October. Between the arrival of the aircraft and the scheduled departure Base Layover maintenance was performed and signed off. This included, amongst others, an oil level check of the Integrated Drive Generators on both engines. This required the opening of the engine cowlings.
The engine the morning after the accident. (Source TSIB)
The aircraft was towed to the departure gate at 19.00 lt (local time) where it arrived at 19.25 lt. The scheduled departure time was 45 minutes later. While the crew repaired the aircraft for departure a Licensed Engineer performed a walkaround check before signing the CRS (Certificate of Release to Service), releasing the aircraft for the flight. The co-pilot also performed a walk-around check, while the captain also went outside, but only checked the area around the cargo holds. With a delay of ~30 minutes, the aircraft lifted off from Singapore Changi Airport. During the take-off, the purser was alerted by a passenger that the cowlings of the left-hand engine had fallen off. The purser confirmed the passengers' report and immediately reported the situation to the flight crew.
The crew had received a Landing Gear Control Interface Unit (LGCIU) No.2 fault message but no further system abnormalities were alerted. ATC was informed and the aircraft levelled off in a holding pattern at 8.000 feet, after which the Captain briefly left the cockpit to assess the damage. A return to Changi airport was initiated.
The damaged pylon and remnants of the cowling (TSIB)
On the approach to Changi, the gear was selected a Master Warning came on, warning the crew that the left main landing was not locked in the down position. The approach was aborted and the aircraft entered another holding pattern, allowing the crew to troubleshoot the landing gear issue. Several attempts were made to get all the gears in the down and locked position, including the manual gravity extension of the gear. Whatever the crew did, the left main landing gear ket indicating unsafe, it was not down and locked. A Mayday call was made and the request was made to remain in the holding pattern to burn off fuel, so as to reduce the landing weight.
Later, the flight crew performed a low fly-past, and engineers on the ground reported that the left main landing gear appeared to be down. Subsequently, the aircraft landed at 2318hrs without incident.
Reconstruction of the outboard cowling from debris found on the runway (Source; TSIB)
The Transport Safety Investigation Bureau (TSIB) of Singapore was alerted and an investigation into the loss of the fan cowls was launched. It became apparent that the technician checked the oil level of the integrated drive generator (IDG) of the left and right engines. According to the BLO technician, he checked the right engine IDG first. He lifted the outboard fan cowl on the IDG side to visually sight the oil level before closing it. He proceeded to check the left engine. He closed the fan cowls of the left engine and fastened the latches of the fan cowls after checking the IDGs. He said he was not interrupted while closing the fan cowls. The left engine cowling latches were not secured, causing the loss of the cowlings during the take-off, causing damage to the down and locked sensor on the left main landing gear.
The inboard fan cowl as retrieved from the sea (Source; TSIB)
The TSIB however did not identify a probable cause in their report. Several safety actions were taken by EASA, the operator, the airport operator and the maintenance organisation involved, which are listed in the investigation report. The report, which served as the source for this blog, is available for reference containing all the details on the accident, by clicking on the .pdf file below;