History of the Flight
On 15 October 2015, the day before the incident, the aircraft completed a prior flight and was parked at Bay 702 at Singapore Changi Airport for Base Layover (BLO) maintenance. A BLO technician checked the oil level of the integrated drive generator (IDG) on both engines. He lifted the outboard fan cowl on the right engine, then proceeded to the left engine. After checking, he closed the fan cowls of the left engine and fastened the latches, stating he was not interrupted.
The Licensed Aircraft Engineer (LAE) in charge of the BLO performed a walkaround check. He looked at the sides of the fan cowls, checking for gaps, but did not squat to feel the latches as he normally would. He ended his walkaround at the nose landing gear, inspecting the engines visually from a squatting position without noticing any protrusions of unfastened latches.
The BLO was completed by 0300 hrs on 16 October 2015, and the aircraft remained at Bay 702 until its next flight. At 1900 hrs, the aircraft was towed to the departure gate. The flight crew boarded, and the aircraft was scheduled to depart at 2010 hrs.
The Departure LAE arrived at 1940 hrs and performed a walkaround check. He did not squat to sight the condition of the fan cowl latches, observing the engines from the nose wheel location without noting any protrusions.
During preparation for departure, the First Officer (FO) performed a walkaround check as required by company procedures. He visually inspected the engines from two positions—near the main landing gear and from the outboard side of the engine—but did not bend down or squat. He checked that the fan cowl surfaces were flush and saw no latch protrusions.
The Captain also decided to perform a walkaround but only had time to look at the front cargo door and aft cargo hold areas, noting no abnormalities.
The aircraft took off at 2047 hrs. During take-off, the Cabin Crew-in-Charge (CIC) was alerted by a passenger that the left engine fan cowl had fallen off. She confirmed visually and informed the flight crew via interphone. The flight crew checked cockpit parameters; all were normal, though a fault message from the Landing Gear Control Interface Unit (LGCIU) No. 2 was received during take-off. The Captain asked for reconfirmation, and the CIC reported that the interior of the engine was visible.
The flight crew levelled the aircraft off at 8,000 ft in a holding pattern. The Captain stepped out and observed that the left engine fan cowls were missing, with no visible damage to the surrounding wing area. The right engine fan cowls were intact. He decided to return to Changi Airport.
When the landing gears were selected down during approach, a Master Warning indicated that the left main landing gear was not downlocked. The flight crew discontinued the landing, informed Air Traffic Control (ATC), and returned to holding for troubleshooting. They cycled the landing gears and performed the manual gravity extension procedure, but the Master Warning remained. The flight crew declared Mayday and held to burn fuel to reduce 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. The aircraft landed at 2318 hrs without incident. There was no injury to any person in this incident.
Damage to Aircraft
The left engine’s inboard and outboard fan cowls were missing. The left engine forward pylon was buckled. Debris of the outboard fan cowl was found on the runway. The inboard fan cowl was recovered from the sea by a passing ship, essentially in one piece with a tear near the attachment to the engine forward pylon. The original state of the latches could not be ascertained due to handling before the investigation team received the fan cowl.
All four latches—comprising four hooks at the bottom edge of the inboard fan cowl and four corresponding keepers at the bottom edge of the outboard fan cowl—were recovered. Apart from operational wear, no damages were observed on the latches. Some fan cowl debris lodged into the left main landing gear door and damaged the proximity sensor on the left main landing gear.
Personnel Information
The Departure LAE was 37 years old with six years of experience in his current capacity. The BLO LAE was 32 years old with six years of experience. The BLO technician was 31 years old with one year and four months of experience.
Fan Cowl Latches
For the left engine, each of the four fan cowl latches comprises a handle with hooks and keepers. The investigation found no damage to the hooks or keepers.