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23rd of April 2016

A Boeing 737-800 was operating a scheduled flight between Auckland (New Zealand) and Apia (Samoa). After an early departure (04.33 local times), the crew settled in for the 1800 miles (2900 km) flight to Samoa. During the flight, the crew obtained several weather updates for the destination. While planning the descent and approach, the crew decided to postpone the descent until they has weather info from the tower at Apia. This because of the approaching tropical cyclone AMOS.

Damage to the engine (right hand) cowling. (Source; ATSB, © A/C 0perator)

After some effort, the crew got in touch with Apia ATC via HF Radio and received the latest local weather info. Based on that info they decided to fly one approach into Apia, if they would have to abort the landing they would divert to their alternate. During the initial approach, the crew observed heavy rainfall ahead on their weather radar. Visual contact with runway 08 was established at ~700 feet AGL. At 260 feet AGL the Captain disconnected the Auto Pilot, however, inadvertently activated the TOGA function. This was immediately corrected and the autothrottle was disconnected, as briefed.

20 seconds after the AutoPilot was disconnected the aircraft started to drift to the left of the centerline. The crew noticed they were drifting and immediately manoeuvred the aircraft back to the centerline. Touching down 6 seconds after the aircraft started to drift, on the right-hand main landing gear, followed by the nose landing gear, with the left main landing gear touching down last. While taxing to their parking position the crew discussed the landing. (Later analysis revealed the aircraft was not flared for the touchdown).

The landing was assessed as firm by the crew, but after checking the a/c data system their concerns were alleviated as the recorded data showed an acceleration of 1.45 G and a roll of 10º to the right. (Recorded aircraft data indicated that the aircraft landed with a 5° yaw to the right, greater than 10° of right roll, and nose-down attitude of more than 2°) What the crew didn't know, was that the right engine nacelle had briefly touched the runway surface, Both the captain and an engineer performed a walk-around inspection, independent from each other, in heavy rain and wind. Neither detected the damage. As the weather deteriorated the return flight was delayed till the next day. With improved weather, the aircraft was prepared for the return flight the following morning. Both the engineer and the captain performed a wall around. Neither detected the damage.

Witness marks on the runway (Source; ATSB, © A/C 0perator)

The aircraft returned to New Zealand and continued to operate four more flights before the damage to the engine nacelle was found. Additional inspections revealed the following damage;

  • Abrasion damage to the right engine nacelle.

  • Abrasion damage to the right engine reverser cowl.

  • Abradable liner in fan case worn

  • Lateral wear damage to the #4 mainwheel (right-hand outer)

The incident was investigated by the Australian Transportation Safety Board and they published their final report in June 2020. The report is available by clicking here. The following contributing factors were identified in the report

  • The aircraft drifted left during short final in heavy rain on an approach at night. The pilot flying started to correct the drift, however, the aircraft was not flared and the wings were not level as it touched down. This led to the nose and right-wing being low, resulting in an engine nacelle strike.

  • Due to heavy rain, darkness and limited visual cues, the flight crew did not detect the aircraft's banked, nose-low attitude immediately prior to landing which increased the likelihood of an engine nacelle strike.

  • The operator’s pre-flight external inspection procedure mandated that flight crew check under the engine nacelle for damage. This was not routinely done by the flight crews and was not included in the flight crew training material.

  • Although the operator had a maintenance task card for daily inspections of the Boeing 737, it did not contain a specific requirement to inspect underneath the engine nacelle. This contributed to the damage to the right engine nacelle not being identified during post occurrence maintenance inspections

The damaged abradable liner in the fan case (Source; ATSB, © A/C 0perator)

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