What happened
On January 9, 2008, an Airbus Industrie A319-114, registration N349NB, operated by Northwest Airlines as flight 853, experienced an engine fan cowling separation while on approach to land on runway 27R at Detroit Metro Airport (DTW). The flight originated from LaGuardia Airport (LGA) and was operating under visual meteorological conditions.
During the climb out, the flight crew was notified by a flight attendant that a passenger had observed the number two engine cowling flapping. The captain noted that the N1 vibration on the number two engine was approximately double that of the number one engine, though no warning lights were activated. During the cruise phase, the vibration levels equalized, but the aircraft subsequently experienced a shudder similar to flying through wake turbulence.
While the flight continued normally until landing, the crew was alerted by a flight attendant during taxiing that part of the right engine had detached. The first officer notified ground control of potential debris on the runway. The separation occurred in two parts: one half of the cowling departed the aircraft while it was on a one-mile final, and the other half departed as the aircraft touched down. The detached cowling was later struck by a subsequent landing aircraft.
There were no injuries to the two pilots, three flight attendants, or 68 passengers, though the aircraft sustained substantial damage.
The investigation
Investigators determined that the aircraft had undergone maintenance on the number two engine the previous evening to replace the N1 vibration monitor. Contract maintenance personnel reported that they had closed the fan cowling but had not latched it, as they intended to perform an engine run and leak check.
After the engine run was completed, one mechanic believed the other had latched the cowling. However, both mechanics left the aircraft to assist another mechanic at a different gate and did not return to verify that the cowling was secured. The maintenance log indicated the N1 sensor replacement was performed according to the aircraft maintenance manual, but the specific task to close and secure the fan cowl doors was not completed before the aircraft was returned to service.
Findings
- The separation of the engine cowling was caused by maintenance personnel failing to latch the engine cowling following a maintenance inspection.
- A contributing factor was the diversion of the mechanics' attention when another mechanic requested assistance at another gate.