Northwest Airlines Flight 853 Engine Cowling Separation (N349NB)

Incident Overview and Flight Details On January 9, 2008, at 0749 eastern standard time, 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 the Detroit Metro Airport (DTW) in Detroit, Michigan. The domestic passenger flight, which originated from LaGuardia Airport (LGA) in New York at 0618, was operating under 14 Code of Federal Regulations Part 121. The flight was conducted in visual meteorological conditions with an instrument flight plan filed. The aircraft carried a pilot, co-pilot, three flight attendants, and 68 passengers, none of whom were injured. However, the airplane received substantial damage. ## Maintenance Background and Preflight Inspection The accident flight was the first for the aircraft after maintenance was performed on the number two (right) engine the previous evening. Contract maintenance personnel reported that they replaced the N1 sensor on the number two engine. They shut the fan cowling but did not latch it because an engine run and leak check were still required. After the engine run, one mechanic believed the other had latched the fan cowling, but it was not latched. The mechanics then left the aircraft to assist another mechanic at a different gate and did not return to latch or verify the fan cowling. The maintenance log stated the N1 speed sensor was removed and replaced in accordance with aircraft maintenance manual (AMM) 77-11-10, which required closing the fan cowl doors per AMM TASK 71-13-00-410-040. According to maintenance personnel, this task was not completed before the aircraft was returned to service. During the preflight inspection, the first officer used a flashlight because it was still dark. He reported the engine cowlings were flush and did not see any hanging cowl latches when looking underneath the engines. The captain noted that the logbooks indicated the number two engine vibration monitor had been replaced the previous night. The preflight, taxi, and takeoff were reported as normal. ## In-Flight Observations and Approach During climb out, the lead flight attendant informed the cockpit that a passenger reported the number two engine cowling was flapping after takeoff. A pilot-passenger seated behind the reporting passenger did not see the cowling move, and the flight attendants did not see it move when looking out the window. The captain began monitoring the N1 vibration indications on the number two engine, which were approximately double those of the number one engine, though the indicator was not flashing or amber. During cruise, the number two engine vibration decreased to match the number one engine. About 20 minutes after leveling off, the aircraft shuddered as if flying through wake turbulence. The captain reviewed the logbooks, noticed previous write-ups regarding engine vibration, and sent an ACARS maintenance message about the current vibration. The remainder of the flight was normal until taxiing after landing, when the lead flight attendant reported that part of the right engine had come off. The first officer called ground control to warn of possible runway debris, and the crew shut down the number two engine and taxied to the gate. ## Damage and Aftermath A pilot of another aircraft reported seeing part of the engine cowling come off when flight 853 was on a 1-mile final. The other half of the engine cowling was found on the runway and was contacted by an airplane that landed after the accident aircraft. The separated cowling contacted the right side of the horizontal stabilizer, resulting in substantial damage to the stabilizer. Additionally, the fan cowl doors, number two engine pylon, number two engine reverser, and right wing number one slat were damaged.