What happened
On November 1, 2018, a commercial flight operated by an Icelandic carrier, an Airbus A321 with registration TF-WIN, was climbing through 7,040 feet MSL when the crew received an oil quantity advisory for engine number two. Within minutes, the oil quantity for the right engine dropped to zero, and the Electronic Centralized Aircraft Monitor (ECAM) displayed an "XX" value. Shortly thereafter, the oil pressure also began to decline, triggering an ECAM LOW PRESS warning.
Following the Quick Reference Handbook (QRH) procedures, the flight crew performed an in-flight shutdown of engine number two. The aircraft, carrying 193 persons on board (7 crew and 186 passengers), was cleared to return to Keflavik Airport. The crew declared a PAN-PAN and landed safely at Keflavik at 16:23 local time with no injuries and no damage to the aircraft.
The investigation
An investigation by the RNSA examined the aircraft' and found that the inside of the engine number two cowling was wet with oil. Specifically, the oil drain plug on the main oil supply filter was found to be loose, and the safety wire was also loose. A subsequent inspection of engine number one revealed a similar condition, with both the drain plug and safety wire found loose and the cowling wet with oil.
Technical analysis of the flight data revealed that while both engines experienced a sudden drop in oil quantity during takeoff due to normal "oil gulping" at high power, the loss in engine number two continued until the reservoir was depleted. The investigation also reviewed maintenance records from a recent C-check performed in Slovenia, noting that the main oil supply filters for both engines had been replaced during that period.
Findings
- The primary cause of the oil leak was the incorrect installation of the black O-ring on the oil filter drain plug.
- Maintenance technicians had been practicing a method of installing the O-ring on the drain plug itself rather than into the filter cover recess, which contradicted the Airbus Aircraft Maintenance Manual (AMM).
- The improper assembly made it difficult to seat the O-ring correctly, leading to a leak path.
- Additionally, the investigation found that the filter element may not have been properly seated on the filter cover's locator pin, which, combined with engine vibration, allowed the drain plug to loosen over time.
Safety action
Following the investigation, Airbus and Safran Aircraft Engines updated the AMM instructions to clarify the sequence of installation, specifically stating that the filter element must be installed into the filter cover before being placed into the engine housing. Furthermore, Safran Aircraft Engines introduced a revised supply filter via Service Bulletin 79-0038 to reduce the risk of incorrect assembly.