WOW A321 at Keflavik on Nov 1st 2018, engine shut down in flight, other engine also leaks oil
Last Update: August 9, 2021 / 15:32:49 GMT/Zulu time
Incident Facts
Date of incident
Nov 1, 2018
Classification
Incident
Airline
WOW Air
Flight number
WW-117
Departure
Keflavik, Iceland
Destination
Baltimore, United States
Aircraft Registration
TF-WIN
Aircraft Type
Airbus A321
ICAO Type Designator
A321
The airline reported the aircraft returned due to a "minor engine failure". The crew decided to return for safety reasons prior to the Oceanic crossing.
A replacement A321-200 Neo registration TF-DTR is estimated to reach Baltimore with a delay of about 2.5 hours.
On Nov 23rd 2018 Iceland's RNSA reported the crew declared PAN PAN PAN reporting they had shut the #2 engine down. A post flight inspection revealed a severe oil leak from the engine's oil drain plug, the oil quantity had reduced to levels requiring an engine shut down. Engine #1 (left hand) also revealed oil leaking through the engine's oil drain plug. The aircraft was operating an ETOPS flight. The occurrence was rated a serious incident and is being investigated.
On Aug 9th 2021 the RNSA released their final report concluding the probable causes of the serious incident were:
The RNSA investigation determined that Adria Tehnika did not follow the Airbus AMM subtask 79-21-10-420-060-A correctly during the C-check.
The investigation determined that the cause of the oil leak during this incident was an incorrect installation of the black O-ring.
The RNSA observed that the design of the oil filter element and the oil filter cover is such that it could lead to an incorrect assembly.
The RNSA analysed:
According to the FDR, the oil quantity for Engine no. 1 was 17.5 quarts and for Engine no. 2 it was 15.75 quarts at 15:34:31.
Both Engine no. 1 and Engine no. 2 incurred a sudden drop in the oil reservoir around 15:47:30. About 5 quarts of the sudden oil drop (for both engines) occurred because of oil gulping during takeoff. This happened as the high-power selection required additional volume of oil for the engine operation, which is taken from the oil reservoir.
For Engine no. 1, the drop in oil quantity stabilized at about 13 quarts at 15:47:54. This was at the same time as the aircraft nose pitched up at the end of the takeoff roll, when the aircraft was about to take off from Keflavik Airport.
For Engine no. 2 the oil quantity continued to drop during the climb and reached 0 quarts at 15:53:58, when the aircraft had reached 10,900 feet altitude.
As some of the drop in quantity (for both engines) was because of oil gulping as a result of the engine running at higher power, the actual oil quantity loss can be found by comparing the oil in the oil reservoir during taxi before the flight, to the oil in the oil reservoir during taxi after the flight.
For Engine no. 1, during taxi before the flight at 15:34:31, the engine oil quantity was 17.5 quarts. After the flight, during taxi at 16:28:29, the engine oil quantity was 16.75 quarts.
Engine no. 1 had therefore lost just below 1 quart of its oil during the flight, when comparing the taxi FDR values. Considering that the original oil quantity on both engines was about 18.5 quarts before the flight, as stated by the flight crew, Engine no. 1 lost a little less than 2 quarts of its oil.
The engine oil quantity of Engine no. 2 was 15.75 quarts at 15:34:31, during taxi before the flight. After the flight, during taxi at 16:28:29, the engine oil quantity was 0.75 quarts.
Engine no. 2 had therefore lost almost all its oil during the flight. Comparison of the FDR taxi values for the oil quantity before and after the flight revealed a loss of 15 quarts of oil.
Considering that the original oil quantity on both engines was about 18.5 quarts before the flight, as stated by the flight crew, Engine no. 2 lost a little less than 18 quarts of its oil.
The oil loss on Engine no. 2 therefore also included most of the extra oil that was required by the engine from the oil reservoir during its high-power operation during takeoff and initial climb.
From the data derived it is apparent that the engine oil pressure for both engines increased between 15:47:10 and 15:47:22, which coincides with the selection of takeoff power in the beginning of the takeoff roll of the aircraft at RWY 28 at Keflavik Airport.
The rapid drop in the oil quantity for both Engine no. 1 and Engine no. 2 at 15:47:30 occurred during the takeoff roll, about 8 seconds after both engines had reached their maximum engine oil pressure (after the takeoff power was selected). This is normal as at high power selection the engines require additional oil.
The initial ECAM warning for low oil pressure for Engine no. 2 occurred at 16:00:15. From the data behind Figure 6 it is however apparent that the Engine no. 2 oil pressure started to drop around 15:54:30, or 32 seconds after the oil quantity for Engine no. 2 had reached zero.
The RNSA noted that the oil pressure value for Engine no. 1 oscillated between an upper value around 50-55 psi and a lower value around 25-35 psi after Engine no. 2 lost its oil pressure.
Comparison of the engine pressure (Figure 6), the engine displayed value and the engine throttle value parameters, revealed that Engine no. 1 did not operate continuously at high-power after Engine no. 2 shutdown.
According to the engine manufacturer, this was because the Auto thrust was engaged with N1 regulated without any action on throttle by the flight crew. In this mode, aircraft gives data to EEC9 to drive the engine with specific N1. The Auto thrust was engaged between 15:48:29 and 16:23:19.
When the flight crew shut down Engine no. 2 and turned around to Keflavik Airport at 16:01, the aircraft was located 69 NM from the threshold of RWY 19 and at FL200.
Aircraft TF-WIN underwent a C-check inspection at Adria Tehnika at Ljubljana Airport in Slovenia between October 15th and October 28th, 2018. Adria Tehnika operated under EASA Part 145 certificate SI.145.100 at the time of the C-check.
At the time of the C-check TF-WIN had accumulated a total of 7036:43 flight hours and 1698 flight cycles.
The aircraft was released out of the C-check at 12:00 UTC on October 28th, 2018, 4 days prior to the serious incident. The aircraft flew 13 flight legs after the C-check and until the serious incident flight, or a total of 56 hours and 25 minutes.
According to Airbus Aircraft Maintenance Manual13 (AMM), normal oil consumption is not expected to exceed 0.60 quarts/hour. The oil consumption never exceeded this limit until the serious incident flight.
During the C-check at Adria Tehnika the main oil supply filters for both Engine no. 1 and Engine no. 2 were replaced.
Inspections after the flight revealed that oil had leaked from the drain plug on the main oil supply filters for both Engine no. 1 and Engine no. 2. The drain plugs were found loose as well as their safety wires.
The drain plugs could easily be turned by hand and did not meet the torque values stated in AMM task 79-21-10-920-002 [subtask 79-21-10-420-060-A].
Incident Facts
Date of incident
Nov 1, 2018
Classification
Incident
Airline
WOW Air
Flight number
WW-117
Departure
Keflavik, Iceland
Destination
Baltimore, United States
Aircraft Registration
TF-WIN
Aircraft Type
Airbus A321
ICAO Type Designator
A321
This article is published under license from Avherald.com. © of text by Avherald.com.
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