Bulgaria A320 at Sofia on May 22nd 2021, engine shut down in flight

Last Update: November 2, 2022 / 15:54:37 GMT/Zulu time

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Photo of Bulgaria Air LZ-FBC, Airbus A320 — Bulgaria Air LZ-FBC, Airbus A320 (Photo credit: Mike Burdett / Flickr / License: CC by-sa)

Incident Facts

Date of incident
May 22, 2021

Classification
Incident

Cause
Engine shut down in flight

Airline
Bulgaria Air

Flight number
FB-8509

Departure
Sofia, Bulgaria

Destination
Sharm el Sheikh, Egypt

Aircraft Registration
LZ-FBC

Aircraft Type
Airbus A320

ICAO Type Designator
A320

A Bulgaria Air Airbus A320-200, registration LZ-FBC performing flight FB-8509 from Sofia (Bulgaria) to Sharm el Sheikh (Egypt) with 137 people on board, was climbing out of Sofia's runway 09 when the crew declared PAN PAN and stopped the climb at FL230 reporting an engine (CFM56) failure. The crew shut the engine down, advised they did not need any assistance on the ground and returned to Sofia for a safe landing on runway 27 about 35 minutes after departure.

Passengers reported there was a strong smell of kerosene during takeoff, later the captain announced there was a small technical problem (one engine had failed) and they were returning to Sofia.

A replacement A320-200 registration LZ-FBD reached Egypt with a delay of about 3:40 hours.

On Jul 29th 2021 Germany's BFU reported they have joined the investigation into the serious incident by a foreign investigation authority because a component had been designed/produced in Germany. Shortly after takeoff the left hand engine failed, the aircraft returned to the point of departure.

On Nov 2nd 2022 Bulgaria's AAIU released their final report concluding the probable causes of the serious incident were:

Violations in the technological process by Lufthansa Technik Sofia personnel during the replacement of the fuel pump of the left engine of the aircraft A320-214 with registration LZ-FBC;

Underlying cause:

- Absence of comprehensive flight control by crew of engine parameters during take-off and climb in terms of comparison of rotor speed, exhaust temperature and fuel consumption;

- Lack of awareness of the flight crew of the work performed during the servicing of the aircraft before the flight.

The AAIU analysed:

The serious incident is associated with a fuel leak from the left engine and self-shutdown, caused by flame-out in the combustion chambers due to excessive fuel impoverishment.

Initially, a situation has arisen the hazards the flight safety related to the leakage of fuel in the nacelle of Engine No 1, and subsequently this situation has grown into another situation threatening the safety of flight related to self-shutdown of Engine No 1.

In investigating the causes of the fuel leak, mainly as indicated in paragraphs 2.6.1 and 2.18, the Commission concludes that a decisive influence on its occurrence was due to the technological process failures in the replacement of the main engine fuel pump by Lufthansa Technik Sofia personnel. These violations led to the presence of a leak, but this leak should have been detected in the subsequent engine performance test foreseen in the job card. This did not happen as the test recommended by the manufacturer is performed with the operation of the engine at M inimum Idle mode.

The leak occurs at elevated engine operating modes, but these tests are not recommended by the manufacturer due to the low frequency of such events and the high cost of performing the tests. (Editorial note: emphasis added by investigation)

It is worth noting the fact that the flight crew was not informed, and he did not take the initiative to be informed by the on-board documentation about the change of the fuel pump on the left engine.

Such an awareness would focus the same earlier on the normal operation of this engine and would support the early detection of the fuel leak and the corresponding termination of the flight.

Some indications would also allow this to happen immediately after take-off. For example, the deviation of the aircraft nose to the left when the engines with take-off thrust, the increased fuel consumption of the left engine after its start (detected by decoding the flight data recording).

According to the crew's explanations, there is no established procedure in the climb process as to when and what engine parameters should be monitored with the result that on the flight in question the difference in fuel consumption of the two engines reaches 33.2% and this goes unnoticed by the crew.

The crew reacted when the engine switched itself off.

In FCOM- Abnormal and Emergency Procedures - FUEL-FUEL LEAK of Bulgaria Air JSC it is written that in such conditions the flight should be terminated immediately.

For the transition from a situation associated with the presence of a fuel leak from the left engine in flight to a situation associated with the left engine shutting itself down occurred spontaneously, without flight crew intervention.

Upon detection of the engine shutting itself down, the crew makes the decision to abort the flight and return to the airport from which it took off. These measures were successful and the flight ended without further consequences to the passengers, crew and aircraft.