BEA releases final report on Air France Airbus A380 fan failure accident over Greenland

Status:Final
Date:Saturday 30 September 2017
Time:ca 09:45
Type:
Airbus A380-861
Operator:Air France
Registration:F-HPJE
C/n / msn:052
First flight:2010-08-10 (7 years 2 months)
Total airframe hrs:27184
Engines:Engine Alliance GP7270
Crew:Fatalities: 0 / Occupants: 24
Passengers:Fatalities: 0 / Occupants: 497
Total:Fatalities: 0 / Occupants: 521
Aircraft damage:Substantial
Aircraft fate:Repaired
Location:over southern Greenland (   Greenland)
Phase:En route (ENR)
Nature:International Scheduled Passenger
Departure airport:Paris-Charles de Gaulle Airport (CDG/LFPG), France
Destination airport:Los Angeles International Airport, CA (LAX/KLAX), United States of America
Flightnumber:AF066

Narrative:
An Air France Airbus A380, operating flight 66 from Paris-Charles de Gaulle Airport, France, to Los Angeles International Airport, California, USA, diverted to Goose Bay, Canada after suffering an uncontained GP7270 engine failure over Greenland.
The aeroplane took off at 09:50 UTC with the three pilots (the captain and two first officers, FO/1 and FO/2) in the cockpit. The cruise altitude (FL 330) was reached around 25 minutes later. The crew agreed on the division of the rest time. FO/2 took the first duty period around 30 minutes after take-off. The aeroplane changed levels several times during the cruise and then stabilized at FL370 at 11:14.
At 13:48, the crew asked Gander Oceanic to climb to FL380. The controller accepted and asked them to report when reaching FL380. The low pressure compressor and turbine rotation speed (N1) of the four engines increased from 98% to 107%.
At 13:49, the titanium fan hub of the right outer engine (No 4) separated into at least three parts. This failure was the result of the progression of a crack originating in the part’s subsurface. The central fragment of the hub stayed attached to the coupling shaft between the low pressure compressor and the low pressure turbine. The two other hub fragments were ejected, one upwards and the other downwards. The interaction between the liberated fan rotor fragments and the fixed parts of the engine caused the destruction of the engine casing and the separation of the air inlet which fell to the ground. Debris struck the wing and airframe without affecting the continuation of the flight.

After the failure, the aeroplane’s heading increased by three degrees to the right in three seconds, and there were vibrations in the airframe for around four seconds.
The crew perceived these variations and associated them with engine surging by analogy with the sensations reproduced in simulator sessions. An “ENG 4 STALL” ECAM message came up. The captain requested the “ECAM actions”. He engaged Autopilot 1 and indicated that he was taking the controls and would thus be Pilot Flying. He reduced engine No 4 thrust by positioning the associated lever to IDLE. The engine performed an automatic shutdown and the FO/2 confirmed the sequence by depressing the Engine 4 Master and Engine 4 fire pushbuttons, a few seconds later.

The damaged engine could not be seen from the cockpit or in the image from the camera located on the fin of the A380. A member of the cabin crew brought to the cockpit, a photo of the engine taken by a passenger with his smartphone.
FO/1 who had returned to the cockpit to help the flight crew on duty, went to the upper deck to assess the damage and take other photos. He observed damage on the leading edge slats and small vibrations in the flaps.

From the time of the failure and for around 1 min 30 s, the CAS had decreased from 277 kt to 258 kt and level flight at FL370 was maintained. The captain noticed this reduction in speed and decided to descend to the drift-down level calculated by the FMS (EO MAX FL 346) to maintain a constant speed in level flight. Observing that it was not possible to hold this level and this speed, he continued descending level by level. He selected FL 360, FL 350 then FL 330 and lastly FL 310. The level by level descent obliged the crew to stop their ECAM actions each time a descent was initiated. During level flight at FL310, the N1 rotation speeds of the three remaining engines decreased to 103%. The captain stabilized the descent to FL290 with a constant speed (CAS was 290 kt) by keeping the three engines in maximum continuous thrust (MCT). He decided to continue the descent and stabilize at FL270 in order to spare the engines to destination. The speed stabilized at 279 kt. Around five minutes after the A380 had started its descent, the controller in the Gander Oceanic control centre with which the crew were in datalink contact (CPDLC), detected the deviation from the vertical profile of the path and sent a message: “ATC NOW SHOWS YOU FL330. IS THERE A PROBLEM”.

At the same time, the control centre received an audio Mayday message from AF066, relayed by another aeroplane. One minute later, the PM replied to the CPDLC question with a MAYDAY. Direct audio communication between the flight and ATC resumed a few minutes later.

The crew decided, in agreement with Air France’s Operational Control Centre , to divert to Goose Bay airport and asked the controller for a direct route. After studying the available approaches and taking into consideration the captain’s experience and the airport’s immediate environment, the crew confirmed the selection of Goose Bay airport as the alternate airfield even though it was at a greater distance than Kangerlussuaq airport in Greenland.
The crew started the descent to Goose Bay and were cleared to carry out the RNAV GNSS RWY 26 approach. They were then cleared to land on runway 26. They configured the aeroplane for landing. On approaching the altitude of 1,000 ft, the captain disconnected Autopilot 1 and the flight director (FD) and continued the landing in manual flight. The aeroplane landed at 15:42. The taxiing phase to the stand took some time due to having to stop several times so that the airport services could collect the debris which had fallen onto the runway during the landing. At 16:22, all the engines were shut down.

Probable Cause:
Contributing factors
The following factors may have contributed to the failure of the fan hub on engine No 4:
– engine designer’s/manufacturer’s lack of knowledge of the cold dwell fatigue phenomenon in the titanium alloy, Ti-6-4;
– absence of instructions from the certification bodies about taking into accout macro-zones and the cold dwell fatigue phenomenon in the critical parts of an engine, when demonstrating conformity;
– absence of non-destructive means to detect the presence of unusual macro-zone in titanium alloy parts;
– an increase in the risk of having large macro-zones with increased intensity in th Ti-6-4 due to bigger engines, and in particular, bigger fans.
Accident investigation:

Investigating agency: BEA Status:Investigation completedDuration: 3 yearsAccident number:BEA2017-0568Download report:Final report:  https://www.bea.aero/uploads/tx_elydbrapports/BEA2017-0568.en.pdf

Link: https://aviation-safety.net/database/record.php?id=20170930-1

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