Pilot error was the overriding cause of the January 2010 crash of an Ethiopian Airlines Boeing 737-800 off the coast of Lebanon, according to the final report into the accident.
The aircraft, operating as flight ET409, departed Beirut's Rafic Hariri airport at 00:41 UTC on 25 January 2010 but crashed into the Mediterranean Sea around 5nm south-west of the airport after a flight lasting just 4min 15s, killing all 90 people on board.
In the conclusions, the report, produced by the Lebanese Civil Aviation Authority, said that the probable causes of the accident were the "flight crew's mismanagement of the aircraft's speed, altitude, headings and attitude through inconsistent flight control inputs resulting in loss of control".
The night departure and course changes to avoid weather, combined with the captain's relative inexperience as pilot-in-command on the type, may have led to the captain "reaching a situation of loss of situational awareness similar to a subtle incapacitation and the [first officer's] failure to recognise it or to intervene accordingly".
During the brief flight, the flight data recorder and cockpit voice recorder captured two "prolonged" stick shaker alarms of 27s and 26s as the aircraft entered stall situations, 11 aural "bank angle" warnings and a final overspeed warning towards the end of the 737's descent.
The aircraft had a maximum angle of attack of 32e_SDgr, maximum bank angle of 118e_SDgr left and maximum recorded speed of 407.5kt, said the report.
No mechanical defects were found on the 2002 airframe (ET-ANB) and the two CFM International CFM56-7BE engines performed normally, it said.
It suggests that the pairing of the pilots may have been a contributory factor. The captain had only secured his release to fly solo on the type 51 days prior to the accident, in which time he had accumulated 188h.
While the inquiry report said he had over 3,700h as pilot-in-command, it said nearly 2,500h were on "different light and spray aircraft".
The first officer, however, had a total of 673h, of which 350h were as first officer on 737-700 and -800s.
Although the pairing was within the airline's recommendation, which states that "a captain who has less than 300 hours and first officer who has less than 100 hours on type should not be scheduled together", the report added: "That level of experience, although within the required approved standard, did not constitute a comfortable margin that would allow the crew to have enough confidence in the operation of the aircraft under demanding conditions, especially when we consider that the captain's experience on the 737-700/800 was acquired in the 51 days preceding the accident."
The first officer also demonstrated a lack of assertiveness to intervene when faced with the captain's "strange flying behaviour", it said.
Ethiopian Airlines should revise its cockpit relationship management policies, it said, to stress the leadership and assertiveness required of a first officer. Crew pairings should also be reconsidered, it added.
However, Ethiopian Airlines has angrily dismissed the report as "biased, lacking evidence, incomplete and [failing to] present the full account of the accident". It remains convinced that the aircraft disintegrated in mid-air due to an explosion.
In a statement, Captain Desta Zeru, vice-president flight operations at Ethiopian Airlines, said the flight data and cockpit voice recorders show that the pilot was making "appropriate inputs in an effort to control the aircraft".