Air accident investigators have revealed a vital navigation aide failed seconds before a Korean Air jumbo crashed near Stansted Airport.
A fault had developed with the altitude director indicator, which tells crews the exact position of an aircraft at night and in cloud, on the previous flight of the Boeing 747.
The fault received attention on the ground at Stansted before the plane took off on the evening of December 22.
But after take-off, the crew received warnings the indicator was not working properly and the plane crashed, killing all four crew on board.
After the work had been done on the ground at Stansted, the Korean Air ground engineer said he would complete the technical log - but no copy of the log was left at Stansted.
The engineer was one of those killed in the crash.
"The result was there was no record of what the ground engineer entered in the technical log to clear the fault and no way of knowing if he briefed the on-coming commander (captain) about the fault," said the report from the Air Accidents Investigation Branch.
As a result AAIB investigators are carrying out a detailed review of maintenance at Stansted as well as a review of the airline's engineering and flight crew training practices and standard operating procedures.
The report came to no conclusions about the exact cause of the crash and the AAIB added its investigations were continuing.
The aircraft, bound for Milan, had taken off normally and had reached a height of about 2,000ft before starting a left turn, said the AAIB.
Air traffic controllers saw an explosion south of the airport and other witnesses reported feeling the shock waves.
Both captain and co-pilot would have had altitude director indicators (ADI) to give them an idea of the exact position of the aircraft.
The report said on the previous flight of the aircraft, from Tashkent to Stansted, a warning had gone off to indicate a discrepancy between the two readings of the ADIs.
It was the captain's ADI which was at fault and this was mentioned by the Tashkent flight engineer to the Korean Air ground engineer when the Tashkent flight landed at Stansted.
From recovery of the "black box" flight data recorder, the AAIB was able to reveal a buzzer, indicating a difference in the readings of the two ADIs, had sounded three times, then twice more and then, finally, some nine times.
The flight engineer - who together with the captain, co-pilot and ground engineer made up the crew - made two calls of "Bank". This would have indicated the plane was leaning over sharply.
The AAIB said further areas of investigation would include efforts to refine the cockpit voice recorder and the flight data recorder data.
Jumbo had uranium on board
Air accident investigators have revealed the Korean Air cargo plane which crashed in Essex moments after taking off from Stansted Airport was carrying several hundred kilos of depleted uranium.
An Air Accident Investigation Board spokesman confirmed last night the particular model of Boeing 747 involved was designed using the substance - which is denser than lead - as a counterweight in its tail rudder mechanism.
He said: "Our investigators were able to tell Essex Fire Brigade crews at the scene immediately the plane was likely to be carrying the depleted uranium so they could take appropriate action.
"Our information is that it remained intact after the crash, and that there is no hazard to those working at the site or people living nearby.
"The site is still sealed off and, as part of the clear-up operation, the Environment Agency and the local authority will make arrangements for an approved contractor to remove the uranium."
Bodies not yet found
The bodies of three Korean air men killed in the Stansted air crash have still to be discovered.
Air accident investigators believe the three men's remains are buried deep at the scene of last month's disaster.
The cargo jumbo jet crashed in a ball of flames seconds after taking off from Stansted Airport on December 22. A crew of four were on board, but as yet only one body has been found.
It it is thought the bodies of the men could be in a lake next to the crash site or in the impact crater caused by the plane.
At a press conference at Stansted Airport on Thursday, it was announced the lake would have to be drained and the crater created by the jumbo next to the dam excavated to recover whatever is there.
The Air Accident Investigation Branch has now completed its work at Hatfield Forest and is handing over responsibility for the site to the Agricultural Development and Advisory Service (ADAS), which will clear and restore the area.
The operation will be funded by the airline's insurers.
ADAS has carried out tests on land around the crash area and found no contaminate materials, prompting the re-opening of the National Trust land to the public in around two months' time.
Essex Police, which has been responsible for the security of the site since the crash, will be withdrawing in the middle of next week and handing over to ADAS.
An access road to the crash site is to be created and fencing installed for the safety of Hatfield Forest visitors.
Colin Rudd, a spokesman for ADAS, said cargo from the jumbo fell in the forest's lake when the airliner crashed on the edge of a dam and it was known there was an oxidising agent and cleaning materials on board.
"It is the Fire Service's opinion that most of the hazardous materials were burnt in the fire ball," he added.
Essex County Council head of emergency planning, Peter Pearson, said negotiations would be taking place with the airline's insurers to seek compensation for those living near the crash site as well as the loss incurred by the National Trust.
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