The aircraft involved was a 19-year-old Boeing 747-200F freighter registered HL7451. First flown on 4 April 1980, the aircraft had completed 15,451 flights with a total flight time of 83,011 hours before its fatal flight.
INU failure and failed repair
Following the plane's departure from Tashkent on the previous flight segment, one of its inertial navigation units had partially failed, providing erroneous roll data to the captain's attitude director indicator. The first officer's ADI and a backup ADI were correct, a comparator alarm called attention to the discrepancy, and in daylight the erroneous indication was easily identified. The ADI's input selector was switched to the other INU and the correct indications returned. At Stansted, the engineers who attempted to repair the ADI did not have the correct Fault Isolation Manual available and did not think of replacing the INU. One of them identified and repaired a damaged connecting plug on the ADI. When the ADI responded correctly to its "Test" button, they believed the fault had been corrected, although this button only tested the ADI and not the INU. The ADI's input selector was left in the normal position.
Flight crew
The flight crew consisted of 57-year-old Captain Park Duk-kyu, 33-year-old First Officer Yoon Ki-sik, 38-year-old Flight Engineer Park Hoon-kyu, and 45-year-old maintenance mechanic Kim Il-suk. The captain was a former Colonel and pilot in the Republic of Korea Air Force and a highly experienced airman, with a total of 13,490 flying hours – 8,495 of which were accumulated flying Boeing 747s. The first officer, in contrast, was relatively inexperienced with just 195 hours of flying experience on the 747 and a total of 1,406 flight hours. The flight engineer, like the captain, had a lot of experience flying 747s – 4,511 out of his 8,301 total flight hours were accrued in them. The maintenance mechanic had been involved with the failed INU repair.
Flight
It was dark when the plane took off from London Stansted Airport, with the captain flying. When the captain tried to bank the plane to turn left, his ADI showed it not banking, but the comparator alarm sounded repeatedly. The first officer, whose own ADI would have shown the true angle of bank, failed to participate in full crew resource management techniques, saying nothing to challenge his captain's actions nor made any attempt to take over the flight with his own controls. The older and more experienced flight engineer did call out "bank" four times in 19 seconds, but the captain ignored his warnings, continued to ignore the chiming alarm, made no verbal response, and actually continued to increase the left bank angle. At 18:38, 55 seconds after take-off, Flight 8509's left wing dragged along the ground, then the aircraft plunged into the ground at a speed of between 250 and 300 knots, in a 40° pitch down and 90° left bank attitude. The aircraft exploded on impact.
Aftermath
After the investigation, the United Kingdom'sAir Accidents Investigation Branch issued recommendations to Korean Air to revise its training program and company culture, to promote a more free atmosphere between the captain and the first officer. The first recommendation of the AAIB's final accident report was that:
Korean Air continue to update their training and Flight Quality Assurance programmes, to accommodate Crew Resource Management evolution and industry developments, to address issues specific to their operational environment and ensure adaptation of imported training material to accommodate the Korean culture.
The AAIB also recommended the airline to review its maintenance procedures. The second and third recommendations are that:
Korean Air continue to review its policy and procedures for maintenance support at international destinations with a view to deploying sufficient of its own full-time engineers at the outstation or delegating the entire task to another operator or third-party maintenance organisation locally-based at the destination. If neither of these approaches is practicable then the support arrangements must be detailed and of such clarity as to preclude confusion. Korean Air review its policy and procedures to ensure that a copy of the relevant pages of the Technical Log and any other transit certification documents are left on the ground at the point of departure.
In popular culture
A March 2012 episode of Mayday also called Air Crash Investigation in the U.K. and the rest of the world titled "Bad Attitude" or "Stansted Crash" investigates this accident.
