Aircraft The aircraft involved was a Boeing 747-2B5F,
MSN 22480,
registered as HL7451, which was manufactured in 1980. In its 19 years of service, it had logged approximately 15,451 flights and 83,011 airframe hours before its fatal flight. It was equipped with four
Pratt & Whitney JT9D-7Q engines.
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 () • 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.
INU failure and failed repair Following the plane's departure from
Tashkent on the previous flight segment, one of its
inertial navigation units (INUs) had partially failed, providing erroneous roll data to the captain's
attitude director indicator (ADI or artificial horizon). 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 repair or replace the faulty number 1 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. == Accident ==