Korean Air Cargo Flight 8509

Korean Air Cargo Flight 8509 was a Boeing 747-2B5F, registered HL7451 and bound for Milano-Malpensa Airport, that crashed due to pilot error on 22 December 1999 shortly after take-off from London Stansted Airport]]. The aircraft crashed into Hatfield Forest near the village of Great Hallingbury close to but clear of some local houses. All 4 crew on board were killed.

The aircraft
The aircraft involved was a Boeing 747-2B5F freighter registered HL7451. Built on 4 April 1980, the aircraft had completed 15,451 flights with a total flight time of 83,011 hours before its fatal flight on 22 December 1999.

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 indicator|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 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 (Hangul: 박득규, Hanja: 朴得圭, RR: Bak Deuk-gyu, M-R: Pak Tŭkkyu), 33-year-old First Officer Yoon Ki-sik (Hangul: 윤기식, Hanja: 尹基植, RR: Yun Gi-sik, M-R: Yun Kishik), 38-year-old Flight Engineer Park Hoon-kyu (Hangul: 박훈규, Hanja: 朴薰圭, RR: Bak Hun-gyu, M-R: Pak Hun'gyu), and 45-year-old maintenance mechanic Kim Il-suk (Hangul: 김일석, Hanja: 金日奭, RR: Gim Il-seok, M-R: Kim Ilsŏk). 

The flight
It was dark when the plane took off from Stansted, with the captain flying. When the captain tried to bank the plane to turn left, his ADI showed it not banking and the comparator alarm sounded repeatedly. The first officer, whose instrument would have shown the true angle of bank, said nothing, although the flight engineer called out "bank". The captain made no response and continued banking farther and farther left. At 18:38, 55 seconds after take-off, Flight 8509 plunged into the ground at a speed between 250 and 300 knots, in a 40&deg; pitch down and 90&deg; left bank attitude.

Media
A March 2012 episode of Mayday (Season 11 Episode 7) titled "Bad Attitude" investigated this accident.