ADC Airlines Flight 86
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A Boeing 727 of ADC Airlines, similar to the one involved
|Date||7 November 1996|
|Summary||ATC error, and pilot error after TCAS warning|
|Aircraft type||Boeing 727–231|
|Flight origin||Port Harcourt Airport|
ADC Airlines Flight 86 was a Nigerian domestic flight operated by ADC Airlines from Port Harcourt to Lagos. On 7 November 1996 the crew of the Boeing 727-200 operating the flight lost control of the aircraft while avoiding a mid-air collision on approach; the aircraft crashed inverted at a very high speed, killing all 144 passengers and crew on board. Investigators determined the primary cause of the accident was an air traffic control error. 
Flight 86 was en route to Lagos airport at flight level (FL) 240 (approximately 24,000 ft (7,300 m) altitude). At the same time an aircraft operated by Triax was on its way from Lagos to Enugu at FL160. The Lagos Air Traffic Controller cleared the crew of Flight 86 to descend, but erroneously thought that he had earlier cleared Flight 86 to descend to 10,000 ft (3,000 m) and that it was below the Triax aircraft. The descent from FL240 caused Flight 86 to conflict with the Triax flight at FL160. The traffic collision avoidance system (TCAS) sounded an alert but when the crew took evasive action they overcompensated and it rolled too far; the pilots lost control and within sixteen seconds the aircraft was upside down and diving towards the ground at near-Mach 1 speed. The inverted aircraft disintegrated on impact near Imota (Ejirin) at 17:05 local time.
The primary cause of the accident was determined to be error on part of the air traffic controller, quote "The untidy traffic separation by the radar controller which resulted from the vectoring of ADK 086 towards the track of the opposite traffic TIX 185."
The pilot was also found to be at fault for proceeding on a heading of 330 and the risky maneuver to avoid a collision with the Triax plane.
- "ADC Airlines Flight 86". 20 November 2008. Retrieved 23 January 2012.
- "ADC 727 Crash". Flight International. 13–19 November 1996. p. 6.(misreports registration as 5N-BBF)