ADC Airlines Flight 086

ADC Airlines Flight 086 (ADK086) was a Nigerian domestic flight operated by ADC Airlines from Port Harcourt to Lagos. On the afternoon of 7 November 1996, the crew of the Boeing 727-231 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 into a lagoon, killing all 144 passengers and crew on board. The crash remains as the fourth deadliest plane crash in Nigerian history after Dana Air Flight 0992, the 1992 Nigerian Air Force C-130 crash, and the 1973 Kano Nigeria Airways Boeing 707 crash.

Investigators determined that the primary cause of the accident was due to air traffic control error, the pilot's decision to continue his turn to a certain heading and his erroneous maneuver in evading from an incoming traffic, which ultimately led to the loss of control of the aircraft.

Accident

Flight 086 was a scheduled domestic passenger flight from Port Harcourt, the fifth-largest city in Nigeria, to Lagos, the largest city in the country. Operated by then-major airline ADC Airlines, the flight was operated with a Boeing 727-231, carrying 134 passengers and 10 crew members. The aircraft was flown by Captain Usen, who was on the final part of his training. The pilot in command, Captain Sama, was in charge for the radio exchange.

At 16:52 WAT (UTC +1), the aircraft took off from Port Harcourt and climbed to 24000 ft. The flight was uneventful until the approach to Lagos.

As the flight was approaching Lagos, the crews intended to descend to 16000 ft. However, an aircraft with callsign 5N-MPN had crossed Flight 086 at an altitude of 23000 ft. Since Flight 086 was at 24000 ft, they had to delay their descent. When 5N-MPN had completely crossed Flight 086, the ATC cleared the Flight 086 to descend to 16000 ft. The flight crews then put the aircraft in a high rate of descent. During its descent to 16000 ft, the ATC at Lagos then asked the crew to fly at a heading of 320 and to maintain the flight at FL50. At the same time another 727 operated by Triax was on its way from Lagos to Enugu at FL160. The Lagos Air Traffic Controller erroneously thought that he had earlier cleared Flight 086 to descend to 10000 ft and that it was below the Triax aircraft. As such, the controller immediately asked Flight 086 to redirect its heading to 300.

Flight 086 was descending to 16000 ft while Triax Flight 185 was climbing through 15000 ft. This put both aircraft on a collision course. The traffic collision avoidance system (TCAS) of Flight 086 then sounded an alert, warning the flight crews to reduce its descent and start climbing in order to prevent a collision with Flight 185. At this stage, the flight crew had noticed the incoming Triax Flight 185.

17.02.41 ATC ADKO 086, what is your actual heading now?

17.02.46 CAM-1 We are heading eh, 3 - - - 15, turning 320

17.02.51 ATC Maintain heading 300, maintain heading 300

17.02.56 CAM-1 Ah, we - - - - -

17.02.57 TCAS Traffic, Traffic

As the TCAS sounded the alert, Captain Sama immediately took over the control from Captain Usen. He decided to disobey the controller's order of heading 300 and turned Flight 086 further to the right towards heading 330. The controller noticed this and encouraged the crews by stating "That's better!". Captain Sama turned the aircraft to the right with a bank angle of 44 degrees.

This however was not maintained. After 10 seconds, the bank angle started to increase, reaching 65.6 and 68,8 degree for 5 seconds. It kept increasing until it had reached a bank angle of 83 degree. It had entered an accelerated stall condition, which was caused by the large bank angle of the aircraft. The aircraft rapidly lost its altitude and nosedived in an inverted condition. The vertical acceleration reached 8.44 G.

17.03.20 CAM [Sound of high speed klacker]

17.03.25 CAM [Sound of horn]

17.03.32 CAM [Sound of screaming]

17.03.40 CAM [Sound of knocking]

The flight crew of Flight 086 tried to save the aircraft from crashing. The aircraft appeared to be recovering as the vertical acceleration was reduced to 2.10 G when it crashed into Lagos Lagoon in inverted condition, at a speed of more than 490 kn, killing all 144 people on board.