Nigeria Airways Flight 2120

Nigeria Airways Flight 2120 was a chartered passenger flight from Jeddah, Saudi Arabia, to Sokoto, Nigeria on July 11, 1991 which caught fire shortly after takeoff from King Abdulaziz International Airport and crashed while attempting to return for an emergency landing, killing all 247 passengers and 14 crew members on board. The aircraft was a Douglas DC-8 operated by Nationair Canada for Nigeria Airways. Flight 2120 is the deadliest accident involving a DC-8 and remains the deadliest aviation disaster involving a Canadian airline.

Aircraft And Crew
The aircraft involved in the accident was a 1968 Douglas DC-8-61, C-GMXQ, owned by the Canadian company Nolisair, usually operated by Nationair Canada. At the time of the accident, it was being wet-leased to Nigeria Airways, which in turn sub-leased it to Holdtrade Services to transport Nigerian pilgrims to and from Mecca. The DC-8 was the primary aircraft type used by the airline.

Crew
William Allan, the 47-year-old captain, a former Canadian Air Force pilot, had logged 10,700 flight hours and 1,000 hours in type. Kent Davidge, the 36-year-old first officer, had logged 8,000 flight hours, of which 550 hours were in type, and was the on the accident flight. Victor Fehr, the 46-year-old flight engineer, had logged 7,500 flight hours, of which 1,000 hours were in type.

Crash
The aircraft departed King Abdulaziz International Airport bound for Sadiq Abubakar III International Airport in Sokoto, but problems were reported shortly after takeoff. Unknown to the crew, the aircraft had caught fire during departure, and though the fire itself was not obvious since it started in an area without fire warning systems, the effects were numerous. Pressurization failed quickly, and the crew was deluged with nonsensical warnings caused by fire-related circuit failures. In response to the pressurization failure, Allan decided to remain at 2,000 feet (610 m), but the flight was cleared to 3,000 feet (910 m) as a result of the controller mistaking Flight 2120 for a Saudia flight that was also reporting pressurization problems because Captain Allan had mistakenly identified as "Nationair Canada 2120" rather than "Nigerian 2120," a mix-up that lasted for three minutes, but was ultimately found not to have had any effect on the outcome.

Flames In The Gears
Amidst this, First Officer Davidge, who had been flying C-GMXQ out, reported that he was losing hydraulics. The crew only became aware of the fire when a flight attendant rushed into the cockpit reporting "smoke in the back ... real bad." Shortly afterwards, Davidge reported that he had lost ailerons, forcing Allan to take control; as Allan took over, the cockpit voice recorder failed. At this moment, the air traffic controller realized that Flight 2120 was not the Saudia flight and was in trouble, and directed them towards the runway. Allan subsequently contacted air traffic control multiple times, among his pre-mortem communications being a request for emergency vehicles.

When the aircraft was about 18 km (11 mi; 10 nmi) from the airport and at an altitude of 670 m (2,200 ft), a point where the landing gear could conceivably have been lowered, it began to experience an inflight breakup and a number of bodies fell from it, indicating that the fire by that time had consumed, at least partially, the cabin floor. Just 2.875 km (1.8 mi) short of the runway, the melting aircraft finally became uncontrollable and crashed, killing whatever portion of the 261 occupants on board—including 247 passengers—had not already suffocated or fallen out of the aircraft. Nine of the fourteen crew were identified, but "no attempt was made to identify the passengers".

Deadliest Yet
As of July 2017, the accident remains the deadliest crash involving a Douglas DC-8, as well as the second-deadliest accident taking place on Saudi Arabian soil, after Saudia Flight 163.

Cause
Prior to departure, the lead mechanic had noticed that the "#2 and #4 tyre pressures were below the minimum for flight dispatch," and attempted to inflate them, but no nitrogen gas was readily available. The project manager, unwilling to accept a delay, disregarded the problem and readied the aircraft for dispatch. As the aircraft was taxiing, the transfer of the load from the under-inflated No. 2 tire to the No. 1 tire on the same portside axle resulted "in overdeflection, over-heating and structural weakening of the No. 1 tyre." "The No. 1 tyre failed very early on the take-off roll," followed almost immediately by the No. 2. The latter stopped rotating "for reasons not established," and the subsequent friction of the wheel assembly with the runway generated sufficient heat to start a self-sustaining fire.

Emergency Declared
The crew realised there was a problem, but not the nature or seriousness of it. The aircraft was not equipped with fire or heat sensors in the wheel assembly. The first officer was recorded remarking, "We gotta flat tire, you figure?" According to Transportation Safety Board of Canada members interviewed for an episode of Mayday about the accident, standard procedures regarding tire failure during the takeoff roll on the DC-8 did not include rejecting takeoff for tire or wheel failures, so the captain proceeded with the takeoff.

Due to common jet aircraft design, the accident became inevitable the moment the landing gear was retracted, mere seconds after takeoff and long before an emergency became apparent. When this occurred, "burning rubber was brought into close proximity with hydraulic and electrical system components," causing the failure of both hydraulic and pressurisation systems that led to structural damage and loss of control of the aircraft. The Transportation Safety Board later concluded, "had the crew left the landing gear extended, the accident might have been averted." Fuel, "probably introduced as a result of 'burn through' of the centre fuel tank," intensified the fire, which eventually consumed the cabin floor. People began falling out of the aircraft when their seat harnesses burned through. "Despite the considerable destruction to the airframe, the aircraft appeared to have been controllable until just before the crash."

Discovered?
It was discovered during the investigation that the mechanics had known about the under-inflated tires since 7 July but that the project manager, lacking the relevant training to make an informed decision, had prevented maintenance on the tires because the aircraft was behind schedule, requiring them to record false pressure readings in the log to make the aircraft seem airworthy. This meant that Nationair Canada executives had pressured the colleagues of the cockpit crew to withhold information that had serious safety implications.