At least nine people have died and 11 left injured after a UPS cargo plane went down while taking off from a major air hub in Louisville, Kentucky on Tuesday evening.
Aircraft specialists suggest the aircraft went down after one engine failed and another appeared to be damaged during take-off.
It is unclear what caused the plane to crash, leading to a massive fireball to erupt after it failed to take-off from the airstrip. Video evidence showed flames were consuming a single wing of the plane during its takeoff attempt, which may have spread through the plane and caused the explosion, or the plane might have ignited after colliding with an object on the ground.
What is apparent is that the 38,000 gallons of fuel aboard the MD-11 jet required for the journey likely escalated the blaze, which quickly spread to several buildings beyond the runway and burned for hours.
How did it start?
UPS operates from the Louisville air hub as a logistics center for its global operations and its designated flight was beginning of a 4,300 mile journey to Honolulu in Hawaii when the freight aircraft attempted to take off.
Data from FlightRadar24 indicates the plane began to taxi along the 17R runway at around 17:15 local time and attained a top speed of 214mph.
But verified footage demonstrate that by the time the plane reached this speed a blaze had fully consumed its left wing and the plane couldn't climb before the massive explosion.
Authorities activated a local safety directive to local residents and scrambled hundreds of firefighters to the scene.
The state's governor verified details visible in security camera recordings that depict the aircraft flying just metres off the ground before a bright flash consumed the aircraft. It is then observed crashing onto the terrain as a huge fireball erupts around it about a minute after departure.
A verified clip taken by motorists on a nearby highway displayed the fire rising into the air while subsequent recordings showed smoke billowing from the scene.
Aerial images broadcast by local media depicted debris showering the runway and landing on the roofs of multiple nearby establishments.
Potential causes of the accident
ATC transmissions examined are mostly unclear and filled with static so no meaningful conversation can be discerned about the crash as it developed.
However, experts proposed that a dramatic failure of multiple engines may have been responsible for the disaster.
The MD-11 transport plane uses three engines. Two are installed under the wings, and a third is built into the tail at the bottom of the tail fin.
Video verified revealed a blaze engulfing the port wing of the aircraft, which then tilted to the left as it tried to achieve altitude and take-off.
Two experts separately proposed the left engine may have separated from the plane following a mechanical or structural failure.
Separate images captured post-accident displayed a burned powerplant resting on the turf adjacent to the airstrip.
A retired airline pilot and aviation safety expert said that it was "extremely rare" for an engine to detach during operation.
He referenced the 1979 aviation disaster tragedy, in which 273 individuals were fatally injured after the plane's engine detached as it departed from Chicago's major airport. Engine components had been damaged when it was replaced on the plane, but the expert stated it was too early to say whether a comparable issue led to the powerplant separation on the trijet.
The expert explained the cargo plane would have been able to fly with only two powerplants but the damage caused by the fire on the left wing was probably extensive enough it caused the aircraft's remaining engine to lose thrust.
"Given the severe nature of the incident we cannot determine what other damage was done when the engine came adrift," the expert commented.
Another aviation expert observed the video evidence appeared to show the third engine had been compromised because it released smoke. The damage could have occurred while it was pelted with debris from the fire and the engine detaching.
"The tail-mounted powerplant that released smoke seems to shut down right after," the expert said. "This left just the starboard powerplant producing thrust, creating a severe power imbalance and making the plane incapable to gain height.
"Losing two engines while departing results in only a fraction of its thrust and minimal opportunity of maintaining flight, especially at full departure mass," the specialist added.
Why did the crash cause such damage?
Footage from the aftermath showed a scene of complete chaos with multiple fires burning across a large swathe of the location and smoke billowing into the sky.
The plane, which was three decades old and had been used as a passenger plane before conversion, had already completed one round trip from the Kentucky hub to Baltimore in Maryland on Tuesday.
It has not been confirmed which goods was aboard the flight bound for Hawaii, though authorities said the aircraft didn't contain anything that would pose an increased danger of contamination.
"This was a long-haul cargo flight from Louisville to Honolulu, so the trijet was transporting a lot of jet fuel," an expert said. "The substantial fuel quantity not only reduced performance but also accounts for the large fireball observed post-accident."
Authorities informed media that the plane was carrying 144,000 litres of jet fuel for the extended trip when it went down. The fire was probably intensified on the surface because the plane crashed into a fuel processing facility adjacent to the airfield.
A specialist indicated investigators will now focus on the origin of the blaze, and "if wreckage hit the centre engine, and whether earlier maintenance on the portside powerplant were a factor." The expert continued: "Weather conditions were calm and clear, so weather-related causes are unlikely."
The National Transportation Safety Board has dispatched personnel to the location and will take charge of the investigation into the causes of the crash, though such inquiries may require years to complete.
