No fewer than nine people have died and 11 left injured after a freight aircraft crashed during departure from an international airport in Kentucky's largest city on Tuesday night.
Aviation experts suggest the plane crashed due to one engine failed and a second seemed compromised during take-off.
The exact cause remains unknown what caused the plane to crash, prompting a huge explosion to ignite after it failed to take-off from the runway. Footage showed fire had already engulfed a single wing of the aircraft while it was attempting to take off, potentially spreading through the plane and caused the explosion, or the jet could have caught fire after colliding with an object on the ground.
What is apparent is that the 144,000 litres of fuel on board the trijet aircraft required for the journey likely escalated the fire, which quickly spread to several buildings past the airstrip and burned for hours.
How did it start?
UPS uses Louisville Muhammad Ali International Airport as a distribution hub for its worldwide network and its designated flight was beginning of a 6,920 kilometer journey to Hawaii's capital when the cargo plane initiated departure.
Data from flight monitoring services indicates the plane started moving along the 17R runway at around 17:15 local time and managed to reach a maximum velocity of 344km/h.
But verified footage shows that by the time the plane reached this speed a fire had completely engulfed its left wing and the aircraft failed to gain altitude before the enormous detonation.
Authorities issued a shelter-in-place order to local residents and dispatched numerous fire crews to the scene.
The state's governor confirmed particulars seen in CCTV footage that depict the plane traveling just metres off the ground before a intense light consumed the aircraft. It is then seen slamming into the ground as a massive fire explosion ignites surrounding it about a minute after departure.
Authenticated footage recorded by motorists on a nearby highway showed the fire rising into the air while subsequent recordings showed smoke billowing from the scene.
Overhead photographs shown on local media showed wreckage scattering across the airstrip and landing on the roofs of at least two local businesses.
What could have caused the crash?
ATC transmissions reviewed are mostly unclear and filled with static so no clear dialogue can be discerned about the crash as it unfolded.
But analysts proposed that a dramatic failure of two of the engines may have been responsible for the disaster.
The trijet cargo aircraft employs three powerplants. Two are mounted under the airfoils, and a third is built into the tail at the base of the vertical stabilizer.
Footage confirmed showed a fire consuming the port wing of the plane, which then leaned leftward as it tried to achieve altitude and take-off.
Multiple specialists separately proposed the left engine may have detached from the plane following a technical or physical breakdown.
Separate images taken after the crash displayed a charred engine sitting on the grass adjacent to the airstrip.
A retired airline pilot and aircraft safety specialist said that it was "almost unheard of" for an powerplant to separate in flight.
The expert recalled the 1979 aviation disaster tragedy, in which 273 people were fatally injured after the aircraft's powerplant separated as it took off from O'Hare International Airport. Engine components had been damaged when it was replaced on the plane, but the specialist said it was premature to determine whether a similar fault led to the engine to detach on the MD-11.
The expert said the freight aircraft would have been able to fly with only two powerplants but the destruction caused by the wing blaze was likely so great it caused the plane's third engine to lose thrust.
"With such a catastrophic event we cannot determine additional destruction was caused when the engine came adrift," he said.
A different aircraft specialist said the video evidence seemed to indicate the remaining powerplant had been damaged because it expelled a burst of smoke. The damage could have occurred while it was struck by wreckage from the blaze and the engine detaching.
"The tail-mounted powerplant that expelled a puff of smoke appears to wind down almost immediately afterwards," the specialist stated. "That left only the starboard powerplant producing thrust, resulting in a significant thrust asymmetry and making the plane incapable to achieve altitude.
"Failing two powerplants while departing leaves the aircraft with only a fraction of its thrust and little chance of staying airborne, particularly under maximum take-off weight," the expert continued.
Why did the crash cause such damage?
Post-accident videos showed a situation of total disorder with numerous blazes burning across a extensive area of the site and smoke rising upward.
The aircraft, which was three decades old and had been operated for passenger travel until 2006, had already completed one return journey from Louisville to the East Coast on Tuesday.
It has not been confirmed which goods was on board the Hawaii-bound aircraft, though officials stated the aircraft didn't contain anything that would create a heightened risk of environmental hazard.
"This was a long-haul cargo flight from Louisville to Honolulu, so the MD-11 was carrying a significant fuel quantity," an expert commented. "The substantial fuel quantity not only diminished capability but also accounts for the large fireball observed post-accident."
Officials told reporters that the plane was carrying 38,000 gallons of jet fuel for the long journey when it went down. The blaze was probably intensified on the ground because the aircraft slammed into a fuel processing facility adjacent to the airfield.
A specialist said authorities will concentrate on the origin of the blaze, and "whether debris struck the centre engine, and if previous repairs on the portside powerplant played a role." He added: "Atmospheric conditions were favorable, so environmental factors are unlikely."
The National Transportation Safety Board has dispatched personnel to the location and will now lead the probe into the accident's origins, though such inquiries may require years to finalize.
