No fewer than nine people have died and 11 left injured after a freight aircraft crashed while taking off from an international airport in Kentucky's largest city on Tuesday evening.
Aviation experts believe the plane crashed after one engine failed and a second seemed compromised while lifting off.
The exact cause remains unknown why the aircraft failed, prompting a huge explosion to ignite after it failed to take-off from the airstrip. Footage revealed flames were consuming a single wing of the plane during its takeoff attempt, potentially spreading across the aircraft and caused the explosion, or the plane might have ignited after colliding with an object on the ground.
What's clear is that the 144,000 litres of jet fuel on board the trijet aircraft needed for the flight likely escalated the blaze, which rapidly extended to multiple structures past the airstrip and continued burning for hours.
How did it start?
The shipping giant uses Louisville Muhammad Ali International Airport as a distribution hub for its global operations and its Flight 2976 was beginning of a 4,300 mile trip to Honolulu in Hawaii when the freight aircraft attempted to take off.
Tracking information from flight monitoring services shows the plane started moving along the designated runway at around 17:15 local time and attained a top speed of 214mph.
However, confirmed videos demonstrate that by the time the plane reached this speed a fire had completely engulfed its port side and the plane couldn't climb before the massive explosion.
Authorities issued a shelter-in-place order to area inhabitants and scrambled numerous fire crews to the location.
The state's governor confirmed details seen in CCTV footage that shows the aircraft flying just feet above the surface before a bright flash engulfed the plane. It is then observed crashing onto the terrain as a massive fire explosion erupts around it about a minute into its journey.
A verified clip recorded by motorists on a nearby highway showed the fire rising into the air while subsequent recordings showed smoke pouring from the area.
Aerial images broadcast by regional news outlets depicted wreckage scattering across the airstrip and falling onto the tops of at least two local businesses.
Potential causes of the accident
ATC transmissions examined are mostly unclear and full of interference so no clear dialogue can be heard about the crash as it developed.
However, experts suggested that a dramatic failure of multiple engines may have been responsible for the tragedy.
The trijet cargo aircraft employs three powerplants. Two are mounted under the airfoils, and a third is positioned in the tail at the bottom of the tail fin.
Video verified revealed a fire consuming the port wing of the plane, which then leaned leftward as it tried to achieve altitude and become airborne.
Two experts independently suggested the left engine may have separated from the plane following a mechanical or structural failure.
Additional photographs taken after the crash displayed a charred engine sitting on the grass next to the runway.
A retired airline pilot and aviation safety expert said that it was "almost unheard of" for an powerplant to separate in flight.
The expert recalled the 1979 American Airlines Flight 191 tragedy, in which 273 people were fatally injured when the aircraft's powerplant separated as it departed from Chicago's major airport. Parts of the engine had been damaged when it was replaced on the plane, but the expert said it was premature to determine whether a similar fault led to the engine to detach on the trijet.
The specialist said the freight aircraft would have been capable of flight with just two engines but the destruction resulting from the fire on the left wing was probably extensive enough it resulted in the plane's third engine to fail to produce power.
"Given the severe nature of the incident we cannot determine what other damage was done when the powerplant separated," he said.
A different aircraft specialist observed the footage seemed to indicate the third engine had been damaged because it released smoke. The issue could have happened while it was pelted with debris from the fire and the engine detaching.
"The upper engine that released smoke seems to shut down almost immediately afterwards," the expert stated. "That left only the right engine producing thrust, creating a severe power imbalance and leaving the aircraft unable to achieve altitude.
"Failing two powerplants during take-off leaves the aircraft with only a third of its power and little chance of staying airborne, particularly under full departure mass," the specialist added.
Why did the crash cause such damage?
Footage from the aftermath revealed a scene of complete chaos with multiple fires burning across a extensive area of the site and smoke rising upward.
The plane, which was 34 years old and had been used as a passenger plane until 2006, had previously made one return journey from Louisville to Baltimore in Maryland on the same day.
It has not been confirmed what cargo was aboard the flight bound for Hawaii, though authorities stated the plane was not carrying anything that would pose an increased danger of environmental hazard.
"This was a long-haul cargo flight from Louisville to Honolulu, so the MD-11 was transporting a significant fuel quantity," a specialist commented. "That heavy fuel load not only diminished capability but also accounts for the large fireball observed post-accident."
Authorities informed media that the aircraft was transporting 38,000 gallons of fuel for the extended trip when it crashed. The fire was probably intensified on the ground because the aircraft slammed into a fuel recycling business adjacent to the airfield.
A specialist said authorities will concentrate on the origin of the blaze, and "whether debris struck the central powerplant, and whether earlier maintenance on the portside powerplant were a factor." He added: "Atmospheric conditions were favorable, so environmental factors are unlikely."
The National Transportation Safety Board has dispatched personnel to the site and will now lead the probe into the causes of the crash, though such inquiries may require years to complete.
