No fewer than nine people lost their lives and 11 others were hurt after a freight aircraft went down during departure from an international airport in Kentucky's largest city on Tuesday evening.
Aircraft specialists 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, leading to a huge explosion to erupt after it failed to take-off from the airstrip. Video evidence showed fire had already engulfed a single wing of the aircraft while it was attempting to take off, which may have spread across the aircraft and triggered the blast, or the jet could have caught fire after colliding with an object on the ground.
What is apparent is that the 38,000 gallons of jet fuel on board the MD-11 jet required for the journey probably intensified the blaze, which rapidly extended to multiple structures past the airstrip and continued burning for hours.
What initiated the incident?
UPS operates from the Louisville air hub as a distribution hub for its global operations and its Flight 2976 was at the start of a 4,300 mile journey to Honolulu in Hawaii when the cargo plane attempted to take off.
Tracking information from FlightRadar24 indicates the plane began to taxi along the 17R runway at around 5:15 PM local and attained a maximum velocity of 344km/h.
But verified footage shows that by the time the plane reached this speed a blaze had fully consumed its left wing and the aircraft failed to gain altitude before the enormous detonation.
Authorities issued a local safety directive to area inhabitants and dispatched hundreds of firefighters to the location.
The state's governor confirmed particulars seen in CCTV footage that shows the aircraft flying just metres off the ground before a intense light consumed the aircraft. It is then observed crashing onto the terrain as a huge fireball ignites surrounding it about a minute into its journey.
Authenticated footage recorded by drivers on adjacent roads displayed the fire rising into the air while subsequent recordings showed smoke pouring from the area.
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
Air traffic control communications reviewed are largely garbled and full of interference so no clear dialogue can be heard about the crash as it developed.
But analysts suggested that a catastrophic malfunction of two of the engines may have been responsible for the tragedy.
The trijet cargo aircraft uses three engines. Two are mounted under the airfoils, and a third is positioned in the tail at the base of the vertical stabilizer.
Video verified showed a fire consuming the port wing of the aircraft, which then tilted to the left as it tried to achieve altitude and take-off.
Multiple specialists independently suggested the left engine may have separated from the plane after suffering from a technical or physical breakdown.
Separate images captured post-accident displayed a charred engine resting on the grass adjacent to the airstrip.
An experienced former aviator and aircraft safety specialist commented that it was "almost unheard of" for an engine to detach in flight.
He referenced the 1979 American Airlines Flight 191 tragedy, in which 273 people were killed after the aircraft's powerplant separated as it took off from O'Hare International Airport. Parts of the engine had been compromised when it was replaced on the plane, but the expert said it was too early to say whether a comparable issue caused the engine to detach on the trijet.
The expert said the cargo plane would have been able to fly with only two powerplants but the destruction caused by the fire on the left wing was probably extensive enough it resulted in the aircraft's remaining engine to fail to produce power.
"Given the severe nature of the incident we cannot know what other damage was done when the engine came adrift," the expert commented.
A different aircraft specialist observed the footage seemed to indicate the third engine had been compromised because it expelled a burst of smoke. The issue could have occurred while it was struck by wreckage from the fire and the powerplant separation.
"The upper engine that expelled a puff of smoke seems to shut down right after," the specialist stated. "This left just the starboard powerplant producing thrust, creating a severe power imbalance and making the plane incapable to achieve altitude.
"Losing two engines while departing results in only a fraction of its thrust and minimal opportunity of staying airborne, especially at maximum take-off weight," the specialist continued.
Why did the crash cause such damage?
Post-accident videos showed a situation of total disorder with multiple fires blazing across a large swathe of the location and smoke rising upward.
The plane, which was 34 years old and had been used as a passenger plane until 2006, had already completed one return journey from the Kentucky hub to the East Coast on Tuesday.
Authorities haven't verified what cargo was on board the flight bound for Hawaii, though authorities said the plane was not carrying anything that would create a heightened risk of contamination.
"This involved extended freight transport from Louisville to Honolulu, so the MD-11 was carrying a lot of jet fuel," an expert commented. "The substantial fuel quantity not only diminished capability but also accounts for the large fireball observed post-accident."
Authorities told reporters that the aircraft was carrying 144,000 litres of fuel for the long journey when it went down. The fire was likely amplified on the surface because the plane crashed into a fuel recycling business adjacent to the airfield.
A specialist said investigators will now focus on how the initial fire began, and "if wreckage hit the central powerplant, and if previous repairs on the left engine played a role." He added: "Weather conditions were calm and clear, 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 finalize.
