No fewer than nine people have died and 11 others were hurt following a freight aircraft went down while taking off from an international airport in Kentucky's largest city on Tuesday evening.
Aircraft specialists believe the plane crashed after a single engine malfunctioned and a second seemed compromised while lifting off.
It is unclear why the aircraft failed, leading to a massive fireball to erupt after it failed to take-off from the runway. Video evidence revealed fire had already engulfed a single wing of the aircraft while it was attempting to take off, potentially spreading across the aircraft and caused the explosion, or the plane might have ignited upon hitting an object on the ground.
What is apparent is that the 38,000 gallons of jet fuel aboard the MD-11 jet needed for the flight likely escalated the blaze, which quickly spread to several buildings past the airstrip and continued burning for hours.
What initiated the incident?
UPS uses Louisville Muhammad Ali International Airport as a distribution hub for its global operations and its designated flight was at the start of a 4,300 mile journey to Hawaii's capital when the freight aircraft initiated departure.
Data from FlightRadar24 indicates the plane began to taxi along the designated runway at around 17:15 local time and attained a maximum velocity of 214mph.
But verified footage demonstrate that by the time the plane achieved this velocity a fire had completely engulfed its left wing and the plane couldn't climb before the enormous detonation.
Authorities activated a local safety directive to local residents and dispatched hundreds of firefighters to the scene.
The state's governor verified particulars seen in CCTV footage that depict the aircraft flying just feet above the surface before a intense light consumed the aircraft. It is then seen slamming into the terrain as a massive fire explosion ignites surrounding it about a minute after departure.
Authenticated footage recorded by drivers on adjacent roads displayed the flames erupting into the skyline while subsequent recordings revealed smoke billowing from the scene.
Overhead photographs shown on regional news outlets showed debris showering the runway and falling onto the tops of at least two local businesses.
Potential causes of the accident
Air traffic control communications reviewed are largely garbled and filled with static so no meaningful conversation can be heard about the incident as it developed.
But analysts suggested that a dramatic failure of multiple engines may have been the cause of the tragedy.
The trijet cargo aircraft employs three engines. Two are mounted under the airfoils, and a third is built into the rear section at the base of the vertical stabilizer.
Footage confirmed revealed 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 following a mechanical or structural failure.
Additional photographs captured post-accident displayed a burned powerplant resting on the grass next to the runway.
A retired airline pilot and aircraft safety specialist said that it was "extremely rare" for an engine to detach in flight.
He referenced the 1979 American Airlines Flight 191 disaster, in which 273 people were killed after the aircraft's powerplant separated as it took off from O'Hare International Airport. Engine components had been damaged when it was installed on the aircraft, but the specialist said it was too early to say whether a similar fault caused the powerplant separation on the trijet.
The specialist said the freight aircraft would have been capable of flight with only two powerplants but the damage resulting from the wing blaze was likely so great it resulted in the aircraft's remaining engine to lose thrust.
"With such a catastrophic event we cannot know additional destruction was done when the engine came adrift," he said.
Another aviation expert said the video evidence appeared to show the remaining powerplant had been compromised because it released smoke. The issue could have happened while it was struck by wreckage from the fire and the powerplant separation.
"The upper engine that released smoke appears to wind down right after," the expert said. "This left just the starboard powerplant producing thrust, resulting in a significant thrust asymmetry and leaving the aircraft unable to achieve altitude.
"Losing two engines during take-off leaves the aircraft with only a third of its power and minimal opportunity of staying airborne, especially at maximum take-off weight," the expert added.
Why did the crash cause such damage?
Footage from the aftermath revealed a scene of complete chaos with numerous blazes blazing across a large swathe of the location and smoke rising upward.
The aircraft, 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 Tuesday.
It has not been confirmed which goods was on board the flight bound for Hawaii, though officials said the aircraft didn't contain anything that would pose an increased danger of environmental hazard.
"This involved extended freight transport from Kentucky to Hawaii, so the trijet was transporting a significant fuel quantity," a specialist commented. "The substantial fuel quantity not only diminished capability but also accounts for the massive explosion observed post-accident."
Officials told reporters that the aircraft was carrying 144,000 litres of fuel for the extended trip when it crashed. The blaze was likely amplified on the ground because the plane crashed into a fuel processing facility next to the airport.
A specialist said investigators will now focus on how the initial fire began, and "if wreckage hit the centre engine, and whether earlier maintenance on the portside powerplant played a role." The expert continued: "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 investigation into the causes of the crash, though this can take up to two years to finalize.
