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No fewer than nine individuals have died and 11 left injured after a UPS cargo plane crashed while taking off from a major air hub in Kentucky's largest city on Tuesday night.

Aviation experts suggest the aircraft went down after a single engine malfunctioned and another appeared to be damaged 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 plane while it was attempting to take off, which may have spread across the aircraft and triggered the blast, 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 on board the trijet aircraft needed for the flight probably intensified the fire, which rapidly extended to several buildings beyond the runway and burned for hours.

How did it start?

The shipping giant operates from the Louisville air hub as a logistics center for its worldwide network and its Flight 2976 was beginning of a 4,300 mile journey to Honolulu in Hawaii when the freight aircraft initiated departure.

Tracking information from flight monitoring services indicates the plane began to taxi along the 17R runway at around 17:15 local time and attained a top speed of 344km/h.

But verified footage demonstrate that when the plane reached this speed a blaze had fully consumed its left wing and the aircraft failed to gain altitude before the massive explosion.

Authorities activated a local safety directive to local residents and dispatched hundreds of firefighters to the scene.

The state's governor verified details seen in CCTV footage that shows the plane traveling just feet above the surface before a bright flash consumed the aircraft. It is then seen slamming into the ground as a massive fire explosion erupts around it about a minute after departure.

A verified clip recorded by motorists on a nearby highway showed the fire rising into the air while subsequent recordings revealed smoke billowing from the scene.

Aerial images broadcast by regional news outlets depicted wreckage scattering across the airstrip and landing on the roofs of multiple nearby establishments.

Potential causes of the accident

ATC transmissions reviewed are largely garbled and full of interference so no clear dialogue can be heard about the crash as it developed.

However, experts proposed that a catastrophic malfunction of two of the engines may have been the cause of the disaster.

The trijet cargo aircraft employs three engines. Two are mounted under the airfoils, and a third is positioned in the tail at the base of the vertical stabilizer.

Footage confirmed revealed a blaze engulfing the port wing of the aircraft, which then tilted to the left as it attempted to gain lift and become airborne.

Multiple specialists independently suggested the portside engine may have separated from the plane following a mechanical or structural failure.

Separate images taken after the crash showed a charred engine resting on the turf next to the runway.

An experienced former aviator and aircraft safety specialist said that it was "extremely rare" for an powerplant to separate in flight.

He referenced the 1979 aviation disaster tragedy, in which 273 people were fatally injured after the plane's engine detached as it took off from O'Hare International Airport. Parts of the engine had been compromised when it was installed on the aircraft, but the expert stated it was too early to say whether a similar fault led to the engine to detach on the MD-11.

The expert said the cargo plane would have been able to fly with just two engines but the damage caused by the fire on the left wing was likely so great it caused the plane's third engine to lose thrust.

"Given the severe nature of the incident we cannot know additional destruction was done when the engine came adrift," the expert commented.

Another aviation expert said the video evidence appeared to show the remaining powerplant had been damaged because it released smoke. The damage could have occurred while it was struck by wreckage from the fire and the engine detaching.

"The tail-mounted powerplant that released smoke appears to wind down right after," the expert said. "This left just the starboard powerplant generating power, resulting in a severe power imbalance and leaving the aircraft unable to gain height.

"Failing two powerplants during take-off leaves the aircraft with only a third of its power and minimal opportunity of maintaining flight, particularly under maximum take-off weight," the specialist continued.

Reasons for extensive destruction

Footage from the aftermath showed a situation of total disorder with numerous blazes burning across a extensive area of the site 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 return journey from Louisville to the East Coast on the same day.

Authorities haven't verified what cargo was on board the Hawaii-bound aircraft, though authorities stated the aircraft didn't contain anything that would create a heightened risk of contamination.

"This involved extended freight transport from Kentucky to Hawaii, so the trijet was carrying a lot of jet fuel," an expert commented. "The substantial fuel quantity not only diminished capability but also explains the massive explosion observed post-accident."

Authorities told reporters that the aircraft was transporting 144,000 litres of fuel for the long journey when it crashed. The blaze was probably intensified on the surface because the aircraft slammed into a fuel processing facility adjacent to the airfield.

The expert said authorities will concentrate on how the initial fire began, and "whether debris struck the centre engine, and if previous repairs on the left engine were a factor." He added: "Weather conditions were calm and clear, so weather-related causes are unlikely."

The National Transportation Safety Board has dispatched personnel to the site and will take charge of the probe into the causes of the crash, though such inquiries may require years to complete.