What caused Emirates flight to crash-land?

One firefighter dies but all passengers and crew escape
An airport firefighter was killed when an Emirates flight crash-landed in Dubai yesterday – but all 282 passengers and 18 crew were evacuated safely. An investigation is underway as to what caused the accident.
Dramatic images and video posted on media and social media show people leaving the plane via the escape routes before a fireball and flames destroy the fuselage.
It is too early to say what caused the accident, said Emirates’ chairman and chief executive Sheikh Ahmed Bin Saeed Al Maktoum afterwards, but he ruled out “anything in terms of a security issue at this stage”.
He praised the pilots and crew, who were the last to abandon the aircraft and showed a “maximum level of professionalism”. Aviation experts have said it was extraordinary there were no casualties.
“What we do know is that the aircraft slid along the runway without its undercarriage being down. We can see from the videos that one of the engines broke off, and the sliding along the runway on the bottom of the fuselage and the wings caused this very big fire,” aviation analyst and former pilot Sean Maffett tells Al Jazeera.
Another expert, Alex Macheras, said the incident was unusual based on flight tracking information.
“This aircraft was coming in on a steady and normal textbook approach to the airport, which is very congested. Looking at these shocking photos, the landing gear is nowhere to be seen.”
Flight EK521, a Boeing 777, was arriving on a routine flight from Thiruvananthapuram in Kerala, India. One passenger said the plane came down suddenly and bounced upwards.
Al Jazeera