MH370 was travelling from Kuala Lumpur to Beijing, China, on March 8, 2014 when the jet mysteriously vanished with 239 people on board. Captain Zaharie Shah was in control of the plane when it last communicated with air traffic control at 1:19am over the South China Sea. However, moments later, the plane vanished from civilian radar screens following a routine handover from Malaysian to Vietnamese channels.
Analysis of radar and satellite data shows that it suddenly changed course and flew back across Malaysia before turning south of Penang and then towards the southern Indian Ocean.
Some have claimed this move proves Mr Shah attempted an emergency landing, following an uncontrollable fire on board.
His sister Sakinab Shah believes there is more proof of this theory too.
In a final message sent from the plane, either the pilot or co-pilot is believed to have said “good night Malaysian three seven zero”.
However, Ms Shah believes this was her bother’s voice and the message was slurred.
In an interview with aviation expert Simon Gunson in 2016, Ms Shah claimed her brother suffered from hypoxia – a deficiency in the amount of oxygen reaching the brain.
Mr Gunson said in 2016: “It shook me to hear this as it made sense to me.
“A logical reason for the messages would be if there was electrical smoke in the avionics bay, called the MEC, causing the aircraft to automatically open a vent to evacuate smoke.
“Pilots would not have been alerted to any fire or smoke, nor interestingly to depressurisation, because the MEC override valve inhibits the cabin pressure warning on a Boeing 777.”
He added that he believed this oxygen deficiency eventually overcame Mr Shah, leaving the plane unattended, before spiralling out of control.
He said: “It seems increasingly likely that MH370 suffered a gradual decompression rather than a sudden decompression, or rather that it failed to properly pressurise in the climb.
“In theory had the Boeing 777 sensed a drop in duct pressure from the air conditioning system then an alarm should have sounded in the cockpit as the pressure in the cabin dropped to 14,000ft pressure altitude.
“To put it simply, MH370 flamed out from fuel exhaustion and fell into an uncontrolled, ever-accelerating spiral.
“This is a specific manoeuvre characteristic of hypoxia.”
The idea of a fire breaking out on board has been popular over the last five years.
US pilot and aviation engineer Bruce Robertson previously suggested the 221kgs of lithium-ion batteries in MH370’s cargo caught fire sending a cloud of deadly carbon monoxide into the cabin, forcing Mr Shah to try and save the doomed jet.
He said in 2015: “There you have it – no conspiracies, no evil intent, no fuzzy pictures.
“It was just a simple industrial accident that took a while to play out due to automation trying to save the situation.
“The wounded bird did its best to survive but it was not to be.
“Too much time and money has been wasted on a fruitless search in an area much further southwest.”
However, a report released in 2018 went out of its way to dismiss these claims.
The document, produced by The Malaysian ICAO Annex 13 Safety Investigation Team for MH370, said it was ”highly improbable”.
It reads: “There were concerns that the batteries could have produced hazardous fumes or in a worst-case scenario caused a short circuit and/or fire.”
After carrying out tests, Malaysia’s Science & Technology Research Institute for Defence was “convinced that the items tested could not be the cause in the disappearance of MH370,” the report claims.
The batteries were not registered as dangerous goods as their packaging adhered to guidelines.
They went through customs inspection and clearance before the truck was sealed and left the factory, but were not given any additional security screening before loaded onto the plane.