On March 8, 2014, flight MH370 left Kuala Lumpur Airport on route to Beijing, China, 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.
Radar and satellite data shows how the jet suddenly changed course and flew back across Malaysia before turning south of Penang and then towards the southern Indian Ocean.
Some investigators, including Christine Negroni, believe this change in direction by the jet proves an emergency broke out on board, such as a fire.
This is supported by a discovery made by an investigation team appointed by the Malaysian government in 2015 to probe the missing plane.
They found the emergency oxygen system on the flight deck of MH370 had to be repaired shortly before takeoff.
MH370 went missing in 2014
Captain Zaharie Shah was in charge
He knew there was a problem but didn’t have the brain processing power to act appropriately
A pressurisation fault was one of eight defects reported to maintenance staff the morning before the doomed flight took off, according to the team.
The report also disclosed that batteries on the flight data recorder had gone flat 15 months before the aircraft vanished – meaning that searchers would have had less chance of finding it even if they were in the right area.
It also stated that the 12-year-old Boeing 777 had been involved in an accident on the ground at Shanghai airport 19 months earlier that required “major repairs”.
The right wing tip was damaged when it collided with an Airbus A340-600 and the aircraft was grounded for almost two months.
The 600-page report offers no elaboration on that theory but does support the idea of some kind of fire on board.
This led the Australian Transport Safety Bureau, who headed up the search for MH370, to suggest that a catastrophic event on the aircraft such as oxygen starvation might have caused those aboard to become incapacitated.
It would then have continued flying on autopilot until the fuel finally ran out.
Ms Negroni has been a long-term supporter of this idea, citing the flight path as clear evidence.
She wrote on her blog in 2018: “To me, that insensible action [the turn] is a bright and shining clue that the pilots’ actions were illogical because they were incapable of logical thought.
“My scenario is that the plane depressurised at 35,000 feet.
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“The first officer, alone in the cockpit, put on his emergency oxygen mask but failed to get 100 percent oxygen under pressure which would be required to restore his intellectual acuity.
“Instead, with the insidious feeling of wellbeing that characterises hypoxia – or oxygen starvation – the pilot turned the plane back towards Kuala Lumpur.”
Ms Negroni went on to detail what she believed happened next.
She added: “He knew there was a problem but didn’t have the brain processing power to act appropriately.
“This explains why he turned in one direction then another before passing out as the plane headed into the world’s most remote sea.”
This theory is centred around the idea that the First Officer was in control of the plane when the disaster struck.
However, others – using the same hypoxia idea – have centred their beliefs around Mr Shah being in control.
Former pilot Christopher Goodfellow claims the change in route was carried out on purpose as the veteran captain attempted to land at Langkawi International Airport in Malaysia.
He wrote in a blog post in 2014: “The turn is the key here.
“Zaharie Shah was a very experienced senior captain with 18,000 hours of flight time.
We old pilots were drilled to know what is the closest airport of safe harbour while in cruise.
“Airports behind us, airports abeam us, and airports ahead of us – they’re always in our head, always.
“If something happens, you don’t want to be thinking about what are you going to do, you already know what you are going to do.”
However, hypoxia is just one theory among a mountain of others.
While more outrageous theories claim the plane was a “flying bomb” due to the cargo of five tonnes of mangosteens and 221kg of lithium-ion batteries.