Ms Negroni believes the plane suffered a sudden depressurisation while the experienced captain was taking a bathroom break.
She wrote last year: “I find it logical to assume that Zaharie visited the business-class bathroom near the flight deck that is also used by the flight crew.
“In this and all the airline’s 777’s bathrooms, a drop-down mask is there to provide oxygen in the case of depressurisation.
Captain Zaharie Shah may not have been confident in his co-pilot
Malaysia Airlines flight 370 went missing five years ago
’m guessing Zaharie wasn’t confident in Fariq’s ability to handle the emergency
“Imagine what it would have been like for Zaharie to see the yellow plastic cup bob down after depressurisation.
“He would have been momentarily rattled, but with his experience, he would have realised immediately what had happened and what needed to be done.”
However, rather than stay in the bathroom with an oxygen mask, Ms Negroni believes the captain headed back to the cockpit.
She claims he made this choice as he did not think his co-pilot could handle the situation.
She added: “He had to make a choice – try to get back to the cockpit without supplemental oxygen, or remain in the bathroom and wait for Fariq to get the plane to a lower altitude and rejoin him on the flight deck.”
239 people were on board the doomed flight
“I’m guessing Zaharie wasn’t confident in Fariq’s ability to handle the emergency and chose the former course of action.
“But the effects of oxygen deprivation would have been crippling for Zaharie, air would have been exploding from his respiratory and digestive systems.
“He would have struggled to get out of the bathroom. Perhaps he looked for a flight attendant or a portable oxygen tank.
“Perhaps he stopped to assess the situation in the cabin. Perhaps he retained focus and moved quickly to the cockpit door.”
However, Ms Negroni believes the captain may have felt heightened effects over lack of oxygen.
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She continued: “The distance between the bathroom and the cockpit s just a few steps, but like Fariq, Zaharie was a smoker and probably more susceptible to the effects of oxygen deprivation.
“If he got out of the bathroom, if he got down the narrow corridor, if he got to the door of the cockpit without losing consciousness, another challenge would have awaited him.
“The cockpit door unlocks automatically when cabin altitude is lost. Would Zaharie have remembered that?
“Or did he, by force of habit, stop outside the door and enter the code?
“Did he lose precious seconds struggling to remember a passcode he did not need?”
Families hope they will soon get the answers
Ms Negroni also detailed her entire theory on what she belives happened while Zaharie was apparently out of the cockpit.
She wrote: “My theory is that an electrical malfunction knocked out the systems on the Boeing 777 and that the plane lost pressurisation incapacitating the pilots.
“Whatever happened, it could not have caused damage serious enough to affect the airworthiness of the plane, since it flew on until running out of fuel many hours later.
“Likely, the men in the cockpit were overcome by the altitude sickness known as hypoxia, which robbed them of the ability to think clearly and land the plane safely.
“Many of the links in the bizarre chain of events that night can be explained by hypoxia, because past cases have shown how rapidly those who fall victim to it turn imbecilic.”
However, this idea is just one theory among hundreds of others proposed over the last five years.
While more outrageous ideas have claimed the plane was a “flying bomb” due to the cargo of five tonnes of mangosteens and 221kg of lithium-ion batteries.
However, we are still no closer to knowing the truth.