Fresh theories have emerged on the third anniversary of the disappearance of Malaysia Airline Flight MH370.

A lawsuit filed in the US against Boeing alleges that an electrical fire could have caused the Boeing 777 plane to depressurise, incapacitating the crew and causing the transponder to fail. It claims that this led to the plane flying undetected until it ran out of fuel and crashed.

The flight which took off from Kuala Lumpur for Beijing on 8 March 2014, has yet to be found, despite a massive two-year search operation. The search operation was called off in January 2017.

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The second theory, floated by volunteer investigator and the Director of Investigations of Canadian Human Rights NGO ASOVE, Andrew Milne, claims that there was an unaccounted-for passenger on board the flight.

Milne, who has set up an appeal for a £1.3m fund to search the Bay of Bengal for the aircraft, claims that 228 seats were sold two hours before the flight took off.

Speaking to express.co.uk, he said: "The 228 does not include the 2 children who sit with their parents. It has been claimed that four people did not board the plane. That would make the final number of seats used down at 224."

After taking into account the two children and 12 crew members, there should be only 238 missing people and not 239 as the official record states.

"So now we have an 'extra' person on board MH370," he said.

Milne added: "The extra passenger likely acted in conjunction with larger external operational support to take full command and control of the cockpit of MH370."

The newspaper said a spokesperson for the MH370 safety investigation team has acknowledged that it is aware of the discrepancy in the number of people on board the aircraft.

The spokesperson said that the computerised load sheet which was transmitted about two hours before the aircraft took off listed 228 passengers. "The actual figures can differ from what is transmitted on the load sheet due to last-minute changes," he said

Neither Malaysia Airlines nor the investigating team could be immediately contacted to verify how many people were on board the missing aircraft.

Lawsuit blames electrical fault

The lawsuit filed in the US District Court in South Carolina by Gregory Keith, a special administrator representing family members of 44 victims, gives a long list of manufacturing defects in the missing airline that had been reported before the airline disappeared.

Newscom.au said the allegations backs the "zombie plane" theory that the aircraft flew on autopilot until it ran out of fuel after its avionic systems were destroyed.

"The defects caused and/or allowed a massive and cascading sequence of electrical failures on board the lost plane which disabled vital systems, including the lost plane's ACARS (Aircraft Communications Addressing and Reporting System) and Mode S Transponder.

"Boeing elected to equip the lost plane with these ineffective ELTs (Emergency Locator Transmitters) and ULBs (Underwater Locator Beacons) despite the presence of other readily available and reasonable alternative technologies that would have allowed the lost plane, the FDR (Flight Data Recorder), and the CVR (Cockpit Voice Recorder) to be tracked in real-time anywhere in the world, especially in cases of crashes, disruption of communications and other losses," the legal papers say.

Neither Malaysia Airlines nor the Malaysian government have yet to respond to these new theories.

Malaysia Airlines Flight MH370