Malaysia Airlines is investigating an Australian television report that the co-pilot on its missing flight had invited two women to stay in the cockpit for the duration of a flight two years ago.
Jonti Roos spoke about her flight on A Current Affair, which aired photographs showing the women in the cockpit.
The airline said it wouldn't comment about the report until its inquiry was complete.
Roos said she and her friend were allowed to stay in the cockpit during the entire one-hour flight in December 2011, from Phuket, Thailand, to Kuala Lumpur. Fariq Abdul Hamid and the other pilot talked to them, smoked and posed for photos, she said.
In other breaches of international protocol, it has emerged that Malaysia Airlines has twice been convicted of allowing passengers using stolen passports to fly on their planes.
In 2007, two passengers using passports taken during a burglary in Auckland were allowed to board a flight, despite a computer database warning that flagged the documents as suspect.
As the passengers were checking in, a staff member received an automatically generated directive from New Zealand's Advanced Passenger Processing (APP) system not to board the pair, but ignored the instruction and allowed them on the flight.
The airline received a 12-month suspended sentence over the incident, according to Immigration New Zealand spokesman Marc Piercey.
Watch: What we know about Malaysia Airlines flight MH370
Five years later, the carrier was again found guilty of a similar offence, when a check-in staff member generated a false passport number to allow a passenger to board, despite an APP warning from New Zealand. A New Zealand court fined the Malaysian carrier NZ$5,500 (HK$36,000).
The traveller was a Malaysian national and was the holder of a passport bearing the same number as a passenger on a previous international flight who was arrested in Thailand. It is unclear why the Malaysian was not stopped.
Malaysia Airlines declined to comment.
Two Iranian passengers travelling on flight 370 had boarded with stolen passports.
Security and risk consultant Steve Vickers, a former head of the Hong Kong police criminal-intelligence bureau, said New Zealand had a particularly effective system, adding that "security checks were a matter for governments, rather than airlines".
"Malaysia Airlines hasn't been the only airline subject to prosecutions around the region," he said.
Cathay Pacific, Chile's LAN Airlines and Aerolineas Argentinas have been fined a combined total of HK$200,000 under similar prosecutions by New Zealand.