The head of Malaysia’s civil aviation regulator has resigned after an official report found failings in air traffic control when flight MH370 disappeared.

In a long-awaited report released on Monday, the official investigation team pointed to numerous lapses by air traffic controllers in both Malaysia and Vietnam, which ensured the plane was missing for about 20 minutes before an alert was sent.

Play Video 0:43 MH370 report: 'We cannot exclude the possibility of a third party or unlawful interference' – video

While the report offered no new information about the reasons for the plane’s disappearance or where it may have fallen, one of the few conclusive findings was that air traffic control failed to initiate standard “emergency phases” after the flight, which was travelling from Kuala Lumpur to Beijing with 239 people onboard, vanished from radar displays as it entered Vietnamese airspace.

Azharuddin Abdul Rahman, the director general of the department of civil aviation, said the report had found that the air traffic control did not comply with standard operating procedures.

“Therefore, it is with regret and after much thought and contemplation that I have decided to resign as the chairman of Civil Aviation Authority of Malaysia effective 14 days from the date of the resignation notice which I have served today,” he said in a statement.

The disappearance of flight MH370 more than four years ago remains one of aviation’s greatest mysteries. Despite two major searches involving more than 20 countries, no sign of the Boeing 777-200 has been found in a 46,000 sq mile (120,000 sq km) search zone in the Indian Ocean, except for three wing fragments, which washed ashore. The search officially came to an end in May when the private company Ocean Infinity, which offered to look for the plane on a “no find, no fee” basis admitted defeat, and the Malaysian government chose not to renew the contract.

In the 495-page report, investigators said they still did not know why the plane vanished, leaving families of those onboard – who have long awaited closure – devastated and highly critical of the investigation.

The safety investigating team, however, did officially conclude that the course of the Malaysia Airlines aircraft was changed manually, rather than due to autopilot mechanisms.

After investigations demonstrated that the pilot had been both adequately trained and under no pressures or mental strain that could have led him to crash the plane on purpose in a suicide mission, Dr Kok Soo Chon, the investigator in charge of the MH370 safety investigation, said “interference by a third party” could be a reason the jet suddenly diverted off course.

The transport minister, Anthony Loke, said on Monday that “the aspiration to locate MH370 has not been abandoned” and vowed to take action against any misconduct committed based on the findings.