Malaysia Airlines Flight 370 (MH370/MAS370) was a scheduled international passenger flight from Kuala Lumpur International Airport in Malaysia to Beijing Capital International Airport in China. On March 8, 2014, the flight vanished from the radar. What caused its removal is still unknown. When the Boeing 777-200ER, registered as 9M-MRO, was over the South China Sea about 38 minutes after takeoff, the crew last spoke with air traffic control (ATC). Minutes after it vanished from ATC's secondary monitoring radar screens, the aircraft was watched for a further hour by the Malaysian military's primary radar system. During that time, it veered westward from its intended flight path and crossed the Andaman Sea and the Malay Peninsula. 200 nautical miles (370 km; 230 mi) northwest of Penang Island in northwest Peninsular Malaysia, it was out of radar range.

The disappearance of Flight 370, which left all 227 passengers and 12 crew members presumed dead, was the deadliest incident involving a Boeing 777, the deadliest of 2014, and the deadliest in Malaysia Airlines history until Malaysia Airlines Flight 17, which was shot down while flying over Ukraine four months later on July 17, 2014, surpassed it in three categories.

The lost aeroplane search turned into the most costly search in aviation history. Prior to a fresh examination of the aircraft's automated communications with an Inmarsat satellite revealing that the it had flown far southward across the southern Indian Ocean, it first concentrated on the South China Sea and the Andaman Sea. Since most of the passengers on board Flight 370 were of Chinese descent, the lack of official information in the days following the disappearance drew harsh condemnation from the Chinese public, especially from relatives of the passengers. In the western Indian Ocean, a number of wreckage fragments washed up on the coast in 2015 and 2016, with numerous of them being positively identified as having come from Flight 370.

In January 2017, after searching 120,000 km³ (46,000 sq mi) of ocean for three years without success, the Joint Agency Coordination Centre, which was in charge of the mission, ceased operations. Six months later, a second search, initiated in January 2018 by private contractor Ocean Infinity, proved fruitless as well. The Australian Transport Safety Bureau (ATSB), primarily relying on data analysis from the Inmarsat satellite with which the aircraft last communicated, initially suggested that a hypoxia event was the most likely cause given the available evidence; however, investigators have not come to a consensus regarding this theory. Possible hijacking scenarios were taken into consideration at different points during the investigation. These included crew involvement and suspicions about the cargo manifest of the aircraft. The media has also reported on a number of disappearance hypotheses related to the flight.

The final assessment from the Malaysian Ministry of Transport in July 2018 was not conclusive. It brought attention to Malaysian ATC's inability to get in touch with the aircraft soon after it vanished. Air transport sector safety recommendations and regulations referencing Flight 370 have been put into place to prevent a recurrence of the conditions surrounding the loss, even in the lack of a conclusive cause of disappearance. These include longer recording durations for flight data recorders and cockpit voice recorders, longer battery lives for underwater locator beacons, and revised guidelines for aircraft position reporting over open waters.

Less than an hour after takeoff, the Malaysia Airlines Boeing 777-200ER last spoke with ATC on March 8 at 01:19 MYT (17:19 UTC). The aircraft was over the South China Sea at the time. When it turned sharply away from its original northeastern course to head west and cross the Malay Peninsula, it was still being tracked by military radar. It continued on this course until it left the military radar's coverage at 02:22 while over the Andaman Sea, 200 nautical miles (370 km; 230 mi) northwest of Penang Island in northwest Malaysia. It vanished from ATC radar screens at 01:22 MYT. After the aircraft's signal was last picked up by secondary surveillance radar in the South China Sea and the Gulf of Thailand, the international search and rescue operation for the aircraft - which would turn out to be the most costly aviation search in history - was quickly expanded to include the Andaman Sea and the Strait of Malacca. The flight proceeded until at least 08:19 and flew south into the southern Indian Ocean, according to an analysis of satellite communications between the aircraft and Inmarsat's satellite communications network, albeit the exact location remains unknown. As the search effort started to focus more on the southern Indian Ocean on March 17, Australia took over leadership of the operation. The final location identified by the satellite communication was far from any potential landing places, the Malaysian government concluded on March 24. As a result, they declared that "Flight MH370 ended in the southern Indian Ocean."

A thorough survey of 120,000 km (46,000 sq mi) of sea bottom conducted between October 2014 and January 2017 in the vicinity of 1,800 km (1,100 km; 970 nmi) southwest of Perth, Western Australia, produced no sign of the aircraft. It has been shown that a number of pieces of marine debris that have been found off the coast of Africa and on Indian Ocean islands have been identified as parts of Flight 370. The first piece was found on Réunion on July 29, 2015. There are numerous theories on the disappearance of the aircraft because the majority of it has not been found.

Private US maritime exploration company Ocean Infinity launched a search on January 22, 2018, in the vicinity of 35.6°S 92.8°E, which was determined to be the most likely crash site based on a 2017 drift assessment. Following an earlier search effort, Malaysia formed a Joint Investigation Team (JIT) to look into the incident and collaborate with experts and foreign aviation authorities. In October 2017, Malaysia published the final report on Flight 370. Before the aircraft disappeared, neither the crew nor the communication systems of the aircraft transmitted a distress signal, any signs of inclement weather, or any technical issues. After an investigation, two people who were travelling with stolen passports were declared not to be suspects.

After exonerating everyone else on the aircraft from suspicion about potential reasons, Malaysian investigators named the pilot as the main suspect in the event that human interference caused the disappearance. The satellite data unit (SDU) of the aircraft lost power at some point between 01:07 and 02:03. Three minutes after the aircraft had departed the radar's detection range, at 02:25, the SDU connected to Inmarsat's satellite communication network. It was hypothesised, based on an examination of the satellite communications, that the aircraft passed north of Sumatra, turned south, and flew straight and true for six hours, running out of fuel.

With all 239 people lost, Flight 370 is the second-deadliest incident of Malaysia Airlines history and the second-deadliest incident involving a Boeing 777, trailing only Flight 17 in both categories. By the end of 2014, Malaysia Airlines had been renationalized due to financial difficulties that were made worse by a decline in ticket sales following the disappearance of Flight 370 and the downing of Flight 17. The Malaysian government was heavily criticised, particularly by China, for withholding information in the early weeks of the hunt.

The disappearance of Flight 370 exposed to the public the limitations of flight recorders and aircraft tracking, as well as the short battery life of underwater locator beacons - a problem that had been brought up approximately four years prior with the disappearance of Air France Flight 447, but had never been addressed. The International Civil Aviation Organisation responded to the disappearance of Flight 370 by establishing new guidelines for aircraft position reporting over open ocean, extending the recording time for cockpit voice recorders, and requiring new aircraft designs to have a method of retrieving the flight recorders or the data they contain before they submerge into the water, effective from 2020.

Ocean Infinity promised in March 2022 to start up its search again in 2023 or 2024, subject to Malaysian government consent. To be sure nothing was overlooked, Ocean Infinity was going over the data from their 2018 search in 2023. Oliver Plunkett, the CEO, intended to use Ocean Infinity's new Armada vessel to recommence the hunt in the summer of 2023.

Plunkett is purportedly in possession of the credible new evidence that Ocean Infinity was asked to provide by Malaysia's Transportation Minister, Wee Ka Siong, in order to resume the search. The families of the victims have been further incentivized to advocate for another search due to claims of unidentified new evidence.

Days before the tenth anniversary of the disappearance, in March 2024, Malaysia said that it would confer with Australia on cooperation on an additional Ocean Infinity team voyage.

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