CANBERRA, Australia -- As police investigate the two pilots of a Malaysian passenger jet that disappeared more than a week ago, a possibility they must consider is that one of them committed suicide by deliberately crashing the plane.
While such incidents have happened before, the topic remains almost taboo, with investigators and officials reluctant to conclude that a pilot purposely crashed a plane in order to commit suicide even when the evidence appears compelling.
A dozen years ago, U.S. investigators filed a final report into the 1999 crash of EgyptAir Flight 990, which plunged into the Atlantic Ocean near the Massachusetts island of Nantucket, killing all 217 aboard. They concluded that when co-pilot Gameel El-Batouty found himself alone on the flight deck, he switched off the auto-pilot, pointed the plane downward, and calmly repeated the phrase "I rely on God" over and over, 11 times in total.
Yet while the National Transportation Safety Board concluded that the co-pilot's actions caused the crash, they didn't use the word "suicide" in the main findings of their 160-page report, instead saying the reason for his actions "was not determined." Egyptian officials, meanwhile, rejected the notion of suicide altogether, insisting instead there was some mechanical reason for the crash.
There was also disagreement over the cause of the crash of SilkAir Flight 185, which plunged into a river in 1997 during a flight from Jakarta, Indonesia, to Singapore, killing all 104 passengers and crew. A U.S. investigation found that the Boeing 737 had been deliberately crashed, but an Indonesian investigation was inconclusive.
Mozambique officials have been investigating a crash that killed 33 people in November. They say preliminary investigations indicate that the pilot of the Mozambican Airline plane bound for Angola intentionally brought it down, and they're continuing to look into his possible motives.
A 2014 study by the Federal Aviation Administration indicates that in the U.S. at least, flying remains a remarkably safe mode of transport and pilot suicide is a rare occurrence.
The study found that during the 10 years ending in 2012, just eight of 2,758 fatal aviation accidents in the U.S. were caused by pilot suicide, a rate of 0.3 percent. The report found that all eight suicides were men, with four of them testing positive for alcohol and two for antidepressants.
The cases ranged from a pilot celebrating his 21st birthday who realized a woman didn't want a relationship with him, to a 69-year-old pilot with a history of drinking and threatening suicide by plane. Seven of the cases involved the death of only the pilot; in the eighth case, a passenger also died.
"Aircraft-assisted suicides are tragic, intentional events that are hard to predict and difficult to prevent," the FAA's report found, adding that such suicides "are most likely under-reported and under-recognized."
In at least one case, a major international airline allowed a pilot who had expressed suicidal thoughts to continue flying. He flew nearly three more years, without incident, before he resigned in 1982 with severe obsessive-compulsive disorder, anxiety and depression.
The Sydney Morning Herald newspaper reported that the Workers Compensation Commission heard that the Qantas pilot struggled several times to resist an overwhelming urge to switch off the plane's engines. Once during a flight to Singapore, the pilot's hand moved "involuntarily" toward the start levers and he was forced to "immobilize his left arm in order not to act on the compulsion."
"He left the flight deck and, once he felt calm enough, returned to his seat," the newspaper reported.
After telling his colleagues of his urges, the newspaper said, the pilot was examined by several doctors and ultimately declared fit to fly.
Malaysia's government said police on Saturday searched the homes of both the pilot and the co-pilot of the missing Malaysia Airlines jet. It said police were examining an elaborate flight simulator taken from the home of 59-year-old pilot Zaharie Ahmad Shah.
Shah, and his first officer, 27-year-old Fariq Abdul Hamid, have now become the centerpieces of the investigation into the missing jet.
Shah is said to be a very experienced pilot with 33 years under his belt at the airline. Those who knew him said he liked his job so much, he made his own flight simulator in his home.
Hamid is a much less experienced pilot and has flown for Malaysia airlines for just over six years, officials said.
Police also are investigating engineers who may have had contact with the plane before it took off.
Mike Glynn, a committee member of the Australian and International Pilots Association, said Friday that he considers pilot suicide to be the most likely explanation for the plane's disappearance.
A pilot rather than a hijacker is more likely to be able to switch off the communications equipment, he said, adding that he thinks suicide was to blame in the EgyptAir and SilkAir crashes.
"The last thing that I, as a pilot, want is suspicion to fall on the crew, but it's happened twice before," Glynn said.
MORE: Final words from jet came after systems shutdown
CHRIS BRUMMITT and JIM GOMEZ, Associated Press
KUALA LUMPUR, Malaysia -- The final words from the missing Malaysian jetliner's cockpit gave no indication anything was wrong even though one of the plane's communications systems had already been disabled, officials said Sunday, adding to suspicions that one or both of the pilots were involved in the disappearance.
As authorities examined a flight simulator that was confiscated from the home of one of the pilots and dug through the background of all 239 people on board and the ground crew that serviced the plane, they also were grappling with the enormity of the search ahead of them, warning they needed more data to narrow down the hunt for the aircraft.
The Malaysia Airlines Boeing 777 took off from Kuala Lumpur at around 12:40 a.m. on March 8, headed to Beijing. On Saturday, Malaysia's government confirmed that the plane was deliberately diverted and may have flown as far north as Central Asia, or south into the vast reaches of the Indian Ocean.
Authorities have said someone on board the plane first disabled one of its communications systems - the Aircraft and Communications Addressing and Reporting System, or ACARS - at 1:07 a.m. Around 14 minutes later, the transponder, which identifies the plane to commercial radar systems, was also shut down. The fact that they went dark separately is strong evidence that the plane's disappearance was deliberate.
On Sunday, Malaysian Defense Minister Hishammuddin Hussein said at a news conference that that the final, reassuring words from the cockpit - "All right, good night" - were spoken to air traffic controllers after the ACARS system was shut down. Whoever spoke did not mention any trouble on board, seemingly misleading ground control.
Air force Maj. Gen. Affendi Buang told reporters he did not know whether it was the pilot or co-pilot who spoke to air traffic controllers.
Given the expanse of land and water that might need to be searched, the wreckage of the plane might take months - or longer - to find, or might never be located. Establishing what happened with any degree of certainty will likely need key information, including cockpit voice recordings, from the plane's flight data recorders.
The search area now includes 11 countries the plane might have flown over, Hishammuddin said, adding that the number of countries involved in the operation had increased from 14 to 25.
"The search was already a highly complex, multinational effort. It has now become even more difficult," he said.
The search effort initially focused on the relatively shallow waters of the South China Sea and the Strait of Malacca, where the plane was first thought to be. Hishammuddin said he had asked governments to hand over sensitive radar and satellite data to try and help get a better idea of the plane's final movements.
"It is our hope with the new information, parties that can come forward and narrow the search to an area that is more feasible," he said.
Malaysia is leading the multinational search for the plane, as well as the investigation into its disappearance.
In the United States, Dan Pfeiffer, senior adviser to President Barack Obama, told NBC's "Meet the Press" that the FBI was supporting the criminal probe.
Rep. Peter King, who is chairman of the House Homeland Security subcommittee on counterterrorism and intelligence, said on ABC's "This Week" that so far "there's nothing out there indicating it's terrorists."
Investigators are trying to answer these questions: If the two pilots were involved in the disappearance, were they working together or alone, or with one or more of the passengers or crew? Did they fly the plane under duress or of their own volition? Did one or more of the passengers manage to break into the cockpit, or use the threat of violence to gain entry and then pilot the plane? And what possible motive could there be for flying off with the plane?
Malaysia's police chief, Khalid Abu Bakar, said he requested countries with citizens on board the plane to investigate their background, no doubt looking for any ties to terrorist groups, aviation skills or evidence of prior contact with the pilots. He said that the intelligence agencies of some countries had already done this and found nothing suspicious, but that he was waiting for others to respond.
The government said police searched the homes of both pilots on Saturday, the first time they had done so since the plane went missing. Asked why it took them so long, Khalid said authorities "didn't see the necessity in the early stages."
Khalid said police confiscated the elaborate flight simulator that one of the pilots, Zaharie Ahmad Shah, had built in his home and reassembled it in their offices to study it for clues.
Zaharie, 53, who has three grown children and one grandchild, had previously posted photos online of the simulator, which was made with three large computer monitors and other accessories. Earlier this week, the head of Malaysia Airlines said this was not in itself cause for any suspicion.
Malaysian police are also investigating engineers and ground staff who may have had contact with the plane before it took off, Khalid said.
ACARS is used to send information about the plane's engines and other parts to the airline. Even though it was disabled on Flight 370, it continued to send out faint hourly pulses that were recorded by a satellite. The last "ping" was sent out at 8:11 a.m. - 7 hours and 31 minutes after the plane took off. It placed the jet somewhere in a huge arc as far north as Kazakhstan in Central Asia or far into the southern Indian Ocean.
While many people believe the plane has crashed, there is a very small possibility it may have landed somewhere and be relatively intact. Affendi, the air force general, and Hishammuddin, the defense minister, said it was possible for the plane to "ping" when it was on the ground if its electrical systems were undamaged.
Australia said it was sending one of its two AP-3C Orion aircraft involved in the search to remote islands in the Indian Ocean at Malaysia's request. The plane will search the north and west of the Cocos Islands, a remote Australian territory with an airstrip about 1,200 kilometers (745 miles) southwest of Indonesia, military chief Gen. David Hurley said.
Given that the northern route the plane may have taken would take it over countries with busy airspace, most experts say the person in control of the aircraft would more likely have chosen the southern route. The southern Indian Ocean is the world's third-deepest and one of the most remote stretches of water in the world, with little radar coverage.
Malaysian officials and aviation experts said that whoever disabled the plane's communication systems and then flew the jet must have had a high degree of technical knowledge and flying experience, putting one or both of the pilots high on the list of possible suspects.
Zaharie, the pilot, was a supporter of a Malaysian opposition political party that is locked in a bitter dispute with the government, according to postings on his Facebook page and a friend, Peter Chong, who is a party member.
Chong said that he last saw Zaharie a week before the pilot left on the flight for Beijing, and that they had agreed to meet on his return to organize a shopping trip for poor children.
"If I am on a flight, I would choose Captain Zaharie," he said. "He is dedicated to his job, he is a professional and he loves flying."
Associated Press writers Ian Mader and Eileen Ng in Kuala Lumpur and Kristen Gelineau in Sydney contributed to this report.