A Royal New Zealand Air Force P-3 Orion aircraft searches for missing Malaysia Airlines Flight MH370 . (AP Photo/Rob Griffith, File)

As leads dwindle and pressure mounts on international authorities to unearth some clue that would locate the missing Malaysian jetliner, U.S. officials have now turned to an unsettling possibility. The pilot killed himself.

“You have to ask the question,” one U.S. aviation official, who was not authorized to discuss the matter publicly, told the Post on Monday.

“Everything is on the table,” Steve Wallace, the former head of the FAA accident investigation division, told Bloomberg.

While incredibly rare for a pilot to kill himself — and everyone else on a plane — there is both national and international precedent for what experts call “aircraft-assisted pilot suicides.” According to Federal Aviation Administration data, 24 American pilots have killed themselves while flying their planes in the last two decades. Twenty-three of those pilots intentionally crashed their craft, and one student pilot jumped out of his plane mid-flight.

All of the pilots who killed themselves were male and middle-aged.

While none of of the American pilots who killed themselves were flying a big commercial aircraft, it has happened elsewhere.

In November of last year, a Mozambique Airlines E-190 jet  carrying 33 passengers went down in Namibia. No one survived the crash, which became the subject of great mystery because the plane was only one year old, flown by an experienced pilot, in good weather.

According to cockpit voice recordings reported by the International Business Times, the co-pilot left to use the bathroom, and when he returned, he found the door shut. Inside, the pilot had switched the plane’s altitude reading from 38,000 feet to ground level, IBT reports. Recordings show someone pounded on the door to the cockpit as the plane plummeted. Investigators later concluded the plane had crashed because of “intentional actions by the pilot.”

Echoes of that tragedy were found in a pair of late 1990’s crashes. In 1997, more than 100 people were killed with a pilot or crew member forced a plane to crash in Indonesia.  Two years later, a Cairo-bound airliner that plummeted into the Atlantic Ocean off Nantucket in 1999. All 217 passengers and crew were killed. During the plane’s tailspin, its pilot, Gamal al-Batouti whispered the Arabic phrase, “I rely on God,” — traditionally uttered moments before death.

Depression appears to be the leading cause of aircraft-assisted suicides, and in 2010, the FAA did away with a generations-old ban on pilots taking anti-depressants . The aviation agency, which has mental health restrictions for pilots, now can issue certificates permitting pilots to take Prozac, Zoloft, Celexa, and Lexapro, CNN reports.

But only clues such audio recordings and blackbox data about the position of an aircrafts tailplanes can lead investigators to a conclusion that a pilot killed himself.

For the moment, then, the Malaysian Airlines suicide question will probably remain unanswered.