New Zealand pilots have been permanently grounded after testing revealed concerns about their medical fitness to fly, with some suspended because of depression, the aviation regulator has confirmed.
Commercial pilots are subject to rigorous psychological tests designed to weed out unstable individuals, who pose a potential risk to passenger safety.
The Civil Aviation Authority said some pilots' licences had been suspended because of medical fitness, which can include psychological health concerns, though such cases were rare.
The monitoring process has numerous checks and balances, but an industry expert warns the system is not foolproof.
"Pilots like anyone else have problems in their life and that can affect their performance," New Zealand Airline Pilots Association technical officer Dave Reynolds said.
"People do go off the rails."
Authorities investigating the disappearance of Malaysia Airlines Flight 370 are probing the psychological backgrounds of pilots and crew.
A fellow pilot told the Herald Captain Zaharie Ahmad Shah was in no state to fly the day the flight disappeared and could have taken the Boeing 777 for a "last joyride" after separating from his wife.
Mr Reynolds said Kiwi pilots operating commercial aircraft are regularly assessed for physical and mental health under a three-tier monitoring regime, involving the Civil Aviation Authority, airlines and peer support.
Pilots are assessed at least once a year by specialist aviation doctors and also undergo psychometric tests to assess psychological fitness.
The doctors are legally bound to "flag up" any concerns to the regulator and airline employer, and a pilot's licence can be immediately revoked.
Pilots are also monitored in the cockpit by flight inspectors and undergo high-stress exercise scenarios every six months in flight simulators to test their ability, for instance, trying to safely land a badly disabled jet.APNZ