The Royal Flying Doctor Service in Queensland says it had no option but to sack a pilot who failed a drug and alcohol test after the plane he was flying lost contact with air traffic control.
The pilot was forced to take the test after the incident, during which contact was lost for 13 minutes while the plane was carrying a nurse and two patients from Bundaberg to Brisbane.
Chief executive Nino di Marco says it is unclear if those on board knew something was wrong.
"At this stage, that's all subject to the investigation," he said.
"What we do know is that there was a 13-minute period where the aircraft did lose contact, so in terms of what happened, that is part of the investigation process." Mr Di Marco says the service has a zero-tolerance policy on drugs and alcohol.
"The two key areas of importance for us is patient welfare and employee safety and that's something that we value highly," he said.
"The fact that this is the first incident of its nature in the organisation's history, it's shocked and disappointed us."