French prosecutors’ assertion that this week’s air crash of a German airliner into a rugged mountainside was a deliberate act of the co-pilot points to the possible need for a third pilot in airline cockpits, several aviation safety experts said Thursday.

“The flight deck is capable of accommodating three pilots and there shouldn’t ever be a situation where there is only one person in the cockpit,” said James Hall, a former chairman of the National Transportation Safety Board, referring to the “jump seats” in airliners.

Prosecutors said the co-pilot of the Germanwings Flight 9525 had apparently locked himself in the cockpit before the plane crashed into a mountainside in the Alps. The captain, who had left the cockpit, could be heard on the cockpit voice recorder demanding to be let back in. All 150 people aboard were killed.

Hall was head of the safety board in 1999 when the board investigated the crash of an EgyptAir plane into the Atlantic Ocean shortly after takeoff from John F. Kennedy International Airport in 1999. All 217 people on board died. The co-pilot had been left alone in the cockpit while another pilot used the restroom.

The safety board determined that crash was deliberate, saying the co-pilot could be heard uttering a Muslim prayer as he pointed the plane into the ocean. A separate investigation by Egyptian authorities found the crash was caused by mechanical failure of the aircraft’s elevator control system, but U.S. investigators ruled out a mechanical failure.

There have been a series of murder-suicide crashes over the past 30 years, and in each case they were committed by pilots alone in cockpits, said Ewan Wilson, a commercial pilot and author of a book theorizing that the disappearance of Malaysia flight 370 last year was a deliberate act.

“We can mitigate that immediately with the introduction of a third pilot,” he said. “We have to start planning for the rogue pilot element because it’s a clear and present danger and the traveling public wants that certainty.”

Howard Wheeldon, aviation analyst at Wheeldon Strategic Advisory Ltd., said a third pilot “has to be considered.”

The Germanwings crash “will lead to a change in thinking in what we need to do,” he said. “We cannot allow a situation like this to destroy confidence in the industry. If we have to consider a third pilot on each flight, then so be it.”

In the U.S., most airlines require that a flight attendant enter the cockpit before a pilot leaves for the restroom. The attendant remains there until the pilot returns, so that no pilot is left alone in the cockpit.

That has not generally been the practice of European airlines, although some companies such as Finnair, the Finnish national carrier, already require two crew members in the cockpit at all times. On Thursday, Europe’s third-largest budget airline, Norwegian Air Shuttle, said it will impose the same requirement.

Dan Elliott, an aviation consultant and former Federal Aviation Administration official, was skeptical of any new requirement for a third pilot, noting that the global airline industry is struggling to find enough qualified pilots to meet growing travel demands.

“There would be no justification on a safety basis with the current procedures we have (in the U.S.) today,” he said.

(AP)