Airlines rushed on Thursday to change their rules so as to require a second crew member in the cockpit at all times, hours after French prosecutors suggested a co-pilot who barricaded himself alone at the controls of a jetliner had crashed it on purpose.
The United States already requires two crew members to be in the cabin at all times, but many other countries do not, allowing pilots to leave the flight deck, for example to use the toilet, as long as one pilot is at the controls.
That is precisely what French prosecutors suspect happened on the Germanwings flight on Tuesday. They say Andreas Lubitz, 27, locked the captain out and appears to have set the controls to crash into a mountain, killing all 150 people on board.
Airlines including Norwegian Air Shuttle, Britain's easyJet, Air Canada, Air New Zealand and Air Berlin all said within hours that they had introduced a requirement that two crew members be in the cockpit at all times.
Canada said it would immediately impose such a rule on all its airlines while those that already had such rules in place, including Ryanair, rushed to reassure customers.
Among the companies that did not announce such a policy change was Germanwings parent Lufthansa, whose CEO Carsten Spohr said he believed it was unnecessary.
"I don't see any need to change our procedures here," Spohr told journalists. "It was a one-off case. But we will look at it with the various experts at Lufthansa and the authorities. We shouldn't lose ourselves in short-term measures."
His comments drew criticism on Twitter, with some people demanding the airline introduce the two person-rule.
I'm flying with you
"@lufthansa will you insist on having 2 crew in the cockpit at all times from today? I'm flying with you this weekend...," asked Twitter user @kazababes.
Later on Thursday Spohr told German broadcaster ARD that Lufthansa would sit down with other German carriers and the country's aviation authority on Friday to discuss the matter. "We will see whether there are measures that can be taken quickly to further improve safety," he said.
Germany's aviation association BDL said all airlines in the country, including Lufthansa, had agreed to discuss such rule changes.
"Today we spoke with all our members about possible consequences," BDL managing director Matthias von Randow told Reuters. "We will therefore look at introducing these new procedures without delay."
Australia's Qantas Airways Ltd and Singapore Airlines Ltd said they have strict, multi-layered systems in place to protect the cockpit but declined to comment further.
The incident is likely to provoke further debate about the future of cockpit protections. Since the Sept. 11 attacks on the United States, regulators have required cockpit doors to be impenetrable when locked from the inside.
But the idea that pilots themselves could be a danger creates reason to re-examine such policies, said retired French crash investigator Alain Bouillard.
"Today we have the reverse question: should we be blocking doors?" he said.
Last year's disappearance of Malaysia Airlines 370 raised such questions, although whether the pilots played any role in that plane's disappearance has never been confirmed.
LAM Flight TM-470 crashed in Namibia in November 2013 after what investigators said were "intentional actions by the pilot" after the first officer left the flight deck, causing the death of 33 people.
An Egypt Air flight 990 from Los Angeles to Cairo crashed into the Atlantic Ocean, killing all 217 on board, in 1999. The cause is disputed but U.S. investigators determined the probable cause was deliberate action by the relief first officer.
U.S.-based Adams Rite Aerospace, a unit of Transdigm which supplies systems to secure cockpit doors on all Airbus planes, did not immediately respond to requests for comment.