Tuesday’s crash of Germanwings Flight 9525 has raised questions about minimum cockpit occupancy requirements and the differences in flight deck access regulations between Europe and the U.S. Reacting to a French prosecutor’s determination that 27-year-old copilot Andreas Lubitz had deliberately crashed the Airbus A320 into the French Alps, the air transport industry has understandably seemed stunned and confused about how it came to pass that his captain had been locked out of the cockpit, powerless to intervene.

There has been confusion as to the extent to which European and U.S. regulations on cockpit access are in sync. According to the U.S. Federal Aviation Administration, airlines must develop FAA-approved procedures that include a requirement that, when one of the pilots exits the cockpit for any reason, another “qualified” crewmember must lock the door and remain on the flight deck until the pilot returns to his or her station. A qualified crewmember could be a flight attendant or a relief pilot serving as part of the crew. In essence, the rule requires that no fewer than two crewmembers occupy a cockpit at any time during the flight.

In Europe, however, the rules appear less clear-cut. According to an EASA spokesman, European rules require both pilots to stay in their respective seats unless one develops a physiological need to leave the cockpit or wants to get up to fix or tidy something on the flight deck. “There is no such thing as a requirement like ‘always have two people in the cockpit,’” he said. He asserted, however, that the European rule does not differ from that in force in the U.S.—a point that seems far from clear to several European airlines now moving to change their own procedures (see below).

Indeed, both European and U.S. rules require operators to follow a procedure to monitor cockpit access. In Europe, however, one measure could involve use of a closed-circuit TV display visible from the pilots’ seats, said the spokesman. If an airline deems CCTV too expensive, for example, it can opt for an alternate means of compliance, he added. He specifically cited Ryanair’s procedure, which, in fact, requires a cabin crewmember to enter the cockpit when one pilot leaves it. The flight attendant would then monitor admittance via the door’s spyhole.

So if Germanwings opted to follow the Ryanair model, it seems quite unlikely that the copilot could have commandeered the airplane without resistance. In fact, the apparently deliberate altitude change by the Germanwings copilot and what appears his subsequent refusal to allow the captain back into the cockpit has already prompted Norwegian Air Shuttle to change its cockpit procedures to require two crewmembers in the cockpit, “in line with U.S. regulations.” It added that it would implement the change upon approval from the Norwegian Civil Aviation Authority. UK-based carriers Easyjet, Monarch and Virgin Atlantic all followed suit, announcing plans to unilaterally move to a two-in-the-cockpit policy after the country’s Civil Aviation Authority urged its carriers to “review” their policies. The Canadian transport ministry has ordered all of Canada’s airlines to require the presence of two crewmembers in the cockpit at all times.