Why No One Agrees Whether Cockpit Doors Are Safer Locked or Open

Prosecutors claiming the crash of Germanwings Flight 9525 was deliberate revealed on Thursday a chilling piece of evidence.

Co-pilot Andreas Lubitz, 27, whom investigators believe locked the captain out of the cockpit before putting the plane into a fatal descent, had researched the doors’ security on his iPad before the March 24 crash, investigators said. The discovery has heightened concerns about whether locked cockpit doors — fortified and enforced in the wake of 9/11 — are more dangerous than they are safe.

The debate, however, is nothing new. For decades, aviation officials have struggled with the paradox of a cockpit that is both secure, in the event of a threat from outside, and accessible, in the event of a threat from within. As a result, many planes — including the Germanwings jet — now have emergency codes to enter the cockpit, which are known only by the flight crew, according to an Airbus manual. The code unlocks the cockpit door within 30 seconds unless someone inside hits the “lock” toggle, in which case there is no way to gain entrance. (Investigators have not said whether the emergency codes were used on the Germanwings plane, though the flight data recorder presumably will provide this information.)

While some believe the solution to better cockpit security is obvious — the “rule of two,” which requires two crew members to be in the cockpit at all times — the problem is in fact much more complex. History shows that there is no perfect level of accessibility when it comes to airplanes: sometimes it’s important to keep people out; sometimes it’s important to get inside. Here’s a look at how locked or open cockpit doors have been both life-saving and life-threatening throughout history:

The case for open cockpit doors:

Helios Airways Flight 522 (Aug. 14, 2005)

The Boeing 737 crashed in the mountains near Athens, killing all 121 on board, after the co-pilots became incapacitated after they mistook an in-flight depressurization — which deprives the plane of oxygen — for an air-conditioning malfunction. Moments before the plane exhausted its fuel, a flight attendant had managed to enter the locked cockpit using an emergency code and attempted unsuccessfully to control the plane. The Guardian reported in 2006 that on this flight, only the senior steward had been permitted to know the code, raising questions of whether open doors — or less protected doors — would have allowed the flight attendant to reach the cockpit sooner. (It is not known how the flight attendant obtained the code.)

Mozambique Airlines Flight 470 (Nov. 29, 2013)

The Embraer 190 crashed in Namibia en route to Angola after descending rapidly from an altitude of 38,000 ft., killing all 33 passengers and crew. Investigators believe the captain had a “clear intention” to crash the jet. “[Moments before the crash] you can hear low and high-intensity alarm signals and repeated beating against the door with demands to come into the cockpit,” a Mozambican Civil Aviation Institute official said after the jet’s cockpit voice recorder was retrieved — but the person banging on the cockpit door could not get inside.

Air New Zealand Flight 176 (May 21, 2014)

Midflight, the captain of a Boeing 777 carrying 303 people locked the first officer out of the cockpit after they had an argument over a take-off delay, the New Zealand Herald reported. The captain did not immediately respond to requests from the crew to open the door, alarming the first officer and cabin crew. After two minutes, the first officer used “an alternative method” to access the cockpit, the airline said, though it did not specify what method for security reasons. After the incident, both pilots were ordered to receive counseling and training.

The case for locked cockpit doors:

Pacific Southwest Airlines Flight 1771 (Dec. 7, 1987)

This routine flight between Los Angeles and San Francisco crashed after a newly terminated employee, who had brought a gun on board the jet, shot five people. The plane entered a nosedive, resulting in the deaths of all 43 people aboard, investigators said. Analysis of the cockpit voice recorder suggests a flight attendant had opened the cockpit door to warn the pilot that a gunshot had been fired in the cabin, after which the suspect shot the woman and both pilots and seized controls. Though fortified cockpit security may have prevented the crash, investigators were concerned primarily with how exactly the employee managed to board the plane with a gun. They attributed the incident to a now-defunct policy that had allowed airline employees to bypass normal security if they displayed credentials, which the suspect had not surrendered upon termination.

JetBlue Flight 191 (March 27, 2012)

The 100-some passengers on the New York to Las Vegas flight had a scare when the captain began to behave erratically, telling the first officer things like “we’re not going to Vegas,” according to an FBI statement. When the captain left the cockpit to go to the lavatory, the first officer asked a flight attendant to bring an off-duty captain aboard the plane into the cockpit. The two pilots locked the door, ordering passengers on the intercom to restrain the on-duty captain as he attempted to enter the cockpit with his emergency access code. All on board were unharmed.

United Airlines Flight 1074 (March 17, 2015)

A flight headed from D.C. to Denver returned to the airport 20 minutes into the flight after a passenger became violent and ran toward the cockpit, the airline said. The man was immediately restrained by other passengers while the pilot safely landed the Boeing 737, carrying 33 passengers and six crew. During the process, the pilot reassured the controllers that the cockpit was locked, according to recordings of the radio communications from the flight.