Reports that a pilot deliberately crashed the Germanwings Airbus 320 in the French Alps throws the spotlight not only on aircraft security but also on flight-deck manning.
Questions have been raised over the Germanwings flight that crashed on Tuesday killing all 150 on board the plane, after Marseille prosecutor Brice Robin said the co-pilot “voluntarily” refused to open the cockpit door.
Read more: Germanwings crash - co-pilot 'wanted to destroy the plane'
Since the 9/11 attacks in the US, it has been mandatory for cockpit doors to be locked. Airlines not only installed locking mechanisms but also strengthened the doors.
Germanwings’ parent company, Lufthansa, said on Thursday that the cockpit door on the A320 in the Alps disaster was fitted with a keypad on the outside in which a code has to be entered to afford entry into the cockpit.
However, it is believed the co-pilot – named as Andreas Lubitz by French prosecutors – had “intentionally” kept the door closed, bringing into question whether the measures need re-addressing.
According to an Australian Airbus A320 pilot, quoted in the Sydney Morning Herald, in the case of the pilot flying the aircraft being incapacitated, the door will automatically open after a set period of time if the correct code is entered.
But he added that, if the pilot flying the aircraft does not want the other pilot to enter the flight deck, the one in the cockpit has the ability to block entry if he reacts before the door would open automatically.
A 2002 Airbus promotional video showed the reinforced flight deck could be entered after 30 seconds provided the right code was used in the event of no response from pilots, but there is a manual override on the feature during that period.
Dominique Fouda, a spokesman for the European Aviation Safety Agency in Cologne, Germany, said that there was no regulatory requirement in Europe for a cabin crew member to be present in the cockpit when one of the pilots leaves.
Speaking to The New York Times, Mr Fouda said: “Basically, unless they have a physiological need, they have to be in the cockpit.”
But regulations in Europe “allow for the case one pilot leaving the cockpit, and there is no requirement that the cabin crew should enter cockpit at this time.”
Unlike many American airlines, Lufthansa has no “rule of two” in place, which ensures that there are always two people in the cockpit, even if it is another member of staff.
Read more: Andreas Lubitz - what we know about Germanwings co-pilot
In January 2015, a Delta Airlines plane travelling from Minneapolis to Las Vegas, was forced to make an emergency landing after the pilot was locked out of the cockpit.
An airport spokeswoman said that the door had malfunctioned, forcing the captain to do an emergency unassisted landing.
Nicolas Redier, an experienced pilot, told French newspaper Le Figaro that the person inside the cockpit could voluntarily block the opening of a door by “typing a secret code”.
A pilot can barricade themselves in the cockpit. Nicolas Redier
But added that there was a “flaw” in the system, saying: “A pilot can barricade themselves in the cockpit.”
The A320 locked-out claim is reminiscent of an incident in which an LAM Mozambique Airlines flight with 27 passengers and six crew on board crashed in Namibia in November 2013.
The investigation found that the captain had a clear intention to crash the Embraer 190 aircraft, with the cockpit voice recorder capturing repeated loud bangs on the cockpit door from the co-pilot who was locked out of the flight deck until shortly before the crash.
Norman Shanks, visiting professor in aviation security at Coventry University, said: “If I was the security head of an airline I would say there would have to be at least two people in the cockpit at all times.
“It seems that the heightened security, brought in to prevent terrorism, has created another problem – that of apparent pilot suicide.
“Airlines have got to move very quickly to reassure passengers. They have to say that there is a problem and we have procedures in place to prevent this.
It seems that the heightened security, brought in to prevent terrorism, has created another problem. Norman Shanks
“They don’t have to say what those procedures are but the most obvious one would be to have a minimum of two people in the cockpit at all times.”
Mr Shanks added: “It appears that the co-pilot on the Germanwings Airbus A320 refused to have the door opened. It had to be a deliberate act.”