Airlines are changing procedures to ensure two crew members are in the cockpit at all times during flights following the French Alps plane disaster.

The UK’s Civil Aviation Authority said it had contacted all UK operators to urge them to review safety procedures in the wake of the tragedy, in which 150 people were killed.

Monarch, easyJet, Virgin Atlantic and Thomas Cook all confirmed they had changed their policies, while Ryanair, Jet2 and Flybe said they already required two crew members to be in the cockpit at all times.

British Airways said it did not discuss “issues of security”.

Three Britons were among those on board the Airbus A320 which crashed on Tuesday.

In a dramatic turn yesterday, it emerged that black box recordings pointed to the co-pilot deliberately crashing the Germanwings-operated plane into the mountains.

French prosecutors said that, according to evidence from the recovered cockpit voice recorder, co-pilot Andreas Lubitz, 28, had deliberately put the plane into a descent after the captain left the cockpit.

He then repeatedly refused to allow the captain back into the cockpit, with the captain being heard pounding on the door in a desperate attempt to break in.

Marseille prosecutor Brice Robin said: “The most probable interpretation is that the co-pilot refused to open the cockpit door to the pilot and actioned the button which started the descent procedure.

“We can only deduce that it destroyed this plane.”

A Virgin Atlantic spokeswoman said: “We always ensure we have the highest safety standards and, while it is our common practice to have two members of our crew in the flight deck at all times, in light of recent events we are now in the process of formalising this to be policy.”

An easyJet spokesman said: “easyJet can confirm that … it will change its procedure which will mean that two crew members will be in the cockpit at all times. This decision has been taken in consultation with the Civil Aviation Authority.

“The safety and security of its passengers and crew is the airline’s highest priority.”

Monarch said it had revised its flight deck policy so that all passenger flights will require a member of cabin crew to stand in when the pilot or co-pilot leaves the cockpit for any reason.

The airline already practised an “eyes-on” check, when a cabin crew member enters the flight deck to check on the captain and first officer every 15 to 20 minutes.

A British Airways spokeswoman said: “We never discuss issues of security.”

The cockpit voice recording revelations yesterday led to the spotlight being thrown on the fact that Mr Lubitz’s training had been interrupted for a long period.

He had been employed as a flight attendant when he first tried to become a pilot in 2008 after waiting for eight months, but did not start working as a first officer for Lufthansa until September 2013.

Carsten Spohr, chief executive of Lufthansa, Germanwings’s parent company, said: “The co-pilot interrupted his training for six years, I would be interested to know why.

“I cannot tell you anything about the reasons of this interruption, but anybody who interrupts the training has to do a lot of tests so the competence and fitness would be checked again.”

Matthias Gebauer, chief correspondent for the online edition of German newspaper Der Spiegel, tweeted: “Schoolmates of co-pilot who crashed tell German reporters he took six-months break from flight training in 2009 due to burnout-syndrome.”

In his startling account of the doomed plane’s final half hour, Mr Robin said: “I think the victims only realised at the last moment because on the recording we only hear the screams on the last moments of the recording.”

He added: “I believe that we owe the families the transparency of what the investigation is pointing to and what is going on, we owe it to them to tell them what happened.

“The families have been informed of everything I just told you.”

Asked about Mr Lubitz’s ethnicity, Mr Robin said: “He was a German national and I don’t know his ethnic background. He is not listed as a terrorist, if that is what you are insinuating.”

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