It's certainly not the first time in the last year that the safety of air travel has been brought into question. But as it's revealed the Germanwings plane was brought down on purpose by the co-pilot, Katie Gregory asks if anything could have been done to prevent this latest tragedy.

New Zealand's flight deck procedure has been tightened following the Germanwings crash.

The Civil Aviation Authority (CAA) change requires at least two crew members to be present in the cockpit of large jets at all times. It applies to domestic and international flights operated by Air New Zeland and Jetconnect. Qantas and subsidiary brand Jetstar are based out of Australia so are not regulated by the CAA.

It comes into effect immediately.

Reuters DEBRIS: Part of the wreck of the Airbus A320.

The move comes as disturbing details of the Germanwings crash have emerged. The French authorities believe one of the co-pilots deliberately crashed the plane, using a security feature to lock the other pilot out of the flight deck.

It was announced just hours after Air New Zealand made a similiar change to their policy.

Several international carriers responded to the crash by adopting flight deck procedures from the United States, which requires two crew members to be inside the cockpit at all times.

"This new stipulation recognises that temporary inflight incapacitation could occur for a number of reasons, including a medical event," said Acting Director of Civil Aviation John Kay in a statement.

Kay also detailed the annual health checkups all airline pilots were required to take.

According to the law cited, pilots must have "no history or diagnosis of any neurological, physicatric or psychological condition [...] that is of aeromedical significance."

"As with medical certificates the CAA will always take a precautionary approach on such matters," he said.

Air New Zealand said their move came in response to the tragedy.

"The safety of our customers, staff and aircraft is paramount and non-negotiable and this procedural change will further strengthen our protocols and mitigate any risk posed by one pilot becoming incapacitated while operating an aircraft," Chief Flight Operations and Safety Officer Captain David Morgan said in a statement.

"If one of the two pilots operating the flight needs to leave the cockpit for a short time a crew member will be required to enter the cockpit in their place."

Air New Zealand was criticised in 2014 after a pilot locked his co-pilot out of the cockpit over an argument.

Other airlines have also changed practices. Canada has ordered its airlines to post two people at all times in cockpits of passenger planes, effective immediately. British airline easyJet, Norwegian Air Shuttle, and Icelandair also announced they will require two people to remain in their planes' cockpit.

LOCKED OUT

Ever since 9/11, the cockpit of a plane has been an extremely secure place.

Now that same security seems to have played a part in another tragedy.

French authorities are working with the theory that the Germanwings jet was deliberately crashed by the co-pilot - who locked the other pilot out of the cockpit.

His attempts to enter the Airbus's flight deck became increasingly frantic, but the reinforced doors offered too much resistance.

How could a pilot be locked out of his own cockpit? Very easily.

A video from Airbus has surfaced explaining the locking mechanisms of cockpit doors.

By default, the cockpit doors are locked from the outside.

If a crew member wishes to enter the flight deck they use the intercom to request access.

As a backup, crew members have a special code which can unlock the doors in emergencies - if the pilot has suffered a heart attack, for example.

Crucially however, the pilot can override this emergency unlocking by simply moving the knob to the 'lock' position.

READ MORE: Crashes and near misses related to cockpit door locks

* Why did the co-pilot do it?

* Doorway to disaster on Germanwings Flight 9525

This override keeps the door locked for a predetermined amount of time - anywhere between five and 20 minutes.

This feature is intended to keep the door locked in case the crew member is being forced to enter the code. It seems to have tragically backfired.