The Guardian spoke to a long-haul commercial pilot and a former Thomas Cook flight attendant – people who understand aeroplane emergency procedures and rules about access to the cockpit and communication systems – about key details in the competing theories doing the rounds about the plane's fate.
In what circumstances would you communicate with the ground to say there was an emergency?
In an emergency all pilots are trained in a golden rule: ANC, which is to aviate, navigate, communicate, in that order. We first of all make sure the aircraft is flying safely. Once that is achieved within the flight envelope [appropriate limits], and away from any potential threats we will then navigate the aircraft. We may then consider navigating towards an airport or safe area if the emergency is very time pressing. Once the aviate and navigate tasks are taken care of, we would then communicate our situation or emergency in the form of a pan-pan or mayday to air traffic control.
How could someone access the cockpit?
There is a door code you can enter which only the crew know, or you can press a doorbell, which prompts the crew inside the flight deck to check the camera and monitor screen to check who is trying to access the flight deck. We will generally not open the door if a passenger is within close proximity to the door. The door and the locking mechanism are incredibly strong, bulletproof, and once locked nobody will be able to break the door down.
Can a pilot override this access?
Yes. I won't say how for good reason.
Could a pilot access the transponder and Aircraft Communications Addressing and Reporting System without being questioned by cabin crew?
To stop the ACARS system from transmitting, you simply have to turn it off on the flight computer within the flight deck. Another way of stopping the ACARS system from working is to simply pull a circuit breaker within the flight deck, which would stop electronic power being supplied to the system.
To turn the transponder off, there is a simple switch within the flight deck. It would take two seconds to turn off. To turn the ACARS off you would need to know where the circuit breaker was. Alternatively if someone had broken into the flight deck, and they were aware of the various communication systems, then they could force the pilots to turn them off.
One question I keep being asked by friends and family is: "Can the pilots turn off the black box?" The answer is no.
How dangerous is it for a commercial aircraft to fly at 45,000ft, and does the theory that MH370 was flown to that height in order to deprive the cabin of oxygen hold up?
No, it doesn't. The cabin and flight deck atmosphere at high cruise altitude generally has the atmospheric pressure of 8,000ft above sea level. In terms of the conditions within the cabin and flight deck, there would be no issue with 45,000ft.
Could a pilot force decompression to occur and prepare for it?
No - impossible.
Would the cabin crew be aware that the flight had changed direction or taken an unplanned turn?
Any severe turns or dips would be noted ... and would probably result in a call to the flight deck from the senior cabin crew member.
Do you know of a technical event where the cabin occupants would be unconscious but the cockpit may function normally?
Not on a commercial aircraft but I'm pretty sure that has happened on a private jet flight.
What are cabin crew trained to do in a hijack situation?
Cabin crew are taught in the main to comply with hijackers; however their first action is to maintain the safety and welfare of the passengers – and I don't know a single cabin crew member that wouldn't fight to death to prevent a terrorist gaining access to the flight deck.