Speculation about what really happened on missing flight 370 has been rampant. A commercial long-haul pilot and an experienced cabin crew member discuss the possibilities. Follow live updates here

We may never know what happened to missing Malaysia Airlines flight MH370 and the 239 people on board.

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.



Commercial long-haul pilot for a major airline (anonymous)



An airline pilot. Photograph: Alamy

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; if it isn’t then this is our priority before anything else. Once the aircraft is flying safely within the flight envelope [appropriate limits], and away from any potential threats such as terrain, severe weather, traffic, 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. However, if an emergency is severe, any of the two pilots can make a very quick mayday call at any time such as: "Mayday mayday mayday, MH370, smoke on board, stand by." It would only take two or three seconds to transmit.

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; also if we leave the flight deck for a toilet break, we won't attempt to re-enter the flight deck if there are passengers within close proximity. 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 (ACARS) system without being questioned by cabin crew?

The flight computers will be in what we call the avionics bay; pilots would not enter the avionics bay unless they have good reason to do so, and it’s also not possible in some types of aircraft. If a pilot wanted to enter the avionics bay for no apparent reason, the other pilot would question why they were doing this, as well as cabin crew.



But to stop the ACARS system from transmitting, you simply have to turn it off on the flight computer within the flight deck. Boeing call this the FMS and Airbus call this the FMGC. 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 how to navigate through an FMS system, or 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.



Is it normal for a pilot to have a flight simulator at home?



It’s not that uncommon; pilots generally love their job. I’ve got a flight simulator programme on my computer but rarely use it. Some pilots love their job so much that in their spare time they like to fly simulators, fly aerobatics and train other pilots. The job is more of a lifestyle than a 9-5 job, so I don’t see it as concerning that the captain had set up a very basic flight simulator at home.

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.

Rapid decompression is a theory, and if the plane experienced a decompression the crew would have to don their masks quickly to avoid passing out. But on the emergency procedure, step one in case of decompression is to don masks. We have an oxygen supply, separate systems for the passengers and crew.

The altitude at which an aircraft can fly depends on its weight, essentially. When an aircraft takes off, fully fuelled, with a full load of passengers, it will initially climb to an optimum cruising altitude. Over time as fuel is burnt off, the optimum cruising altitude increases, so pilots perform a step climb throughout the flight as the plane becomes lighter and lighter.



There are also limitations on the maximum altitude a plane can fly for a given weight, and if exceeded there is a risk of high speed stall. If you Google "coffin corner" it may make more sense. 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.

What do you think of the existing theories as to what might have happened?

It would be wrong of me to speculate about what has happened, but I think it’s important to try to separate what we know and what we don’t know.



We know the aircraft has changed course, intentionally. We know the ACARS and transponder have been turned off intentionally, or have simultaneously failed, which is unlikely. We know there hasn’t been a mayday call. We know the aircraft has flown for several more hours, which would indicate it hasn’t been the victim of a bomb or other attack.



What we don’t know is whether someone breached the flight deck, the aircraft suffered decompression, the aircraft experienced an electrical fire which has incapacitated the crew, knocked out the ACARS and transponder but has not been severe enough to disable the aircraft completely.

I would say someone breaching the flight deck is possible, decompression is possible and fire is a possibility.



The crew may have been dealing with an electrical fire and began turning off the electrical systems which supply power to the transponder and ACARS system, but as previously stated it would take them two seconds to say: “Mayday, mayday, mayday, MH370, electrical fire, stand by.”

Once they find pieces of the fuselage they can quickly establish basic facts such as: did the aircraft break up in the air, or on impact with the ocean or ground? If it broke up in the air was it because of an explosion or major malfunction of the airframe? And if there are any signs of fire on the wreckage. The ultimate objective will be to locate the black box and cockpit voice recorder, but as in the case of Air France 447, it may take a long time.

Lee Cobaj, long-haul cabin crew member of 18 years



Lee Cobaj, long-haul cabin crew member

If you saw a pilot accessing the cargo or area where communication systems were positioned would you question what they were doing?



I’ve never seen flight crew have to enter those areas in flight so would probably ask what they were up to but would likely believe whatever they told us. We don’t have that kind of technical knowledge.

How much communication do you have with the pilots throughout a flight as lengthy as the one from Kuala Lumpur to Beijing?

Lots. The purser - the person in charge of cabin crew - will be liaising with the flight crew throughout boarding. The cockpit then becomes sterile for take-off so there would be no communication for the first 20 minutes of the flight, and it's 40 minutes before we’re allowed to enter the cockpit. Along with 20-minute checks, we’ll be chatting regularly with the pilots. Crew quite often pop up front when they’re on breaks too for a face-to-face chat.

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.

How long could the autopilot fly an aircraft, for example if the pilots were incapacitated, without cabin crew knowing?

The aircraft could fly to its destination and even land on autopilot but the cabin crew are trained to communicate with the flight crew at least every 20 minutes to ensure that neither of them are ill or incapacitated. Procedures are in place to gain access to the flight deck if necessary, for example in the event of no response.

If someone locked themselves in the cockpit what would the cabin crew do?



We have a procedure to gain access to the cockpit in an emergency. Entry is rather a sensitive situation, and even as ex-crew I feel a bit weird giving it away.



Ultimately, we would do everything we could not to let a hijacker in, even if that meant they would kill us. Sounds dramatic but I don’t doubt for a moment that the majority of crew would lay down their lives to stop it happening. The flight crew have cameras outside the door so they can see what’s going on, it only covers the forward galley ... but they would be able to see any strange goings-on in that area.

But if there was someone in there that was familiar with the systems they would be able to override our entry and there’s nothing else we can do.

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.



The Helios flight, where the pilots passed out in the cockpit, was part of our annual training. Before that happened we had post-9/11 steel doors which could only be unlocked from the inside either by switch or manually. After Helios, keypads with normal entry codes and emergency entry codes which give us five seconds to enter were brought in.

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.

Do you have any questions for the pilot and cabin crew about Malaysia Airlines flight MH370? Leave your comment in the thread and they will answer a selection

