The fact that a Continental airlines flight from Brussels to Newark landed safely, despite the death of the pilot, is no surprise, says David Learmount, operations and safety editor of Flight International magazine.
That's what co-pilots are for, he says - to stand in for the pilot in case of emergency.
Do you need two pilots to land a passenger aeroplane?
Aeroplanes are always landed single-handed - you cannot have two pilots struggling with the controls. It's decided at the beginning of every leg which pilot is going to do the flying and which will do the supporting. Flying the plane, making the radio calls and handling all the systems is a very busy job, but it can be done - and air traffic control will give every assistance to a pilot flying on his own, making the job a lot easier.
A modern plane like the 777 can be flown from take-off to landing by a single pilot. In fact, all pilots are tested when they qualify to ensure they can handle a multi-engined jet on their own. The main reason for having two pilots is that something like this occasionally happens - though it's less common for a pilot to die than to be incapacitated by something like food-poisoning.
Pilots and co-pilots are required to choose different meals from the in-flight menu for precisely this reason.
Can a plane be landed without any pilots at the controls?
No. A system called autoland has been available to airlines since the 1960s but you have to tell it what to do next, where to go - up, down, left, right - you have to direct it. If there is someone on the flight deck to do that, the plane does not need to be flown - but it cannot be done from the ground. Also, planes cannot taxi and reach terminals by themselves.
If both pilots died, you would just have to hope that there was someone else on hand with some experience of flying an aeroplane.
In this case there were three pilots on board, a pilot and two co-pilots. How common is that?
It is essential on very long flights, Singapore to London say, to allow the pilot to have a break. It's not necessary on a regular transatlantic flight. It was probably just fortuitous they had an extra co-pilot, in this case.
Should the passengers have been told that the pilot had died?
There was no reason to tell them because they were not exposed to any risk. They were not going to face an emergency landing.
Would the request for a doctor to come forward have alarmed passengers?
Not necessarily. If the crew had drawn a curtain across the galley it may not have been obvious that the doctor was taken to the flight deck. It's another matter what the doctor would have told his neighbours when he returned to his seat.
The crew will also have faced a decision whether to leave the dead pilot harnessed in his seat, or in one of the jump seats behind the pilots' seats, or to move him from the flight deck. There is not much room on the flight deck, but moving the body could have caused passengers some consternation.
The pilot who died was aged 60. At what age do pilots retire?
They can keep flying until they are 65, but there is a rule that if one pilot is between 60 and 65 the other pilot has to be younger than 60. That is a standard set by the International Civil Aviation Organisation to reduce the risk of both pilots suffering health problems on the same flight.
How frequently do pilots undergo health checks?
They have annual medical tests until they are 60. After that it's every six months.