There are 400,000 people in the air at any given time. Now, if you were on an aeroplane in which both the pilot and the co-pilot had fallen ill, it would be incredibly difficult for anyone else to land the plane down safely. Luckily, an incident such as this has never occurred in commercial airline travel history.
To prevent food-poison related illness or more harmful poisonings, the pilot and co-pilot on a plane always have different meals from each other. In the case of extra long haul flights there are three pilots instead of two.
Simulations with people with civil private pilot licences taking over the control of a large commercial jet have been carried out in the USA. In these cases one person could not move the seat that moved them towards the control, another turned the radio off, and another turned off the autopilot and crashed the plane immediately.
One of the first problems is getting into the cockpit, which is much more secure these days following 9/11. The pilot and co-pilot may be too ill to let you in.
If the plane was on autopilot (a device invented in 1914 no less) you could continue to fly level, and once you began to land people would talk you through the procedure, but there are so many variables that it is really difficult.
Thankfully there is an auto-land system. The chances of an intelligent person landing the aircraft in such a situation are 1 in 10 if it is in autopilot, and 1 in 100 if it is not in autopilot.
The flight on which it is most unlikely for such a disaster to happen is – unsurprisingly – the shortest commercial flight in the world: in the Orkney Islands, from Westray and Westray Papa. It usually takes two minutes, but the shortest it has ever taken is 58 seconds. The distance is shorter than the runaway of Edinburgh Airport. A return ticket is £39; however, you do get a certificate and a miniature of Highland Park whisky.