In an exam paper, there was a picture of an air stewardess in the aeroplane serving passengers. One of my pupils wrote the following:
The air stewardess works on an aeroplane.
Shouldn't it be the air stewardess works in an aeroplane?
Both are correct. However, I would say the student's answer is more apt.
Terminology for airplanes is similar to ships (they are in effect airships).
One works on a ship. Passengers on a flight manifest are quaintly referred to as souls, as they are on a ship. The pilot is a captain. The co-captain is also the first officer. Stewardesses are so named because of ship's stewards before them.
If you would say a captain works on a ship, then a flight attendant works on an airplane.
I have to disagree with medica's answer a bit. Although both are used interchangeably, one actually agrees more with the ear.
A person works on a ship because they can actually work on the outside (deck) of the ship. This is usually what the word on conveys.
So a stewardess and pilot work in an airplane.
The mechanics and ground crew work on an airplane.
One of my American editor friends said it is "on a plane," "on a train," "on a bus," but "in a car." The reason is very simple: you could stand inside all those things and walk around if you wanted, whereas in a car you have to be seated. However, what do you say when you're on/in a truck? "On the deck of a truck, in the cabin of a truck." On the deck of the truck, you could stand if you wanted.
In Indian schools, we are taught IN a plane, which is probably a British usage.
Both would seem acceptable and in everyday use.
The second is however the one I prefer. The first could possibly be seen as ambiguous. A design engineer who was sitting in an office designing some part of a plane's structure could justifiably say 'I am currently working on an aeroplane'.
Working 'on' something means one of two things. It could mean that you are physically located on the thing whilst you are doing your work, as the air stewardess is. Or it could mean that you are engaged with work on the thing in question, e.g. 'I am working on my maths project'. The last does not mean you are actually sitting on your maths project whilst you are doing your work.
This sentence sounds weird. Why? Who would actually say or write such a sentence in real life? No one. It's like saying a major league baseball pitcher works on the mound. More details accompany these situations. The stewardess serves drinks and meals on the plane. The baseball pitcher stepped off the mound.