In any case :-
Aeroplane, originally a French loanword with a different meaning, is the older spelling. The oldest recorded uses of the spelling airplane are British. According to the OED, "[a]irplane became the standard American term (replacing aeroplane) after this was adopted by the National Advisory Committee for Aeronautics in 1916. Although A. Lloyd James recommended its adoption by the BBC in 1928, it has until recently been no more than an occasional form in British English."
In the British National Corpus, aeroplane outnumbers airplane by more than 7:1 in the UK. The case is similar for the British aerodrome and American airdrome, although both of these terms are now obsolete. Aerodrome is used merely as a technical term in all of Canada, Australia, and New Zealand. The prefixes aero- and air- both mean air, with the first coming from the Ancient Greek word ἀήρ (āēr). Thus, the prefix appears in aeronautics, aerostatics, aerodynamics, aeronautical engineering, and so on, while the second occurs (invariably) in aircraft, airport, airliner, airmail etc.
In Canada, airplane is more common than aeroplane, although aeroplane is not unknown, especially in parts of French Canada (where it is however used only in English – the French term is avion, and the French word aéroplane designates 19th-century flying machines).