Translation:Twelve planes are flying above the city.
What is the difference between plane and airplane? I used plane and my answer was rejected. I believe you should adjust it.
I can not adjust it but if you report it via "Report a problem", hopefully they will. Otherwise, both versions could be accepted. Hungarian can also choose to say "repülőgép" or just "repülő".
I think you will probably find that "Aeroplane" isn't accepted either, but as vvsey says we can only keep reporting these problems.
A helicopter is an aircraft, but not an airplane.
And aeroplane sounds like an affectation, even in British English. But I may be wrong . . .