Although you are grammatically right, since if this sentence could also be a generic one (usually, at any point of time), present continuous is a better translation, since "to watch" something usually takes a bit more time, therefore at the time of the speech someone is actively laying her/his eyes on the planes.
"planes" is more natural in English. I rarely hear "airplanes" (or "aeroplanes") these days.
This question is not accepting aircraft - reported. When translating a number of other questions aircraft has been accepted. It seems that once a word has been accepted, it applies in that circumstance only, as no global substitution has occurred. Shame, as this would be a big time-saver for the team.