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.
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.
And I know someone who communicates in Hungarian with only the infinitive - people get the gist of what she is saying. This is a language learning site - and I assure you the definite conjugation is covered in a beginner course. I think it is even covered in A1 - which is the beginning of a beginner course.