літаки

In a sentence

• Літаки пролітають високо в небі.

  The airplanes fly high in the sky.

  Here, 'літаки' is used in its nominative plural form to denote the subject of the sentence.

• Я бачив багато сучасних літаків на авіашоу.

  I saw many modern airplanes at the airshow.

  In this context, 'літаків' is the genitive plural form used to express 'of airplanes' showing possession or quantity.

• Маленький хлопчик грається з іграшковими літаками.

  The little boy is playing with toy airplanes.

  Here, 'літаками' is the instrumental plural form, showing the instrument or means by which the action is performed—playing with toy planes.