hey ......

in both the cases we are having a system of variable mass ......

in the rocket , the burnt fuel leaves the rocket with some relative velocity wrt the rocket ( as gases )... this produces the thirst force in the upward direction which accelerates the rocket ..but there is also gravitational field...

so you can write the equation of motion as :

in the case of an aeroplane the thrust force acts horizontally , pushing the rocket in he horizontal direction ........so for that you can say

now this is the basic concept of system with variable mass ..... for knowing how to write these equations explicitly you can always go to the theory that will be uploaded on the goiit site or you can ask a question on variable mass .........