The effect of your walking will create a force on the airline acting downwards, due to the weight.

• By Newton's thirds law the airline will exert an equal and opposite reaction force directed downwards.

If we observe from outside,

• The weight of all the passengers acts downwards on the floor of the Airplane.
• The Airplane exerts an equal and opposite force on the passengers, with the help of its propulsion due to which the flight keeps on flying without falling down.
• Hence by changing the frame of reference we can observe the force which is responsible for the reaction.