SOLUTION: Evaluate the decrease in pressure, in Kpa, on an aircraft corresponding to a drop in flying altitude of 3km.

              For your info:  aircraft is a flying apparatus heavier than air.



An aircraft flies (not drops) only because it moves with sufficiently great speed in the air.



Under such condition, calculation of the net force of the pressure distribution along the aircraft surface is 

complex aerodynamics problem - not for school Math students.



So, as it is worded, printed, posted and presented, this "problem" makes no sense at this forum.

    if instead of aircraft, you consider an air balloon, then the net force of the pressure distribution 

    around the balloon surface is closed to the weight  of the balloon (at normal - not catastrophic - conditions).


    But the local air pressure at the balloon surface INCREASES when the flying altitude of the balloon decreases.