Distance between runway and pilot position along the ground is 285430.9336 feet that is 53.9464 miles.
Solution:
Given that
Height of position of pilot from the ground = 30000 feet
Angle of depression when he looks down at runway = 6o
Need to measure along the ground, distance between runway and pilot that is horizontal distance between runway and pilot.
Consider the figure attached below
D represents position of runway.
P represents position of pilot.
PG represents height of position of pilot from the ground that means PG = 30000 feet
PH is virtual horizontal line and HPD is angle of depression means ∠ HPD = 6 degree
AS DG and HP are horizontals, so DG is parallel to HP.
=> ∠ HPD =∠ PDG = 6 degree [ Alternate interior angle made by transversal PD of two parallel lines ]
We need to calculate DG
Consider right angles triangle PGD right angles at G



As one foot = 0.000189 miles

Hence distance between runway and pilot position along the ground is 285430.9336 feet that is 53.9464 miles.