Question

1) A utility airport is being planned to serve a small community. The visual runway is to be 3600 ft. long. Indicate whether or not the following objects will be considered obstructions to air navigation by the FAA. (HINT: 1 nautical mile = 6076 ft.)

a) A 220-ft radio tower that is not in the landing approach, located 3.1 miles from the airport reference point. The ground elevation at the tower is 25ft higher than the established airport elevation.

b) A planned 75-ft-high office building within the landing approach 1/2 mile from the end of the runway.

2) For the utility airport indicated above, what length of runway is required if the airport is located at 6000 ft above sea level and has a mean daily maximum temperature of 75°F? The effective gradient is 1.2 percent. The airport must accommodate small airplanes having more than 10 seats.

Answer 1

1)

a) Runway length = 3600 ft

Tower height = 220 + 255 = 245 ft

Tower distance = 3.1 mile = 16270 ft (from airport reference point)

From above chart

Horizontal + Conical surface lengths = 5000 + 4000 = 9000 ft

Tower is located at a distance of 16270 ft (from airport reference point), which is beyond the above distance

Hence tower is not considered obstructions to air navigation

b) A planned 75-ft-high office building within the landing approach 1/2 mile (= 2624 ft) from the end of the runway

Approach surface length = 5000 ft and approach surface slope = 20:1 (As per FAA)

Permissible Height at a distance = 2624ft /20 = 131.2 ft

Hence object is not considered obstructions to air navigation

2)

Red line is shown for example

From above chart for  mean daily maximum temperature of 75°F & airport location at 6000 ft above sea level

For 95% of fleet, Runway length = 6900 ft

For 100% of fleet, Runway length = 6900 ft

length of runway is required = 6900 ft