FAA Private Pilot Helicopter (PRH)Performance and LimitationsMedium
A pilot is using a takeoff distance chart to clear a 50-foot obstacle. At the planned pressure altitude and temperature, the chart shows a required distance of 600 feet at a gross weight of 2,200 lb and 750 feet at 2,400 lb. If the helicopter's actual takeoff weight is 2,300 lb, what is the best estimate of the takeoff distance required to clear the obstacle?
- A700 feet
- B675 feet
- C750 feet
- D600 feet
Show answer & explanationAnswer & explanation
Correct answer: B. 675 feet
2,300 lb is exactly halfway between 2,200 lb and 2,400 lb, so the takeoff distance is interpolated halfway between 600 and 750 feet: (600+750)/2 = 675 feet.
Why the other options are wrong
- A. Not supported by linear interpolation between the given data points.
- C. This is the distance for 2,400 lb, heavier than the actual weight.
- D. This is the distance for 2,200 lb, not the actual 2,300 lb weight.
Performance Chart Interpolation
A method of estimating a value that falls between two known chart values by proportionally averaging them.
- Find the weight's position between the two known values
- Apply the same proportion to the performance values
- Never round down for conservative planning if unsure
Memory trick: Halfway weight = halfway distance.