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Refer to figure.
Given the following data, what ground roll is required?

Airfield elevation: 1910 ft
QNH: 1010 hPa
OAT: +4°C
Weight: 2440 lbs
Wind: zero wind

  • A

    650 ft

  • B

    725 ft

  • C

    575 ft

  • D

    800 ft

Refer to figure.
Step 1: Calculate pressure altitude

The pressure difference between actual QNH and standard is 1010 - 1013 = -3 hPa. 

Each 1 hPa below standard increase the pressure altitude by approximately 30 ft, so the correction is +3 × 30 = 90 ft to add to the elevation.

Pressure altitude = 1910 + 90 = 2000 ft

Step 2: Draw on chart

With a pressure altitude of roughly 2000 ft, OAT of +4°C, and weight of 2440 lbs, the chart is entered at the temperature axis at +4°C, a line is drawn up to intersect the pressure altitude curve 2000 ft, then horizontally to the weight reference line, adjusted for 2440 lbs (between 2400 and 2500 lbs), and finally projected horizontally into the wind section at zero wind, reading the ground roll. 

The result obtained from this process is approximately 650 ft.

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