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(For this question use annex or CAP 698 figure 2.2).
Calculate the maximum take off mass given the following data:

TODA=ASDA=TORA=2150 ft
Runway: Wet paved
Downslope: 2%
Pressure altitude: 2500 ft
Temperature: 38°C
Headwind component: 8 kt

  • A
    3650 lb
  • B
    2860 lb
  • C
    3200 lb
  • D
    2960 lb

Refer to figure.

Note that the runway is wet and paved so there is no correction to TODA, TORA and ASDA for that but they do need to be defactored for the regulation factor. There is also no correction for downslope. (See CAP 698 Section 2 page 1 and 2).


Field Length Requirements

a) When no stopway or clearway is available the take-off distance when multiplied by 1.25 must not exceed TORA.

  • 2150 ft ÷ 1.25 = 1 720 ft

b) When a stopway and/or clearway is available the take-off distance must:

i) not exceed TORA
ii) when multiplied by 1.3, not exceed ASDA iii) when multiplied by 1.15, not exceed TODA


To solve this exercise, we will need to draw 2 lines. The mass will be found in the mass grid at the intersection of such lines:

(1) Enter the graph at the bottom left at a temperature of +38ºC, track vertically up to a pressure altitude of 2 500 ft. Continue to the right to the mass reference line;
(2) Enter the graph on the right at a distance of 1 720 ft, follow the reference line diagonally down and to the left to the "REF LINE". From this point continue horizontally to the left and apply a headwind correction of 8 kt. Continue horizontally to the left. The mass will be found at the intersection of these lines => 2 960 lb.

Very tricky graph work but the spread of answers should be wide enough to get the required answer and the probable crux of the question is to know the regulation corrections to TODA, TORA and ASDA and that there is no surface correction for a paved wet runway and there is no correction for downslope. You must learn the factors.

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