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Refer to figure. 
What will be the approximate change in ground distance covered per 1000 kg of fuel burnt if the headwind increases from 25 kt to 35 kt?

Aircraft mass at start of cruise leg: 50 000 kg 
Cruise level: FL280, LRC 
ISA conditions

  • A
    Reduces by 4 NM
  • B
    Increases by 4 NM
  • C
    Reduces by 11 NM
  • D
    Increases by 11 NM

Refer to figure.
(1) Calculate the Range after consuming 1000 kg of fuel.
Enter the table at the first column "Gross WT. kg" at 50 000 kg and intersect with "0" (0 hundreds of kg). Read the result of 2889 NAM.
Now, enter the table again at the first column, at 49 000 kg (1 000 kg of fuel have been burnt). Read the result of 2 711 NAM.

  • Range = 2 889 NAM - 2 711 NAM = 178 NAM

(2) Find out TAS.
The TAS will be the average from 50 000 kg and 49 000 kg:

(427 kt + 425 kt) / 2 = 426 kt

(2) Calculate the Ground distance for a headwind of 25 kt.
NM = NAM x GS/TAS

  • NM = 178 x 401 / 426 = 167.6 NM

(3) Calculate Ground distance for a headwind of 35 kt.

  • NM = 178 x 391 / 426 = 163.4 NM

=> As we can see, the range reduced = 167.6 NM - 163.4 NM = 4.2 NM

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