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Refer to figure or CAP 697 Figure 4.5.3.2 for Pressure Altitude 35000 ft.
What will be the change in air range available from 1000 kg of fuel for the following situation if the OAT increases from -55° C to -45° C?

Aircraft mass at start of cruise leg: 50000 kg
Cruise level: FL350
Cruise speed: Mach 0.74
Forecast OAT at FL350: -55° C
Wind component at FL350: -25 kt

  • A
    An increase of 10 NAM.
  • B
    A reduction of 1 NAM.
  • C
    A reduction of 11 NAM.
  • D
    An increase of 4 NAM.

Refer to figure.

Let's start by calculating the range when OAT = -55ºC. ISA temp at FL350 = 15 - 2 x 35 = -55ºC, therefore in this case => OAT = ISA.
1. Enter the table at 50 000 kg and read the corresponding distance: 3261 NM.
After consuming 1000 kg of fuel, we will have a mass of 49 000 kg. Enter the table at 49 000 kg and read the corresponding distance: 3063 NM

  • Which gives us a range of 3261 NM - 3063 NM = 198 NM for 1000 kg

2. Since the temperature changed from ISA conditions to ISA +10ºC (-45ºC) => we must perform the fuel adjustment:

Read Note 2 at the bottom of the table:

  • "A) Increase fuel required by 0.6 percent per 10 degrees C above ISA"
    1000 kg x 0.6% = 6
    1000 kg + 6 kg = 1006 kg
    (meaning that at ISA +10ºC, the aircraft will consume 1006 kg to cover 198 NAM. Therefore, the distance we can travel on 1000 kg = 198 x (1000/1006) = 196.8 NAM, a reduction of 198 - 196.8 = 1.2 NAM

ATPLQ Note: We would kindly ask anyone who has further information on this question to contact us. Thanks in advance!

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