1 / 20

Given:

True altitude: 3 000 ft
OAT: -45°C
CAS: 150 kts

What is the TAS?

  • A
    139 kts
  • B
    215 kts
  • C
    210 kts
  • D
    175 kts

This question gives true altitude and you want PA.

(1) Convert True Altitude to Calibrated Altitude

Comparing the standard temperature and the actual OAT, determine the ISA deviation:
Standard temperature at 3 000 ft, 15 - 2 x 3 = 9º C
ISA dev. = -54 C

  • Using a temperature correction of 4% per 10 degrees ISA dev:
    Correction: 21.6%
3 000 ft x 21.6% = 648 ft
Therefore, calibrated altitude = 3 000 ft + 648 ft = 3 648 ft

(2) Find out TAS using the flight computer:

Use AIR SPEED Window:

  1. Align -45ºC with pressure altitude of “3.5” (3 500 ft approx.);
  2. Find CAS “15” (150 kt) on the inner scale of the outer ring;
  3. Read the corresponding value of approx. 144 kt on the outer scale.

Closest option: 139 kt

Note: A common error is to use PA 3 000 ft instead of 3 500 ft (approx. 3 648 ft). Temperature correction is added because ISA deviation is minus, consequently, true altitude is lower than calibrated altitude.

Your Notes (not visible to others)



This question has appeared on the real examination, you can find the related countries below.