You are intending to fly in accordance with the quadrantal rule on a magnetic track of 120. The QNH is 996 hPa. Which of the following is your correct flight level?
A FL 30
B FL 35
C FL 55
D FL 60
NewMan123 has it spot on but just to clarify it from an instructional point of view.
This question requires you to know the difference between an Indicated Altitude (above mean sea level and based on QNH) and a Pressure Altitude (Flight Level based on 1013 hPa).
The quadrantal rule requires ODD + 500’ to be flown on magnetic tracks between 090°M – 179°M.
This immediately restricts the answers to B (FL35) and C (FL55).
For the purpose of this examination, the Transition Altitude in the UK is 3,000’, therefore the lowest Flight Level is FL35.
The purpose of the QNH in this question is to find out whether or not you are above the Transition Altitude. A QNH LESS than 1013 hPA tells me immediately that the Indicated Altitude will be LESS than the Pressure Altitude.
First of all, find out the pressure correction.
This is my method for calculating an Indicated Altitude from a Pressure Altitude.
Pressure Correction = (QNH-1013) x 30’
Pressure Correction = (996-1013) x 30’
Pressure Correction = -17 x 30’
Pressure Correction = - 510’
That looks immediately suspicious for FL35 (Pressure Altitude of 3,500’) being correct but let’s check.
Indicated Altitude = Pressure Altitude +/_ Pressure Correction
Indicated Altitude = 3,500’ – 510’
Indicated Altitude = 2,990’
This is below the Transition Altitude and therefore you would not fly on a Flight Level.
This only leaves C (FL55) as the only possible answer.
Hope that helps.
