2. Altimetry

Question 1

QFF

Answer 1

Sea level pressure derived from station pressure adjusted for station height using actual atmospheric temperature and lapse rate (accurate sea level pressure, used on Isobar charts)

Question 2

Altimeter temperature error correction (formula)

Answer 2

4% difference in height for ever 10 degrees celsius ISA deviation

Question 3

Altimeter temperature error calculation (process)

Answer 3

1. Adjust for barometric error first
2. Apply temperature error for the band of air between correct datum and aircraft (station elevation for QNH, touchdown for QFE, sea level for QFF)

Question 4

Relationship between ONH and QFF

Answer 4

Above sea level to get from QFE to QNH airfield elevation is divided by 27 (ft / 1mb), if actually air is colder the height per mb is less than 27ft/mb, resulting in a higher QFF (QNH < QFF)

Question 5

If actual temperature deviates from ISA and QNH is set, when will altimeter indicate the correct altitude?

Answer 5

Only when on the ground at the airfield

Question 6

Drift and altimeter error (general explanation)

Answer 6

Northern hemisphere right drift = going from high to low = true altitude decreases

Question 7

Density altitude (2 definitions)

Answer 7

• Altitude in ISA atmosphere where density is equal to density at place of observation
• Pressure altitude adjusted for ISA temperature deviation

Question 8

Density altitude (formula)

Answer 8

120ft per degree celsius ISA temp deviation (subtract from or add to observed altitude)