Altimetry

Question 1

In what atmosphere is an altimeter calibrated to read?

Answer 1

ISA atmosphere

Question 2

What is the definition of the ISA?

Answer 2

Average conditions of atmosphere at 40N latitude, from the sea level to 105 000 feet.

Question 3

State 6 numerical specifications for the ISA up to 65000’?

Answer 3

MSL Temp = 15 Celsius
MSLP = 1013,25hpa or 29,92 in of Hg
Lapse rate = 1,98 Celsius/1000feet
Tropopause Temp = -56,5 Celsius
Tropopause height = 36 089,24 feet
Stratospheric lapse rate = 0 Celsius/1000feet

Question 4

What us the Temp in the ISA at 40T feet

Answer 4

-56,5 Celcius

Question 5

What is the magnitude of error for pressure deviations from ISA standard?

Answer 5

30’ per hpa OR 1000’ per inch of Hg

Question 6

True or False?

An altimeter indicates altitude by sensing temperature changes

Answer 6

False

Question 7

True or False?

When flying at constant indicated altitude, true altitude is constant

Answer 7

False

Question 8

True or False?
When flying along a constant pressure surface, the indicated altitude is always constant (no change to altimeter setting)

Answer 8

True

Question 9

True or False?

When flying along a constant pressure surface the true altitude is always constant

Answer 9

False

Question 10

True or False?

When flying at the same indicated altitude towards lower MSL pressure, you will gain true altitude.

Answer 10

False

Question 11

True or False?
When flying at the same indicated altitude with the same MSL pressure at the surface, but temperature below you increasing, you will gain true altitude.

Answer 11

True

Question 12

Without changing altimeter setting, by how much would your true altitude change if you were to fly from a 960hpa low to a 1040hpa high?

Answer 12

PC = (1040-960) * 30’/hpa = +2400 feet

Question 13

An aircraft flying at FL300 from a warm airmass to a cold air mass should anticipate its true altitude to…

Answer 13

decrease

Question 14

You are flying east and are experiencing starboard drift. Where is the low pressure?

Answer 14

East

Question 15

2 aircraft are separated vertically by 2000’, both flying northward at constant indicated altitude. As they fly toward colder Temp, the actual vertical distance between the aircraft will….

Answer 15

remain constant

Question 16

An aircraft flying from an area of high to low pressure and trying to maintain the same indicated altitude without adjusting the altimeter will experience….

Answer 16

decreasing true altitude

Question 17

Increasing the Temperature below and through a layer will…

Answer 17

• Increase the separation between pressure level

- Raise the pressure levels

Question 18

At altitude you observe a tail wind with no drift. Your true altitude is….

Answer 18

Staying the same

Question 19

You are off from 0 MSL and clim to 10T indicated with the correct altimeter setting. At 10T the temperature is +6. What is the true altitude of the A/C?

Answer 19

Temp ISA at 10T=15-(2*10)= -5
\+6 - (-5) = 11
10 000 - 0 = 10 000
4 * 11 * 10 = 440'
True altitude = 10000 + 440 = 10440' ASL

Question 20

The altimeter setting at Edmonton is 29,92’’ and at Winnipeg it’s 30,62’’. If you flew from Edmonton to Winnipeg without updating your altimeter, the true altitude would be…

Answer 20

1000’ per inch of Hg

30,62 - 29,12 = 1.5 * 1000 = +1500 feet

Question 21

At Calgary the elevation is 3000’ and the surface temp is -35. At indicated 17000, the temp is -30. What is your true altitude?

Answer 21

Temp @ 17000 = 15 - (2*17) = -19
-30 - (-19) = -11
17000 - 3000 = 14000
4 * -11 * 14 = -616 * 1.5 = -924
17000 - 924 = 16 076'

Question 22

You are flying at indicated 10T over Calgary. You have 29.92’’ on your altimeter and report an OAT of -20. Calgary’s elevation is 3000’. Calgarys’s altimeter setting is 29,42’’ and surface temp is -30. What is the true altitude of the aircraft?

Answer 22

**Pressure 1st, Temp 2nd**
29,42-29.92 = -0.5 * 1000 = -500 (donc 9500')
15 - (2*9.5) = -4
-20 - (-4) = -16
9500 - 3000 = 6500
4 * -16 * 6.5 = -416 * 1,5 = -624'
9500' - 624' = 8876'