# Aircraft Performance Questions and Answers – Measurement of Height

This set of Aircraft Performance Multiple Choice Questions & Answers (MCQs) focuses on “Measurement of Height”.

1. What is meant by altimeter reading?
a) It is the reading of individual mechanical instrument which calculates the pressure
b) It is the reading of individual electrical instrument which calculates the pressure
c) It is the reading of individual mechanical instrument which calculates the density
d) It is the reading of individual electrical instrument which calculates the density

Explanation: Altimeter reading is the reading of individual mechanical instrument which calculates the pressure. During these calculations some corrections are made to avoid errors that are caused due to mechanical tolerance.

2. What is meant by indicated altitude?
a) It is the pitot-static reading corrected for performance error
b) It is the altimeter reading corrected for instrument error
c) It is the pitot-static reading corrected for instrument error
d) It is the altimeter reading corrected for performance error

Explanation: Indicated altitude is the altimeter reading corrected for instrument error. The indicated altitude will be measured with reference to the appropriate altimeter datum pressure setting.

3. Altimeter indicates the height as a function of barometric static pressure in the atmosphere.
a) True
b) False

Explanation: Altimeter indicates the height as a function of barometric static pressure in the atmosphere. Altimeter reading is the reading of individual mechanical instrument which calculates the pressure. During these calculations some corrections are made to avoid errors that are caused due to mechanical tolerance.

4. What is meant by pressure altitude?
a) It is the indicated altitude measured with respect to appropriate datum pressure setting
b) It is the indicated altitude measured with respect to appropriate gauge pressure setting
c) It is the indicated altitude measured with respect to appropriate static pressure setting
d) It is the indicated altitude measured with respect to appropriate vacuum pressure setting

Explanation: Pressure altitude it is the indicated altitude measured with respect to appropriate datum pressure setting. It is corrected for static pressure error. This error is caused due to the static source being located within the disturbed pressure field caused due to presence of aircraft.

5. What is meant by geopotential height interval?
a) It is the pressure height interval measured by the pitot-static tube
b) It is the pressure height interval measured by the altimeter
c) It is the temperature height interval measured by the pitot-static tube
d) It is the temperature height interval measured by the altimeter

Explanation: Geopotential height interval it is the pressure height interval measured by the altimeter. Geopotential height interval is corrected for temperature difference from ISA model atmosphere.
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6. The geopotential height of the isothermal lower stratosphere (i.e. at 11km) is given by __________
a) H=11000-$$\frac{RT_{11}}{g_0}$$ln($$\frac{p}{p_{11}}$$)
b) H=11000-$$\frac{RT_{11}}{g_0}$$ln($$\frac{p_{11}}{p}$$)
c) H=11000+$$\frac{RT_{11}}{g_0}$$ln($$\frac{p}{p_{11}}$$)
d) H=11000+$$\frac{RT_{11}}{g_0}$$ln($$\frac{p_{11}}{p}$$)

Explanation: The height of the isothermal lower stratosphere is given by H=11000-$$\frac{RT_{11}}{g_0}$$ln($$\frac{p}{p_{11}}$$) where,
H=geopotential height
R=characteristic gas constant
T11=temperature at 11km
P11=pressure at 11km
g0=acceleration due to gravity
p=pressure.

7. Find the geopotential height of an aircraft flying sea level where L0=-0.0065 k/m, p=30070.36Pa.
a) 9120 km
b) 9144 km
c) 9854 km
d) 9874 km

Explanation: The answer is 9144 km. Given L0=-0.0065 k/m, p=30070.36 Pa.
We know T0=288.15K, p0=101325Pa, R=287 J/kg-K, g0=9.81m/s2.
From H=$$\frac{T_0}{l_0}$$[$$(\frac{p}{p_0})^\frac{-L_0R}{g_0}$$-1]
H=$$\frac{288.15}{-0.0065}$$[$$(\frac{30070.36}{101325})^\frac{-(-0.0065)*287}{9.81}$$-1]
H=9144 km.

8.The geopotential height in troposphere is given by __________
a) H=$$\frac{T_0}{l_0}$$[($$\frac{p}{p_0}$$)$$\frac{-L_0R}{g_0}$$+1]
b) H=$$\frac{T_0}{l_0}$$[($$\frac{p}{p_0}$$)$$\frac{L_0R}{g_0}$$-1]
c) H=$$\frac{T_0}{l_0}$$[($$\frac{p}{p_0}$$)$$\frac{-L_0R}{g_0}$$-1]
d) H=$$\frac{T_0}{l_0}$$[($$\frac{p}{p_0}$$)$$\frac{L_0R}{g_0}$$+1]

Explanation: The geopotential height in troposphere is given by H=$$\frac{T_0}{l_0}$$[($$\frac{p}{p_0}$$)$$\frac{-L_0R}{g_0}$$-1] where
H=geopotential height
R=characteristic gas constant
T0=temperature at 11km
P0=pressure at 11km
g0=acceleration due to gravity
p=pressure
L0=lapse rate.

9. What is a barometric altimeter?
a) A device used to measure the height above a fixed level with the help of barometric pressure changes
b) A device used to measure the pressure above a fixed level with the help of barometric pressure changes
c) A device used to measure the height above a fixed level with the help of pitot tube pressure changes
d) A device used to measure the pressure above a fixed level with the help of pitot tube pressure changes

Explanation: Barometric altimeter is a device used to measure the height above fixed level with the help of barometric pressure changes. Barometric altimeter is calibrated as soon as the flight is reached to a known altitude, at this point the barometric altimeter will accurate to 1metre.

10. QNH is a sea-level pressure which is used to measure the height above sea level.
a) True
b) False

Explanation: QNH is a sea-level pressure which is used to measure the height above sea level with the help of altimeter, when the QNH is set in the aircraft then the altimeter reads altitudes above mean sea level.

11. The installation of QNH in an aircraft helps the altimeter in reading the heights above air field level whereas the installation of QFE in an aircraft helps the altimeter in reading the heights above mean sea level.
a) True
b) False

Explanation: The installation of QNH in an aircraft helps the altimeter in reading the heights above mean sea level whereas the installation of QFE in an aircraft helps the altimeter in reading the heights above air field level.

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