Answers - Aircraft Instrument Systems

Fill in the Blanks

1. senses; display
2. air; gyroscopes
3. bourbon tube, diaphragm or bellows, solid‐state
4. sensed air pressure, digital values
5. pitot static, aircraft systems
6. altitude, pressure, pressure
7. true airspeed
8. machmeter
9. synchro
10. electro, permanent
11. crankshaft
12. tachometer probes, tach generator
13. forces, inertial reference
14. ADC
15. direction, angle
16. vacuum systems, pressure systems, electrical systems
17. artificial horizon, pitch, roll.
18. laterally, vertically, longitudinally
19. sensing elements, computing elements, output elements, command elements
20. attitude, electric attitude indicators
21. ECAM
22. flight management system (FMS)
23. flight, engine, airframe
24. 24
25. electromagnetic, electrical

True or False

1. true
2. false; flight, engine, navigation
3. true
4. false; an aneroid
5. false; remote
6. true
7. true
8. true
9. false; direct current systems often use DC Selsyn systems.
10. true
11. true
12. false; pushes the control yoke forwards to lower the nose
13. true
14. false; total air temperature is the static air temperature plus any rise in temperature caused by high speed movement of the aircraft through the air.
15. true
16. false; swinging the compass is the process for adjusting magnetic deviation.
17. true
18. false; the magnetic compass is not a sensing element of the autopilot system.
19. true
20. false; attitude indicator and directional gyro.
21. true
22. true
23. false; the master caution light can be cancelled.
24. false; low frequency
25. true

Knowledge Application

1. aircraft specification; type certificate data sheets; flight manuals
2. caution
3. a sensitive altimeter
4. scale, hysteresis, and installation
5. rate of climb, airspeed, and altimeter
6. a leak test
7. vacuum, air pressure, or electricity
8. transmits information from one point to another point
9. crankshaft or main turbine rotor speed
10. a thermocouple‐type system
11. correct for deviations by adjusting compensating magnets
12. flight instruments, engine instruments, navigation instruments
13. the total exhaust pressure to the pressure of the ram air at the inlet of the engine
14. air data computer (ADC)
15. vane type which uses an alpha vane externally mounted to the outside of the fuselage; probe type which uses two slots in a probe that extends out of the side of the fuselage
16. cylinder head temperature in reciprocating engines and exhaust gas temperature in turbine engines
19. certificated A & P mechanics can remove, inspect, troubleshoot, and perform operation checks of instruments
20. EICAS or ECAM, Air DATA Computer, thrust management computer, EIFIS symbol generators, ADFS, Inertial reference system, collision avoidance system, radio navigational aids.

Multiple Choices

1. b
An aircraft's magnetic compass is swung to correct for magnetic disturbances within the aircraft, called deviation.

2. a
A hydraulic pressure gage generally uses a Bourdon tube and a gear-and-pinion mechanism by which the Bourdon tube's motion is amplified and transferred to the pointer.

3. b
The fixed reference marker attached to the compass bowl of a magnetic compass is called a lubber line.

4. a
Instrument range markings indicate at a glance whether a system or component is operating in a safe range or an unsafe range. See also FAR 23.

5. c
A compensating device containing small permanent magnets is incorporated in the compass to correct for deviations of the compass which result from the magnetic influences of the aircraft structure and electrical system.

6. b
An aircraft's altimeter and airspeed indicator rely on the static pressure reading to accurately indicate their readings. The altimeter displays altitude as a function of outside (ambient) pressure, a reading which comes from the static system. The airspeed indicator displays a reading by comparing the total pressure in the pitot system to the static pressure reading. If the static pressure value being supplied to both of these systems is coming from a pressurized cabin, it will cause the altimeter and the airspeed indicator to both read low.

7. a
According to FAR 23, the maximum deviation (during level flight) permitted in a magnetic direction indicator installed in an airplane is 10.

8. a
The magnetic compass consists of a liquid filled bowl containing a pivoted float element to which one or more bar magnets, called needles, are fastened. The liquid in the bowl dampens the oscillations of the float and decreases the friction of the pivot.

9. b
When suction is applied to the static system in an aircraft, the altimeter is made to read a higher altitude (as a function of the decreased pressure). By observing the rate of change (decreasing altitude) in the altimeter, it is possible to check the static system for leakage.

10. b
According to FAR 23, the maximum altitude loss permitted during an unpressurized aircraft instrument static pressure system integrity check is 100 ft in one minute.

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