Aircraft Instruments Systems

Question 1

What instruments in an aircraft are connected to the static system?

Answer 1

The airspeed indicator, the vertical speed indicator, and the altimeter.

Question 2

What types of repairs or alterations can a certificated A&P mechanic make to aircraft instruments?

Answer 2

None. All repairs and alterations must be made by the instrument manufacturer or by an FAA-approved repair station certificated for the particular instruments.

Question 3

What is the significance of a red radial line on the dial of an aircraft instrument?

Answer 3

A red radial line marks a never-exceed condition.

Question 4

What is the significance of a yellow arc on the dial of an aircraft instrument?

Answer 4

A yellow arc marks a caution range of operation.

Question 5

What is the significance of a green arc on the dial of an aircraft instrument?

Answer 5

A green arc indicates the normal range of operation.

Question 6

What is the significance of a white arc on the dial of an airspeed indicator?

Answer 6

A white arc on an airspeed indicator indicates the airspeeds at which the flaps may be lowered.

Question 7

What is used to warn a mechanic that the glass on an aircraft instrument that contains the range marks has slipped?

Answer 7

A white slippage mark that extends across the lower part of the instrument cover glass and the instrument case bezel shows whether or not the glass has slipped. A slipped glass would put the range marks over the incorrect numbers.

Question 8

Where can a mechanic find the range markings that are required on the instruments in a particular aircraft?

Answer 8

In the Type Certificate Data Sheets for the aircraft.

Question 9

What check must be made if a mechanic replaces any instrument that is connected to the instrument static system?

Answer 9

The static system must be checked for leaks.

Question 10

Why are many of the electrical instruments mounted in steel cases?

Answer 10

A steel case concentrates the flux produced by magnets in the instrument and keeps it from affecting other nearby instruments.

Question 11

Why must an aircraft instrument panel be electrically bonded to the primary aircraft structure?

Answer 11

The bonding straps carry the return current from the instruments into the aircraft structure.

Question 12

What error is corrected when an aircraft compass is swung?

Answer 12

Deviation error.

Question 13

What fluid is used in an aircraft magnetic compass?

Answer 13

A special water-clear fluid that is similar to kerosine.

Question 14

What is the maximum amount of deviation error that is allowed when a magnetic compass is installed in an aircraft?

Answer 14

10 degrees.

Question 15

What is the maximum amount of leakage that is allowed when checking the static system of an aircraft that is operated under Instrument Flight Rules?

Answer 15

In an unpressurized aircraft, the static system is checked with a 1,000-foot indication on the altimeter. It must not leak more than 100 feet in one minute.
In a pressurized aircraft, the system is checked at the maximum certificated pressure differential of the cabin. It must not leak more than 2 percent of the equivalent altitude of the maximum differential pressure or 100 feet, whichever is greater, in one minute.

Question 16

Why must the length of the thermocouple leads not be altered when installing a cylinder head temperature indicator?

Answer 16

An instrument operated by a thermocouple is a current measuring device. The resistance of the thermocouple and its leads must be kept at the value specified for the indicator.

Question 17

What should a manifold pressure gage read when the engine is not operating?

Answer 17

It should read the existing barometric pressure.

Question 18

What is the difference between a two-minute and a four-minute turn and slip indicator?

Answer 18

A two-minute turn indicator is for a standard rate turn (three degrees per second), while a four-minute turn indicator is for a half-standard rate turn (1-1/2 degrees per second) and has doghouse-shaped marks indicating a standard rate turn when aligned with the needle.

Question 19

What is the difference between a turn and slip indicator and a turn coordinator?

Answer 19

A turn and slip indicator is sensitive about only the yaw (vertical axis of the aircraft) A turn coordinator uses a canted gyro which makes it sensitive about both the roll and yaw axes.

Question 20

What is used as the sensor in the fuel tank for an electronic-type fuel quantity indicating system?

Answer 20

Tubular capacitors which extend across the fuel tank from top to bottom.

Question 21

Why is a dual tachometer used on a single-engine helicopter?

Answer 21

One needle indicates the speed of the engine, and the other indicates the speed of the main rotor. When the needles are married, the clutch is not slipping and the rotor is solidly engaged to the engine.

Question 22

In what units is the tachometer used on a turbine engine calibrated?

Answer 22

In percentage of the takeoff RPM.

Question 23

What kind of system is used to measure the exhaust gas temperature of a turbine engine?

Answer 23

An averaging system made up of a series of thermocouples arranged around the inside of the exhaust duct of the engine.

Question 24

What would likely cause the needle of an electrical oil temperature gage to peg on the high side of the instrument dial?

Answer 24

an open circuit in the bulb circuit. This open circuit causes the instrument to perceive infinite resistance, causing the needle to move further across the dial as resistance increases.

Question 25

What is used as a flowmeter for most of the small horizontally opposed fuel injected aircraft engines?

Answer 25

A pressure gage that measures the pressure drop across the injector nozzles.

Question 26

What two sources of power are used to operate the gyro instruments in an aircraft?

Answer 26

They may be air operated, either by suction or pressure, or they may be electrically operated.

Question 27

What is an annunciator panel in an aircraft?

Answer 27

A single location that contains all of the warning and condition lights for the aircraft. This makes it easy for the pilot to monitor all of the systems at a glance.

Question 28

What condition could cause a takeoff warning system to actuate?

Answer 28

The takeoff warning system gives an aural warning when the power lever is advanced for takeoff if the flight controls for the stabilizer, the flaps, and the speed brakes are in an unsafe condition for takeoff.

Question 29

What would cause the warning horn to sound when the throttles are pulled back, reducing the engine power for landing?

Answer 29

The warning horn will sound if any of the landing gears are not down and locked.