H. Aircraft Instrument Systems
What is the maximum amount of deviation error allowed when a magnetic compass is installed in an aircraft? (AM.II.H.K2)
10 degrees.
How much difference is allowed between the altitude indication on the automatic pressure altitude reporting equipment and that on the altimeter? (AM.II.H.K10)
125 feet.
Where are the requirements for the altimeter system tests found? (AM.II.H.K10)
14 CFR Part 43, Appendix E.
What is the allowable difference between the surveyed elevation of the airport and the indication on the altimeter when it is set to the local altimeter setting? (AM.II.H.K10)
75 feet.
What type of electrical circuit is used to measure small changes of resistance in an electrical resistance temperature probe? (AM.II.H.K5)
A Wheatstone-bridge circuit.
A failure of an airspeed indicator needle to move is likely caused by what problem? (AM.II.H.K4)
A blockage in the pitot head will prevent the creation of a differential pressure.
What type of filter is used with a vacuum system for gyros? (AM.II.H.K7)
A central air filter.
Who is authorized to conduct a static system test specified in 14 CFR §91.411? (AM.II.H.K19)
A certificated Aviation Mechanic holding an Airframe rating.
What mechanical means is used to measure pressure in an airspeed indicator? (AM.II.H.K4)
A diaphragm.
What two types of pumps are used in the low-pressure pneumatic system? (AM.II.H.K9)
A dry-type and a wet-type air pump.
What mechanical means can be used to measure oil temperature? (AM.II.H.K5)
A fluid filled, sealed system comprising of a bulb and capillary tube connected to a Bourdon tube. As temperature increases, the volume of the fluid increases and expands the Bourdon tube, which is connected to an indicator dial.
What is a head-up display (HUD)? (AM.II.H.K18)
A head-up display proved critical flight information to the pilot on a see-through display that is in the pilot's line of sight.
What are two types of filters used with a pressure system for gyros? (AM.II.H.K7)
A pump inlet filter and an inline filter.
What conditions are indicated by a landing gear warning system? (AM.II.H.K22)
A red light will illuminate if any of the gear is in an unsafe condition. A green light shows when all landing gear are down and locked. An aural warning will sound a horn if the landing gear are not down when the throttles are retarded for landing.
What fluid is used in an aircraft magnetic compass? (AM.II.H.K2)
A special water-clear fluid similar to kerosine.
Why is it important for a stall warning system to be adjusted correctly? (AM.II.H.K21)
A stall warning system is adjusted to allow sufficient margin and warning prior to an actual stall.
What information is allowed to be depicted on electronic displays? (AM.II.H.K16)
All information relating to flight and aircraft systems can be displayed on electronic displays. The main flight instruments are displayed on what is referred to as the primary flight display (PFD) or electronic flight instrument system (EFIS). Data displays for engine parameters, hydraulics, fuel, and other airframe systems are displayed on secondary flight displays or independent displays. These secondary displays are often referred to as multifunction displays (MFDs).
What must be done to the gyro pressure system if a dry-type air pump fails? (AM.II.H.K9)
All of the filters must be replaced to prevent any debris from the pump vanes getting into the gyro instruments.
What are the differences between absolute, gauge, and differential pressure instrument systems? (AM.II.H.K10)
An absolute pressure instrument, such as an altimeter, measures actual pressure. Gauge pressure instruments measure the difference between exiting barometric pressure and pressure inside a sealed container such as a Bourdon tube or a bellows. Differential pressure instruments display the difference between two pressures, such as pitot pressure and static pressure used to display airspeed.
What device is used with a wet-pump vacuum system to prevent oil from getting into the deicer boots? (AM.II.H.K7)
An oil separator.
When should a static system leak check be performed? (AM.II.H.K19)
Any time the static system has been opened.
Where on an airport is a compass rose located? (AM.II.H.K3)
At a location where there is little traffic and the area is free from magnetic interference caused by electrical power lines or buried pipes.
What is meant by built-in test equipment (BITE)? (AM.II.H.K15)
BITE is a standard component of maintenance panels that are a part of Electronic Centralized Aircraft Monitor (ECAM) systems. It is standard for monitoring systems to monitor themselves as well as the aircraft systems. All of the system inputs to the flight warning computers can also be tested for continuity from this panel, as well as inputs and outputs of the system data analog converter.
What are the vanes of a dry-type air pump made of? (AM.II.H.K9)
Carbon.
What is the difference between variation and deviation in a compass system? (AM.II.H.K2)
Compass variation is caused by the difference between the earth's magnetic and geographic poles. Aeronautical charts display magnetic variation. Compass deviation is caused by all other magnetic fields aside from the earth's magnetic and geographic poles. Deviation may be caused by magnetic fields in the aircraft.
What error is corrected when an aircraft compass is swung? (AM.II.H.K3)
Deviation error.
What are the basic methods of measuring fuel quantity in an aircraft? (AM.II.H.K11)
Direct reading systems (sight gauges), floats that actuate a variable resistor, and capacitance-type systems.
How often should an altimeter be checked if it is installed in an aircraft used in IFR flight? (AM.II.H.K10)
Every 24 calendar months.
What do the green, yellow, and red arc markings on an instrument mean? (AM.II.H.K12)
Green indicates normal operating range, yellow indicates caution operating range, and red indicates prohibited operating range.
What may be causing an attitude indicator to not properly erect or display? (AM.II.H.K7)
Gyroscopes are dependent on achieving and maintaining proper rotational speed. Failure to do so may be caused by low vacuum created by the vacuum system or motor failure in an electrically-driven gyroscope.
What are the gyroscopic instruments that are connected to the low-pressure pneumatic system of an aircraft? (AM.II.H.K7)
Heading indicator, attitude indicator, and turn-and-slip indicator.
Where should the compass correction card be placed? (AM.II.H.K2)
In plain sight of the pilot, near the compass.
Where are instructions found for adjustments to a system that is displayed on an electronic display? (AM.II.H.K13)
In the aircraft maintenance manual.
Where are the system descriptions found for annunciator indications and the meaning of the associated warnings, cautions, and advisory lights? (AM.II.H.K1)
In the pilot's operating handbook (POH)/airplane flight manual (AFM) and the aircraft instructions for continued airworthiness (ICAs).
Why is grounding and bonding important for aircraft electrical systems? (AM.II.H.K14)
Inadequate bonding or grounding can lead to unreliable operation of systems, EMI, electrostatic discharge damage to sensitive electronics, personnel shock hazard, or damage from lightning strike.
What is the purpose of a stick shaker used on some aircraft? (AM.II.H.K21)
It provides an artificial stall warning to the pilot.
What should be done to the static port that is not being used to conduct the leak test? (AM.II.H.K19)
It should be taped over in such a way that the tape can not be overlooked or forgotten when the test is completed.
Do the tests described in 14 CFR Part 43, Appendix E, apply to the altimeters installed in all certificated aircraft? (AM.II.H.K19)
No, only those operated under instrument flight rules in controlled airspace.
Can an aviation mechanic with an A&P Rating repair an instrument with a cracked glass? (AM.II.H.K20)
No. The instrument must be replaced.
What are six tests that must be made when testing an altimeter? (AM.II.H.K20)
Scale error, hysteresis, after-effect, friction, case leak, and barometric scale error.
What type of direction-finding compass has no moving parts and easily integrates with digital systems? (AM.II.H.K8)
Solid state magnetometers.
What are the vanes of a wet-type air pump made of? (AM.II.H.K9)
Steel.
What does an angle of attack (AOA) indicator provide for the pilot? (AM.II.H.K21)
The AOA offers a visual indication of the amount of lift the wing is producing at a given airspeed or angle of bank. The AOA delivers critical information to indicate the actual safety margin above an aerodynamic stall.
To what avionic equipment is the output from an encoding altimeter connected? (AM.II.H.K10)
The ATC transponder.
What are the three fundamental pressure-sensing mechanisms used in aircraft instrument systems? (AM.II.H.K4)
The Bourdon tube, the diaphragm or bellows, and the solid-state sensing device.
What basic mechanism is used to measure oil, fuel, and oxygen pressures? (AM.II.H.K4)
The Bourdon tube.
What record must be made of a test of an altimeter? (AM.II.H.K10)
The aircraft permanent maintenance record must show the date, the maximum altitude to which the altimeter was tested, and the name of the person approving the aircraft for return to service after the test.
What instruments in an aircraft are connected to the static system? (AM.II.H.K10)
The airspeed indicator, vertical speed indicator, and altimeter.
What indication on the altimeter shows that the pressure inside the static system has been decreased by 1 inch of mercury? (AM.II.H.K20)
The altimeter will show an increase of approximately 1,000 feet.
What is done to a compass to correct for deviation error? (AM.II.H.K3)
The compensating magnets in the compass are adjusted to minimize the effect of outside magnetic fields.
How does a flux gate compass operate? (AM.II.H.K8)
The flux gate compass consists of a very magnetically permeable circular segmented core frame called a spider. The earth's magnetic field flows through this iron core and varies its distribution through segments of the core as the flux valve is rotated via the movement of the aircraft. Pickup coil windings are located on each of the core's spider legs that are positioned 120° apart. The signal from the flux gate is passed to the flight deck via an autosyn transmitter.
Why is it important to use the correct gasket when replacing a wet-type air pump? (AM.II.H.K9)
The gasket must have a hole through which the pump lubricating oil can flow.
Who is authorized to perform the altimeter tests to determine the accuracy of the altimeter? (AM.II.H.K10)
The manufacturer of the aircraft on which the tests are conducted, or a certificated repair station properly equipped and authorized to perform the test.
What information is shown by the wing flap position indicator? (AM.II.H.K6)
The number of degrees the flaps are lowered.
Why do dry-type air pumps not need to be lubricated? (AM.II.H.K9)
The special carbon material of which the vanes are made wears away in microscopic amounts to provide the needed lubrication.
What is the purpose of an engine-indicating and crew alerting system (EICAS)? (AM.II.H.K17)
The system monitors aircraft systems for the pilot and displays engine and airframe parameters.
What systems does a takeoff warning system monitor? (AM.II.H.K22)
The takeoff warning system senses when the power lever is advanced and checks for proper position of flaps and trim systems. A warning horn and caution light will be activated if the takeoff configuration is incorrect.
How does a thermocouple measure temperature? (AM.II.H.K5)
The unit is comprised of two unlike metals. As temperature increases, a small voltage is produced and sent to a temperature indicator. The higher the temperature, the higher the voltage.
Why is the length of a thermocouple lead important? (AM.II.H.K5)
Thermocouple accuracy is dependent on the resistance of the circuit. Lead lengths are designed for specific installations and should never be altered.
Why are instrument panels shock-mounted? (AM.II.H.K24)
To absorb low-frequency, high-amplitude shocks.
What is the purpose of bonding straps between flight controls and the attaching structure? (AM.II.H.K23)
To provide an electrical path for dissipation of static electricity and to reduce damage from electrostatic discharges and lightning strikes.
To what altitude must altimeters be tested? (AM.II.H.K10)
To the highest altitude the aircraft will be flown on IFR flight.
What type of system is used to indicate the position of the wing flaps? (AM.II.H.K6)
Usually a resistance-type remote-indicating system such as the DC Selsyn system.
How much leakage is allowed in the static system of a pressurized aircraft? (AM.II.H.K20)
With a pressure differential equal to the maximum cabin differential pressure for which the aircraft is certificated, the system must not show a loss of indicated altitude of more than 2 percent of the equivalent altitude of the maximum cabin differential pressure or 100 feet, whichever is the greater, in one minute.
How much leakage is allowed in the static system of an unpressurized aircraft? (AM.II.H.K20)
With a pressure differential of 1 inch of mercury, the system must not show a loss of indicated altitude of more than 100 feet in one minute.
How are the vanes of a wet-type air pump lubricated? (AM.II.H.K9)
With engine oil directed into the pump through a small hole in the base of the pump.
