Communication and Navigation Systems

Question 1

Which frequency band is used for long-range communications from an aircraft?

Answer 1

The high frequency band (2 to 25 megahertz)

Question 2

What are the two methods of modulating carrier waves for transmitting information?

Answer 2

Amplitude modulation (AM) and frequency modulation (FM).

Question 3

What is meant by a transceiver?

Answer 3

It is a piece of radio communications equipment in which all of the circuits for the receiver and transmitter are contained in one housing.

Question 4

Is a certificated airframe mechanic allowed to adjust a communications transmitter?

Answer 4

No, this requires a license issued by the Federal communications commission.

Question 5

What kind of antenna is ued for the ATC transponder?

Answer 5

A UHF stub antenna.

Question 6

What is the preferred location for the ATC transponder atenna?

Answer 6

On the center line of the belly of the aircraft as far from any other antenna as is practical.

Question 7

What are the three basic types of antennas used in aviation?

Answer 7

Dipole antenna, Marconi antenna, and loop antenna.

Question 8

What type of antenna are most aircraft VHF communication antennas?

Answer 8

Marconi antennas.

Question 9

How do static wicks aid the aircraft communication radios?

Answer 9

Static wicks aid in the dissipation of static that builds up on the aircraft. Built-up static can cause radio receiver interference caused by corona discharge emitted from the aircraft as a result of precipitation static.

Question 10

What is the purpose of an intercom system?

Answer 10

To aid in communication between the flight crew, or between the flight crew and the cabin crew.

Question 11

What kind of conductor is used to connect a VHF or UHF antenna to the receiver or transmitter?

Answer 11

coaxial cable.

Question 12

What is a coaxial cable?

Answer 12

A type of two-conductor electrical cable in which the center conductor is encased in insulation inside a braided shield that serves as the outer conductor. Coaxial cables are normally used for attaching radio receivers and transmitters to antennas.

Question 13

How can you determine the proper coaxial cable and connectors to use in an aircraft radio installation?

Answer 13

Refer to the radio installation instructions for the correct part number for the cable and connectors.

Question 14

What precautions should be taken when installing coaxial cable between a radio transmitter and its antenna?

Answer 14

The routing should be as direct as possible, there should be no sharp bends in the coax, and it should be kept away from heat that could soften the insulation.

Question 15

What is a BNC connector?

Answer 15

A coaxial cable connector that is connected by inserting the guide pins on the male connector into slots in the female connector and twisting the connector one quarter turn.

Question 16

What kind of antenna is used for VHF communications?

Answer 16

A vertically polarized whip antenna.

Question 17

Which frequency band is used for most aircraft communications?

Answer 17

The VHF band, between 30 and 300 megahertz.

Question 18

What is the Aircraft Communications Addressing and Reporting System (ACARS), and how does it work?

Answer 18

ACARS is a two-way communication link between an airliner in flight and the airline’s main ground facilities. Data is collected in the aircraft by digital sensors and is transmitted to the ground facilities. Replies from the ground may be printed out so the appropriate flight crewmember can have a hard copy of the response.

Question 19

On what two frequencies does the emergency locator transmitter operate?

Answer 19

121.5 and 243.0 megahertz.

Question 20

Where is the ELT transmitter normally located on an aircraft?

Answer 20

In the tail of the aircraft or as far aft as possible, so it will be least likely to be damage in the crash.

Question 21

How often should the ELT batteries be replaced or recharged?

Answer 21

When the transmitter has been in use for more than 1 cumulative hour, when the battery expiration date has been reached, or when 50% of their useful life or charge has expired.

Question 22

How can you know when an ELT battery must be replaced or recharged?

Answer 22

By the date marked on the outside of the transmitter.

Question 23

How often must ELTs be inspected for proper installation, battery corrosion, operation of the controls and sensor, and the presence of the radiated signal?

Answer 23

Every 12calendar months.

Question 24

What causes an ELT to actuate?

Answer 24

An inertia switch that detects an impact parallel to the longitudinal axis of the aircraft as would occur in a crash.

Question 25

How is an ELT tested to determine that it is working?

Answer 25

Actuate the test switch and listen on 121.5 or 243.0 MHz. Make the test during the first five minutes of the hour and do not allow the ELT to operate for more than 3 sweeps. If the ELT is operated outside of this time frame, you should contact the control tower before conducting the test.

Question 26

What two types of antenna are used with most ADF receivers?

Answer 26

A directional loop antenna and a nondirectional sense antenna.

Question 27

Why is it necessary to install a double on the inside of the aircraft skin when antenna is mounted on the skin?

Answer 27

The double reinforces the skin so wind loads on the antenna will not cause the skin to flex and crack.

Question 28

What is the preferred location for a VOR antenna on an airplane?

Answer 28

On top of the aircraft, along the center line of the fuselage.

Question 29

Which component of the Instrument Landing System shares the antenna with the VOR?

Answer 29

The ILS localizer.

Question 30

In which frequency band does the VOR equipment operate?

Answer 30

In the VHF band, between 108.0 and 117.98 MHz.

Question 31

What is the preferred location for a DME antenna?

Answer 31

Along the center line of the belly of the aircraft, as far rom any other antenna as is pratical.

Question 32

In what frequency band does the DME equipment operate?

Answer 32

In the UHF band, between 962 and 1,024 MHz, and between 1,115 and 1,213 MHZ.

Question 33

What does the DME system measure?

Answer 33

Direct distance to the station that the signal is received from.

Question 34

What two signals are transmitted from an ILS ground-based station and then received in the aircraft?

Answer 34

A localizer signal provides horizontal guidance to the centerline of the runway. A separate glideslope provides vertical guidance of the aircraft down the proper slope to the touchdown point on the runway.

Question 35

Whaere do GPS units receive their signal from?

Answer 35

From satellites that orbit around the earth.

Question 36

How many satellites are typically in view of a GPS receiver?

Answer 36

Between five and eight satellites.

Question 37

How does a GPS receiver determine its position?

Answer 37

The amount of time it takes for signals to reach the aircraft GPS receiver from transmitting satellites is combined with each satellite’s exact location to calculate the position of an aircraft.

Question 38

What aircraft system does TCAS (traffic collision avoidance system) use for air-to-air monitoring and alerting?

Answer 38

The aircraft transponder.

Question 39

What is a TCAS Resolution Advisory (RA)?

Answer 39

This is an aural command to the pilot to take a specific evasive action (i.e., DESCEND). The computer is programmed such that the pilot in the encroaching aircraft receives an RA for evasive action in the opposite direction (if it is TCAS equipped).

Question 40

What type of weather is shown by an onboard weather radar system?

Answer 40

Onboard weather radar signals bounce off of precipitation only. Clouds do not create a return.

Question 41

Weather aids referred to as weather radar cover what three types of systems?

Answer 41

Onboard weather radar, lightning detectors, and satellite or other source weather radar information that comes from an outside source.

Question 42

What is the primary advisory that a radio altimeter is used for?

Answer 42

The landing decision height when on an instrument approach.

Question 43

Where does a ground proximity warning system receive its information from?

Answer 43

From a radio altimeter.

Question 44

What is the basic purpose of an autopilot?

Answer 44

It frees the human pilot from continuously having to fly the aircraft, and flies with a high degree of precision. It also couples with various electronic navigation aids.

Question 45

What are the basic subsystems of an automatic flight control system?

Answer 45

command, error-sensing, correction, and follow-up.

Question 46

What type of device is normally used in the error-sensing subsystem?

Answer 46

Gyros.

Question 47

What are three types of servos that are used in the correction subsystem?

Answer 47

Hydraulic, pneumatic, and electric.

Question 48

What is the purpose of the follow-up subsystem in an autopilot?

Answer 48

It stops the control movement when the surface has deflected the proper amount for the signal sent by the error sensor.

Question 49

What are the two parameters that auto-throttles can maintain or attain, and how do they function?

Answer 49

The two parameters are speed mode and thrust mode. In speed mode, the throttle is positioned to maintain a set target speed. In thrust mode, the engines are maintained at a fixed power setting to meet the different phases of flight (takeoff, climb, descent, etc.).

Question 50

What are the two types of helicopter stability augmentation systems?

Answer 50

A force trim system holds the cyclic control in the position at which it was released. A more advanced system uses electric actuators that make inputs to the hydraulic servos based on control commands from a computer that senses helicopter attitude.

Question 51

At what altitudes does a radio altimeter begin to measure aircraft height above the ground?

Answer 51

Below 2,500 ft.

Question 52

What data does an ADS-B Out system transmit?

Answer 52

Aircraft GPS location, altitude, velocity, and speed.

Question 53

Where does an ADS-B Out system transmit its data to?

Answer 53

Ground-based stations and other aircraft.

Question 54

In addition to information on other aircraft, what other information is available on ADS-B In?

Answer 54

Weather text and graphics information, ATIS information, and NOTAMs.

Question 55

What is the purpose of a transponder?

Answer 55

A transponder provides positive identification and location of an aircraft on the radar screens of ATC.

Question 56

How does an altitude encoder interface with a transponder?

Answer 56

For aircraft equipped with an altitude encoder, the transponder also provides the pressure altitude of the aircraft to be displayed adjacent to the ATC on-screen blip that represents the aircraft.

Question 57

Why is it important to follow the recommended procedures for testing ELTs?

Answer 57

A signal from an ELT can trigger a search and rescue operation, or at the very least, an inquiry to find out where the signal is coming from. Testing inside a metal hangar does not prevent the ELT’s signal from being picked up by Cospas-Sarsat satellite system.

Question 58

What precautions should be considered when routing wire harnesses?

Answer 58

Wire harnesses need to be protected from chafing and from interfering with other systems, especially those that have movement (retractable landing gear, flight controls, etc.). The routing of wire bundles also needs to consider the environmental condition that will be encountered (heat, corrosive environments, moisture, etc.). Wire bundles also generate magnetic fields and should not be routed close to other equipment that is sensitive to magnetic interference.

Question 59

What risks are associated with mounting aircraft antennas?

Answer 59

Antennas must be able to withstand high air loads and require a mounting doubler to be installed on the aircraft skin. The location of the antenna must not interfere with other locations and must be mounted in an area where signals can be optimally transmitted and received. Antennas must be electrically matched to the receiver and transmitter that they serve.

Question 60

Why is it important for static discharge wicks to be mounted on the trailing edges of control surfaces, wing tips, and the vertical stabilizer?

Answer 60

It is important that static wicks discharge static at points a critical distance away from avionics antennas where there is little or no coupling of the static to cause interference or noise in the radios.

Question 61

What risks are associated with working on live electrical systems?

Answer 61

The risks of working on live electrical circuits include inadvertent shorting of a positive voltage to ground, which could cause damage to a component, or inadvertent activation of systems. Additionally, power systems can cause electrical shock and injure to personnel.