Chapter 17 - Radio Altimeter

Question 1

Low altitude rad alt is calibrated to?

Answer 1

0 - 2500 ft

Question 2

What EM radiation does a Rad Alt use?

Answer 2

Radio waves

Question 3

The rad alt will provide height and/or rate of change of height above ground level to the following systems:

Answer 3

• Autopilot, auto-throttle and flight director
• Ground Proximity Warning System (GPWS)
• Some Traffic Collision and Avoidance System (TCAS) systems

Question 4

What are the system components of the Rad Alt?

Answer 4

• Transmit/Receive Unit
• Two antennas: one for the transmission, and an other for the reception

Question 5

Detail the incident and reflected wave transmitted by a rad alt?

Answer 5

Question 6

The aircraft transmits a _____ downwards and awaits its return. The time taken is multiplied by the _______, giving a reading of _____ below the aircraft.

Answer 6

• radio wave
• speed of radio waves and divided by 2
• absolute height

Question 7

The Radio Altimeter uses primary radar principles and assesses the AGL height by? 2 things

Answer 7

• Measuring the time taken for the signal to travel from the aircraft to the ground and back again.
• Calculating the distance using the known speed for the radio waves.

Question 8

What does FMCW mean?

Answer 8

Frequency Modulated Continuous Wave

Question 9

What are the frequencies associated with the Rad Alt?

Answer 9

4300 MHz modulated ±50 MHz

100 MHz bandwidth

SHF band – 4200 MHz to 4400 MHz

Modulation sweep rate: 0.01sec to eliminate ambiguity

Question 10

Rad Alt frequencies:

_____ modulated _____

____ MHz bandwidth

_____ band – ____ MHz to ____ MHz

Modulation sweep rate: ____sec to eliminate ambiguity

Answer 10

• 4300 MHz
• ±50 MHz
• 100
• SHF
• 4200
• 4400
• 0.01

Question 11

What shape is the beam of the Rad Alt?

Answer 11

Elliptical Conical Beam

Question 12

The beam of a Rad Alt allows for in pitch and roll?

Answer 12

30 Deg in Pitch
60 Deg in Roll

Question 13

The Rad Alt is required to read 0 as the ____ touch down

When the aircraft settles on the ground expect it to read a ____?

Answer 13

• Main wheels
• Negative value

Question 14

You have to calibrate a Rad alt to take into account?

Answer 14

Cable length (causes delay)

Question 15

What is the normal operating range of the Rad Alt?

Answer 15

-20 ft to 2500 ft

Question 16

Rad Alt:

Expected accuracy below 500 ft is the greater of:

____ of indicated height or ____

Above 500 ft, expect ____

Answer 16

• ± 2 %
• ± 2 ft
• ± 5%

Question 17

A failure of the RA will cause the following systems to operate in a degraded mode?

Answer 17

• Autopilot – no autoland as RA triggers several events
• Autothrottle – no autoland as events such as RETARD will no longer function
• Ground Proximity Warning System (GPWS) the aircraft will be unable to sense that it is near the ground
• Traffic Collision and Avoidance System (TCAS) systems – input to TCAS to inhibit certain types of warnings near the ground

Question 18

The Rad Alt supplies data to the:

Answer 18

TCAS, GPWS, Automatic Landing System