Chapter 17 - Radio Altimeter Flashcards
Low altitude rad alt is calibrated to?
0 - 2500 ft
What EM radiation does a Rad Alt use?
Radio waves
The rad alt will provide height and/or rate of change of height above ground level to the following systems:
- Autopilot, auto-throttle and flight director
- Ground Proximity Warning System (GPWS)
- Some Traffic Collision and Avoidance System (TCAS) systems
What are the system components of the Rad Alt?
- Transmit/Receive Unit
- Two antennas: one for the transmission, and an other for the reception
Detail the incident and reflected wave transmitted by a rad alt?
The aircraft transmits a _____ downwards and awaits its return. The time taken is multiplied by the _______, giving a reading of _____ below the aircraft.
- radio wave
- speed of radio waves and divided by 2
- absolute height
The Radio Altimeter uses primary radar principles and assesses the AGL height by? 2 things
- 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.
What does FMCW mean?
Frequency Modulated Continuous Wave
What are the frequencies associated with the Rad Alt?
4300 MHz modulated ±50 MHz
100 MHz bandwidth
SHF band – 4200 MHz to 4400 MHz
Modulation sweep rate: 0.01sec to eliminate ambiguity
Rad Alt frequencies:
_____ modulated _____
____ MHz bandwidth
_____ band – ____ MHz to ____ MHz
Modulation sweep rate: ____sec to eliminate ambiguity
- 4300 MHz
- ±50 MHz
- 100
- SHF
- 4200
- 4400
- 0.01
What shape is the beam of the Rad Alt?
Elliptical Conical Beam
The beam of a Rad Alt allows for in pitch and roll?
30 Deg in Pitch
60 Deg in Roll
The Rad Alt is required to read 0 as the ____ touch down
When the aircraft settles on the ground expect it to read a ____?
- Main wheels
- Negative value
You have to calibrate a Rad alt to take into account?
Cable length (causes delay)
What is the normal operating range of the Rad Alt?
-20 ft to 2500 ft
Rad Alt:
Expected accuracy below 500 ft is the greater of:
____ of indicated height or ____
Above 500 ft, expect ____
- ± 2 %
- ± 2 ft
- ± 5%
A failure of the RA will cause the following systems to operate in a degraded mode?
- 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
The Rad Alt supplies data to the:
TCAS, GPWS, Automatic Landing System
