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Flashcards in Rad Alt Deck (12):
1

What is a radio altimeter?

Equipment which measures the distance to the ground via radio waves. It is much more accurate than an altimeter, esp. required when LDG.

2

Which instruments rely on accurate Rad Alt data?

GPWS
Auto throttle
Autopilot responses to ILS deviations
TCAS

3

What is the limit of a Rad Alt?

≤ 2,500'

2,450' to be precise.

4

What is the freq band used for Rad alt?

400mHz
SHF

Wavelength 7.1cm
Centrimetric

5

How are Rad Alt modulated?

FM using a continuous wave (CWFM)

6

How does the Rad Alt work?

By sending out a CWFM and measuring the difference between the transmission and reflection of the signal.

How out of phase the waves are indicate the height of the A/C. So the greater the difference of waves, the higher the A/C is from the ground.

7

What are the antenna characteristics of a Rad Alt?

A beam sweeps 30 to 60˚ (manufacturer dependent) in pitch and roll. There is a separate antennae for transmission and reception.

The beam sweeps wider in roll so that accuracy can be maintained. As terrain is uneven, Rad Alt will lock on the strongest signal rather than give an ave read out.

8

For a Rad Alt, what is residual distance and cable length compensation?

During LDG, the Rad Alt is programmed to measure the height from the wheels

9

What is the accuracy of Rad Alt during the later stages of approach within?

The greater of:
• +/- 2' below 500'
• +/- 1.5%

10

What are the main types of Rad Alt displays?

• Standalone: those without an EFIS system is analogue
• Boeing is digital > 1000' > digital and analogue
• Airbus: digital

11

For most radio altimeters, when a system error occurs during approach...

Height indication is removed.

12

Rad alt is supplies data to which systems?

TCAS
GPWS
Autoland