AS 18 - AHRS Doppler Flashcards
Review Questions
What happens when the GPS is down to 3 satellites?
2 satellites?
GPS fails?
Lat/Long still valid
Altitude info no longer valid
Lat/Long not valid
GPS not usable, revert to degraded ops
GPS position becomes erratic and varies randomly with large errors
NTS time still operates
What is the purpose of the Standby Compass? Where is it located?
Provides a back-up heading reference independent of AHRS
Located on windshield center post.
What are the AHRS components?
Remote compass transmitter - flux valve
Attitude heading reference unit - AHRU
AHRS control panel
What is the Remote Compass Transmitter and how is it situated on the aircraft?
A sensing element (flux valve) pendulously suspended on a universal joint within the bowl
Damping fluid is added to prevent excessive swinging
Why are the Remote Compasses located on each wing tip?
To achieve the greatest distance from magnetic disturbances from the AC
Describe the construction of the Flux Valve
One primary exciter coil. three secondary pick-off coils, surrounded by three collector horns
(resembles a three spoke wheel)
What does the flux valve do?
Detects the magnitude and direction of the earth’s magnetic field (H component)
Converts this to electrical information
The info is then used to align the Directional Gyro in the AHRU.
The magnitude of the induced current in the pickoff coils in the flux valve depends on what?
Varies according to the number of magnetic lines cutting them
Where is the AHRU located?
Under the floor, aft the air-stair door
What data can be input into the AHRU?
TAS, from the appropriate ADC via the ADC data bus
Magnetic heading information, from the flux valve via the AHRS Control Panel
What systems receive output data from the AHRS?
Flight instruments Flight guidance computers Air data computers Advisory displays FMS
Which flight instruments receive output data from the AHRS?
EFIS
ADIs & HSIs
Pilot/ Co-pilot RMI
True or false
The RMI heading is simulating an AHRS provided mag hdg.
True
Define Doppler
Frequency shift observed due to the relative motion of the source and/or receiver
True or false
The motion of the observer produces a real shift in frequency while the motion of the source produces only an apparent shift in frequency.
False, vice versa