AHRS

Question 1

That is the purpose of AHRS?

Answer 1

Monitors the change of aircraft attitude in free space and provides secondary source of data for nav system.

Question 2

What does the AHRS provide?

Answer 2

Attitude - Pitch, roll + yaw
Yaw rate - angular rate about the vertical axis
Pitch and roll rates
Accelerations - in three earth axis (Lat, long + vert)
Velocity - vertical velocity
Magnetic heading - angle of the aircraft longitudinal axis relative to magnetic north.
True Heading - angle obtained from magnetic heading compensated by mag variation.

Question 2

How is the difference between the mounting plates and aircraft datum adjusted?

Answer 2

Electronically in the SEU during the alignment phase.

Question 3

How many SEU’s are there and where are they located?

Answer 3

2

AV Bay upper forward shelf, left and right. inside of the GCU’s.

Question 4

How are the SEU’s mounted?

Answer 4

-/+ 2 deg to the three principal aircraft axes (lat, long, normal)
Residual misalignments (boresight angles) measured to -/+ 0.05 and is stored in the SEU Nonvolatile memory (NVM)

Question 5

What does each SEU contain?

Answer 5

3 single axis fibre-optic gyros

3 silicon accelerometers

Question 6

How is the MDU aligned?

Answer 6

Within 1 deg of the longitudinal axis.

Question 7

Where is the Magnetic detector unit? (MDU)

Answer 7

Rear fuselage (Tail cone) right side.

Question 8

What is the purpose of the MDU?

Answer 8

It detects the direction of the earths magnetic field to establish a heading reference through a pendulous flux valve.

Question 9

How is the MDU powered?

Answer 9

26Vac from a step-down transformer.

Question 10

How are the SEU’s powered?

Answer 10

28Vdc supply SEU 1 DC ESS BB 1 + SEU 2 DC ESS BB 2

26 V 400Hz AC Supply for synchro and MDU referencing (No 1 +2 Vac BB)

Question 11

Where are the AHRS Switches?

Answer 11

Left side of the overhead console.

Question 13

What happens after the AHRS are selected on?

Answer 13

After 5 secs, the SEU initialisation and alignment phase starts and automatically aligns, on ground and air.

Question 14

What information does AHRS display on the PFD?

Answer 14

Attitude Indicator (AI)
Vertical Speed Indicator (VSI)
Horizontal Situation Indicator (HSI)

Question 15

How is extreme slip indicated on the AI?

Answer 15

Half of the simulated ball disappearing at the outer scale marks.

Question 16

On the HSI how is the aircraft heading shown?

Answer 16

As a digital readout at the top of the compass card.

Question 17

What indications will you get on the IDU’s if the AHRS system is in any condition other than fully aligned?

Answer 17

Functional status indicators display:
STANDBY
COMP CAL
ALIGNING
DG
flashing for 5 secs at 1 Hz and then remain steady.
Repeated on IDU map format and hover format displays.

Question 18

After power is applied to the AHRS how long does it take to start the alignment phase?

Answer 18

5 secs.

Question 19

If the AHRS does not receive inputs of latitude and mag variations from the AMS what happens?

Answer 19

Stored parameters are used but accuracy is not guaranteed.

Question 20

During alignment what is the automatic mode of operation?

Answer 20

Slave (to the MDU)

Question 21

How long approximately does it take the system for ground alignment?

Answer 21

30 secs.

Question 22

What is the purpose of a compass swing?

Answer 22

To calibrate the AHRS

Compensate for magnetic disturbances in the aircraft Determine any residual errors in the system

Question 23

How often does the compass swing need to be carried out?

Answer 23

Every 52 weeks.

Question 24

How long will it take to align the AHRS on a ship?

Answer 24

120 seconds.

Question 25

When will you get a “CHECK” indication on the IDU?

Answer 25

Pitch or roll out by more than 2 degrees for 2 seconds or heading out by more than 3 degrees for 3 seconds..

Question 26

What 3 displays is AHRS the primary source to?

Answer 26

(AI) Attitude indicator, (HSI) Horizontal Situation Indicator, (VSI) Vertical Speed Indicator)