Autoflight VPrep Position Computation

Question 1

What does each FMGC use to calculate its position?

Answer 1

Navaids (radio position)
Internal Inertial Reference System (Mix IRS)
GPS

Question 2

What reference point does the FMGC use for initial alignment and position computation?

Answer 2

The departure ARP when the departure airfield is entered in INIT A page on the MCDU

(Can be further refined by entering the stand Lat/Long

Question 3

At what point does the FMGC refine its position prior to take-off?

Answer 3

When TO Thrust is applied

So, must enter take-off shift on Performance Page if using an intersection for take-off

Question 4

What is the FM position?

Answer 4

The combination of:
Radio Position
GPS info
IRS
the FMGC's use to calculate the aircraft's position

Question 5

Normally, what does the FMGC use to compute position?

Answer 5

GPS and IRS

Question 6

When will the FMGC use Radio Navaids to compute position?

Answer 6

If GPS is unavailable

Question 7

When will the FMGC use IRS only to compute position?

Answer 7

When Navaids and GPS are unavailable

Question 8

Are the Navaids shown on the SELECTED NAVAID page the ones which the FMGC is usign for position computation?

Answer 8

Not necessarily.

A variable combination of DME’s, VOR’s and LOC signals are used depending on available aids

Question 9

What type of navaids does the FMGC use to determine position?

Answer 9

A variable combination of DME’s, VOR’s and LOC signals are used depending on available aids

Using:
bearing distance, or
distance distance

Question 10

Which IRS’s do the FMGC’s receive information from?

Answer 10

Both FMGC’s receive information from the calculated position of each IRS (IRS 1, 2 and 3)

Question 11

What is the MIX IRS position?

Answer 11

The average position of the 3 IRS’s

Question 12

If 1 IRS position significantly deviates form the other two, what happens?

Answer 12

The system biases the calculated position to favour the other two positions

Question 13

If an IRS fails is the MIX IRS position calculated?

Answer 13

No

Question 14

What position information do the FMGC’s use if an IRS fails?

Answer 14

The FMGC’s use their own onside IRS or IRS3 to calculate the position

(In this case selecting ATT HDG to CAP3 will trandfer IRS3 to FMGC1)

Question 15

How many GPS receivers are there?

Answer 15

3

An independent GPS receiver is attached to each of the 3 IRS in order to receive GPS position data.

Question 16

How many GPS receiver based positions does the FMGC use?

Answer 16

1

The FMGC selects data from 1 GPS receiver based on the accuracy of the information to calculate the aircrafts position

Question 17

How does the FMGC prioritise which GPS info to use?

Answer 17

Onside IRS GPS first
IRS GPS 3
Offside IRS GPS