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On a scheduled flight, the ATC asks the pilots to change their route. What action is required for the IRS?
  • A
    enter the new waypoints into the control unit of each IRS, ensuring the system in use is updated first.
  • B
    the pilot will need to revert to manual navigation. The aircraft must be stationary to update waypoints in the IRS.
  • C
    modern aircraft have GPS, so the pilot does not need to update waypoints in the IRS.
  • D
    enter the new waypoints into the MCDU of the FMS.

Refer to figure.
Route Page 1/X (Flight Plan Page)

The route is entered and displayed in air traffic control format.
The first route page displays origin and destination data. Route segments are displayed on subsequent route pages.
Individual portions of the route may be manually entered by the flight crew. A pre–defined route may be loaded using the CO ROUTE line. CO ROUTE entries correspond to a company defined route in the navigation database.

Adding Waypoints
A waypoint can be added to the route whenever necessary.

The new waypoint must first be placed into the CDU scratchpad. The new waypoint is then inserted into the route at the desired sequence point by pushing the line select key adjacent to the desired location for the new waypoint.

The new entry automatically links to the preceding waypoint via a direct route.

All new waypoints, except along track waypoints, cause a route discontinuity between the new waypoint and the following waypoint.

Figure legend - 2: Modified Waypoint
YKM waypoint is entered into the route between LAC01 and VAMPS. This modification creates a route discontinuity.

When ATC asked for a change of route pilots can add new waypoints using MCDU. There is no need to be stationary to do this. Waypoint entries are not made on IRS control unit. Since it is an independent navigation mechanism from GPS waypoint entry is required.

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