An A320 flight crew diverted to an enroute airport when their navigation system reverted to IRS navi...

Attributes
ACN	906486
Time
Date	201008
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	A320
Operating Under FAR Part	Part 121
Flight Phase	Climb
Flight Plan	IFR
Component
Aircraft Component	Navigational Equipment and Processing
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 300 Flight Crew Total 17000 Flight Crew Type 6000
Person 2
Function	First Officer Pilot Not Flying
Experience	Flight Crew Last 90 Days 210 Flight Crew Total 8000 Flight Crew Type 4000
Events
Anomaly	Aircraft Equipment Problem Less Severe

Narrative:

This event involved a loss of primary navigation mode (VOR; ILS) for both the captain and first officer. On the ground in ZZZ2 the power cord was removed prior to the APU running. On the airbus this causes numerous electrical problems ecams; warnings and cautions. Once the electrical power was restored and the screens were normal (this took several minutes) we did a check of all the systems and all appeared normal. What we later learned was that apparently the navigation system defaulted to the standby navigation mode with only minimal indication and some abnormal indication it had done so. Once airborne and on climbout we received a navigation accuracy downgrade; followed shortly thereafter by an IRS navigation only message. We were unable to enter anything into the rad/navigation page. After protracted troubleshooting with dispatch and maintenance control we made the decision to divert to ZZZ in order to do a ground reset. ATC did declare us an emergency aircraft although we did not request it. ZZZ was chosen as the divert airport as the weather was clear there while it was IFR with cbs at our destination.

Original NASA ASRS Text

Title: An A320 flight crew diverted to an enroute airport when their navigation system reverted to IRS NAV only and they were unable to program their route. A power interruption at the gate prior to departure may have initiated the anomaly.

Narrative: This event involved a loss of primary navigation mode (VOR; ILS) for both the Captain and First Officer. On the ground in ZZZ2 the power cord was removed prior to the APU running. On the Airbus this causes numerous electrical problems ECAMs; warnings and cautions. Once the electrical power was restored and the screens were normal (this took several minutes) we did a check of all the systems and all appeared normal. What we later learned was that apparently the NAV system defaulted to the standby navigation mode with only minimal indication and some abnormal indication it had done so. Once airborne and on climbout we received a NAV accuracy downgrade; followed shortly thereafter by an IRS NAV only message. We were unable to enter anything into the RAD/NAV page. After protracted troubleshooting with Dispatch and Maintenance Control we made the decision to divert to ZZZ in order to do a ground reset. ATC did declare us an emergency aircraft although we did not request it. ZZZ was chosen as the divert airport as the weather was clear there while it was IFR with CBs at our destination.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

An A320 flight crew diverted to an enroute airport when their navigation system reverted to IRS navigation only and they were unable to program their route. A power interruption at the gate prior to departure may have initiated the anomaly.