Narrative:

Several times during the flight; the FMC display would lock-up and both the captain and first officer's navigation display would lose the route and map displays and heading fail warnings received. Each occurrence would last 15-20 seconds and then both systems would recover. However; in all cases the active route would drop out and have to be reactivated. The first time I advised center of our problem; and they cleared us direct to the next nav aid on our route. Flying nav aid to nav aid worked out well as when we had these momentary problems headings on the rdmis and compass rose of the navigation display were in agreement with the stby compass. I called dispatch and maintenance control to inform them of our situation. As we approached phx we were cleared to descend via the KOOLY3 RNAV arrival. While in the descent and on the arrival the FMC CDU locked up and the navigation display route data went blank. I immediately told center that we were unable the KOOLY3 arrival because of problems with the RNAV equipment but we could continue on the SUNSS7 arrival using the VOR equipment. ATC granted our request and directed us to descend to cross squez at 14000' and 250K. What I heard was cross at 11000' 250K. All of this was occurring in a very compressed time period. The flight was handed off to phx approach. When checking in; we were descending through 13600'. Approach queried us about our assigned altitude and I responded 11000'. They repeated that we had only been cleared to 14000' but that we were now cleared to 11000'. The approach controller gave me a number to call after landing. After landing I did call and we discussed the incident. We both realized that our equipment malfunction occurred at absolutely the wrong time. The change in the arrival at that point also presented some problems for the arrival sector controllers. Fortunately; there were no traffic conflicts.

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Original NASA ASRS Text

Title: With their workload increased due to repeated failures and recoveries of the FMS displays; the flight crew of an MD80 failed to level at 14000' as cleared on their descent.

Narrative: Several times during the flight; the FMC display would lock-up and both the Captain and First Officer's NAV display would lose the route and MAP displays and heading fail warnings received. Each occurrence would last 15-20 seconds and then both systems would recover. However; in all cases the active route would drop out and have to be reactivated. The first time I advised center of our problem; and they cleared us direct to the next nav aid on our route. Flying Nav aid to Nav aid worked out well as when we had these momentary problems headings on the RDMIs and compass rose of the NAV display were in agreement with the STBY compass. I called Dispatch and Maintenance Control to inform them of our situation. As we approached PHX we were cleared to descend via the KOOLY3 RNAV arrival. While in the descent and on the arrival the FMC CDU locked up and the NAV Display route data went blank. I immediately told Center that we were unable the KOOLY3 arrival because of problems with the RNAV equipment but we could continue on the SUNSS7 arrival using the VOR equipment. ATC granted our request and directed us to descend to cross SQUEZ at 14000' and 250K. What I heard was cross at 11000' 250K. All of this was occurring in a very compressed time period. The flight was handed off to PHX Approach. When checking in; we were descending through 13600'. Approach queried us about our assigned altitude and I responded 11000'. They repeated that we had only been cleared to 14000' but that we were now cleared to 11000'. The Approach controller gave me a number to call after landing. After landing I did call and we discussed the incident. We both realized that our equipment malfunction occurred at absolutely the wrong time. The change in the arrival at that point also presented some problems for the arrival sector controllers. Fortunately; there were no traffic conflicts.

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.