Narrative:

While on a scheduled flight in a military C-9B we were en route from NAS lemoore, ca, to NAS north island san diego. We were on our climb out, location was 50 NM south of avenal approaching los angeles from the north. We were instructed by ZLA to level at FL250. As the aircraft was climbing through approximately FL230 center gave us a westerly vector for traffic. As the aircraft was banked right by the copilot to comply with the vector the aircraft HSI on the copilot's side failed to track in the turn with heading flags showing in the window. The copilot started to check his HSI against the RMI to resolve the disparity and I relayed to him our actual heading off of my HSI that was reliable. As he focused on rolling out his turn on the proper heading, I noticed the aircraft going past our leveloff altitude of FL250. I immediately verbalized altitude and took the control wheel and nosed the aircraft over and back to FL250. I saw a peak altitude of FL253.5 as I brought it back to level at FL250. I returned control of the aircraft to the copilot at that time. Center called us and asked our altitude as we leveled back on FL250. Rest of flight completed without further incident.

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Original NASA ASRS Text

Title: DC9 MIL ACFT INSTRUCTED TO LEVEL AT FL250. PF, FO'S HSI STUCK RIGHT AFTER CTLR GAVE TURN CLRNC AND HE WAS DISTR LOOKING AT THE OTHER HSI AND OVERSHOT ALT ASSIGNMENT BY 350 FT.

Narrative: WHILE ON A SCHEDULED FLT IN A MIL C-9B WE WERE ENRTE FROM NAS LEMOORE, CA, TO NAS NORTH ISLAND SAN DIEGO. WE WERE ON OUR CLB OUT, LOCATION WAS 50 NM S OF AVENAL APCHING LOS ANGELES FROM THE N. WE WERE INSTRUCTED BY ZLA TO LEVEL AT FL250. AS THE ACFT WAS CLBING THROUGH APPROX FL230 CTR GAVE US A WESTERLY VECTOR FOR TFC. AS THE ACFT WAS BANKED R BY THE COPLT TO COMPLY WITH THE VECTOR THE ACFT HSI ON THE COPLT'S SIDE FAILED TO TRACK IN THE TURN WITH HDG FLAGS SHOWING IN THE WINDOW. THE COPLT STARTED TO CHK HIS HSI AGAINST THE RMI TO RESOLVE THE DISPARITY AND I RELAYED TO HIM OUR ACTUAL HDG OFF OF MY HSI THAT WAS RELIABLE. AS HE FOCUSED ON ROLLING OUT HIS TURN ON THE PROPER HDG, I NOTICED THE ACFT GOING PAST OUR LEVELOFF ALT OF FL250. I IMMEDIATELY VERBALIZED ALT AND TOOK THE CTL WHEEL AND NOSED THE ACFT OVER AND BACK TO FL250. I SAW A PEAK ALT OF FL253.5 AS I BROUGHT IT BACK TO LEVEL AT FL250. I RETURNED CTL OF THE ACFT TO THE COPLT AT THAT TIME. CTR CALLED US AND ASKED OUR ALT AS WE LEVELED BACK ON FL250. REST OF FLT COMPLETED WITHOUT FURTHER INCIDENT.

Data retrieved from NASA's ASRS site as of July 2007 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.