Narrative:

We were cleared to FL290 and were flying an aircraft with an autoplt that did not have an altitude feature, after 2 legs on an aircraft that did have an altitude capture. The captain set FL290 in the altitude alert window and the alert signaled passing FL285. Then the captain, first officer, and so, were distracted by a radio call and a navigation decision. We noticed at FL294 that we had failed to level off, peaked at FL296, then descended back to FL290. There were no aircraft in the area. The ZLC controller noticed our deviation after we had started the descent and confirmed our assigned altitude of FL290. I think that mixing legs on aircraft with different autoplts definitely leads to altdevs. Supplemental information from acn 300892: block 4 autoplt, had light and aural tone 1000 ft, 500 ft prior. Made reference to 1000 ft to go, then distracted by navigation duty, trying to verify omega navigation to abq. Supplemental information from acn 301198: called out 1000 ft to go. I noticed the plane slowly climbing through FL295 and immediately returned to FL290. There was no immediate traffic conflict and the controller asked our altitude as we were returning to FL290. In the future, all attention will be focused on leveloff rather than less essential tasks.

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Original NASA ASRS Text

Title: DISTR WITH DECISIONS AND NAV DUTIES AND THE RELIANCE ON A SYS THAT WAS NON EXISTENT ONLY, IN THIS PARTICULAR ACFT, LED TO AN ALTDEV.

Narrative: WE WERE CLRED TO FL290 AND WERE FLYING AN ACFT WITH AN AUTOPLT THAT DID NOT HAVE AN ALT FEATURE, AFTER 2 LEGS ON AN ACFT THAT DID HAVE AN ALT CAPTURE. THE CAPT SET FL290 IN THE ALT ALERT WINDOW AND THE ALERT SIGNALED PASSING FL285. THEN THE CAPT, FO, AND SO, WERE DISTRACTED BY A RADIO CALL AND A NAV DECISION. WE NOTICED AT FL294 THAT WE HAD FAILED TO LEVEL OFF, PEAKED AT FL296, THEN DSNDED BACK TO FL290. THERE WERE NO ACFT IN THE AREA. THE ZLC CTLR NOTICED OUR DEV AFTER WE HAD STARTED THE DSCNT AND CONFIRMED OUR ASSIGNED ALT OF FL290. I THINK THAT MIXING LEGS ON ACFT WITH DIFFERENT AUTOPLTS DEFINITELY LEADS TO ALTDEVS. SUPPLEMENTAL INFO FROM ACN 300892: BLOCK 4 AUTOPLT, HAD LIGHT AND AURAL TONE 1000 FT, 500 FT PRIOR. MADE REF TO 1000 FT TO GO, THEN DISTRACTED BY NAV DUTY, TRYING TO VERIFY OMEGA NAV TO ABQ. SUPPLEMENTAL INFO FROM ACN 301198: CALLED OUT 1000 FT TO GO. I NOTICED THE PLANE SLOWLY CLBING THROUGH FL295 AND IMMEDIATELY RETURNED TO FL290. THERE WAS NO IMMEDIATE TFC CONFLICT AND THE CTLR ASKED OUR ALT AS WE WERE RETURNING TO FL290. IN THE FUTURE, ALL ATTN WILL BE FOCUSED ON LEVELOFF RATHER THAN LESS ESSENTIAL TASKS.

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.