Narrative:

Light turbulence at 16000 ft requested descent to 14000 ft and shortcut in route of flight. My understanding was to standby on both requests so I did not arm altitude. Several mins later it smoothed out so I canceled request to descend. Meanwhile I became involved in another cockpit task. I next heard ATC ask us to verify our altitude. I saw that we were passing 15000 ft in descent. I told ATC we were correcting back to 16000 ft and nothing further was said. Upon discussion with copilot, he heard that we were cleared to 14000 ft upon initial request. He was the PF. He armed new altitude and began descent. Since I was involved in other cockpit task I did not notice descent. When I requested cancel lower altitude request (thinking we were level at 16000 ft) copilot did not hear this request and continued descent when we got query from ATC regarding our altitude. Problem appears to be confusion in company procedures regarding which pilot arms altitude alert. For 7 yrs I have flown this aircraft, the PNF arms altitude while PF operates flight director, autoplt, etc. I have heard recently of change in training that PF arms altitude and operates flight director. Upon questioning a chief pilot after this incident, he admits that he has heard that the old procedure may be changed. I feel that procedure should not be changed ie, both pilots should be involved in confirming altitude arming. Secondly, I feel that company needs to insure standardization in our procedures.

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Original NASA ASRS Text

Title: EXCURSION FROM ASSIGNED ALT - FLC COORD PROB.

Narrative: LIGHT TURB AT 16000 FT REQUESTED DSCNT TO 14000 FT AND SHORTCUT IN RTE OF FLT. MY UNDERSTANDING WAS TO STANDBY ON BOTH REQUESTS SO I DID NOT ARM ALT. SEVERAL MINS LATER IT SMOOTHED OUT SO I CANCELED REQUEST TO DSND. MEANWHILE I BECAME INVOLVED IN ANOTHER COCKPIT TASK. I NEXT HEARD ATC ASK US TO VERIFY OUR ALT. I SAW THAT WE WERE PASSING 15000 FT IN DSCNT. I TOLD ATC WE WERE CORRECTING BACK TO 16000 FT AND NOTHING FURTHER WAS SAID. UPON DISCUSSION WITH COPLT, HE HEARD THAT WE WERE CLRED TO 14000 FT UPON INITIAL REQUEST. HE WAS THE PF. HE ARMED NEW ALT AND BEGAN DSCNT. SINCE I WAS INVOLVED IN OTHER COCKPIT TASK I DID NOT NOTICE DSCNT. WHEN I REQUESTED CANCEL LOWER ALT REQUEST (THINKING WE WERE LEVEL AT 16000 FT) COPLT DID NOT HEAR THIS REQUEST AND CONTINUED DSCNT WHEN WE GOT QUERY FROM ATC REGARDING OUR ALT. PROB APPEARS TO BE CONFUSION IN COMPANY PROCS REGARDING WHICH PLT ARMS ALT ALERT. FOR 7 YRS I HAVE FLOWN THIS ACFT, THE PNF ARMS ALT WHILE PF OPERATES FLT DIRECTOR, AUTOPLT, ETC. I HAVE HEARD RECENTLY OF CHANGE IN TRAINING THAT PF ARMS ALT AND OPERATES FLT DIRECTOR. UPON QUESTIONING A CHIEF PLT AFTER THIS INCIDENT, HE ADMITS THAT HE HAS HEARD THAT THE OLD PROC MAY BE CHANGED. I FEEL THAT PROC SHOULD NOT BE CHANGED IE, BOTH PLTS SHOULD BE INVOLVED IN CONFIRMING ALT ARMING. SECONDLY, I FEEL THAT COMPANY NEEDS TO INSURE STANDARDIZATION IN OUR PROCS.

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.