Narrative:

This is a B737-300. While cruising at FL310, ATC cleared us to FL350. At the same time they advised us of turbulence at FL350 for about the next 80 mi. We requested and received clearance to maintain FL310. However, when we were given the FL350 clearance, I set the MCP altitude to FL350 before receiving the maintain FL310. I did not reset the MCP altitude to FL310. Shortly after this we encountered light turbulence. I deselected VNAV to slow our airspeed. At about the same time a flight attendant called. I answered, and while talking to the attendant ATC asked us to confirm our altitude. By this time we were about 1300 ft below our assigned altitude. We climbed back to FL310 with no traffic conflict, and continued to our destination with no further problems. This was a case of 1) poor procedure, 2) being distracted, and 3) not minding the store. Recommend more emphasis be placed on keeping assigned or cleared to altitude in the MCP altitude window. In this case when I deselected VNAV, it reverted to control wheel steering as it should. The problem, I did not notice it because of the flight attendant's call.

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Original NASA ASRS Text

Title: RPTR SETS UP ALT ALERTER FOR CLB TO FL350. ATC ADVISES TURB AT FL350. RPTR REQUESTS AND RECEIVES FL310. ON DSCNT BACK TOWARD FL310 RPTR FAILS TO SET ALT ALERTER TO FL310. WITH MANY DISTRS RPTR DSNDS 1300 FT BELOW FL310 BEFORE CTLR ALERTS PLT OF DEV.

Narrative: THIS IS A B737-300. WHILE CRUISING AT FL310, ATC CLRED US TO FL350. AT THE SAME TIME THEY ADVISED US OF TURB AT FL350 FOR ABOUT THE NEXT 80 MI. WE REQUESTED AND RECEIVED CLRNC TO MAINTAIN FL310. HOWEVER, WHEN WE WERE GIVEN THE FL350 CLRNC, I SET THE MCP ALT TO FL350 BEFORE RECEIVING THE MAINTAIN FL310. I DID NOT RESET THE MCP ALT TO FL310. SHORTLY AFTER THIS WE ENCOUNTERED LIGHT TURB. I DESELECTED VNAV TO SLOW OUR AIRSPD. AT ABOUT THE SAME TIME A FLT ATTENDANT CALLED. I ANSWERED, AND WHILE TALKING TO THE ATTENDANT ATC ASKED US TO CONFIRM OUR ALT. BY THIS TIME WE WERE ABOUT 1300 FT BELOW OUR ASSIGNED ALT. WE CLBED BACK TO FL310 WITH NO TFC CONFLICT, AND CONTINUED TO OUR DEST WITH NO FURTHER PROBS. THIS WAS A CASE OF 1) POOR PROC, 2) BEING DISTRACTED, AND 3) NOT MINDING THE STORE. RECOMMEND MORE EMPHASIS BE PLACED ON KEEPING ASSIGNED OR CLRED TO ALT IN THE MCP ALT WINDOW. IN THIS CASE WHEN I DESELECTED VNAV, IT REVERTED TO CTL WHEEL STEERING AS IT SHOULD. THE PROB, I DID NOT NOTICE IT BECAUSE OF THE FLT ATTENDANT'S CALL.

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.