Narrative:

There were many distractions just prior to level off. Oak ATC cleared to leave cedes on a 230 degree heading, to intercept the sfo 095 degree radial. The first officer, who was still looking for the light transport traffic, had to confirm that the clearance was in fact for us, 'air carrier flight X'. The first officer called '12 for 11', and extinguished the 'altitude alert' light. As I was leveling off and adding power to maintain 250 KTS, and also glancing back at the pressurization panel to try and avoid a pressure surge, the second officer asked, 'what is our cleared altitude?' I had leveled off at 10,000'. Oak ATC asked us to confirm our altitude at 10,000'. We confirmed this, and ATC then cleared us to continue descent to 7000'. In a later crew discussion, we decided that, partly because of our good intentions, we put ourselves in the position of having too many distractions, which resulted in the altitude 'bust'. Fortunately for all, that was the extent of the damage. What we would like to bring to everyone's attention is what we feel is a potentially dangerous habit that we've all seemed to develop. The altitude alert system sounds an aural warning and illuminates the 'altitude alert' light when the aircraft is within 900' above or below the selected altitude. The aural warning is momentary, but the light stays on until the aircraft is within 300' of the selected altitude. The light then goes off, and remains off as long as the aircraft remains within 300' of the selected altitude. Many of us have developed the habit of extinguishing the light as soon as it illuminates ('no-light cockpit' syndrome?). Now the visual warning, which I believe is designed to remain on within 900-300' from the selected altitude, is no longer available. I personally do not extinguish the light for this very reason. I want that light to remain on, so that I do have the visual reminder that I'm close to the assigned altitude. I do not intend to offer this as an excuse for ny altitude 'bust', but I do feel that it could have been a contributing factor. I respectfully suggest that the procedure should be to let the light do the job it was designed to do, which is to serve both as an alert and a reminder light. Supplemental information from acn 117874: the captain was flying the aircraft and we were cleared to descend and maintain 11,000' and 250 KTS at cedes intersection as published. For some reason the captain descended and maintained 10,000' and 250 KTS.

Google
 

Original NASA ASRS Text

Title: ALT DEVIATION OCCURS AS ONE PLT EXTINGUISHES THE ALT ALERT LIGHT IN DESCENT DURING ALT CALLOUT.

Narrative: THERE WERE MANY DISTRACTIONS JUST PRIOR TO LEVEL OFF. OAK ATC CLRED TO LEAVE CEDES ON A 230 DEG HDG, TO INTERCEPT THE SFO 095 DEG RADIAL. THE F/O, WHO WAS STILL LOOKING FOR THE LTT TFC, HAD TO CONFIRM THAT THE CLRNC WAS IN FACT FOR US, 'ACR FLT X'. THE F/O CALLED '12 FOR 11', AND EXTINGUISHED THE 'ALT ALERT' LIGHT. AS I WAS LEVELING OFF AND ADDING POWER TO MAINTAIN 250 KTS, AND ALSO GLANCING BACK AT THE PRESSURIZATION PANEL TO TRY AND AVOID A PRESSURE SURGE, THE S/O ASKED, 'WHAT IS OUR CLRED ALT?' I HAD LEVELED OFF AT 10,000'. OAK ATC ASKED US TO CONFIRM OUR ALT AT 10,000'. WE CONFIRMED THIS, AND ATC THEN CLRED US TO CONTINUE DESCENT TO 7000'. IN A LATER CREW DISCUSSION, WE DECIDED THAT, PARTLY BECAUSE OF OUR GOOD INTENTIONS, WE PUT OURSELVES IN THE POSITION OF HAVING TOO MANY DISTRACTIONS, WHICH RESULTED IN THE ALT 'BUST'. FORTUNATELY FOR ALL, THAT WAS THE EXTENT OF THE DAMAGE. WHAT WE WOULD LIKE TO BRING TO EVERYONE'S ATTN IS WHAT WE FEEL IS A POTENTIALLY DANGEROUS HABIT THAT WE'VE ALL SEEMED TO DEVELOP. THE ALT ALERT SYSTEM SOUNDS AN AURAL WARNING AND ILLUMINATES THE 'ALT ALERT' LIGHT WHEN THE ACFT IS WITHIN 900' ABOVE OR BELOW THE SELECTED ALT. THE AURAL WARNING IS MOMENTARY, BUT THE LIGHT STAYS ON UNTIL THE ACFT IS WITHIN 300' OF THE SELECTED ALT. THE LIGHT THEN GOES OFF, AND REMAINS OFF AS LONG AS THE ACFT REMAINS WITHIN 300' OF THE SELECTED ALT. MANY OF US HAVE DEVELOPED THE HABIT OF EXTINGUISHING THE LIGHT AS SOON AS IT ILLUMINATES ('NO-LIGHT COCKPIT' SYNDROME?). NOW THE VISUAL WARNING, WHICH I BELIEVE IS DESIGNED TO REMAIN ON WITHIN 900-300' FROM THE SELECTED ALT, IS NO LONGER AVAILABLE. I PERSONALLY DO NOT EXTINGUISH THE LIGHT FOR THIS VERY REASON. I WANT THAT LIGHT TO REMAIN ON, SO THAT I DO HAVE THE VISUAL REMINDER THAT I'M CLOSE TO THE ASSIGNED ALT. I DO NOT INTEND TO OFFER THIS AS AN EXCUSE FOR NY ALT 'BUST', BUT I DO FEEL THAT IT COULD HAVE BEEN A CONTRIBUTING FACTOR. I RESPECTFULLY SUGGEST THAT THE PROC SHOULD BE TO LET THE LIGHT DO THE JOB IT WAS DESIGNED TO DO, WHICH IS TO SERVE BOTH AS AN ALERT AND A REMINDER LIGHT. SUPPLEMENTAL INFORMATION FROM ACN 117874: THE CAPT WAS FLYING THE ACFT AND WE WERE CLRED TO DSND AND MAINTAIN 11,000' AND 250 KTS AT CEDES INTXN AS PUBLISHED. FOR SOME REASON THE CAPT DESCENDED AND MAINTAINED 10,000' AND 250 KTS.

Data retrieved from NASA's ASRS site as of August 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.