Narrative:

Descending from higher flight levels to 15000' on center clearance had anticipated and received clearance to hold at bucks (phl area) due to anticipated WX delay. Captain flying on autoplt using LNAV on company stored route (ind-phl) everything routine. Captain is a check airman (line) on this aircraft. I am 5 yr airline pilot, but 3 months only experience on medium large transport LNAV equipment. Captain pulled up 'hold' page on FMC and began to enter data. Were currently descending on rate of descent command to 15000' MSL as assigned. I'm reading holding data to captain as he's entering data via keypad. Both eyes off of primary flight INS but in altitude capture mode (VNAV) and LNAV so both pilots are anticipating automate level off at 15000' MSL. Captain apparently entered hold at ppos in error and aircraft begins left turn unexpectedly. I, in confusion, not knowing he entered position by mistake stated, 'this isn't right,' and saw captain disengage autoplt to stop turn while he goes back to FMC page to find out why aircraft was turning. I immediately went to legs pace to find out where we should be, got to VOR/ILS mode and picked up en route chart to tune in present position. Aircraft descended below 15000'. Horn went off at approximately 14600'. Captain called out 'out of 16 for 15.' I said no (looking up) and said we were at 14500', only cleared to 15000', that that was a low altitude alert, not '1000' to go' horn.' immediately pulled back up. No ATC communication took place by either ATC or us about event. Within 30 seconds ATC gave us new frequency and cleared us to 13000'. No conflict or discussion or event awareness of event was stated by ATC. Below 15000' for about 20 seconds. Cause is obvious--both pilots attention diverted from aircraft flight path. Suggest hold page (not used often) be made more user friendly. Have captain tell first officer to watch flight progress while he is correctly other problems. I personally feel that although the FMC is a great tool, it shouldn't be used all the time, especially below FL180. It takes too much pilot attention, especially when newly assigned to the air carrier. Just because the technology exists doesn't mean it should be used. Better pilot training on FMC/pilot problem areas like this should be taught. Also, loss of an F/east's eyes is ot in the interest of aviation safety.

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Original NASA ASRS Text

Title: ACR MLG ALT DEVIATION OVERSHOT DURING DESCENT AS FLT CREW DEPENDS ON FMC THAT THEY HAVE PROGRAMMED INCORRECTLY.

Narrative: DSNDING FROM HIGHER FLT LEVELS TO 15000' ON CENTER CLRNC HAD ANTICIPATED AND RECEIVED CLRNC TO HOLD AT BUCKS (PHL AREA) DUE TO ANTICIPATED WX DELAY. CAPT FLYING ON AUTOPLT USING LNAV ON COMPANY STORED RTE (IND-PHL) EVERYTHING ROUTINE. CAPT IS A CHK AIRMAN (LINE) ON THIS ACFT. I AM 5 YR AIRLINE PLT, BUT 3 MONTHS ONLY EXPERIENCE ON MLG LNAV EQUIP. CAPT PULLED UP 'HOLD' PAGE ON FMC AND BEGAN TO ENTER DATA. WERE CURRENTLY DSNDING ON RATE OF DSNT COMMAND TO 15000' MSL AS ASSIGNED. I'M READING HOLDING DATA TO CAPT AS HE'S ENTERING DATA VIA KEYPAD. BOTH EYES OFF OF PRIMARY FLT INS BUT IN ALT CAPTURE MODE (VNAV) AND LNAV SO BOTH PLTS ARE ANTICIPATING AUTOMATE LEVEL OFF AT 15000' MSL. CAPT APPARENTLY ENTERED HOLD AT PPOS IN ERROR AND ACFT BEGINS LEFT TURN UNEXPECTEDLY. I, IN CONFUSION, NOT KNOWING HE ENTERED POS BY MISTAKE STATED, 'THIS ISN'T RIGHT,' AND SAW CAPT DISENGAGE AUTOPLT TO STOP TURN WHILE HE GOES BACK TO FMC PAGE TO FIND OUT WHY ACFT WAS TURNING. I IMMEDIATELY WENT TO LEGS PACE TO FIND OUT WHERE WE SHOULD BE, GOT TO VOR/ILS MODE AND PICKED UP ENRTE CHART TO TUNE IN PRESENT POS. ACFT DSNDED BELOW 15000'. HORN WENT OFF AT APPROX 14600'. CAPT CALLED OUT 'OUT OF 16 FOR 15.' I SAID NO (LOOKING UP) AND SAID WE WERE AT 14500', ONLY CLRED TO 15000', THAT THAT WAS A LOW ALT ALERT, NOT '1000' TO GO' HORN.' IMMEDIATELY PULLED BACK UP. NO ATC COM TOOK PLACE BY EITHER ATC OR US ABOUT EVENT. WITHIN 30 SECS ATC GAVE US NEW FREQ AND CLRED US TO 13000'. NO CONFLICT OR DISCUSSION OR EVENT AWARENESS OF EVENT WAS STATED BY ATC. BELOW 15000' FOR ABOUT 20 SECS. CAUSE IS OBVIOUS--BOTH PLTS ATTN DIVERTED FROM ACFT FLT PATH. SUGGEST HOLD PAGE (NOT USED OFTEN) BE MADE MORE USER FRIENDLY. HAVE CAPT TELL F/O TO WATCH FLT PROGRESS WHILE HE IS CORRECTLY OTHER PROBS. I PERSONALLY FEEL THAT ALTHOUGH THE FMC IS A GREAT TOOL, IT SHOULDN'T BE USED ALL THE TIME, ESPECIALLY BELOW FL180. IT TAKES TOO MUCH PLT ATTN, ESPECIALLY WHEN NEWLY ASSIGNED TO THE ACR. JUST BECAUSE THE TECHNOLOGY EXISTS DOESN'T MEAN IT SHOULD BE USED. BETTER PLT TRNING ON FMC/PLT PROB AREAS LIKE THIS SHOULD BE TAUGHT. ALSO, LOSS OF AN F/E'S EYES IS OT IN THE INTEREST OF AVIATION SAFETY.

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.