Narrative:

We were flying from las to sna in an medium large transport equipped with a single FMS CDU on the left side of the forward electronic panel (forward of the thrust levers), and electro-mechanical flight instrument displays. We had been cleared to fly the kayoh one arrival, and had programmed the FMC for a VNAV descent to cross dawna (hdf 353/29) at 13,000, and then cross kayoh (sli 075/23) at 210 KTS and 8000. Before reaching dawna we were cleared direct to hdf. ZLA broadcast a SIGMET that forecast occasional severe turbulence below 10,000 in the area that we would be making our final descent, followed immediately by a clearance for us to cross 20 northeast of hdf at 14,000. We both remarked that hdf was not showing a DME signal, so raw data distance was not available. I asked the first officer if he would like me to enter the restriction into the FMC (since it's awkward to make data entries from his side of the cockpit) and entered hdf 010/20 at 14,000. The first officer indicated agreement with the data entry, and I told him I'd be 'off the radio' while I discussed the anticipated turbulence with the cabin crew. During that discussion I observed the first officer initiate a rapid descent, checked the CDU, and was surprised to see that the waypoint I had just entered was no longer displayed (since we had just passed it). The first officer told me that we had crossed the 20 mi fix passing through 17,000, and that center's only comment was, 'you missed it'. I believe that this incident was not due to any inattention, but rather to human factors problems involved with the automated cockpit and ATC. I also believe that it wouldn't have happened in an older-technology aircraft (which I also fly). For example: 1) in the older-technology aircraft, I wouldn't't have accepted this clearance, once I realized that hdf had no DME. I assume that the controller wouldn't't have issued it unless he knew the aircraft was RNAV equipped. 2) I'm not used to receiving clrncs to a 'distance' point associated with a non-DME facility. I associate the phraseology, 'cross twenty northeast of xyz' with a DME fix, where I can quickly look at a raw-data DME display and make an immediate judgement that a descent must be initiated. I looked for raw data. It wasn't available, so I mentally shifted from the old-technology (raw data) mode to the automated cockpit (data entry and computed solution) mode. 3) most clrncs I've received that require RNAV involve named fixes which are usually in the flight plan or database. I can make a rapid (4 keystrokes) data entry for a RNAV position/altitude if it was previously programmed into the route, ie, direct hdf. The clearance in this incident required 15 keystrokes, and took considerably more time. 4) when I fly an automated aircraft, I have to spend some amount of time programming and monitoring the computer. The decision of when to do this and when it isn't appropriate is a subtle one, and lends itself to generalities such as, 'don't program in the terminal area.' in this case, 'don't program in southern california' would have been appropriate. The data we needed (present distance to hdf) was available in the CDU, so if we had treated it as if we didn't have RNAV available we might have been able to make the mental calculation in time to meet the restriction. In the en route environment however, experience led me to the subconscious decision that there was time available to reprogram the FMC. 5) the controller issued a clearance that was probably delayed due to the SIGMET broadcast. As it was, the clearance was made so close to the fix that by the time it was programmed into the FMC and descent computations made, it was not possible to meet the restriction. 6) it wasn't until the next day and a discussion exploring both of our thought processes that we found anything we (as opposed to the controller) could have done differently under the circumstances to prevent this incident. When either of us is the pilot flying and makes a data entry, we each make a mental validity check using some rule of thumb, ie, 'I'm 13 mi from the fix and 6000' high, so I've got to start down now!' in this case, although I made the data entry I didn't make the validity check because I was not flying, and preoccupied with my concern for the safety of the passenger and cabin crew in the context of the expected severe turbulence. I had subconsciously placed a higher priority on communicating with the cabin crew than on double-checking the computer. It has not escaped me that not double-checking the computer or the pilot flying can lead to a busted altitude and hence a midair collision, which should have been a higher priority. The first officer indicated that since I had made the data entry he assumed that the data was valid (it was, but too late) and didn't double-check it.

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Original NASA ASRS Text

Title: ALT DEVIATION. DESCENT CROSSING RESTRICTION NOT MET.

Narrative: WE WERE FLYING FROM LAS TO SNA IN AN MLG EQUIPPED WITH A SINGLE FMS CDU ON THE LEFT SIDE OF THE FORWARD ELECTRONIC PANEL (FORWARD OF THE THRUST LEVERS), AND ELECTRO-MECHANICAL FLT INSTRUMENT DISPLAYS. WE HAD BEEN CLRED TO FLY THE KAYOH ONE ARR, AND HAD PROGRAMMED THE FMC FOR A VNAV DSCNT TO CROSS DAWNA (HDF 353/29) AT 13,000, AND THEN CROSS KAYOH (SLI 075/23) AT 210 KTS AND 8000. BEFORE REACHING DAWNA WE WERE CLRED DIRECT TO HDF. ZLA BROADCAST A SIGMET THAT FORECAST OCCASIONAL SEVERE TURBULENCE BELOW 10,000 IN THE AREA THAT WE WOULD BE MAKING OUR FINAL DSCNT, FOLLOWED IMMEDIATELY BY A CLRNC FOR US TO CROSS 20 NE OF HDF AT 14,000. WE BOTH REMARKED THAT HDF WAS NOT SHOWING A DME SIGNAL, SO RAW DATA DISTANCE WAS NOT AVAILABLE. I ASKED THE F/O IF HE WOULD LIKE ME TO ENTER THE RESTRICTION INTO THE FMC (SINCE IT'S AWKWARD TO MAKE DATA ENTRIES FROM HIS SIDE OF THE COCKPIT) AND ENTERED HDF 010/20 AT 14,000. THE F/O INDICATED AGREEMENT WITH THE DATA ENTRY, AND I TOLD HIM I'D BE 'OFF THE RADIO' WHILE I DISCUSSED THE ANTICIPATED TURBULENCE WITH THE CABIN CREW. DURING THAT DISCUSSION I OBSERVED THE F/O INITIATE A RAPID DSCNT, CHECKED THE CDU, AND WAS SURPRISED TO SEE THAT THE WAYPOINT I HAD JUST ENTERED WAS NO LONGER DISPLAYED (SINCE WE HAD JUST PASSED IT). THE F/O TOLD ME THAT WE HAD CROSSED THE 20 MI FIX PASSING THROUGH 17,000, AND THAT CENTER'S ONLY COMMENT WAS, 'YOU MISSED IT'. I BELIEVE THAT THIS INCIDENT WAS NOT DUE TO ANY INATTENTION, BUT RATHER TO HUMAN FACTORS PROBLEMS INVOLVED WITH THE AUTOMATED COCKPIT AND ATC. I ALSO BELIEVE THAT IT WOULDN'T HAVE HAPPENED IN AN OLDER-TECHNOLOGY ACFT (WHICH I ALSO FLY). FOR EXAMPLE: 1) IN THE OLDER-TECHNOLOGY ACFT, I WOULDN'T'T HAVE ACCEPTED THIS CLRNC, ONCE I REALIZED THAT HDF HAD NO DME. I ASSUME THAT THE CTLR WOULDN'T'T HAVE ISSUED IT UNLESS HE KNEW THE ACFT WAS RNAV EQUIPPED. 2) I'M NOT USED TO RECEIVING CLRNCS TO A 'DISTANCE' POINT ASSOCIATED WITH A NON-DME FAC. I ASSOCIATE THE PHRASEOLOGY, 'CROSS TWENTY NE OF XYZ' WITH A DME FIX, WHERE I CAN QUICKLY LOOK AT A RAW-DATA DME DISPLAY AND MAKE AN IMMEDIATE JUDGEMENT THAT A DSCNT MUST BE INITIATED. I LOOKED FOR RAW DATA. IT WASN'T AVAILABLE, SO I MENTALLY SHIFTED FROM THE OLD-TECHNOLOGY (RAW DATA) MODE TO THE AUTOMATED COCKPIT (DATA ENTRY AND COMPUTED SOLUTION) MODE. 3) MOST CLRNCS I'VE RECEIVED THAT REQUIRE RNAV INVOLVE NAMED FIXES WHICH ARE USUALLY IN THE FLT PLAN OR DATABASE. I CAN MAKE A RAPID (4 KEYSTROKES) DATA ENTRY FOR A RNAV POSITION/ALT IF IT WAS PREVIOUSLY PROGRAMMED INTO THE ROUTE, IE, DIRECT HDF. THE CLRNC IN THIS INCIDENT REQUIRED 15 KEYSTROKES, AND TOOK CONSIDERABLY MORE TIME. 4) WHEN I FLY AN AUTOMATED ACFT, I HAVE TO SPEND SOME AMOUNT OF TIME PROGRAMMING AND MONITORING THE COMPUTER. THE DECISION OF WHEN TO DO THIS AND WHEN IT ISN'T APPROPRIATE IS A SUBTLE ONE, AND LENDS ITSELF TO GENERALITIES SUCH AS, 'DON'T PROGRAM IN THE TERMINAL AREA.' IN THIS CASE, 'DON'T PROGRAM IN SOUTHERN CALIFORNIA' WOULD HAVE BEEN APPROPRIATE. THE DATA WE NEEDED (PRESENT DISTANCE TO HDF) WAS AVAILABLE IN THE CDU, SO IF WE HAD TREATED IT AS IF WE DIDN'T HAVE RNAV AVAILABLE WE MIGHT HAVE BEEN ABLE TO MAKE THE MENTAL CALCULATION IN TIME TO MEET THE RESTRICTION. IN THE ENRTE ENVIRONMENT HOWEVER, EXPERIENCE LED ME TO THE SUBCONSCIOUS DECISION THAT THERE WAS TIME AVAILABLE TO REPROGRAM THE FMC. 5) THE CTLR ISSUED A CLRNC THAT WAS PROBABLY DELAYED DUE TO THE SIGMET BROADCAST. AS IT WAS, THE CLRNC WAS MADE SO CLOSE TO THE FIX THAT BY THE TIME IT WAS PROGRAMMED INTO THE FMC AND DSCNT COMPUTATIONS MADE, IT WAS NOT POSSIBLE TO MEET THE RESTRICTION. 6) IT WASN'T UNTIL THE NEXT DAY AND A DISCUSSION EXPLORING BOTH OF OUR THOUGHT PROCESSES THAT WE FOUND ANYTHING WE (AS OPPOSED TO THE CTLR) COULD HAVE DONE DIFFERENTLY UNDER THE CIRCUMSTANCES TO PREVENT THIS INCIDENT. WHEN EITHER OF US IS THE PLT FLYING AND MAKES A DATA ENTRY, WE EACH MAKE A MENTAL VALIDITY CHECK USING SOME RULE OF THUMB, IE, 'I'M 13 MI FROM THE FIX AND 6000' HIGH, SO I'VE GOT TO START DOWN NOW!' IN THIS CASE, ALTHOUGH I MADE THE DATA ENTRY I DIDN'T MAKE THE VALIDITY CHECK BECAUSE I WAS NOT FLYING, AND PREOCCUPIED WITH MY CONCERN FOR THE SAFETY OF THE PAX AND CABIN CREW IN THE CONTEXT OF THE EXPECTED SEVERE TURBULENCE. I HAD SUBCONSCIOUSLY PLACED A HIGHER PRIORITY ON COMMUNICATING WITH THE CABIN CREW THAN ON DOUBLE-CHECKING THE COMPUTER. IT HAS NOT ESCAPED ME THAT NOT DOUBLE-CHECKING THE COMPUTER OR THE PLT FLYING CAN LEAD TO A BUSTED ALT AND HENCE A MIDAIR COLLISION, WHICH SHOULD HAVE BEEN A HIGHER PRIORITY. THE F/O INDICATED THAT SINCE I HAD MADE THE DATA ENTRY HE ASSUMED THAT THE DATA WAS VALID (IT WAS, BUT TOO LATE) AND DIDN'T DOUBLE-CHECK IT.

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.