Narrative:

While cruising at FL370 in VMC conditions, ZNY issued us a crossing restriction (30 west of sweet intersection at FL180). At this time we were about 800 DME from the fix. The crossing restriction and altitude were correctly programmed into the FMC. The new altitude was selected into the altitude alert window of the MCP, and VNAV was selected and verified operational (VNAV light on). The captain's FMC was in the 'legs' page (flight plan) and my FMC was displaying the 'descent' page (flight path angle, rate of descent required are displayed on this page). My particular FMC display on this aircraft was very dim and the light intensity could not be increased and further. Both pilots were flying into the sun and wearing sunglasses, which made monitoring my particular FMC even harder. Sometime between 80 DME and 60 DME from the fix, with FMC and MCP accurately programmed and with the appropriate displays in view, the VNAV portion of the FMC/MCP interfacility malfunctioned and did not command the required descent at the top of descent point (no message was ever displayed on the FMC's to alert us of the malfunction). At 60 DME from the fix I became aware that the FMC was not initiating the expected descent, and advised the captain (who was flying) of the need to get down. This day we had in excess of 80 KTS of wind on the tail. The captain initiated a high rate of descent, and I advised ZNY immediately that we were unable to comply with the restriction. ZNY did not respond, even after a second radio call. Eventually we were vectored (center did not seem alarmed). The failure of the VNAV mode west/O a status (malfunction) display either in the FMC or MCP, in conjunction with the 'dim' FMC display on the copilot's side contributed to the 'top of descent' point being overflown west/O the required descent being initiated.

Related reports:

Google
 

Original NASA ASRS Text

Title: ACR MLG ALT DEVIATION UNDERSHOT ALT CROSSING RESTRICTION.

Narrative: WHILE CRUISING AT FL370 IN VMC CONDITIONS, ZNY ISSUED US A XING RESTRICTION (30 W OF SWEET INTXN AT FL180). AT THIS TIME WE WERE ABOUT 800 DME FROM THE FIX. THE XING RESTRICTION AND ALT WERE CORRECTLY PROGRAMMED INTO THE FMC. THE NEW ALT WAS SELECTED INTO THE ALT ALERT WINDOW OF THE MCP, AND VNAV WAS SELECTED AND VERIFIED OPERATIONAL (VNAV LIGHT ON). THE CAPT'S FMC WAS IN THE 'LEGS' PAGE (FLT PLAN) AND MY FMC WAS DISPLAYING THE 'DSNT' PAGE (FLT PATH ANGLE, RATE OF DSNT REQUIRED ARE DISPLAYED ON THIS PAGE). MY PARTICULAR FMC DISPLAY ON THIS ACFT WAS VERY DIM AND THE LIGHT INTENSITY COULD NOT BE INCREASED AND FURTHER. BOTH PLTS WERE FLYING INTO THE SUN AND WEARING SUNGLASSES, WHICH MADE MONITORING MY PARTICULAR FMC EVEN HARDER. SOMETIME BTWN 80 DME AND 60 DME FROM THE FIX, WITH FMC AND MCP ACCURATELY PROGRAMMED AND WITH THE APPROPRIATE DISPLAYS IN VIEW, THE VNAV PORTION OF THE FMC/MCP INTERFAC MALFUNCTIONED AND DID NOT COMMAND THE REQUIRED DSNT AT THE TOP OF DSNT POINT (NO MESSAGE WAS EVER DISPLAYED ON THE FMC'S TO ALERT US OF THE MALFUNCTION). AT 60 DME FROM THE FIX I BECAME AWARE THAT THE FMC WAS NOT INITIATING THE EXPECTED DSNT, AND ADVISED THE CAPT (WHO WAS FLYING) OF THE NEED TO GET DOWN. THIS DAY WE HAD IN EXCESS OF 80 KTS OF WIND ON THE TAIL. THE CAPT INITIATED A HIGH RATE OF DSNT, AND I ADVISED ZNY IMMEDIATELY THAT WE WERE UNABLE TO COMPLY WITH THE RESTRICTION. ZNY DID NOT RESPOND, EVEN AFTER A SECOND RADIO CALL. EVENTUALLY WE WERE VECTORED (CENTER DID NOT SEEM ALARMED). THE FAILURE OF THE VNAV MODE W/O A STATUS (MALFUNCTION) DISPLAY EITHER IN THE FMC OR MCP, IN CONJUNCTION WITH THE 'DIM' FMC DISPLAY ON THE COPLT'S SIDE CONTRIBUTED TO THE 'TOP OF DSNT' POINT BEING OVERFLOWN W/O THE REQUIRED DSNT BEING INITIATED.

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.