B737-300 CLRED TO CROSS A POINT 35 MI S OF RICCS INTXN AT FL240. PRIOR TO DSCNT POINT; CTR REQUESTED TO START DSCNT. SELECTED VERT SPD WHEEL WHICH DISCONNECTED THE VNAV FEATURE OF THE FMC. DSCNT NOT FAST ENOUGH TO MAKE XING. ADVISED CTR UNABLE AND CROSSED AT FL258. SHOULD EMPHASIZE IN TRAINING USING VERT SPD DISENGAGES VNAV.

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APPROX 80-90 MI S OF RICCS INTXN; WHILE LEVEL AT FL290; ATC GAVE US A CLRNC TO CROSS '35 MI S OF RICCS AT FL240.' WE ENTERED THE PROPER WAYPOINT AND ALT IN THE FMC. PRIOR TO REACHING OUR TOP OF DSCNT POINT; ATC TOLD US TO BEGIN OUR DSCNT. WE USED THE VERT SPD WHEEL TO BEGIN OUR DSCNT (WHICH DISCONNECTED THE VNAV). WE DID NOT USE A RATE OF DSCNT THAT WAS STEEP ENOUGH TO MAKE OUR XING RESTR BUT WE DID NOT NOTICE THAT FACT UNTIL WE WERE WITHIN 5 MI OF OUR XING RESTR. THUS; WE WERE APPROX 1800 FT HIGH AT 35 MI S OF RICCS (FL258 INSTEAD OF FL240). WE IMMEDIATELY ADVISED THE CTLR OF OUR MISTAKE AND ALSO ADVISED ATC THAT WE WOULD BE UNABLE TO MAKE THE XING RESTR. AS CAPT; I ADVISED MY CARRIER OF THIS SIT VIA THE AIR SAFETY RPTING SYS. AS A POSSIBLE SOLUTION I RECOMMENDED THAT OUR TRAINING DEPT EMPHASIZE THAT CREWS BEWARE WHEN A VNAV DSCNT IS PROGRAMMED IN THE FMC AND ATC ASKS YOU TO BEGIN YOUR DSCNT PRIOR TO THE TOP OF DSCNT POINT. CREWS SHOULD PROBABLY USE THE 'CAPTURE' FUNCTION OF THE FMC (DSCNT PAGE) INSTEAD OF THE VERT SPD WHEEL ON THE AUTOPLT.