B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 157
Human-Machine Interface
Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Undershoot; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Flight Crew Became Reoriented
Human Factors
In cruise at FL400; we were instructed to cross 125 NM south of OKK at FL300. The restriction was put in the FMC and MCP in accordance with SOP. Due to choppy ride at FL400; we started descent early in V/S. The FMC showed Top of Descent over 90 NM away and we had no magenta vertical path indicator when I noticed the crossing point approaching. I voiced my concern to the First Officer (FO) who immediately increased descent rate. When it was clear that we would be high at the restriction; I notified ATC who; of course; said 'no problem.' We ended up about 1500 feet high. Both FO and I were confused about why the Top of Descent point showed so far away and why we had no magenta vertical path indicator.Later we were given a further crossing restriction and I was unable to execute the altitude in the FMC. I checked the cruise altitude and found that the FO had changed the cruise altitude to FL 310 during the descent without my knowledge. The Top of Descent and vertical guidance were missing because we hadn't yet reached our 'new' cruising altitude.SOP works when both Pilots follow it. In my monitoring and intervening; we caught the error; but a little too late.
B737 Captain reports missing a descent crossing restriction with the First Officer flying due to a new cruise altitude being programed into the FMC.