B737NG flight crew reported they did not fully comply with an altitude clearance on descent while us...

Attributes
ACN	1395514
Time
Date	201610
Place
Locale Reference	ZLA.ARTCC
State Reference	CA
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B737 Next Generation Undifferentiated
Operating Under FAR Part	Part 121
Flight Phase	Descent
Flight Plan	IFR
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 229 Flight Crew Type 25000
Person 2
Function	Pilot Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 191 Flight Crew Type 2500
Events
Anomaly	Deviation - Altitude Undershoot Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy

Narrative:

Center advised us to cross hec at or below FL240; then maintain FL200. PF programmed the FMC and MCP accordingly. The aircraft commenced descent to cross hec at or below FL240. As a crew; we continued with our approach briefing. We neglected to note that the FMC planned on maintaining FL240 for approximately 20 miles before continuing a programmed descent to FL200 rather than immediately descending to FL200 once past hec. We did not notice this fact until approximately seven miles west of hec at which time we continued descent. ATC prompted us to continue descent shortly thereafter. We did not observe any conflict with other crossing traffic visually or with TCAS due to our delayed descent. [We could avoid this by] performing a thorough crosscheck of FMC programming and resultant descent profile prior to continuing other flight deck duties. Crosscheck often to ensure the intended plan is executing properly.

Original NASA ASRS Text

Title: B737NG flight crew reported they did not fully comply with an altitude clearance on descent while using the FMC.

Narrative: Center advised us to cross HEC at or below FL240; then maintain FL200. PF programmed the FMC and MCP accordingly. The aircraft commenced descent to cross HEC at or below FL240. As a Crew; we continued with our Approach Briefing. We neglected to note that the FMC planned on maintaining FL240 for approximately 20 miles before continuing a programmed descent to FL200 rather than immediately descending to FL200 once past HEC. We did not notice this fact until approximately seven miles west of HEC at which time we continued descent. ATC prompted us to continue descent shortly thereafter. We did not observe any conflict with other crossing traffic visually or with TCAS due to our delayed descent. [We could avoid this by] performing a thorough crosscheck of FMC programming and resultant descent profile prior to continuing other flight deck duties. Crosscheck often to ensure the intended plan is executing properly.

Data retrieved from NASA's ASRS site 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.