B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 373
Human-Machine Interface; Situational Awareness
Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Human Factors
Prior to LAXBB; and prior to leveling at the assigned altitude restriction of 5000 FT; SoCal Approach cleared us for the RNAV RNP Z Approach to Runway 20R at SNA. With VNAV PATH established and displayed; the Pilot Flying (PF) set an altitude of 1400 FT in the MCP altitude window. ATC then directed us to slow to 170 knots and switch frequencies. While looking down to switch frequencies; I glanced to confirm 170 knots was set in the MCP panel. It was assumed incorrectly that Speed Intervention had been used; when; in fact; Level Change had been selected. The aircraft started to descend through the 5000 FT altitude crossing restriction. At approximately 4700 FT; the deviation was noticed by both pilots. Pilot Monitoring commanded 'climb back up' and the PF reset 5000 FT in the MCP window and climbed using Vertical Speed. The aircraft had descended to 4600 FT before the climb was recovered. After re-established; and properly on speed; and altitude with VNAV re-engaged; the arrival and approach were executed normally. No inquiry; comment or notification was made by ATC. The most significant reason for this occurrence was the lack of verbalization by the PF for the use of MCP Level Change. Verbalization; verifying and monitoring had been used and practiced throughout the trip but the lack of its use at this time proved consequential.
B737-700 Captain reported overshooting a crossing restriction; due in part to the use of Level Change mode.