Date: 201510
Local time of day: 1201-1800
Location: ZOA.ARTCC, CA
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: B757 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 125
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class E ZOA
ATC / advisory: Center ZOA
Aircraft component: MCP
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Engineer; Flight Crew Multiengine; Flight Crew Instrument
Human factors: Communication Breakdown; Confusion
Anomaly: Deviation - Altitude Overshoot; Flight Deck / Cabin / Aircraft Event Other / Unknown
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Took Evasive Action; Flight Crew Became Reoriented
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: The Pilot Flying (PF) was the Captain. The Pilot Not Flying (PNF) was the First Officer. Enroute to OAK; Oakland Center cleared us to EMZOH for the EMZOH TWO arrival into OAK. We updated our arrival in the FMC from the original arrival to the newly cleared STAR. I; the PNF; got busy listening to and recording the ATIS. The Captain; without coordination with me; changed some altitude restrictions on the STAR in the FMC to the lower altitude where there was a 'between' (i.e. Between 10000 feet & 9000 feet) altitude restriction. Upon completing my other duties and reporting back to the Captain; I reviewed the FMC and noted the changes he made and got confirmation of what he said he had done. Subsequently we were cleared to 'Descend via the EMZOH TWO arrival.' The Captain put the 'bottom' altitude in the MCP altitude window; we got on the VNAV path and started our descent. At some unknown point and without coordination with me the Captain changed from VNAV to FLCH; never changed his altitude in the MCP and never coordinated with me. As we continued our descent on the arrival I continued to monitor our altitude restrictions as amended in the FMC by the Captain. Approaching MYRIB with a 10;000 feet restriction in the FMC and my belief that the Captain had amended the altitude to the lower altitude; I alerted him that he was going to descend through the restriction of 10;000 feet and to climb back to 10;000 feet. The descent was stopped by approximately 9;400 feet while I simultaneously contacted Oakland Center to get relief from the restriction. Oakland told us there was no problem and to contact NORCAL approach. The remainder of the flight was uneventful. Post flight and upon review of the incident; it appears that there may not have been an altitude deviation. Depending upon our precise location we were really limited to 9;000 feet at MYRIB and then cleared down to 7;000 feet at MYNEE. Our descent in the vicinity of MYRIB was never below 9;000 feet; which was the lower altitude restriction. Our error was a failure of adequate coordination when making changes to the FMC. There was a failure to notify the PNF of the modifications made to the FMC altitude profile. The PNF did not make a thorough enough crosscheck of the modifications. The PF did not notify the PNF of his change from VNAV mode to FLCH mode and the PNF did not pick up on the change and subsequently was not able to advise the PF to change the altitude in the MCP. So; in summary; although I don't believe there was an altitude deviation; the lack of adequate crew coordination could have led to an altitude deviation under just slightly different circumstances. Excellent lesson learned and hopefully beneficial for others.




Synopsis: B757 First Officer reports the flying Captain making alterations to the RNAV arrival without advising him; then not complying with the modified crossing restrictions by using Flight Level Change instead of VNAV.