Widebody; Low Wing; 2 Turbojet Eng
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Flight Crew Last 90 Days 170; Flight Crew Total 2901; Flight Crew Type 1122
Human-Machine Interface
Deviation - Altitude Overshoot; Deviation - Altitude Crossing Restriction Not Met
Flight Crew FLC Overrode Automation; Flight Crew Returned To Clearance
Procedure; Human Factors
I was the Relief Pilot (IRO) seated in the middle jump seat. The Captain was the Pilot Monitoring (PM) and the FO was the Pilot Flying (PF). Our arrival was the HYPER 7 RNAV arrival; expecting assignment to Rwy 19L at KIAD. Approximately 15 miles prior to the HYPER fix; ATC cleared our aircraft to descend via the HYPER 7 arrival. The PF asked for; and the PM set; 4;000 ft in the MCP. Passing through 14;000 MSL; the FO seemed to believe we would be unable to make the crossing altitude/speed over the HYPER fix of 10;000 MSL and 250 KIAS. The FMC scratch pad displayed the 'drag required' message; and the entire crew was aware of this FMC message. The PF decided to initiate a FLCH descent to make the HYPER crossing restriction of 10;000 ft and asked for 10;000 ft to be set in the MCP. The PM changed the MCP from 4;000 to 10;000. The PF then selected FLCH and extended the speed brake. Our aircraft descended to rejoin the descent path and the PF selected VNAV approaching 10;000 ft. The PM then reset 4;000 ft in the MCP. The 'preset' FMC speed for passing through 10;000 ft was 240 KIAS; which did display on the airspeed bug. The PM asked the PF if he wanted 240 KIAS (vs 250 KIAS). The PF initiated speed intervention on the MCP and selected 250 KIAS approximately 8 miles prior to crossing the HYPER fix. The FMA changed from VNAV Path to VNAV Speed and the aircraft started a slow descent below 10;000. I believe this FMA change from VNAV Path to VNAV Speed initially went undetected by the entire crew. 2-3 miles prior to the HYPER fix; we (collectively as a crew) noticed our altitude of 9;600 ft. The correct crossing altitude for the HYPER fix is 10;000 ft. The PF disengaged the autopilot to prevent any further descent but remained at 9;600 as we were less than 1 NM from crossing the HYPER fix. After passing the HYPER fix; the PF re-engaged the autopilot and initiated a VNAV Path descent without further deviation during the arrival and approach. ATC did not indicate any awareness of our altitude deviation crossing the HYPER fix. No radio calls about this deviation were made or received.
We were cleared on the HYPER 7 arrival into IAD descending via the star and approaching HYPER intersection. As is often the case; when we were cleared to descend via; we were high and fast. Speed brakes were deployed but as we got closer I felt that we wouldn't be able to slow in time to meet the restriction so I asked the Captain to change the MCP from 4;000 ft to 10;000 ft and I selected FLCH and 250kts in the speed window. As we approached HYPER at a high rate of descent we did not smoothly level off at 10;000 ft and as we passed 9700 ft I turned off the autopilot and manually leveled off the aircraft. We were within a few miles of HYPER and I believe the descent was arrested at 9;500 ft. Shortly thereafter we passed HYPER and I engaged the autopilot and VNAV mode.
Air Carrier flight crew reported that an RNAV arrival crossing altitude was not met due to an undetected FMC Mode change.