Global Express (BD700)
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 100; Flight Crew Total 10000; Flight Crew Type 3600
Situational Awareness
Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors
Cleared to descend to 3000 feet and to maintain 3000 feet until established on the approach. Cleared for the RNAV GPS 35. Pilot flying (PF) thought he was in VNAV and had the altitude selector set to below field elevation. The aircraft was actually in Vertical Speed and didn't level off at 3000 feet. The PF was watching the aircraft as it came upon 3000 feet and thought it was leveling off but didn't confirm that it was leveling off. ATC then called the aircraft as we were going through 2500 feet. We immediately returned to 3000 feet after descending 600 feet below our altitude. I believe contributing factors were not knowing/confirming the flight modes the aircraft was in and not monitoring the aircraft properly while on auto pilot.
Neither pilot noticed the wrong mode; so the altitude selector was set to below field elevation. Just prior to reaching the IAP; ATC advised the crew that the aircraft was at 2600 feet. The PF corrected back to 3000 feet and continued the approach as published.
BD70 (GLEX) flight crew reported overshooting charted altitude during RNAV approach. Crew reported they thought they were in VNAV but were actually in VS mode.