Date: 201301
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Gulfstream V / G500 / G550
Operator: Fractional
Operating under: Part 91
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Descent
ATC / advisory: TRACON ZZZ
Aircraft component: Altitude Hold/Capture
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Human-Machine Interface; Distraction
Second reporter function: Pilot Not Flying; Captain
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Returned To Clearance; Flight Crew Took Evasive Action
Contributing factors: Aircraft; Human Factors
Primary problem: Human Factors

Narrative: On descent while flying the arrival procedure; I was given a clearance to cross an arrival intersection 'at' 14;000 FT. I reset the altitude alerter to 14;000 FT and selected 'VPATH' for the vertical mode of operation. The autopilot was on and the descent mode. At this point in the flight the pilot not flying; was out of the seat to use the lavatory prior to landing. All was in order so I looked at the FMS to review the ATIS information and to further review the arrival. A double check if you will. During this time my attention was diverted from the primary flight display. The automation did not in fact capture the assigned altitude but kept descending until I looked and saw the altimeter at 13;300 FT. I immediately disconnected the autopilot and autothrottles and corrected the aircraft back to 14;000 FT as assigned. As I was leveling back to 14;000 FT; the pilot not flying returned to his station and inquired of me what had happened. A short exchange took place and we pressed on with the flight. No instruction or challenge was made by ATC and no conflict indicated by the TCAS. Shortly thereafter I was given a further descent to 8;000 FT and the rest of the flight proceeded normally.For a long period of time after this flight concluded; I evaluated my performance of duties and identified the source of the occurrence. I failed to adequately monitor the specific flight path of the aircraft during a critical time in the flight. I got complacent with my duty and I believe it was because for so many years of operating this equipment; never had the automation failed to perform as it had been set up. I fully believed that it would do as always; and as such; allowed myself to occupy my attention with other aspects of the flight. Worse; I allowed this to happen when the other pilot was away from his station. I did not discipline myself to avoid distraction from the primary duty when it was necessary that I perform specifically! To avoid said occurrence; or any similar occurrence; it is imperative to pay complete attention to the primary displays while performing flight operations. Complacency contributed directly to this deviation and indeed; does not have any place on the flight deck.


Second narrative: I confirmed that 14;000 FT was indeed set. He said it descended to 13;300 FT when he noted the deviation. He said he didn't know why it didn't level off at the set altitude. The display controller was set correctly; and should have leveled off. There was no conflict or rebuttal from ATC. We continued and landed.I left well before any critical phase of flight. He said he was doing other pilot duties while he was the sole pilot in the cockpit. I believe if you're the sole pilot in the cockpit you need to concentrate on flying the airplane and not doing other pilot duties.


Synopsis: A G-V failed to capture 14;000 FT set in the Mode Control Panel to comply with an ATC assign crossing restriction but the pilot failed to detect the error until 13;000 FT.