Date: 202001
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: IMC
Weather elements / visibility: Icing
Light: Night
Aircraft: Gulfstream G650
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: FMS/FMC
Component problem: Malfunctioning
Reporter organization: Corporate
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP)
Human factors: Human-Machine Interface
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Overshoot; Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew FLC Overrode Automation; Flight Crew Regained Aircraft Control
Contributing factors: Aircraft; Manuals
Primary problem: Aircraft

Narrative: The airplane FMS decided to leave 13;000 feet while in VNAV mode before reaching the crossing restriction point ZZZZZ at 13;000 [feet]. The next crossing restriction would be ZZZZZ1 at 11;000 feet and 250 Knots. The airplane would have attempted to violate that restriction as well if we had not intervened; by disengaging the autopilot and manually flying the arrival at the proper altitudes. So technically; we flew below one crossing restriction by a couple of hundred feet; but made the rest [by] hand flying the aircraft.This flight leg originated at ZZZ; and was on a quick turn from ZZZ1 and then back to ZZZ1. So the airplane was never completely shut down after arriving in ZZZ. There are over 3;000 software fixes for the FMS in the works from Honeywell; but the release date keeps getting pushed back. In addition there are flight control issues that recently resulted in changes to the Aircraft Flight Manual. 15 emergency procedures involving flight controls were revised to state that the airplane should be landed as soon as possible if a flight control message was displayed on the EICAS. For the Gulfstream; that means at the nearest airport that has an approach if one is required; and a runway that the aircraft can be stopped on.There was also an issue recently with the rudder that has restricted the entire G650 fleet to 250 KIAS until the rudder is modified with a trailing edge strip.Clearly; Gulfstream does not have a handle on their new fly-by-wire technology; their revised FMS software; and the aerodynamics of their Flagship high speed long range aircraft.Many of the changes Gulfstream implemented were driven by the FAA demanding that Gulfstream could not continue to build on their old Type Certificate designs; but to start with a clean sheet designs. If we had shut the airplane down on the ground; to a black aircraft; then restarted; the FMS issues probably [would] not have happened. We will do that on every leg from now on.

Callback: The reporter stated that due to software fixes not yet implemented by Honeywell; the FMS will allow the aircraft to fly through altitude and speed restrictions. The reporter said the crew does 'not trust the airplane' and 'workarounds must be done all the time'; such as disconnecting the autopilot and FD command bars and using spoilers to control airspeed during programmed descents.The reporter also said that the aircraft QRH has not been updated with new emergency procedures and an Airworthiness Directive because these have not been pushed by Honeywell. The flight manual is updated; however; the crew would use the QRH; not the flight manual in the event of an abnormal or emergency situation.



Synopsis: Gulfstream G650 Captain reported that the FMS caused a crossing restriction not to be met; requiring the autopilot to be disengaged and the remainder of the arrival was flown manually.