Gulfstream IV / G350 / G450
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 113; Flight Crew Total 3400; Flight Crew Type 600
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Loss Of Aircraft Control
Air Traffic Control Provided Assistance; Flight Crew Overcame Equipment Problem; Flight Crew Regained Aircraft Control; General Maintenance Action; General Flight Cancelled / Delayed
Aircraft
Normal takeoff roll. After gear up and 400ft. flaps up. I noticed the aircraft would not nose trim down as the flaps were going from 10 to 0 as I tried to maintain 10deg to 12deg climb angle. The aircraft was trying to pitch up and it took increasingly excessive force on the yolk pushing forward to try to keep the airplane under 15deg nose up pitch. The trim switch on the yoke was ineffective.I was not using the auto pilot but pressed the autopilot disconnect switch thinking I had an electrical jammed trim motor. I then went to turn off the main trim switch in order to use to manual trim wheel and the trim wheel seemed frozen. We could turn the wheel but it took a lot of effort to get minor movements. At the same time we were getting FGC 1 and FGC 2 CAS messages. I went back to two hands on the yoke and asked for assistance from the non flying pilot. We noticed that we had a flight guidance computer 1 and flight guidance computer2 failure. At the same time the flight guidance panel went blank and the flight director disappear from the PFD. We had no heading reference and no pitch reference. The auto throttles were also not controlling the speed and when selecting Auto throttles 'off' they still appeared engaged but only 'holding' not moving. We were just trying to hold a basic pitch angle and heading and trying to level off. We were now still climbing through 2;500 ft. and ATC. cleared us up to 4;000 ft. we had a hard time controlling the airplane in the pitch mode. It wanted to climb! All of this happened within a few short minutes of flight.I had two hands on the yolk when NAME asked me if he could take the yoke and once he felt the yoke he agreed there was something serious with the aircraft and we notified ATC that we had flight control issues. We were able to adjusted the throttles to maintain pitch and we figured it was best if NAME controlled the yoke and I controlled the throttles adjusting power and I tried to trim the trim wheel. By NAME flying the plane I was able to try to regain some flight director functions. I pulled FGC1 and FGC 2 circuit breakers let them stay unpowered for a few seconds and reengage them and attempt to determine what systems were working and which failure we actually had. Resetting the circuit breakers brought back the heading indicator and the flight director. We switched the FD command to the Right side. We advised ATC we did not want to climb into the clouds we needed to stay VFR. ATC assisted us with radar vectors to final to Runway XX atZZZ1My thoughts are the pitch motor servo or pitch windings failed or became frozen thus causing the flight guidance computer 1 to not be able to get a valid signal from the pitch feedback then it switched over to flight guidance 2 that also was not able to see a valid signal from the pitch and disengaged. When the flight guidance panel did not have a valid signal from either FGC it therefore lost heading; auto throttles; vertical and lateral modes. The primary flight controls all worked (elevator ailerons and rudder all seem to work properly and the flaps could go up and down normally. The landing gear function was also normal. I believe this was a pitch trim issue which triggered a flight guidance issue and made the aircraft extremely uncontrollable. By splitting the pilot duties and using crew coordination we were able to safely land the aircraft.
Gulfstream IV First Officer reported total loss of elevator and stabilizer trim that resulted in major control issues and a diversion.