C560XL flight crew reported the aircraft stabilizer and hydraulic system malfunctioned after climb-out and after climbing to cleared altitude; the aircraft began to violently pitch downwards. The flight crew managed to recover the aircraft by using manual trim and proceeded to safely divert.
Synopsis
C560XL flight crew reported the aircraft stabilizer and hydraulic system malfunctioned after climb-out and after climbing to cleared altitude; the aircraft began to violently pitch downwards. The flight crew managed to recover the aircraft by using manual trim and proceeded to safely divert.
Narrative
On climb out of ZZZ; stab mis comp annunciator showed up and flaps overspeed identified. I reduced power to slow to under 200 kt. and disconnected the autopilot while continuing the climb to our cleared altitude of 11000. Flaps were brought up and we waited until the hyd press annunciator went out. I then applied power and resumed normal climb-out reengaging autopilot and putting in normal settings on Flight Director (FD). About ten seconds later noticing the aircraft was gradually pitching down tried to correct. then nose pitched down extremely and I transferred controls to Person A as I was unsure what the cause of this was. He used me to [call for priority handling and] I then extended the speed brakes noticing our speed rising rapidly and made the call. Eventually Person A was able to fight the aircraft back to straight and level by that time we had lost 4000 feet and had gone at least 330 kt. We regained straight and level flight stabilized the speed and reengaged the autopilot. We then discussed what happened while complying with ATC instruction. Unable to figure out the cause we contacted Chief Pilot and diverted as we were instructed.Flap limitations were well known to us in a task saturated situation with moderate turbulence we missed the call out for flaps up. Once we had cleaned up the aircraft at an acceptable airspeed we had thought the situation was resolved. Why the aircraft suddenly pitched down in that manner is still unknown to us we suspected stab involvement even though we had waited for the hyd press light to extinguish indicating it had finished moving.
Second reporter narrative
On climb out of ZZZ flap STAB MIS COMP due to overspeed identified. Reduced power; continued climbing; cleared to 11000; and slowed aircraft to below 200 kt. Flaps selected up and waited till HYD PRESS caution light went out then. FO re-applied power to continue climb. Within very short period of time; what started as initial gradual pitch nose down violently went extreme nose down.FO handed aircraft over and I asked him to make [priority handling] call. FO extended speed brakes and made call. I fought to pull aircraft out of the uncommanded dive. Using manual trim eventually got the control pressures to normal and recovered to straight and level. Recovering around 4000 feet; we had lost over 4000 feet and saw at least 330 kias. Took a few moments to get aircraft sorted and back to a cleared altitude and heading. Event occurred approximately 5 NM south of ZZZ1.The pitch tendency is well covered in training and we respect the 200-kt. limitation for flap retraction for just the experienced reason. Shock factor was very high. Unknown why the aircraft reacted such.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.