MD-11
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Unstabilized Approach; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
Requested priority for flight control malfunction on descent into ZZZZ. For approximately 5 minutes I was unable to comply with assigned altitude and course while regaining control of the aircraft. We received 3-4 STAB OUT OF TRIM Level 2" alerts. Alert would be presented for 15-20 seconds; disappear; then return after a minute or two. Reviewed stab out of trim level 2 in QRH. Late in the descent; roughly simultaneously; AP1 (Autopilot 1) failed to capture final approach altitude of 2;600 feet; descending and FO (First Officer) reported LSAS (Longitudinal Stability Augmentation System) "ALL FAIL" alert; which I was unable to confirm as I was simultaneously manually arresting the uncommanded descent; close to ground; IFR; night in moderate turbulence and rain; slow; configure; determine what if any stab trim was available; and navigate the aircraft to final. Disconnected AP; slowed and configured the aircraft with FCP speed commands and the pedestal long trim handles. Flew the rest of the ILS XXL manually in approach/ land. Stopped on taxiway for inspection by fire personnel; nothing noted; taxi to gate."
Captain reported an LSAS system failure caused control issues on descent and approach to landing resulting in a precautionary landing.