Date: 202105
Local time of day: 0601-1200
Location: SJU.TRACON, PR
Flight conditions: VMC
Weather elements / visibility: Haze; 5
Light: Daylight
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Final Approach; Initial Approach
Airspace: Class C SJU
ATC / advisory: TRACON SJU
Aircraft component: Autopilot
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Time Pressure; Situational Awareness
Anomaly: ATC Issue All Types; Aircraft Equipment Problem Less Severe
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem; Flight Crew Overrode Automation; Flight Crew Regained Aircraft Control
Contributing factors: ATC Equipment / Nav Facility / Buildings; Aircraft
Primary problem: ATC Equipment / Nav Facility / Buildings

Narrative: Approach control cleared us direct to WESEN for ILS [Runway] 08 [approach] at SJU. Captain was Pilot Flying; First Officer was Pilot Monitoring. This was the second leg of the night for this three day pairing of a long duty day. Level at 3;000 ft. (pilot selected) then cleared descent to 2;500 ft. (pilot selected) accomplished in vertical speed. Aircraft pilot selected speed was 180 kts. Controller assigned heading 110 to intercept and then cleared us for ILS [Runway] 08 approach. Approach/Land was armed and 'Land Armed' was displayed on PFD. The localizer remained identified and aircraft turned to intercept inbound course. Glide slope was above. Halfway through the intercept; the aircraft made an abrupt pitch-up followed by a thrust increase. This was very unusual as I have never experienced or seen an aircraft climb to capture a glide slope. While this was happening the aircraft exited approach/land mode and reverted to heading mode and solid bow tie altitude (2;500 ft.) All FMAs were 'white'. During the automation the aircraft pitched up and altitude was approximately 3;000 ft. in an attempt to capture the glide slope. The FO made a quick analysis and quick calls to the pilot flying while I was simultaneously disconnecting the autopilot and manually retarding the throttles to correct this anomaly. The aircraft was stabilized and a hand flown ILS was accomplished without autopilot assistance. This aircraft was scheduled for an 'auto land' for currency requirements and subsequently not accomplished. The First Officer monitoring that was accomplished and the verbal inputs from the FO were timely and appropriate; solid CRM. A note in our company aircrew briefing guide notes: Safety Alert Runway 08 Intermittent Glideslope Weak or intermittent glideslope signals have been reported when using ILS Runway 08. Exercise caution and intercept glideslope at the altitude depicted on the approach chart to guard against following a false glide slope signal. If the crew experiences any anomalies while conducting the approach; report the incident to tower and file an event report.




Synopsis: Air carrier Captain reported an unreliable glideslope signal at SJU Airport.