On May 3, 2020, an AIRBUS HELICOPTERS AS350 B3 (registration N1WT) operated by MACNEIL AVIATION LLC was involved in an aviation accident near Clewiston, FL. No fatalities were reported. Investigators recorded the probable cause as: Seizure of the hydraulic pump pulley bearing due to its improper installation by the manufacturer, leading to a failure of the hydraulic pump belt and the resultant partial loss of hydraulic assistance to the pedals. This summary draws on records from NTSB; 12 related events involving the same aircraft type or operator are linked below.
An AS350 B3 helicopter made an emergency landing in Clewiston, Florida, after a hydraulic anomaly. Investigation found a fractured belt and bearing damage, leading to new post-installation checks.
Incident Overview and Flight Details On May 3, 2020, an Airbus Helicopters AS350 B3 helicopter, registration N1WT, made an emergency landing at Airglades Airport (2IS) in Clewiston, Florida. The pilot, the sole occupant, reported an inflight hydraulics anomaly and declared an emergency. The flight, conducted under 14 CFR Part 91, originated at Fort Lauderdale Executive Airport (FXE), made an intermediate stop at Palm Beach County Park Airport (LNA), and was en route to 2IS when the incident occurred. The pilot reported no injuries, and the helicopter sustained no substantial damage. During the approach to runway 13 at 2IS, the pilot noted that the pedals felt “rock hard” and that the “HYD2” and “SERVO” caution lights illuminated. Light smoke and a burnt odor were observed in the cockpit, prompting the pilot to open the window. A shallow approach and run-on landing were executed at 2IS. ## Damage Assessment and Component Examination Post-landing inspection revealed that the HYD2 belt had fractured, with significant wear on localized sections of the belt grooves. Remnant belt material was found on the HYD2 pump pulley grooves and the transmission deck. The pulley grooves exhibited a blackened appearance consistent with overheating, and the HYD2 pump pulley and its bearing would not rotate freely. The HYD2 drive assembly, pump, pulley assembly, and belt were retained for further examination. The HYD2 pulley bearing, a double-row ball bearing introduced via modification 07-9568, was shipped to Airbus Helicopters’ materials laboratory in Marignane, France. The hydraulic pump rotated freely with no binding. The bearing’s visible surfaces were thermally discolored, and smearing damage was found within a 140° arc on the inner diameter of the pulley, along with residual grease. Longitudinal scratches parallel to the bearing’s rotational axis were observed on the inner ring. Disassembly revealed black-colored residue consistent with thermally degraded grease on the inner ring, outer rings, cage, and rolling elements. After cleaning, plastic deformation and cage material transfer were found on the raceways, and the cage showed abnormal contact damage. Hardness testing of undamaged portions met drawing requirements. Dented sealing flange regreasing holes were observed, but it could not be determined if this was due to prior regreasing, incident damage, or preexisting condition. ## Test and Research Findings Airbus Helicopters stated that the pulley must be heated to about 110° Celsius before bearing installation to ensure proper fit and alignment. A test installation without preheating resulted in a skewed bearing and smearing damage similar to the incident components. At the time, no post-installation inspection requirement existed to verify proper bearing seating. As an interim measure, Airbus Helicopters instituted a post-installation check using a shim to detect clearance between the bearing ring and pulley shoulder. The company is exploring options for an in-situ check for pulley bearings in the AS350-series fleet. ## Maintenance History and System Design Maintenance records indicated that the helicopter underwent final assembly at Airbus Helicopters’ Columbus, Mississippi facility in March 2019. On June 20, 2019, the main gearbox assembly, including the incident HYD2 pump and pulley bearing, was replaced due to suspected contamination. Subsequent 12-month/150-flight hour inspections on October 24, 2019, January 30, 2020, and April 28, 2020, found no discrepancies in the hydraulic pump belt and pulley bearing. The last maintenance entry before the incident was a main rotor mast retorque on May 1, 2020. The AS350 B3 dual hydraulic system provides redundancy for main rotor servo controls, but the tail rotor servo control and yaw load compensator are powered only by HYD2. Loss of HYD2 pressure increases pedal forces, though the yaw load compensator is designed to keep right pedal forces manageable. Emergency procedures for HYD2 and SERVO caution lights direct pilots to land as soon as practicable.