Helicopter Tail Rotor Control Failure Leads to Emergency Landing at Frankfurt-Hahn

Incident Overview and Flight Details On July 29, 2024, a Eurocopter AS 350 B2 helicopter operated by a German aviation company was conducting vineyard spraying operations near Ockfen. The 35-year-old pilot, holding a commercial helicopter pilot license, took off from a local site at approximately 05:40 local time. After beginning spraying operations at 06:00, the pilot noted an unusual jolt during the fifth flight between 06:58 and 07:14. Initial checks of the instruments and controls yielded no apparent issues, and operations continued. During the sixth flight, while flying up a vineyard slope, the pilot lost tail rotor control authority, noting that the pedals were ineffective. The pilot increased airspeed to utilize the vertical fin for directional control and performed unsuccessful control tests, including pressing the HYDR-TEST switch. The pilot then decided to make a controlled emergency landing at Frankfurt-Hahn Airport. Before landing, the pilot dumped the remaining spray material to reduce weight. The runway was closed to other traffic at 07:56, and the airport fire department was positioned. The helicopter made a sliding landing on runway 03 at 08:00, rotating approximately 180 degrees and coming to a stop after about 24 meters. The pilot shut down the engine normally and communicated with emergency services that all was well. No injuries were reported, and the aircraft sustained minor damage. ## Aircraft and Maintenance History The helicopter, a single-engine Eurocopter AS 350 B2 manufactured in 1990 with serial number 2379, was equipped with a Honeywell LTS101-700D-2 engine and a simplex spray system. The aircraft had a total operating time of approximately 14,344 hours. The tail rotor pitch control assembly, known as the T/R-Spider, had its ball bearing replaced on September 26, 2023, after reaching its service life limit. The new bearing was installed according to maintenance procedures, and the T/R-Spider was installed in the helicopter on May 14, 2024. The assembly had been in operation for 151 hours since the bearing replacement. ## Investigation Findings The investigation revealed that the tail rotor control failure was caused by damage to the ball bearing and T/R-Spider on the tail rotor shaft. The T/R-Spider had fractured into two parts, with the non-rotating portion separating from the rotating portion, which became stuck on the tail rotor shaft. No traces of lubricating grease were found on either part of the T/R-Spider, the bearing, or the bearing shells. The manufacturer's investigation concluded that the rupture of the pitch control assembly was most probably related to the absence of greasing when the new ball bearing was installed. The bearing components showed signs of overheating, smearing, and material creep, with four balls missing. The tightening torque of the cap fixing screws was lower than specified, but this did not affect the bearing degradation sequence. The helicopter was returned to service the same day after replacement of the entire tail rotor drive, control, and tail rotor assembly. No fire was indicated during the flight or emergency landing. The pilot was wearing a four-point harness and helmet.