AD 2021-04-12 Was Prompted By Reports Of Tail Rotor (T/R) Drive Shaft Forward Hanger Bearing Failures

The FAA is adopting a new airworthiness directive (AD) for Robinson Helicopter Company (Robinson) Model R66 helicopters.

This AD was prompted by reports of tail rotor (T/R) drive shaft forward hanger bearing failures. This AD requires installing a certain part numbered kit and removing parts from service or replacing a certain part-numbered T/R drive shaft assembly. This AD also prohibits the installation of certain parts. The FAA is issuing this AD to address the unsafe condition on these products. This AD is effective April 12, 2021.

Supplementary Information: The FAA issued a supplemental notice of proposed rulemaking (SNPRM) to amend 14 CFR part 39 by adding an AD that would apply to Robinson Model R66 helicopters with a T/R drive shaft assembly part number (P/N) D224-3 without B900-11 modification installed. The SNPRM published in the Federal Register on July 28, 2020 (85 FR 45360). The FAA preceded the SNPRM with a notice of proposed rulemaking (NPRM) that published in the Federal Register on March 30, 2018 (83 FR 13706). The NPRM was prompted by two incidents of forward hanger bearing failure of the T/R drive shaft assembly because the bearing was undersized for its housing. Consequently, the bearing was spinning at a speed that caused excessive heating of the bearing during operation and led to the breakdown of the bearing's grease and ultimately seizure of the C647-16 bearing.

To correct this condition, Robinson initially issued R66 Service Bulletin SB-14, dated June 25, 2015 (SB-14), for certain serial-numbered helicopters, which specified installing a temperature recorder on the T/R drive shaft forward hanger bearing assembly and inspecting the temperature recorder during preflight checks and during each 100-hour inspection. If the bearing was found running hot, then Robinson advised upgrading the bearing to a newer design.

Following additional reports of overheating forward hanger bearing assemblies, Robinson superseded SB-14 with R66 Service Bulletin SB-20, dated November 7, 2016 (SB-20), which affected additional serial-numbered helicopters and specified modifying T/R drive shaft assembly P/Ns D224-3 and D224-4 by using kit Robinson KI-235 R66 TRDS Forward Yoke Assembly and Hanger Installation Kit Instructions, Revision A, dated June 23, 2015 (KI-235) and installing yoke assembly P/N D224-5. This installation has an improved, larger bearing that spins with less friction.

SB-20 also specified inspecting the forward and aft sides of the hanger and damper bearings for a minimum of 0.5 inch in length of sealant on the junction of the black seal and bearing outer race and applying sealant if there was less than 0.5 inch in length of sealant. Robinson revised SB-20 with R66 Service Bulletin SB-20A, dated June 6, 2017 (SB-20A), to clarify that helicopters with either T/R drive shaft assembly P/N D224-3 with modification B900-11 or P/N D224-4 installed include the upgraded bearing and do not require kit KI-235.

Robinson later revised SB-20A with R66 Service Bulletin SB-20B, dated December 20, 2017 (SB-20B), which updates writing practices and organizes the procedures into two separate sections, clarifies the “Rotorcraft Affected” section, and reduces the helicopters that need to perform the inspection and sealant application procedures to just helicopters without the latest version damper and housing bearings.

The NPRM proposed to require within 100 hours time-in-service (TIS) replacing an affected T/R drive shaft forward yoke assembly with T/R drive shaft yoke assembly P/N D224-5. The NPRM proposed to require inspections of the forward and aft sides of the hanger bearing and the damper bearing for sealant, and depending on the results of the inspections applying sealant. The SNPRM proposed to revise the NPRM by expanding the applicability, changing the proposed requirements, and correcting nomenclature. The FAA is issuing this AD to address the unsafe condition on these products.

FMI: www.regulations.gov