Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
AIR-22-08
April 11, 2022
This is information only. Recommendations
aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin (SAIB) is intended to
remind owners and operators of any Robinson R44 rotorcraft of the
importance of adhering to existing inspection procedures in the
applicable operating handbooks and maintenance manuals.
At this time, the airworthiness concern is not an unsafe condition that
would warrant airworthiness directive (AD) action under Title 14 of the
Code of Federal Regulations (14 CFR) part 39.
Background
The FAA received a report of a failed C907 yoke in the R44 main rotor
drive system. This failure occurred during preparation to land. A loud
bang was heard from the rear of the helicopter. The helicopter
descended rapidly and there was significant resistance from the flight
controls. The helicopter collided heavily with an adjacent loading
vehicle, coming to rest on its side. No injuries were reported.
A fatigue crack was found in the R44 C907 yoke. The fatigue crack
appears to have initiated near the bolt hole of the C907 on the side of
the C907 arm that mates with the C947-1 forward flex plate. An initial
metallurgical exam found corrosion products and fretting damage on the
surface near the fatigue crack. The C907 yoke failure may have been
caused by corrosion and/or improper hardware torque.
Inadequate inspection and maintenance of all driveshaft yokes may
result in undetected wear and/or corrosion that could lead to yoke
failure and loss of main and tail rotor drive.
Recommendations
We recommend owners and operators of Robinson R44 and R22 series
rotorcraft follow Robinson’s published pre-flight inspection and
periodic maintenance criteria regarding main rotor and tail rotor
driveshaft yokes in order to prevent future failures. The reiterated
items below relate to the yoke and flex plate:
During the preflight
inspection, inspect all torqued joint locations for loose fasteners,
unusual wear, fretting, or corrosion. Since the components are steel,
fretting at the yoke-to-flex plate interface will appear as
reddish-brown colored dust.
During the 100-hour/annual
inspection, inspect clutch shaft forward yoke for cracks, corrosion, or
fretting, and inspect the yoke-to-flex-plate joint to verify the
security of the bonded washers on each side of the flex plate arm.
During the 12-year/2200-hour
overhaul, the yoke-to-flex-plate joint is disassembled to facilitate
removal of nearby clutch and gearbox components. We recommend ensuring
the clamping surfaces of yoke-to-flex-plate interfaces are smooth and
clean prior to reassembly.
For Further Information Contact
Jeffrey Chang, Aerospace Engineer, 3960 Paramount Blvd, Lakewood, CA
90712, United States; phone: (562) 627-5263; fax: (562) 627-5210;
e-mail: jeffrey.chang@faa.gov.
For Related Service Information Contact
Robinson Helicopter Company, 2901 Airport Drive, Torrance, CA 90505;
telephone 310-539-0508; fax 310-539-5198; or at
https://www.robinsonheli.com.