Problems Found With The Main Rotor Piston Rod
The FAA has issued an Emergency AD for several models of Bell
Helicopters prompted by a main rotor hydraulic servo actuator
(servo actuator) malfunction and a subsequent investigation that
revealed the output piston rod assembly (piston rod) had fractured
at the threaded end because of stress corrosion cracking. Also,
during the investigation of that servo actuator malfunction, a
nonconforming grind relief was discovered on a separate piston rod.
The actions specified by this AD are intended to detect corrosion
or a nonconforming piston rod that, if not detected and corrected,
could result in failure of the piston rod, failure of the servo
actuator, and subsequent loss of control of the helicopter.
The FAA says it has reviewed Bell Alert Service Bulletin (ASB)
No. 222-10-109 for the Model 222 and 222B helicopters, ASB No.
222U-10-80 for the Model 222U helicopters, ASB No. 230-10-41 for
the Model 230 helicopters, and ASB No. 430-10-44 for the Model 430
helicopters. Each ASB is dated August 18, 2010, and specifies a
one-time inspection of all affected servo actuators to verify the
condition of the piston rod. They have also reviewed Woodward HRT
ASB No. 141600-67-02, dated August 18, 2010, attached to each Bell
ASB, which specifies inspecting the piston rod for corrosion and
nonconforming grind relief. It also contains instructions for
reworking and reassembling the unit for operation.
Transport Canada, the airworthiness authority for Canada,
notified the FAA that an unsafe condition may exist on these
helicopter models. Transport Canada advises that it has been
determined that the piston rods of the servo actuators “may
be corroded and, consequently, prone for corrosion cracking.”
Also, in one case, an unapproved repair was found on the piston
rod. This situation, if not corrected, could result in loss of
control of the helicopter. Transport Canada classified the ASBs as
mandatory and issued AD No. CF-2010-29, dated August 26, 2010, to
ensure the continued airworthiness of these helicopters.
These helicopters have been approved by the aviation authority
of Canada and are approved for operation in the United States.
Pursuant to our bilateral agreement with Canada, they have notified
us of the unsafe condition described in the Transport Canada
AD.
The FAA is issuing this AD because it evaluated all information
provided by Transport Canada and determined the unsafe condition
exists and is likely to exist or develop on other helicopters of
these same type designs. Therefore, this AD requires, before
further flight:
- Disassembling the actuator to gain access to the piston
rod.
- Cleaning the entire piston rod and nut using Acetone and a
nylon bristle brush removing all contaminates to allow for
inspections.
- Inspecting the grind relief configuration for the piston rod
and nut. If the grind relief is unacceptable, replacing the piston
rod and the nut with airworthy parts.
- Using a 10x or higher magnifying glass, visually inspecting the
nut for corrosion or damage to the threads. If you find any
corrosion or damage to the threads, replacing the nut with an
airworthy nut.
- Using a 10x or higher magnifying glass, visually inspecting the
piston rod for any corrosion, visible lack of cadmium plate (gold
or grey color), or damage to the piston rod. If you find any
corrosion, visible lack of cadmium plate (gold or grey color), or
damage to the piston rod in the “Critical Areas,”
replacing the piston rod with an airworthy piston rod.
- If you find any corrosion or visible lack of cadmium plate on
the piston rod in areas that are not considered “Critical
Areas,” reworking the piston rod by removing any surface
corrosion that has not penetrated into the base material by lightly
buffing with scotch-brite. Cleaning the part using Acetone and a
nylon bristle brush to remove any residue.
- If you find any corrosion that is red or orange in color,
magnetic particle inspecting the piston rod for a crack. If you
find a crack, replacing the piston rod with an airworthy piston
rod.
- Inspecting the portion of the piston rod for any bare base
metal that is not coated with cadmium plate. If you find any bare
base metal on the piston rod in this area, reworking the piston rod
by applying brush cadmium plating to all bare and reworked
areas.
- Reassembling the servo actuator.
- After reassembling the servo actuator, marking it with the
letter “B” following the serial number on the name
plate using a scribe or vibrating stylus.
- Performing a hydraulic system check.
These actions must be accomplished by following specified
portions of the ASBs described previously.
This AD differs from the Transport Canada AD in that the FAA
require the initial inspection before further flight rather than no
later than 5 hours air time upon receiving the AD. Also, this AD
requires replacing unairworthy parts with airworthy parts if
certain conditions are found and this AD does not add a life limit
to the servo actuator. This AD does not require a one time
rectification and a complete overhaul of the servo actuator after
the initial inspection. Issuing the AD is an interim action. The
FAA says it may supersede this AD to require reducing the life
limit and overhaul of the affected servo actuators.