(3) Aircraft that have a DD Form 250 and are still at Boeing will be inspected prior to ferry to final
Maintenance Trainers (Category A, B)
Components/Parts in Stock including War Reserves at All Levels (Depot and others). N/A.
2. Task/Inspection Suspense Date.
One-time torque check (paragraph 8.a.) of all AH-64 Tail Rotor Gearbox Output Shaft Stud Nuts
no later than next 10 hour/l 4 day inspection.
If any nuts fail the torque check, all three studs must be replaced in accordance with paragraph 9,
prior to next flight.
inspection procedures no later
than next 250 hour phase inspection.
3. Reporting Compliance Suspense Date. N/A.
4. Summary of Problem.
a. A past AH-64A mishap investigation determined the presence of an improperly installed (incorrectly
indexed) Tail Rotor (T/R) Fork Assembly. The interface between the T/R Fork and the Gearbox Output
Shaft (Curvic Coupling) was designed so that installation could be accomplished in only one way. The
studs are in a triangular pattern but are not equally spaced (i.e., 115 degrees, 120 degrees, and 125
degrees of separation). An anomaly was discovered in this design, which may allow the curvic coupling
and fork assembly to be incorrectly indexed during installation. If the fork is incorrectly indexed, binding of
the studs occurs, stress levels increase, and fatigue life of the studs is greatly reduced. Improper
installation of the fork could lead to failure of the Tail Rotor. Recently, more occurrences of misindexed
T/R Fork Assemblies have been discovered.
b. For manpower/downtime and funding impacts, refer to paragraph 12.
c. The purpose of this message is to:
(1) Direct a one-time and recurring inspection of three T/R Gearbox Output Shaft Stud Nuts for
torque. (If any of the nuts fail the torque check, all three studs must be replaced in accordance with
(2) Direct a one-time inspection of T/R Fork alignment to ensure proper indexing and that
improper indexing has not occurred in past installations.
(3) Determine the condition of the T/R Gearbox Output Shaft Studs.
(4) Require positive verification of alignment prior to each installation of the Tail Rotor Head.
5. End Items to be Inspected. All AH-64 aircraft.