d. Aircraft in Transit.
f. Component/Parts in Stock at All Levels (Depot and Others) Including War Reserves. Upon
receipt of this TB, the material condition tags of all items in all condition codes listed in paragraph 6. shall be
annotated to read "TB 1-2840-229-20-17 (SOF AH-1-98-01) not complied with."
2. Task/Inspection Suspense Date. 10 flight hours or 15 days.
3. Reporting Compliance Suspense Date.
No later than
17 July 1998 lAW paragqh 14.a
of this TB.
Summary of the Problem.
a. In November 1997, the Army placed flight restrictions on all UH-1 helicopters in response to a trend
of N2 Spur Gear failures in the aircraft's T-53 Engines caused by vibration. The AH-1 aircraft equipped with
the T53-L-703 Engine have also exhibited the same vibration found in the T53-L-13B Engines. However,
the T53-L-703 Engine fleet has experienced a lower Spur Gear failure rate. After careful consideration, and
as a prudent safety measure, the Army has determined that all AH-1 aircraft T53-L-703 Engines shall be
inspected for vibration levels.
(1) An Inspection procedure has been established to screen and detect the presence of the
vibration associated with failure of the spur gear (P/N 1-070-062-04, NBN 3020-00-453-9441). This
procedure utilizes the Aviation Vibration Analyzer (AVA), with a specialized application program (memory
card) specifically designed to detect the vibration.
(2) Aircraft that are screened and are found to exhibit the damaging vibration shall be grounded
until the engine is replaced or a long-term corrective action is implemented. This long-term corrective action
is expected to be implemented by the second quarter of FY 99. Aircraft that are screened and do not exhibit
the damaging vibration will be released to fly. Aircraft released to fly will be required to repeat the vibration
inspection every 25 flight hours.
(3) Specialized reporting procedures are required to document the results of the vibration
screening. Accurate and timely reporting is crucial to procuring the correct numbers of replacement
assemblies and restoring the entire fleet to unrestricted flight status as soon as practical.
c. The purpose of the TB is to:
(1) Direct a one-time screening inspection and 25-hour recurring inspections of all AH-1 aircraft
with T53-L-703 Engines installed for damaging engine vibration levels.
(2) ldentify the procedure to obtain the preprogrammed AVA Memory Cards to perform the
(3) Direct special reporting of vibration screening results.
5. End Items to be Inspected. All AH-1 series aircraft with T53-L-703 Engines (P/N 1-000-060-23)
Assembly Components to be Inspected.
NATIONAL STOCK NUMBER