ASB UH-1H-22-23 TAILBOOM ATTACHMENT HARDWARE
ASB UH-1H-22-23
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ALERT SERVICE BULLETINUH-1H-22-23
20 July 2022
MODEL AFFECTED:UH-1H
SUBJECT: TAILBOOM ATTACHMENT HARDWARE,
INSPECTION AND REPLACEMENT OF
HELICOPTERS AFFECTED:ALL UH-1H
COMPLIANCE:Part I: Within the next 300 flight hours or 90 days after
the release date of this bulletin.
Part II:Within 1 to 5 flight hours after accomplishment
of Part1.
Part III:Within the next 600 flight hours or 12 months,
whichever comes first after accomplishment ofPart II
and every 600 flight hours or 12 months thereafter.
Part IV:Within the next 5,000 hours or 5 years,
whichever comes first after accomplishment ofPart I
and every 5,000 flight hours or 5 years thereafter.
DESCRIPTION:
Bell receives occasional reports of tailboom attachment barrel nuts found cracked. The
root cause for cracking can vary from corrosion damage, high time in service or
hydrogen embrittlement. In a recent case, the upper left-hand barrel nut was found
cracked with less than 1000 hours in service. The investigation revealed that cracking
was due to hydrogen embrittlement.
Bell investigated two recent reports of in-flight upper left hand tailboom attachment bolt
fracture. The root cause of the fracture has been attributed to fatigue and low torque is
suspected as being a contributing factor. In both cases, a loud bang was heard followed
by a yaw.
ASB UH-1H-22-23
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Part Iof this bulletin mandates the removal of the tailboom to inspect the fuselage and
tailboom bulkheads for mechanical and corrosion damage, replacement of the upper
left tailboom attachment bolt and a detailed visual inspection of the other three bolts for
mechanical or corrosion damage. This bulletin also mandates the replacement of the
current steel alloy barrel nut NAS577BxA with a nickel alloy barrel nut NAS577CxA that
offers better corrosion resistance and is not susceptible to hydrogen embrittlement. This
will mitigate the risk of barrel nut cracking that can lead to loss of attachment bolt torque
and subsequent fracture.
Due to the criticality of the tailboom attachment points and, since the upper left
attachment is the most critical,Part Iof this bulletin also mandates the replacement of
the upper left tailboom attachment bolt as well as a detailed visual inspection of the
three other bolts. Any bolt that requires replacement must be replaced with a new bolt.
NOTE
Bell Helicopter does not write or revise the AMCOM Technical Manuals. These AMCOM
manuals will not be updated to reflect this Alert Service Bulletin (ASB).Bell Textron
recommends at 5000 Hours or every 5 years the replacement of the upper L/H bolt,
while the remaining 3 bolts will require a detailed visual inspection.
Part IIof this bulletin changes the existing 100 Hours After Installation of Tailboom
Special Inspection requirement. The torque check is now to be accomplished between
1 and 5 flight hours after tailboom installation or bolt replacement and repeated until
torque has stabilized (three times maximum).Part IIwill require accomplishment
anytime the tailboom is installed or a tailboom attachment bolt is replaced
Part IIIof this bulletin introduces a new recurring torque check of all four attachment
bolts. This new torque check requirement will also be performed every 600 flight hours
/12 months. Any bolt found below the minimum specified torque will require replacement
and an inspection of the associated barrel nut for condition will be required.
Part IVof this bulletin introduces a new recurring inspection every 5,000 flight hours or
5 years, whichever comes first. This inspection requires removal of the tailboom to allow
for a detailed visual inspection of the aft fuselage and tailboom structure. As part of the
recurring 5000 Hour / 5 Year inspection, the upper left-hand bolt shall be replaced with
a new bolt and a detailed visual inspection of the three other bolts shall be carried out.
Installation torques of the tailboom attachment hardware were normalized across the
fleetaccountingforbothflight/landingloadsandhardwarematerialproperties.
Accordingly, the revised tailboom installation instructions in this bulletin reflect a higher
torque of the tailboom attachment bolts as shown in the accomplishment instructions of
this bulletin. The higher torques will help to mitigate loosening of the bolts.
ASB UH-1H-22-23
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Applicability of this bulletin to any spare part shall be determined prior to its installation
on an affected helicopter.
APPROVAL:
The engineering design aspects of this bulletin are Bell Engineering approved.
CONTACT INFO:
For any questions regarding this bulletin, please contact:
Bell Military Technical Support
Tel: 1-817-280-3548 / mts-medium@bellflight.com
MANPOWER:
Approximately 10.0 man-hours are required to complete this bulletin.This estimate is
based on hands-on time and may vary with personnel and facilities available.
WARRANTY:
There is no warranty credit applicable for parts or labor associated with this bulletin.
MATERIAL:
Required Material:
The following material is required for the accomplishment of this bulletin and may be
obtained through your Bell Supply Center.
Part NumberNomenclatureQty (Note)
NAS577C8ABarrel nut2
NAS577C6ABarrel nut2
NAS578C8ARetainer2
NAS578C6ARetainer2
NAS628-22Bolt2 (1)
NAS626-18Bolt2 (1)
NOTE 1:Only the upper left-hand bolt will require replacement. Replacement of the
three other bolts is based on condition.
Consumable Material:
ASB UH-1H-22-23
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The following material is required to accomplish this bulletin, but may not require
ordering, depending on the operator’s consumable material stock levels. This material
may be obtained through your Bell Supply Center.
Part NumberNomenclatureQty (Note)Reference*
2400-00259-00
2010-00088-00
2230-10536-00
Aeriol Thixo NO 2 Aviation
Grease
Sealant
Torque Seal Lacquer
14.4 oz
2 oz
1 oz (2,3,4)
C-561(1)
C-308
C-049
* C-XXX numbers refer to the consumables list in the BHT-ALL-SPM, Standard Practices Manual
NOTES:
1. High Pressure grease (C-172) can be used as an alternate.
2.Quantity indicated is the format that the product is delivered in. Actual quantity
required to accomplish the instructions in this bulletin may beless than what has
been delivered.
3.2230-10536-00 torque seal lacquer (C-049) is color yellow, however other colors are
available, at customer’s option, as shown in BHT-ALL-SPM Standard Practice
Manual, in Chapter 13 under C-049.
4.Polyurethane paint (C-245) or 2230-10547-00 (Vibra-TITE Viz-Torque® 202) are
acceptable alternates to C-049.
SPECIAL TOOLS:
None required.
WEIGHT AND BALANCE:
Not affected.
ELECTRICAL LOAD DATA:
Not affected.
REFERENCES:
TM 55-1520-210-23P Illustrated Parts Breakdown, Figure 5
TM 55-1520-210-23 Technical Manual, Chapter 2
BHT SPM Standard Practices Manual
PUBLICATIONS AFFECTED:
TM 55-1520-210-23P Illustrated Parts Breakdown, Figure 5
ASB UH-1H-22-23
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TM 55-1520-210-23 Technical Manual, Chapter 2
ACCOMPLISHMENT INSTRUCTIONS:
Part 1. Tailboom attachment hardware inspection and replacement
1.Prepare the helicopter for maintenance.
2.Remove the tailboom assembly (TM 55-1520-210-23 Technical Manual, Chapter 2).
3.Discard the upper left-hand bolt and the four barrel nuts with retainers. Retain the
upper right-hand and the two lower bolts with countersunk washer and plain
washers.
4.Inspect the tailboom bulkhead at BS 17.31, for corrosion and cracks. Fuselage
attachment bolt holes for damage and corrosion.
5.Install barrel nuts NA577C8A with retainers NAS578C8A at the two upper tailboom
attachmentlocations.Iftheupperright-handbarrelnutisfoundcracked,its
associated bolt shall be replaced with a new one
6.Install barrel nuts NAS577C6A with retainers NAS578C6A at the two lower tailboom
attachment locations.If a barrel nut is found cracked, its associated bolt shall be
replaced with a new one.
7.InspectfuselagebulkheadatFS243.89,fordamage,corrosion,andcracks.
Tailboom attachment fittings for damage, cracks, and loose fasteners. Inspect the
tailboom attachment bolt holes for damage and corrosion.
8.Inspect the upper right-hand and the two lower bolts for condition. Any evidence of
corrosion is cause for rejection.
9.Visually inspect bolts for mechanical or corrosion damage. Any corrosion including
surface corrosion is cause for rejection. Damaged threadsand detectable wear or
mechanical damage on the bolt shank or bolt head radii are cause for rejection.
-NOTE-
The tailboom attachment hardware torque has been
increased as follows: Torque of the two upper bolts,
is now 1000 to 1200 in-lbs. (113 to 136 Nm). Torque
of the two lower bolts is now 400 to 430 in-lbs. (45.2
to 48.6 Nm).
ASB UH-1H-22-23
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CAUTION
Grease (C-561) or (C-172) shall be applied on bolt shank
only. Grease shall not be applied to bolt threads.
10. Install tailboom after completion of inspection with a new upper left-hand bolt
(NAS628-22), a serviceable upper right-hand bolt (NAS628-22) and two lower bolts
(NAS626-18) (TM 55-1520-210-23 Chapter 2) with the torque values noted above.
Apply a coating of grease (C-561) or (C-172) to bolt shank only.
11. Apply sealant (C-308) to plug buttons and install.
12. Make an entry in the helicopter logbook and historical service records indicating
compliance withPart 1of this Alert Service Bulletin.
Part II.Between 1 and 5 flight hours after tailboom installation or attachment bolt
replacement.
1. Carry out a torque check of the tailboom attachment bolts using the torque values
specified inPart I. Torque check must be repeated every 1 to 5 flight hours until torque
has stabilized (Three times maximum).If after three attempts the torque has not
stabilized; inspect bolt and replace barrel nut.
2. Once the torque is stabilized, apply torque seal (C-049) witness mark to all four bolt
heads.
3. Make an entry in the helicopter logbook and historical service records indicating
compliance withPart IIof this Alert Service Bulletin.
Part III. Recurring torque check of the tailboom attachment hardware.
-NOTE-
The tailboom attachment hardware torque has been
increased as follows: Torque of the two upper bolts,
is now 1000 to 1200 in-lbs (113 to 136 Nm). Torque
of the two lower bolts is now 400 to 430 in-lbs (45.2
to 48.6 Nm).
1. Carry out a torque check of the tailboom attachment bolts every 600 flight hours or
12 months, whichever comes first after accomplishment ofPart II,and every 600
ASB UH-1H-22-23
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flight hours or 12 months thereafter. Use the tailboom attachment torque values from
the above Note. Re-apply torque seal (C-049) required.
2.Any bolt found below the minimum torque specified inPart Imust be replaced.
Inspect the associated barrel nut for condition and for loss of tare torque; replace as
necessary.Anyboltthatrequiresreplacementmustbetorquedcheckedin
accordance withPart II.
3. Make an entry in the helicopter logbook and historical service records indicating
compliance withPart IIIof this Alert Service Bulletin.
Part IV.Recurring inspection of the tailboom attachment hardware every 5,000
flight hours or 5 years, whichever comes first.
1.Carry out steps 1 through 11 inPart Iof the Accomplishment Instructions of this
bulletin every 5,000 flight hours or 5 years, whichever occurs first and every 5,000
flight or 5 years thereafter.
2.Make an entry in the helicopter logbook and historical service records indicating
compliance withPart IVof this Alert Service Bulletin.
