[Federal Register Volume 63, Number 62 (Wednesday, April 1, 1998)]
[Rules and Regulations]
[Pages 15748-15751]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-8456]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 97-SW-67-AD; Amendment 39-10428; AD 97-24-17]
RIN 2120-AA64
Airworthiness Directives; Bell Helicopter Textron Canada Model
407 Helicopters
AGENCY: Federal Aviation Administration, DOT.
ACTION: Final rule; request for comments.
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SUMMARY: This document publishes in the Federal Register an amendment
adopting priority letter airworthiness directive (AD) 97-24-17, which
was sent previously to all known U.S. owners and operators of Bell
Helicopter Textron Canada (BHTC) Model 407 helicopters by individual
letters. This AD requires inspections of components in the tail rotor
drive system for scratches, cracks, fretting, corrosion, and proper
torquing, lubrications of the oil cooler blower shaft hanger bearings
and oil cooler hanger bearings (hanger bearings), and removal of
corrosion inhibitive adhesive barrier tape (barrier tape) from the tail
rotor gearbox and the tail rotor gearbox support assembly faying
surfaces. This amendment is prompted by numerous reports of three
problems, all of which are related to the tail rotor drive system. The
actions specified by this AD are intended to: detect scratches, cracks,
fretting, and corrosion in the disc pack couplings; prevent inadequate
lubrication of the hanger bearings and oil cooler blower shaft; and
prevent loss of mounting torque on the tail rotor gearbox. Failure of
any of these components could result in loss of power to the tail rotor
and subsequent loss of control of the helicopter.
DATES: Effective April 16, 1998, to all persons except those persons to
whom it was made immediately effective by priority letter AD 97-24-17,
issued on November 20, 1997, which contained the requirements of this
amendment.
Comments for inclusion in the Rules Docket must be received on or
before June 1, 1998.
ADDRESSES: Submit comments in triplicate to the Federal Aviation
Administration (FAA), Office of the Regional Counsel, Southwest Region,
Attention: Rules Docket No. 97-SW-67-AD, 2601 Meacham Blvd., Room 663,
Fort Worth, Texas 76137.
FOR FURTHER INFORMATION CONTACT: Mr. Jurgen Priester, Aerospace
Engineer, Rotorcraft Certification Office, Rotorcraft Directorate, FAA,
2601 Meacham Blvd., Fort Worth, Texas, 76137-4298, telephone (817) 222-
5159, fax (817) 222-5783.
SUPPLEMENTARY INFORMATION: Transport Canada, which is the airworthiness
authority for Canada, recently notified the FAA that an unsafe
condition may exist on the BHTC Model 407 helicopter. Transport Canada
advises that some operators have reported a number of cracked disc pack
couplings in Thomas disc coupling packs, part number (P/N) 406-040-340-
101, and a few reports of cracks and breaks in the oil cooler blower
and oil tank support brackets and associated airframe components.
Transport Canada issued AD CF-97-19, dated September 30, 1997, to
require a one-time inspection of the disc pack couplings, inspection of
the oil cooler blower and oil tank support brackets for cracks, and
general condition of the tail rotor assembly, tail rotor gearbox, tail
rotor drive system, and tailboom. Later, Transport Canada also issued
AD CF-97-20, dated October 17, 1997, to require repetitive inspections
of the disc pack couplings every 25 hours time-in-service (TIS).
This helicopter model is manufactured in Canada and is type
certificated for operation in the United States under the provisions of
section 21.29 of the Federal Aviation Regulations (14 CFR 21.29) and
the applicable bilateral airworthiness agreement. Pursuant to this
bilateral airworthiness agreement, Transport Canada has kept the FAA
informed about the situation described above. The FAA has examined the
findings of Transport Canada, reviewed all available information
including the information contained in the FAA service difficulty data
base, and determined that AD action is necessary for products of this
type design that are certificated for operation in the United States.
After reviewing the information received from Transport Canada, the
reports from operators of service difficulties, and discussions with
the manufacturer, the FAA further determined that AD actions relating
to other tail rotor drive system components was necessary.
On November 20, 1997, the FAA issued priority letter AD 97-24-17,
applicable to BHTC Model 407 helicopters, which requires visually
inspecting each disc pack coupling for scratches, cracks, fretting, or
corrosion and for proper torque of the disc pack coupling retaining
nuts and bolts;
[[Page 15749]]
lubricating the oil cooler blower shaft hanger bearings; listening and
feeling for binding roughness of the hanger bearings; inspecting the
splines on the oil cooler blower shaft and splined flywheel adapter;
removing the adhesive barrier tape from between the tail rotor gearbox
(gearbox) and the gearbox support assembly; inspecting the gearbox,
gearbox support assembly, and gearbox mounting pads for wear, cracks,
or elongated holes; inspecting the nuts that secure the gearbox to the
tailboom for proper torquing; and inspecting the skin around the area
of these components for corrosion or loose, cracked, or missing rivets.
Priority Letter AD 97-24-17 superseded priority letter AD 97-22-15,
Docket No. 97-SW-56-AD, issued October 23, 1997, which required a
portion of the same AD actions as are currently required by this AD.
Those actions were prompted by numerous reports of problems related to
the tail rotor drive system.
There have been several reports of disc cracks in some disc pack
couplings after as few as 35 hours TIS. A crack in the disc pack
coupling can result in failure of the disc pack coupling, loss of tail
rotor drive, and subsequent loss of control of the helicopter.
There have also been several reports of hanger bearing roughness
due to insufficient lubrication. The cause of the insufficient
lubrication has not been determined. There have also been at least two
reports of bearing cages and balls separating from the hanger bearing
due to the lack of lubrication. Failure of a hanger bearing can result
in an unsafe level of vibration, failure of the tail rotor drive
system, and subsequent loss of control of the helicopter.
Finally, there have been at least ten (10) reports of undertorqued
tail rotor gearbox attachment nuts. In one case, a foreign operator
reported that the gearbox attachment nuts were properly torqued during
an inspection at 119 hours TIS. A subsequent inspection at 300 hours
TIS revealed that the gearbox attachment nuts were loose. Further
inspection revealed a separated dowel pin, damaged threads on all four
studs, and elongated gearbox attachment holes on the tailboom. The
pilot reported feeling some vibration prior to the inspection. Another
operator reported that all four gearbox attachment nuts were determined
to be undertorqued after only 27.5 hours TIS since manufacture. There
have also been several reports of excessive tail rotor drive system
vibration from other operators. These vibrations may indicate
improperly torqued tail rotor gearbox attachment nuts. There is concern
that the thickness of the corrosion inhibitive adhesive barrier MIL-T-
23142 tape, which was installed at the factory between the gearbox and
gearbox support assembly, is reduced when the gearbox attachment nuts
are torqued to the required torque value. This reduction in tape
thickness results in a lower clamping force, which allows relative
motion between the gearbox and the gearbox support assembly due to loss
of torque on the gearbox attachment nuts and studs. The helicopter
manufacturer has already incorporated a design change that eliminates
the barrier tape, starting with helicopter serial number (S/N) 53225.
Loss of torque on the gearbox attachment nuts could result in
separation of the tail rotor gearbox from the tailboom and subsequent
loss of control of the helicopter.
Since the unsafe condition described is likely to exist or develop
on other BHTC Model 407 helicopters of the same type design, the FAA
issued superseding priority letter AD 97-24-17. The AD requires
visually inspecting each disc pack coupling for scratches, cracks,
fretting, or corrosion and for proper torque of the disc pack coupling
retaining nuts and bolts; lubricating the oil cooler blower shaft
hanger bearings; listening and feeling for binding or roughness of the
oil cooler blower shaft hanger bearings; inspecting the splines on the
oil cooler blower shaft and splined flywheel adapter; removing the
adhesive barrier tape from between the tail rotor gearbox (gearbox) and
the gearbox support assembly; inspecting the gearbox, gearbox support
assembly, and gearbox mounting pads for wear, cracks, or elongated
holes; inspecting the nuts that secure the gearbox to the tailboom for
proper torquing; and inspecting the tailboom skin around the area of
these components for corrosion or loose, cracked, or missing rivets.
The tail rotor drive system provides the power to the tail rotor to
permit the operator to offset the torque effects of the main rotor
system during flight. Due to the criticality of these tail rotor drive
system components to the continued safe flight of this model helicopter
and the short times before compliance is required, this AD must be
issued immediately.
Since it was found that immediate corrective action was required,
notice and opportunity for prior public comment thereon were
impracticable and contrary to the public interest, and good cause
existed to make the AD effective immediately by individual letters
issued on November 20, 1997 to all known U.S. owners and operators of
BHTC Model 407 helicopters. These conditions still exist, and the AD is
hereby published in the Federal Register as an amendment to section
39.13 of the Federal Aviation Regulations (14 CFR 39.13) to make it
effective to all persons.
Comments Invited
Although this action is in the form of a final rule that involves
requirements affecting flight safety and, thus, was not preceded by
notice and an opportunity for public comment, comments are invited on
this rule. Interested persons are invited to comment on this rule by
submitting such written data, views, or arguments as they may desire.
Communications should identify the Rules Docket number and be submitted
in triplicate to the address specified under the caption ADDRESSES. All
communications received on or before the closing date for comments will
be considered, and this rule may be amended in light of the comments
received. Factual information that supports the commenter's ideas and
suggestions is extremely helpful in evaluating the effectiveness of the
AD action and determining whether additional rulemaking action would be
needed.
Comments are specifically invited on the overall regulatory,
economic, environmental, and energy aspects of the rule that might
suggest a need to modify the rule. All comments submitted will be
available, both before and after the closing date for comments, in the
Rules Docket for examination by interested persons. A report that
summarizes each FAA-public contact concerned with the substance of this
AD will be filed in the Rules Docket.
Commenters wishing the FAA to acknowledge receipt of their comments
submitted in response to this rule must submit a self-addressed,
stamped postcard on which the following statement is made: ``Comments
to Docket No. 97-SW-67-AD.'' The postcard will be date stamped and
returned to the commenter.
The regulations adopted herein will not have substantial direct
effects on the States, on the relationship between the national
government and the States, or on the distribution of power and
responsibilities among the various levels of government. Therefore, in
accordance with Executive Order 12612, it is determined that this final
rule does not have sufficient federalism implications to warrant the
preparation of a Federalism Assessment.
The FAA has determined that this regulation is an emergency
regulation that must be issued immediately to correct an unsafe
condition in aircraft, and that it is not a ``significant
[[Page 15750]]
regulatory action'' under Executive Order 12866. It has been determined
further that this action involves an emergency regulation under DOT
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If
it is determined that this emergency regulation otherwise would be
significant under DOT Regulatory Policies and Procedures, a final
regulatory evaluation will be prepared and placed in the Rules Docket.
A copy of it, if filed, may be obtained from the Rules Docket at the
location provided under the caption ADDRESSES.
List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Safety. Adoption of
the Amendment
Accordingly, pursuant to the authority delegated to me by the
Administrator, the Federal Aviation Administration amends part 39 of
the Federal Aviation Regulations (14 CFR part 39) as follows:
PART 39--AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701.
Sec. 39.13 [Amended]
2. Section 39.13 is amended by adding a new airworthiness directive
to read as follows:
AD 97-24-17 Bell Helicopter Textron Canada: Amendment 39-10428.
Docket No. 97-SW-67-AD.
Applicability: Model 407 helicopters, certificated in any
category.
Note 1: This AD applies to each helicopter identified in the
preceding applicability provision, regardless of whether it has been
modified, altered, or repaired in the area subject to the
requirements of this AD. For helicopters that have been modified,
altered, or repaired so that the performance of the requirements of
this AD is affected, the owner/operator must use the authority
provided in paragraph (g) to request approval from the FAA. This
approval may address either no action, if the current configuration
eliminates the unsafe condition, or different actions necessary to
address the unsafe condition described in this AD. Such a request
should include an assessment of the effect of the changed
configuration on the unsafe condition addressed by this AD. In no
case does the presence of any modification, alteration, or repair
remove any helicopter from the applicability of this AD.
Compliance: Required as indicated, unless accomplished
previously.
(a) Tail Rotor Drive Coupling Disc Pack Inspections:
To prevent failure of a tail rotor drive coupling disc pack
(disc pack coupling), part number (P/N) 406-040-340-101, loss of
tail rotor drive and subsequent loss of control of the helicopter,
within 25 hours time-in-service (TIS), and thereafter at intervals
not to exceed 25 hours TIS, accomplish the following:
(1) Visually inspect each of the eight (8) disc pack couplings
for any scratch, crack, fretting, or corrosion. This inspection can
be accomplished with the disc pack couplings installed. If any
scratch, crack, fretting, or corrosion is found, remove and replace
the disc pack coupling with an airworthy disc pack coupling. Torque
on replacement disc pack coupling nuts and bolts must be a minimum
of the run-on-tare torque plus 150 inch-lbs. to a maximum of the
run-on-tare torque plus 180 inch-lbs.
(2) Inspect the four nuts and bolts that attach each of the disc
pack couplings to the driveshaft and tail rotor gearbox adapters for
proper torque. Apply a minimum torque of 170 inch-lbs. to a maximum
torque of 175 inch-lbs., which includes a 20 inch-lbs. run-on-tare
torque.
Note 2: This torque inspection should be performed on the nuts
instead of the bolt heads wherever possible.
(i) If there is no nut or bolt movement, the torque is
acceptable.
(ii) If any nut or bolt moved, remove and replace the disc pack
coupling with an airworthy disc pack coupling. Torque on the
replacement disc pack coupling nuts and bolts must be a minimum of
the run-on-tare torque plus 150 inch-lbs. to a maximum of the run-
on-tare torque plus 180 inch-lbs.
(b) Oil Cooler Blower Shaft (Fan Shaft) Hanger Bearing
Lubrication:
To prevent failure of an oil cooler blower shaft hanger bearing
(hanger bearing), P/N 406-040-339, that can result in an unsafe
level of vibration, failure of the tail rotor drive system, and
subsequent loss of control of the helicopter, within 25 hours TIS,
and thereafter at intervals not to exceed 25 hours TIS, accomplish
the following:
(1) Gain access to the oil cooler blower, P/N 206-061-432-115.
(2) Grease both oil cooler blower shaft hanger bearings.
(c) Oil Cooler Blower Hanger Bearing Inspection:
To prevent failure of the hanger bearing, P/N 406-040-339, that
can result in an unsafe level of vibration, failure of the tail
rotor drive system, and subsequent loss of control of the
helicopter, within 25 hours TIS, and thereafter at intervals not to
exceed 100 hours TIS, accomplish the following:
(1) Gain access to the oil cooler blower, P/N 206-061-432-115.
(2) Remove the forward short shaft, P/N 406-040-315-111.
(3) Remove the aft short shaft, P/N 407-040-325-101.
(4) Manually rotate the oil cooler blower shaft, P/N 406-040-
320-101, at various speeds and feel both the bearing hanger housings
and the oil cooler blower shaft. If there is any binding or
roughness indicated by feel or sound, remove the oil cooler blower
shaft and replace any unairworthy hanger bearing with an airworthy
hanger bearing.
(5) Grease both oil cooler blower hanger bearings.
(6) Inspect the splines on the oil cooler blower shaft and on
the splined flywheel adapter, P/N 407-040-316-101, for airworthy
condition.
(d) Adhesive Barrier Tape Between Tail Rotor Gearbox and Gearbox
Support Assembly Removal From Helicopters Prior
To Serial Number (S/N) 53225:
To prevent separation of the tail rotor gearbox from the
tailboom and subsequent loss of control of the helicopter, for
helicopters prior to S/N 53225, within 25 hours TIS, accomplish the
following:
(1) Remove cowling and covers to expose the tail rotor gearbox
(gearbox) and the gearbox support assembly, P/N 407-030-833-101.
(2) Remove the gearbox from the gearbox support assembly.
(3) Remove all corrosion inhibitive adhesive barrier tape (MIL-
T-23142) between the gearbox and the gearbox support assembly faying
surfaces.
(4) Reinstall the gearbox.
(i) When reinstalling the gearbox, DO NOT use barrier tape on
faying surfaces.
(ii) Coat the dowel pins and the shank portion of the gearbox
studs that interface with the gearbox support assembly with epoxy
polyamide primer (MIL-P-23377).
(iii) Coat the gearbox support assembly mounting pads with
corrosion inhibitive sealant conforming to MIL-S-81733.
(iv) Reinstall the gearbox on the gearbox support assembly and
torque the nuts to the required torque within 15 minutes of primer
and sealant application. Torque on the gearbox attachment nuts must
be a minimum of the run-on-tare torque plus 100 inch-lbs. to a
maximum of the run-on-tare torque plus 140 inch-lbs.
(e) Tail Rotor Gearbox Attachment Inspection:
To prevent separation of the tail rotor gearbox from the
tailboom and subsequent loss of control of the helicopter, within 25
hours TIS, and thereafter at intervals not to exceed 25 hours TIS,
accomplish the following:
(1) Remove cowling and covers to expose the tail rotor gearbox
(gearbox) and gearbox support assembly, P/N 407-030-833-101.
(2) Inspect the four nuts that attach the gearbox to the
tailboom for proper torque. Apply a minimum torque of 120 inch-lbs.
to a maximum torque of 125 inch-lbs., which includes a run-on-tare
torque of 20 inch-lbs.
(i) If there is no nut or bolt movement, the torque is
acceptable.
(ii) If any of the nuts or bolts move, remove the gearbox from
the gearbox support assembly and accomplish the following:
(A) Inspect the tail rotor gearbox.
(1) If there is any wear on a gearbox mounting pad, replace the
gearbox with an airworthy gearbox.
(2) If there is a loose, missing, or unairworthy stud or dowel
pin, replace the gearbox with an airworthy gearbox.
(B) Inspect the gearbox support assembly.
(1) If there is any wear on a gearbox support assembly mounting
pad, remove and replace the gearbox support assembly with an
airworthy gearbox support assembly.
(2) If there is a crack or elongated hole in the gearbox support
assembly, remove and
[[Page 15751]]
replace the gearbox support assembly with an airworthy gearbox
support assembly.
(3) If there is any loose, cracked, or missing rivets, or
cracked or corroded skin in the area of the double rivet row at the
aft tailboom-to-gearbox support assembly attachment, replace all
loose, cracked, or missing rivets. Repair or replace a tailboom that
has cracked or corroded skin.
(C) When installing the gearbox on the gearbox support assembly:
(1) DO NOT use barrier tape on faying surfaces.
(2) Coat the dowel pins and the shank portion of the gearbox
studs that interface with the gearbox support assembly with epoxy
polyamide primer (MIL-P-23377).
(3) Coat the gearbox support assembly mounting pads with
corrosion inhibitive sealant conforming to MIL-S-81733.
(4) Torque the nuts to the required torque within 15 minutes of
primer and sealant application. Torque on the gearbox attachment
nuts must be a minimum of the run-on-tare torque plus 100 inch-lbs.
to a maximum of the run-on-tare torque plus 140 inch-lbs.
(D) Inspect the tailboom.
(f) Report any instances of loose or undertorqued tail rotor
gearbox attachment nuts, unairworthy oil cooler blower hanger
bearings, unairworthy oil cooler blower shafts, unairworthy splined
flywheel adapters, or disc pack couplings with more than one
unairworthy disc, within 10 working days after discovery to Mr.
Jurgen Priester, Aerospace Engineer, Rotorcraft Certification
Office, Rotorcraft Directorate, FAA, 2601 Meacham Blvd., Fort Worth,
Texas 76137-4298, telephone (817) 222-5159, fax (817) 222-5783.
Reporting requirements have been approved by the Office of
Management and Budget and assigned OMB control number 2120-0056.
(g) An alternative method of compliance or adjustment of the
compliance time that provides an acceptable level of safety may be
used if approved by the Manager, Rotorcraft Certification Office.
Operators shall submit their requests through an FAA Principal
Maintenance Inspector, who may concur or comment and then send it to
the Manager, Rotorcraft Certification Office.
Note 3: Information concerning the existence of approved
alternative methods of compliance with this AD, if any, may be
obtained from the Rotorcraft Certification Office.
(h) Special flight permits may be issued in accordance with
sections 21.197 and 21.199 of the Federal Aviation Regulations (14
CFR 21.197 and 21.199) to operate the helicopter to a location where
the requirements of this AD can be accomplished.
(i) This amendment becomes effective on April 16, 1998, to all
persons except those persons to whom it was made immediately
effective by Priority Letter AD 97-24-17, issued November 20, 1997,
which contained the requirements of this amendment.
Note 4: The subjects of this AD are addressed in Transport
Canada AD CF-97-19, dated September 30, 1997, and AD CF-97-20, dated
October 17, 1997.
Issued in Fort Worth, Texas, on March 24, 1998.
Eric Bries,
Acting Manager, Rotorcraft Directorate, Aircraft Certification Service.
[FR Doc. 98-8456 Filed 3-31-98; 8:45 am]
BILLING CODE 4910-13-P