[Federal Register Volume 62, Number 222 (Tuesday, November 18, 1997)]
[Rules and Regulations]
[Pages 61438-61441]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-30201]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 97-ANE-40-AD; Amendment 39-10162; AD 97-21-09]
RIN 2120-AA64
Airworthiness Directives; Allison Engine Company Model 250-C47B
Turboshaft Engines
AGENCY: Federal Aviation Administration, DOT.
ACTION: Final rule; request for comments.
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SUMMARY: This amendment supersedes existing airworthiness directive
(AD) 96-24-09, applicable to Allison Engine Company Model 250-C47B
turboshaft engines, that currently requires replacing the engine main
electrical harness assembly with an improved assembly, disabling the
overspeed solenoid, inspecting the engine control unit (ECU) internal
PW10 voltage to determine electrical noise characteristics, and
replacing units not considered serviceable. In addition, the existing
AD requires adding a placard to the helicopter instrument panel
notifying the pilot that the overspeed protection system is disabled
and removes a placard which was required by priority letter AD 96-21-
12; revises the Bell Helicopter Textron, A Division of Textron Canada
Ltd. (BHTC) Model 407 Rotorcraft Flight Manual (RFM); and requires
maintenance actions to clear the ECU of faults prior to each flight.
This amendment continues to require replacing the engine main
electrical harness assembly with an improved assembly, but adds the
requirements to install a new hydromechanical unit (HMU) and ECU,
removing the placard notifying the pilot that the overspeed protection
system is disabled, and revises the BHTC Model 407 RFM. This amendment
is prompted by the development of overspeed protection system
modifications to reactivate the overspeed solenoid in conjunction with
raising the power turbine overspeed trip point and revising the
overspeed system to default to a minimum fuel flow in the event of its
activation. The actions specified by this AD are intended to prevent
uncommanded inflight engine shutdowns, which can result in
autorotation, forced landing, and possible loss of the helicopter.
DATES: Effective December 3, 1997.
The incorporation by reference of certain publications listed in
the regulations is approved by the Director of the Federal Register as
of December 3, 1997.
Comments for inclusion in the Rules Docket must be received on or
before January 20, 1998.
ADDRESSES: Submit comments in triplicate to the Federal Aviation
Administration (FAA), New England Region, Office of the Assistant Chief
Counsel, Attention: Rules Docket No. 97-ANE-40-AD, 12 New England
Executive Park, Burlington, MA 01803-5299. Comments may also be sent
via the Internet using the following address: ``engineprop@faa.dot.gov''.
[[Page 61439]]
Comments sent via the Internet must contain the docket number in the
subject line.
The service information referenced in this AD may be obtained from
Allison Engine Company, P.O. Box 420, Speed Code P-40A, Indianapolis,
IN 46206-0420; telephone (317) 230-2720, fax (317) 230-3381. This
information may be examined at the FAA, New England Region, Office of
the Assistant Chief Counsel, Burlington, MA; or at the Office of the
Federal Register, 800 North Capitol Street, NW., suite 700, Washington,
DC.
FOR FURTHER INFORMATION CONTACT: Patricia Bonnen, Aerospace Engineer,
Chicago Aircraft Certification Office, FAA, Small Airplane Directorate,
2300 East Devon Ave., Des Plaines, IL 60018; telephone (847) 294-7134,
fax (847) 294-7834.
SUPPLEMENTARY INFORMATION: On October 11, 1996, the Federal Aviation
Administration (FAA) issued priority letter airworthiness directive
(AD) 96-21-12, applicable to Bell Helicopter Textron, A Division of
Textron Canada Ltd. (BHTC) Model 407 helicopters, which prohibited
further flight. That action was prompted by reports of uncommanded
inflight engine shutdowns on Allison Engine Company Model 250-C47B
turboshaft engines installed in those helicopters. In each case, the
harness failed and caused the electronic control unit (ECU) to go into
a fail fixed fuel flow condition. Subsequent pilot action (reduction in
collective), caused the engine to reach the overspeed trip point, with
resultant default to zero fuel flow and engine shutdown. That
condition, if not corrected, could result in uncommanded inflight
engine shutdowns, which can result in autorotation, forced landing, and
possible loss of the helicopter.
Following issuance of priority letter AD 96-21-12, the
investigation revealed that the cause of the uncommanded inflight
engine shutdowns was an ECU fault to a fail fixed fuel flow condition,
and subsequent main rotor and power turbine overspeed limit exceedances
coincident with pilot collective input. These overspeed conditions
activated the analog overspeed trip, which resulted in a command to
zero fuel flow and engine flameout. The ECU fault resulted from a
manufacturing defect in the engine main electrical harness assembly.
Additionally, in a related incident involving another Allison
Engine Company engine model, an ECU fault to fail fixed fuel flow was
attributed to the electrical noise characteristics of the ECU internal
PW10 voltage, as affected by certain ECU power modulator subcomponents.
This same power modulator Part Number (P/N) was in use on the Allison
Engine Company Model 250-C47B engine application. The noted ECU power
modulator problem could have also led to the overspeed condition and
uncommanded engine shutdown described above, and was therefore
addressed in the following AD action.
On November 15, 1996, the FAA issued AD 96-24-09, Amendment 39-9834
(61 FR 59828, November 25, 1996), applicable to Allison Engine Company
Model 250-C47B turboshaft engines, to require replacing the engine main
electrical harness assembly with an improved assembly, disabling the
overspeed solenoid (thereby deactivating the engine overspeed
protection system), inspecting the ECU internal PW10 voltage to
determine electrical noise characteristics, and replacing units not
considered serviceable due to excessive electrical noise. In addition,
AD 96-24-09 requires adding a helicopter instrument panel placard
notifying the pilot that the overspeed protection system is disabled;
removes the placard required by AD 96-21-12 which prohibited further
flight; and revises the BHTC Model 407 Rotorcraft Flight Manual (RFM)
to clarify emergency flight procedures and to require maintenance
actions to clear Full Authority Digital Engine Control (FADEC) fault
annunciations prior to each flight. That action was prompted by
investigation into the causes of the inflight engine shutdowns.
The original decision to disconnect the overspeed protection system
was arrived at by comparing the safety of operating with the system
enabled to the safety of operating with the system disabled. By
operating with the system enabled, there was a likely consequence of
other FADEC failures leading to an overspeed trip and resulting in an
engine shutdown as had happened previously. Disabling the overspeed
protection system eliminated the possibility of inadvertent activation
and engine shutdown, but introduced new risks associated with engine
power turbine shaft failure or rotorcraft drive train failure leading
to uncontained blade shedding and hazards to the aircraft. Based on
service data for comparable applications, and the estimated length of
time for a final fix to be designed and tested, the FAA considered
operations with the overspeed protection disabled acceptable. The
redesign of the system has taken longer than estimated, which now puts
in question the original analysis concerning operations with the
overspeed protection disabled. The FAA has determined that immediate
action is necessary to prevent possible turbine shaft failure, or
rotorcraft drive train failure, from leading to an uncontained blade
shedding due to the lack of overspeed protection. For these reasons,
the FAA has determined that implementation of the redesigned overspeed
system must proceed without further delay.
Since the issuance of AD 96-24-09, Allison Engine Company has
developed certain modifications that raise the power turbine overspeed
trip point, and revise the overspeed system to default to a minimum
fuel flow in the event of its activation. With these changes
incorporated, the overspeed solenoid can be reactivated. Additionally,
a capacitor was added to the ECU PW10 circuit thereby eliminating the
problematic electrical noise characteristic.
The FAA has reviewed and approved the technical contents of:
Allison Engine Company Alert Commercial Engine Bulletin (CEB) A-73-
6015, Revision 1, dated July 30, 1997, and Revision 2, dated October
31, 1997, that describe procedures for installing a new hydromechanical
unit (HMU) and ECU; Allison Engine Company Alert CEB-A-73-6010, dated
October 15, 1996, that describes replacing the engine main electrical
harness assembly with an improved assembly; and BHTC RFM BHT-407-FM-1,
Revision 5, dated June 24, 1997, that adds new instructions for the
revised overspeed system.
Since an unsafe condition has been identified that is likely to
exist or develop on other engines of this same type design, this AD
supersedes AD 96-24-09 to continue to require replacing the engine main
electrical harness assembly with an improved assembly, and adds the
requirements to install a new HMU and ECU, to remove the placard
notifying the pilot that the overspeed protection system is disabled,
and to revise the BHTC Model 407 RFM. Installation of the new HMU and
ECU will reactivate the overspeed solenoid in conjunction with raising
the power turbine overspeed trip point and revising the overspeed
system to default to a minimum fuel flow in the event of its
activation. These actions must be completed by January 31, 1998. This
calendar end-date was determined based upon parts availability. The
requirements of paragraph (c) of this AD have been coordinated with the
Rotorcraft Directorate. The actions are required to be accomplished in
accordance with the service information described previously.
[[Page 61440]]
Since a situation exists that requires the immediate adoption of
this regulation, it is found that notice and opportunity for prior
public comment hereon are impracticable, and that good cause exists for
making this amendment effective in less than 30 days.
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 notice must submit a self-addressed,
stamped postcard on which the following statement is made: ``Comments
to Docket Number 97-ANE-40-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 is not a ``significant 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, Incorporation by
reference, 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 removing Amendment 39-9834, (61 FR
59828, November 25, 1996), and by adding a new airworthiness directive,
Amendment 39-10162, to read as follows:
97-21-09 Allison Engine Company: Amendment 39-10162. Docket 97-ANE-
40-AD. Supersedes AD 96-24-09, Amendment 39-9834.
Applicability: Allison Engine Company Model 250-C47B turboshaft
engines, installed on but not limited to Bell Helicopter Textron, A
Division of Textron Canada Ltd. (BHTC) Model 407 helicopters.
Note 1: This airworthiness directive (AD) applies to each engine
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 engines that have been
modified, altered, or repaired so that the performance of the
requirements of this AD is affected, the owner/operator must request
approval for an alternative method of compliance in accordance with
paragraph (d) of this AD. The request should include an assessment
of the effect of the modification, alteration, or repair on the
unsafe condition addressed by this AD; and, if the unsafe condition
has not been eliminated, the request should include specific
proposed actions to address it.
Compliance: Required as indicated, unless accomplished
previously.
To prevent uncommanded inflight engine shutdowns, which can
result in autorotation, forced landing, and possible loss of the
helicopter, accomplish the following:
(a) Prior to further flight, replace the engine main electrical
harness assembly, Part Number (P/N) 23062796, with an improved
assembly, P/N 23065805, in accordance with Allison Engine Company
Alert Commercial Engine Bulletin (CEB) CEB-A-73-6010, dated October
15, 1996.
(b) Prior to January 31, 1998, install a new hydromechanical
unit (HMU) and engine control unit (ECU) in accordance with Allison
Engine Company Alert CEB-A-73-6015, Revision 1, dated July 30, 1997,
or Revision 2, dated October 31, 1997.
(c) After completing the requirements of paragraph (b) of this
AD, and then prior to further flight:
(1) Remove the ``OVRSPD SYSTEM INOP'' placard required by
paragraph (d) of AD 96-24-09, and
(2) Revise the FAA-approved Rotorcraft Flight Manual (RFM) by
removing the pages added by paragraph (f) of AD 96-24-09, and
incorporate BHTC Flight Manual BHT-407-FM-1, Revision 5, dated June
24, 1997.
(d) 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, Chicago Aircraft Certification
Office. Operators shall submit their requests through an appropriate
FAA Principal Maintenance Inspector, who may add comments and then
send it to the Manager, Chicago Aircraft Certification Office.
Note 2: Information concerning the existence of approved
alternative methods of compliance with this airworthiness directive,
if any, may be obtained from the Chicago Aircraft Certification
Office.
(e) 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 aircraft to a location where
the requirements of this AD can be accomplished.
(f) The actions required by this AD shall be done in accordance
with the following service documents:
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Document No. Pages Revision Date
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Allison Engine Company Alert, CEB- 1-7................... Original................. Oct. 15, 1996.
A-73-6010.
Total Pages: 7
Allison Engine Company Alert, CEB- 1-4................... 1........................ July 30, 1997.
A-73-6015.
[[Page 61441]]
Total Pages: 4
Allison Engine Company Alert, CEB- 1-4................... 2........................ Oct. 31, 1997.
A-73-6015.
Total pages: 4
BHTC Flight Manual BHT-407-FM-1... Cover................. 5........................ June 24, 1997.
NP.................... 3........................ July 30, 1996.
A,B................... 5........................ June 24, 1997.
C/D................... 5........................ June 24, 1997.
1-3................... 5........................ June 24, 1997.
1-4................... 4........................ Nov. 4, 1996.
1-7, 1-8.............. 5........................ June 24, 1997.
1-13.................. 4........................ Nov. 4, 1996.
1-14.................. 5........................ June 24, 1997.
1-14A/14B............. 5........................ June 24, 1997.
1-19/1-20............. 5........................ June 24, 1997.
2-3................... 5........................ June 24, 1997.
2-4................... 1........................ Mar. 8, 1996.
2-7--2-10............. 5........................ June 24, 1997.
2-13, 2-14............ 5........................ June 24, 1997.
3-3--3-5.............. 5........................ June 24, 1997.
3-6................... 2........................ May 9, 1996.
3-7, 3-8.............. 5........................ June 24, 1997.
3-15.................. 5........................ June 24, 1997.
3-16.................. 2........................ May 9, 1996.
3-17--3-22............ 5........................ June 24, 1997.
4-5, 4-6.............. 5........................ June 24, 1997.
4-9................... Original................. Feb. 9, 1996.
4-10--4-12............ 5........................ June 24, 1997.
Total pages: 40
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This incorporation by reference was approved by the Director of the
Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part
51. Copies may be obtained from Allison Engine Company, P.O. Box
420, Speed Code P-40A, Indianapolis, IN 46206-0420; telephone (317)
230-2720, fax (317) 230-3381. Copies may be inspected at the FAA,
New England Region, Office of the Assistant Chief Counsel, 12 New
England Executive Park, Burlington, MA; or at the Office of the
Federal Register, 800 North Capitol Street, NW., suite 700,
Washington, DC.
(h) This amendment becomes effective on December 3, 1997.
Issued in Burlington, Massachusetts, on November 10, 1997.
Jay J. Pardee,
Manager, Engine and Propeller Directorate, Aircraft Certification
Service.
[FR Doc. 97-30201 Filed 11-17-97; 8:45 am]
BILLING CODE 4910-13-P
