[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: ``9-ad-
[email protected]''.

[[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:

----------------------------------------------------------------------------------------------------------------
           Document No.                      Pages                   Revision                     Date          
----------------------------------------------------------------------------------------------------------------
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