Airworthiness Directives; Allison Engine Company Model 250-C47B Turboshaft Engines

[Federal Register Volume 61, Number 228 (Monday, November 25, 1996)]
[Rules and Regulations]
[Pages 59828-59831]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-29861]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 96-ANE-41; Amendment 39-9834, AD 96-24-09]
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 adopts a new airworthiness directive (AD) that 
is applicable to Allison Engine Company Model 250-C47B turboshaft 
engines. This action supersedes priority letter AD 96-21-12, applicable 
to Bell Helicopter Textron, A Division of Textron Canada Ltd. (BHTC) 
Model 407 helicopters, that currently prohibits further flight, due to 
uncommanded inflight engine shutdowns. This action 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, this 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 BHTC Model 407 Rotorcraft Flight Manual 
(RFM); and requires maintenance actions to clear the engine electronic 
control unit (ECU) of faults prior to each flight. Accomplishment of 
these actions will enable operators to resume flight operations. This 
amendment is prompted by investigation into the causes of the inflight 
engine shutdowns. 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 November 25, 1996, except effective upon receipt to 
all persons receiving a copy of this AD directly from the FAA.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of November 25, 1996.
    Comments for inclusion in the Rules Docket must be received on or 
before January 24, 1997.


[[Page 59829]]


ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), New England Region, Office of the Assistant Chief 
Counsel, Attention: Rules Docket No. 96-ANE-41, 12 New England 
Executive Park, Burlington, MA 01803-5299.
    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, 12 New England Executive Park, 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 prohibits 
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.
    Since the issuance of that priority letter AD, the investigation 
revealed that the cause of the uncommanded inflight engine shutdowns 
was an ECU hard 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 results in default to a zero 
fuel flow condition. The ECU fault resulted from a manufacturing defect 
in the engine main electrical harness assembly.
    Additionally, in a related incident involving a not yet 
certificated Allison Engine Company engine, an ECU hard 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) is 
currently in use on the Allison Engine Company Model 250-C47B engine 
application. The noted ECU power modulator problem can also lead to the 
overspeed condition and uncommanded engine shutdown described above, 
and is therefore addressed in this AD action.
    The FAA has reviewed and approved the technical contents of Allison 
Engine Company Alert Commercial Engine Bulletin (CEB) No. CEB-A-73-
6010, dated October 15, 1996, that describes procedures for replacing 
the engine main electrical harness assembly with an improved assembly; 
CEB-A-73-6011, dated October 31, 1996, that describes procedures for 
disabling the overspeed solenoid (thereby deactivating the engine 
overspeed protection system); and CEB-A-73-6012, dated October 31, 
1996, that describes procedures for inspecting the ECU internal PW10 
voltage to determine electrical noise characteristics.
    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 priority letter AD 96-21-12, applicable to BHTC Model 407 
helicopters, to require the following actions: 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, 
this AD 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. Accomplishment of these actions will enable operators 
to resume flight operations on an interim basis. Additional rulemaking 
may reactivate the engine overspeed protection system in conjunction 
with raising the overspeed trip speed, and require additional control 
system modification of going to minimum fuel flow as a terminating 
action. The actions are required to be accomplished in accordance with 
the CEBs described previously.
    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 96-ANE-41.'' 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

[[Page 59830]]

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 USC 106(g), 40113, 44701.


Sec. 39.13--[Amended]

    2. Section 39.13 is amended by adding the following new 
airworthiness directive:
96-24-09 Allison Engine Company: Amendment 39-9834. Docket No. 96-
ANE-41. Supersedes AD 96-21-12, applicable to Bell Helicopter 
Textron, A Division of Textron Canada Ltd. (BHTC) Model 407 
helicopters.

    Applicability: Allison Engine Company Model 250-C47B turboshaft 
engines, installed on but not limited to 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 (h) 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 prior to further flight, 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) 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) Disable the overspeed solenoid in accordance with Allison 
Engine Company CEB-A-73-6011, dated October 31, 1996.
    (c) Inspect the electronic control unit (ECU) internal PW10 
voltage to determine electrical noise characteristics, and replace 
ECUs not considered serviceable, in accordance with Allison Engine 
Company CEB-A-73-6012, dated October 31, 1996.
    (d) Install the following placard on the instrument panel near 
the overspeed test switch, notifying the pilot that the engine 
overspeed protection system is disabled, ``OVSPD SYSTEM INOP''. The 
placard shall be manufactured of a material that cannot be easily 
defaced or erased, and the lettering shall be block-style and at 
least 2 inches in height, but not greater than 6 inches in height. 
Additionally, the color of lettering must contrast with the 
background (color of placard material) such that it is legible.
    (e) Remove the placard required by AD 96-21-12, which states, 
``Flight Of This Helicopter Is Prohibited''.
    (f) Revise the FAA-approved Rotorcraft Flight Manual (RFM) by 
incorporating Appendix 1 of this AD in the Normal Procedures. This 
may be accomplished by inserting a copy of Appendix 1 of this AD in 
the RFM:

Appendix 1

    Note: Operators must initiate action to notify and ensure that 
flight crewmembers are appraised of this change.

    (1) Revise the FAA approved Rotorcraft Flight Manual (RFM) by 
incorporating the following Limitation placard to page 1-14A/14B.

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OVSPD
SYSTEM
INOP

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    Location: Instrument panel near overspeed test switch

    (2) Revise the FAA-approved RFM by incorporating the following 
to the Normal Procedures.

Section 2-4. INTERIOR AND PRESTART CHECK

* * * * *
    18. Caution lights--ENG OUT, XMSN OIL PRESS, RPM, HYDRAULIC 
SYSTEM, GEN FAIL, FADEC DEGRADED, FADEC FAULT, L/FUEL BOOST, R/FUEL 
BOOST, L/FUEL XFR, and R/FUEL XFR will be illuminated.

NOTE

    L/FUEL XFR and R/FUEL XFR will not be illuminated when forward 
fuel tank is empty.
    18a. Throttle--Idle position.

NOTE

    GPU or battery cart power, if being used, must be cycled when 
the BATT switch is OFF.
    18b. BATT switch--Cycle OFF, ON.

NOTE

    Observations of Step 16 will be repeated. FADEC DEGRADED and 
FADEC FAULT lights, that are due to the overspeed system being 
inoperative, will be extinguished.
    18c. Throttle--Closed position.
    18d. Horn Mute button--Press to mute.
* * * * *

Section 2-11. ENGINE SHUTDOWN

* * * * *
    14. Delete
* * * * *
    23. BATT switch--OFF.

CAUTION

    Applicable maintenance action must be performed prior to further 
flight if a FADEC light has illuminated during the flight or on 
engine shutdown.
    (3) Revise the FAA approved RFM by incorporating the following 
to the Emergency/Malfunction Procedures.

Section 3-3-J. DRIVE SHAFT FAILURE

* * * * *
    7. Delete

PROCEDURE:

    1. Maintain heading and attitude control.
    1a. Throttle--idle
* * * * *

3-3-K. FADEC FAILURE

NOTE

    Takeoff power may not be available in the MANUAL mode.
    Maximum continuous power will be available for all ambient 
conditions.

INDICATIONS:

    1. FADEC fail audio activated.
    2. FADEC FAIL warning light illuminated.

PROCEDURE:

WARNING

    Raising or lowering of the collective during a FADEC fail 
condition will result in rotor droop or engine overspeed, 
respectively.
    If increasing the collective when the failure occurs, smoothly 
lower collective to eliminate the NR/NP droop while simultaneously 
retarding the throttle to the 90% bezel position.
    If reducing the collective when the failure occurs, smoothly 
increase the collective to correct the overspeed while 
simultaneously retarding the throttle to the 90% bezel position.
    1. Collective--Maintain position. (if steady state flight 
condition)

WARNING

    Within 2 to 7 seconds after the FADEC FAIL warning, NR/NP may 
increase very rapidly, requiring positive movements of collective to 
control NR/NP.
    2. Throttle--Immediately retard to approximately 90% bezel 
position. (if not previously accomplished)

[[Page 59831]]

    3. FADEC MODE switch--Depress one time.

NOTE

    Initial engine response to manual control of fuel flow with 
throttle may take up to 7 seconds.
    4. NR/NP--Maintain 95 to 100% with the throttle and collective.
    5. Land as soon as practical.

NOTE

    It may be necessary to use FUEL VALVE switch to shutdown engine 
after landing.
    6. Normal shutdown if possible.

NOTE

    When throttle is repositioned to the idle stop (during engine 
shutdown) the PMA will go off-line and engine may flameout.
    (g) After accomplishing all the actions of this AD, operators 
may resume flight operations of the BHTC Model 407 helicopter.
    (h) An alternative method of compliance that provides an 
acceptable level of safety may be used if approved by the Manager, 
Chicago Aircraft Certification Office. The request should be 
forwarded through an appropriate FAA 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.
    (i) The actions required by this AD shall be accomplished in 
accordance with the following Allison Engine Company Alert CEBs:

------------------------------------------------------------------------
          Document No.              Page       Revision         Date    
------------------------------------------------------------------------
CEB-A-73-6010..................  1-7        Original.....  Oct. 15,     
                                                            1996.       
  Total pages: 7.                                                       
CEB-A-73-6011..................  1-12       Original.....  Oct. 31,     
                                                            1996.       
        Total pages: 12.                                                
CEB-A-73-6012..................  1-11       Original.....  Oct. 31,     
                                                            1996.       
  Total pages: 11.                                                      
------------------------------------------------------------------------

    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.
    (j) This amendment supersedes priority letter AD 96-21- 12, 
issued October 11, 1996.
    (k) This amendment becomes effective November 25, 1996, except 
effective upon receipt to all persons receiving a copy of this AD 
directly from the FAA.

    Issued in Burlington, Massachusetts, on November 15, 1996.
Jay J. Pardee,
Manager, Engine and Propeller Directorate, Aircraft Certification 
Service.
[FR Doc. 96-29861 Filed 11-21-96; 12:14 pm]
BILLING CODE 4910-13-U

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