AD 96-24-09

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 actionsto 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.

Final rule; request for comments.

96-24-09 Allison Engine Company: Amendment 39-9834. Docket No. 96-ANE-41. Supersedes Priority Letter 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.

(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
Total Pages: 7.
1-7
Original
October 15, 1996
CEB-A-73-6011
Total Pages: 12.
1-12
Original
October 31, 1996
CEB-A-73-6012
Total Pages: 11.
1-11
Original
October 31, 1996

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.

Appendix 1

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

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

OVSPD
SYSTEM
INOP
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)

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.

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 commentswill 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 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.

39.13 - [AMENDED]
2. Section 39.13 is amended by adding the following new airworthiness directive: