# AD 2004-24-04: Hydromechanical unit (HMU) Power Lever Angle (PLA) potentiometer

- Type: Airworthiness directive
- Status: Current
- Products: Rolls-Royce 250-C30R/3, 250-C30R/3M, 250-C47B and 250-C47M
- Effective: January 3, 2005
- Published: November 26, 2004, 69 FR 68769–68771
- Issued: November 15, 2004
- Issued as: Final rule
- Supersedes: [AD 2003-13-10](https://openairdocs.org/ad/2003-13-10)
- Superseded by: Nothing supersedes this AD
- Product type: Engine
- Amendment: 39-13880
- Docket: 2003-NE-23-AD
- Registered aircraft: 1,012 may be affected, by airframe or engine model (OpenAirDocs)
- Official PDF: https://openairdocs.org/files/sha256/15/2c/152c690ebd031d95594c8a917329be74544a0587db8a7a013bfebf4e94c3d556 (from https://www.govinfo.gov/content/pkg/FR-2004-11-26/pdf/04-25791.pdf)
- Federal Register: https://www.federalregister.gov/documents/2004/11/26/04-25791/airworthiness-directives-rolls-royce-corporation-formerly-allison-engine-company-allison-gas-turbine
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/CEFF5DF879496FD986256F58005953CF.0001
- DRS record last changed: May 30, 2024
- Page: https://openairdocs.org/ad/2004-24-04

## Summary

The FAA is superseding an existing airworthiness directive (AD) for RRC models 250-C30R/3, -C30R/3M, -C47B, and -C47M turboshaft engines. That AD currently requires initial and repetitive electrical signal inspections of the hydromechanical unit (HMU) Power Lever Angle (PLA) potentiometer. This ad continues to require those inspections and adds replacement of the existing HMU with a new design HMU as a mandatory terminating action to the repetitive inspection requirements. This AD results from the manufacturer releasing a redesigned HMU that has a dual-element potentiometer. We are issuing this AD to prevent uncommanded and sudden changes in engine power.

## The airworthiness directive

### Adoption of the Amendment

Accordingly, under the authority delegated to me by the Administrator, the Federal Aviation Administration amends 14 CFR part 39 as follows:

1. The authority citation for part 39 continues to read as follows:

2. The FAA amends § 39.13 by removing Amendment 39-13210 (68 FR 38590, June 30, 2003) and by adding a new airworthiness directive, Amendment 39-13880, to read as follows:

2004-24-04 Rolls-Royce Corporation (formerly Allison Engine Company, Allison Gas Turbine Division, and Detroit Diesel Allison): Amendment 39-13880. Docket No. 2003-NE-23-AD. Supersedes AD 2003-13-10, Amendment 39-13210.

### (a) Effective Date

  (a) This AD becomes effective January 3, 2005.

### (b) Affected ADs

  (b) This AD supersedes AD 2003-13-10.

### (c) Applicability

  (c) This AD applies to Rolls-Royce Corporation (formerly Allison Engine Company, Allison Gas Turbine Division, and Detroit Diesel Allison) (RRC) models 250-C30R/3, -C30R/3M, -C47B, and -C47M turboshaft engines that have a hydromechanical unit (HMU) with a part number (P/N) listed in 1.A. Group A of RRC Alert Commercial Engine Bulletins (ACEB) No. CEB A-73-3103, Revision 4, dated December 2, 2003; and No. CEB A-73-6030, Revision 4, dated December 2, 2003. These engines are installed on, but not limited to, Bell OH-58D, Bell Helicopter Textron 407, Boeing AH/MH-6M, and MD Helicopters Inc. 600N helicopters.

### (d) Unsafe Condition

  (d) This AD results from the manufacturer releasing a redesigned HMU that has a dual-element potentiometer. The actions specified in this AD are intended to prevent uncommanded and sudden changes in engine power.

### (e) Compliance

  (e) Compliance with this AD is required as indicated, unless already done.

### (f) Initial Inspection

  (f) Perform an initial electrical signal inspection of the HMU Power Lever Angle (PLA) potentiometer, within 300 flight hours (FH) after the effective date of this AD. Use paragraphs 2.B. through 2.B.(8) and 2.B.(10) of the Accomplishment Instructions of RRC ACEB No. CEB A-73-3103, Revision 4, dated December 2, 2003; or No. CEB A-73-6030, Revision 4, dated December 2, 2003; to perform the inspection.

  (g) Replace the HMU before further flight if the electrical signal inspection result is unacceptable.

### (h) Repetitive Inspections

  (h) Thereafter, perform repetitive electrical signal inspections of the HMU PLA potentiometer within 300 FH of the last inspection. Use paragraphs 2.B. through 2.B.(8) and 2.B.(10) of the Accomplishment Instructions of RRC ACEB No. CEB A-73-3103, Revision 4, dated December 2, 2003; or No. CEB A-73-6030, Revision 4, dated December 2, 2003; to perform the inspection.

    (i) Replace the HMU before further flight if the electrical signal inspection result is unacceptable.

### (j) Mandatory Terminating Action

  (j) Replace the HMU with an HMU that has a P/N not specified in this AD within 600 FH after the effective date of this AD, or January 31, 2005, whichever occurs earlier. Replacing the HMU with an HMU that has a P/N not specified in this AD terminates the repetitive inspection requirement specified in paragraph (h) of this AD.

### (k) Alternative Methods of Compliance

  (k) Alternative methods of compliance must be requested in accordance with 14 CFR part 39.19, and must be approved by the Manager, Chicago Aircraft Certification Office, FAA.

### (l) Material Incorporated by Reference

    (l) You must use the Rolls-Royce Corporation Alert Commercial Engine Bulletins (ACEBs) listed in Table 1 of this AD to perform the inspections required by this AD. The Director of the Federal Register approved the incorporation by reference of the documents listed in Table 1 of this AD in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. You can get a copy from Rolls-Royce Corporation, P.O. Box 420, Indianapolis, IN 46206-0420; telephone (317) 230-6400; fax (317) 230-4243. You can review copies at the FAA, New England Region, Office of the Regional Counsel, 12 New England Executive Park, Burlington, MA; or at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, call 202-741-6030, or go to: http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html. Table 1 follows:

*Table 1.—Incorporation by Reference*

| Service bulletin | Page number(s) shown on the page | Revision level shown on the page | Date shown on the page |
| --- | --- | --- | --- |
| CEB A-73-3103, Total Pages: 20 | All | 4 | December 2, 2003. |
| CEB A-73-6030, Total Pages: 20 | All | 4 | December 2, 2003. |

### (m) Related Information

  (m) None.

## Rule preamble

### Dates

This AD becomes effective January 3, 2005. The Director of the Federal Register approved the incorporation by reference of certain publications listed in the regulations as of January 3, 2005.

### Addresses

You can get the service information identified in this AD from Rolls-Royce Corporation, P.O. Box 420, Indianapolis, IN 46206-0420; telephone (317) 230-6400; fax (317) 230-4243.

You may examine the AD docket at the FAA, New England Region, Office of the Regional Counsel, 12 New England Executive Park, Burlington, MA. You may examine the service information, at the FAA, New England Region, Office of the Regional Counsel, 12 New England Executive Park, Burlington, MA; or at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, call 202-741-6030, or go to: http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html.

### For further information contact

Khailaa Hosny, Aerospace Engineer, Chicago Aircraft Certification Office, FAA, 2300 East Devon Avenue, Des Plaines, IL 60018-4696; telephone (847) 294-7134; fax (847) 294-7834.

### SUPPLEMENTARY INFORMATION

The FAA proposed to amend 14 CFR part 39 with a proposed AD. The proposed AD applies to RRC models 250-C30R/3, -C30R/3M, -C47B, and -C47M turboshaft engines. We published the proposed AD in the Federal Register on June 9, 2004 (69 FR 32287). That action proposed to require initial and repetitive electrical signal inspections of the HMU PLA potentiometer and replacement of the existing HMU with a new design HMU as a mandatory terminating action to the repetitive inspection requirements.

### Examining the AD Docket

You may examine the AD Docket (including any comments and service information), by appointment, between 8 a.m. and 4:30 p.m., Monday through Friday, except Federal holidays. See ADDRESSES for the location.

### Comments

We provided the public the opportunity to participate in the development of this AD. We received no comments on the proposal or on the determination of the cost to the public.

### Conclusion

We have carefully reviewed the available data and determined that air safety and the public interest require adopting the AD as proposed.

### Costs of Compliance

We estimate that 700 engines installed on helicopters of U.S. registry will be affected by this AD. We estimate that it will take about 4 work hours per engine to replace a single-element HMU with a dual-element HMU. We also estimate that 12 percent of the single-element HMUs will fail the required inspection and require replacing the HMU. The average labor rate is $65 per work hour. Required parts cost about $615 per engine. Based on these figures, we estimate the total cost of the AD to U.S. operators to be $686,000.

### Regulatory Findings

We have determined that this AD will not have federalism implications under Executive Order 13132. This AD will not have a substantial direct effect 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.

For the reasons discussed above, I certify that this AD:

  (1) Is not a “significant regulatory action” under Executive Order 12866;

  (2) Is not a “significant rule” under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and

  (3) Will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act.

We prepared a summary of the costs to comply with this AD and placed it in the AD Docket. You may get a copy of this summary by sending a request to us at the address listed under ADDRESSES. Include “AD Docket No. 2003-NE-23-AD” in your request.

## Affected data sheets (1) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS E1GL](https://openairdocs.org/tcds/E1GL): Rolls-Royce Corporation; names 4 of 23 models: 250-C47M, 250-C30R/3M, 250-C30R/3, 250-C47B

## Registered aircraft it may apply to (OpenAirDocs)

Matched by airframe and engine model; the AD's applicability may narrow it by serial number, part number or equipment.

- Aircraft: 1,012 (0 by airframe model, 1,012 by engine model)
- Makers: Bell 541, Bell Helicopter Textron Canada 365, MD Helicopters 16, Hiller 15, Mcdonnell Douglas Helicopter 14, Enstrom Helicopter 9, Sikorsky 8, Bell Helicopter Textron 7, Cessna 7, Beech 6

Models with the most aircraft:

- [Rolls-Royce 250-C47B](https://openairdocs.org/engine/rolls-royce-250-c47b): 537 aircraft (engine model)
- [Allison 250-C30 series](https://openairdocs.org/engine/allison-250-c30-series): 224 aircraft (engine model)
- [Allison 250-C47 series](https://openairdocs.org/engine/allison-250-c47-series): 123 aircraft (engine model)
- [Allison 250 series](https://openairdocs.org/engine/allison-250-series): 79 aircraft (engine model)
- [Rolls-Royce 250-C47 series](https://openairdocs.org/engine/rolls-royce-250-c47-series): 16 aircraft (engine model)
- [Allison 250-C47B](https://openairdocs.org/engine/allison-250-c47b): 15 aircraft (engine model)
- [Rolls-Royce 250-C47M](https://openairdocs.org/engine/rolls-royce-250-c47m): 13 aircraft (engine model)
- [Allison 250-C47M](https://openairdocs.org/engine/allison-250-c47m): 3 aircraft (engine model)
- [Rolls-Royce 250-C30R/3](https://openairdocs.org/engine/rolls-royce-250-c30r-3): 1 aircraft (engine model)
- [Rolls-Royce 250-C30R/3M](https://openairdocs.org/engine/rolls-royce-250-c30r-3m): 1 aircraft (engine model)

All 11 models: https://openairdocs.org/ad/2004-24-04/models.md
Every aircraft: https://openairdocs.org/ad/2004-24-04/aircraft.md

## Related documents

- [AD 2003-13-10](https://openairdocs.org/ad/2003-13-10) (historical): Hydromechanical unit (HMU) power lever angle (PLA) · 250-C30R/3, 250-C30R/3M, 250-C47B and 1 more. Effective Jul 15, 2003. Replaced by this AD

No proposed rule in this release led to it. Its text cites no advisory circulars or STCs.

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