# AD 98-25-14: Barometric Flow Control Unit - Type: Airworthiness directive - Status: Current - Products: Rolls-Royce Limited, Bristol Engines Division Viper Mk. 521, Viper Mk. 522, Viper Mk. 526 and Viper Mk. 601-22 - Effective: February 12, 1999 - Published: December 14, 1998, 63 FR 68674–68675 - Issued as: Final rule - Superseded by: Nothing supersedes this AD - Product type: Engine - Amendment: 39-10940 - Docket: 98-ANE-06-AD - Registered aircraft: 6 may be affected, by airframe or engine model (OpenAirDocs) - Official PDF: https://openairdocs.org/files/sha256/d1/ea/d1ea82538e9c7005df14995f96b5b11e0afa128948b5cf25ba76ad15492183ff (from https://www.govinfo.gov/content/pkg/FR-1998-12-14/pdf/98-32800.pdf) - Federal Register: https://www.federalregister.gov/documents/1998/12/14/98-32800/airworthiness-directives-rolls-royce-limited-bristol-engines-division-and-rolls-royce-1971-limited - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/8889C5C3A69FDFA986256880007A4E1A.0001 - DRS record last changed: May 30, 2024 - Page: https://openairdocs.org/ad/98-25-14 ## The airworthiness directive 98-25-14 Rolls-Royce plc: Amendment 39-10940. Docket 98-ANE-06-AD. Applicability: Rolls-Royce plc (R-R) Viper Mk. 521, 522, 526 and 601 series turbojet engines, installed on but not limited to Raytheon (formerly British Aerospace, Hawker Siddeley) Models BH.125 and DH.125 series aircraft. 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 a high pressure fuel leak, which could result in an engine nacelle fire and damage to the aircraft, accomplish the following: (a) For R-R Viper Mk. 521, and 522 series engines, perform a one-time inspection of the barometric flow control unit (BFCU) augmentor and bypass valve joint washer for joint washer integrity, and replace, if necessary, with serviceable parts, in accordance with R-R Alert Service Bulletins (ASBs) Nos. 73-A120 and 73-A121, as applicable, dated November 1997, as follows: (1) For engines with less than 200 hours time in service (TIS) since new, overhaul, or repair of the BFCU, inspect within 2 months, or 100 hours TIS after the effective date of this AD, whichever occurs first. (2) For engines with 200 or more hours TIS since new, overhaul, or repair of the BFCU, inspect at the next engine removal after the effectivedate of this AD. (b) For R-R Viper Mk. 526 series engines, perform a one-time inspection of the barometric flow control unit (BFCU) augmentor and bypass valve joint washer for joint washer integrity, and replace, if necessary, with serviceable parts, in accordance with R-R ASBs Nos. 73-A68 and 73-A69, as applicable, dated November 1997, as follows: (1) For engines with less than 200 hours time in service (TIS) since new, overhaul, or repair of the BFCU, inspect within 2 months, or 100 hours TIS after the effective date of this AD, whichever occurs first. (2) For engines with 200 or more hours TIS since new, overhaul, or repair of the BFCU, inspect at the next engine removal after the effective date of this AD. (c) For R-R Viper Mk. 601 series engines, perform a one-time inspection of the BFCU augmentor and bypass valve joint washer for joint washer integrity, and replace, if necessary, with serviceable parts, in accordance with R-R ASBs Nos. 73-A35 and 73-A36, as applicable, dated November 1997, as follows: (1) For engines with less than 200 hours TIS since new, overhaul, or repair of the BFCU, inspect within 2 months, or 100 hours TIS after the effective date of this AD, whichever occurs first. (2) For engines with 200 or more hours TIS since new, overhaul, or repair of the BFCU, inspect at the next engine removal after the effective date of this AD. (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, Engine 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, Engine 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 Engine Certification Office. (e) Special flight permits may beissued 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 R-R ASBs: Document No Pages Date 73-A35 1-6 November 1997 Total Pages: 6. 73-A36 1-6 November 1997 Total Pages: 6. 73-A68 1-6 November 1997 Total Pages: 6. 73-A69 1-6 November 1997 Total Pages: 6. 73-A120 1-6 November 1997 Total Pages: 6. 73-A121 1-6 November 1997 Total Pages: 6. 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 Rolls-Royce Limited, Bristol Engines Division, Technical Publications Department CLS-4, P.O. Box 3, Filton, Bristol, BS34 7QE England; telephone 117-979-1234, fax 117-979-7575.Copies may be inspected at the FAA, New England Region, Office of the Regional 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. (g) This amendment becomes effective on February 12, 1999. ## Affected data sheets (2) (OpenAirDocs) The type certificate data sheets whose models the AD names. - [TCDS E3EU](https://openairdocs.org/tcds/E3EU) (historical): Rolls-Royce Deutschland Ltd & Co KG; names 2 of 2 models: Viper Mk. 521, Viper Mk. 522 - [TCDS E15EU](https://openairdocs.org/tcds/E15EU) (historical): Rolls-Royce Deutschland Ltd & Co KG; names 1 of 1 models: Viper Mk. 601-22 ## 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: 6 (0 by airframe model, 6 by engine model) - Makers: Soko 2, Aero Vodochody 1, Aerovodochody 1, Bac Jet Provost 1, Hawker Siddeley 1 Models with the most aircraft: - [Rolls-Royce VIPER MK60122](https://openairdocs.org/engine/rolls-royce-viper-mk60122): 3 aircraft (engine model) - [Rolls-Royce VIPER MK522](https://openairdocs.org/engine/rolls-royce-viper-mk522): 2 aircraft (engine model) - [Rolls-Royce VIPER MK 601 series](https://openairdocs.org/engine/rolls-royce-viper-mk-601-series): 1 aircraft (engine model) All 3 models: https://openairdocs.org/ad/98-25-14/models.md Every aircraft: https://openairdocs.org/ad/98-25-14/aircraft.md ## Related documents - [Proposed rule 98-ANE-06-AD](https://openairdocs.org/proposed/98-ANE-06-AD): Notice of proposed rulemaking (NPRM), published Apr 30, 1998 Its text cites no advisory circulars or STCs. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.