# AD 96-25-15: Honeywell Standard Windshear Detection System - Type: Airworthiness directive - Status: Current - Products: BAE Systems Avro 146-RJ100A, Avro 146-RJ70A, Avro 146-RJ85A, 727-200 Series, MD-11 and MD-11F - Effective: January 23, 1997 - Published: December 19, 1996, 61 FR 66898–66900 - Issued as: Final rule - Superseded by: Nothing supersedes this AD - Product type: Aircraft, Large airplane - Amendment: 39-9858 - Docket: 96-NM-121-AD - Registered aircraft: 146 may be affected, by airframe or engine model (OpenAirDocs) - Official PDF: https://openairdocs.org/files/sha256/6f/6a/6f6aafb595e7020068c71c1b06e24d550ac09ca929fc5c743a98da8a85ee5232 (from https://www.govinfo.gov/content/pkg/FR-1996-12-19/pdf/96-32050.pdf) - Federal Register: https://www.federalregister.gov/documents/1996/12/19/96-32050/airworthiness-directives-boeing-model-727-200-series-airplanes-mcdonnell-douglas-md-11-airplanes-and - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/6E2FE91C0AF9F3248625697B0072BAE2.0001 - DRS record last changed: May 30, 2024 - Page: https://openairdocs.org/ad/96-25-15 ## Summary This amendment adopts a new airworthiness directive (AD), applicable to certain transport category airplanes equipped with certain Honeywell Standard Windshear Detection System (WSS). It requires a revision to the airplane flight manual to alert the flightcrew of the potential for significant delays in the WSS detecting windshear when the flaps of the airplane are in transition. This amendment also requires replacement of the currently-installed line replaceable unit (LRU) with a modified LRU having new software that eliminates delays in the WSS. This amendment is prompted by a report of an accident during which an airplane encountered severe windshear during a missed approach. The actions specified by this AD are intended to prevent significant delays in the WSS detecting hazardous windshear, which could lead to the loss of flight path control. ## The airworthiness directive 96-25-15 BOEING; MCDONNELL DOUGLAS; AND BRITISH AEROSPACE REGIONAL AIRCRAFT LIMITED, AVRO INTERNATIONAL AEROSPACE DIVISION (Formerly British Aerospace, plc; British Aerospace Commercial Aircraft Limited): Amendment 39-9858. Docket 96-NM-121-AD. Applicability: The following models and series of airplanes, certificated in any category, equipped with Honeywell Standard Windshear Detection Systems (WSS) having the part numbers indicated below: Manufacturer and Model of Airplane Type of Computer Part Numbers Boeing 727-200 series Expandable Windshear (Honeywell STC) 4053818-904, -905, or -906 McDonnell Douglas MD-11 series Flight Control Computer (OEM TC) 4059001-906 British Aerospace Avro 146-RJ70A, -RJ85A, and -RJ100A series Flight Control Computer (OEM TC) 4068300-903 NOTE 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been otherwise modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes 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 significant delays in the Honeywell Standard Windshear Detection Systems (WSS) detecting hazardous windshear, which could lead to the loss of flight path control, accomplish the following: (a) Within 14 days after the effective date of this AD, revise the Limitations Section of the FAA-approved Airplane Flight Manual (AFM) to include the following statement. This may be accomplished by inserting a copy of this AD in the AFM. "During sustained banks of greater than 15 degrees or during flap configuration changes, the Honeywell Windshear Detection and Recovery Guidance System (WSS) is desensitized and alerts resulting from encountering windshear conditions will be delayed." (b) Within 30 months after the effective date of this AD, replace the currently-installed line replaceable unit (LRU) with a modified LRU having new software that eliminates delays in the WSS detecting windshear when the flaps of the airplane are in transition, in accordance with a method approved by the Manager, Los Angeles Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. Accomplishment of this replacement constitutes terminating action for the requirements of paragraph (a) of this AD. After the replacement has been accomplished, the AFM limitation required by paragraph (a) of this AD may be revised to read as follows: "During sustained banks of greater than 15 degrees, the Honeywell Windshear Detection and Recovery Guidance System (WSS) is desensitized and alerts resulting from encountering windshear conditions will be delayed." (c) As of 12 months after the effective date of this AD, no person shall install on any airplane an LRU that has not been modified in accordance with paragraph (b) of this AD. However, an unmodified LRU may be installed on the airplane for up to 12 months after the effective date of this AD, provided that, during that time, the AFM limitation required by paragraph (a) of this AD remains in effect. (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, Los Angeles ACO. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Los Angeles ACO. NOTE 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Los Angeles ACO. (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 airplane to a location where the requirements of this AD can be accomplished. (f) This amendment becomes effective on January 27, 1997. ## Rule preamble ### Supplementary information A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to certain transport category airplanes equipped with certain Honeywell Standard Windshear Detection System (WSS) series airplanes was published in the Federal Register on September 13, 1996 (61 FR 48431). That action proposed to require a revision to the FAA-approved AFM to alert the flightcrew of the potential for significant delays in the WSS detecting windshear when the flaps of the airplane are in transition. That action also proposed to require replacement of the currently-installed LRU with a modified LRU having new software that eliminates delays in the WSS. Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received. Request to Eliminate Installation Requirement One commenter objects to paragraph(b) of the proposal, which would require operators to replace the currently installed LRU with a modified LRU having new software that eliminates delays in the WSS detecting windshear when the flaps of the airplane are in transition. This commenter considers that the proposed replacement would not enhance safety of the affected airplanes. This commenter also asserts that the proposed replacement requirement would result in changes in the aircraft configuration that would increase nuisance alerts, since the sensitivity reduction factor would be totally eliminated during flap transition. The FAA does not concur with the commenter's request to withdraw the proposal for the following reasons: First, the criteria for reactive windshear systems state that a warning must be issued once a windshear phenomenon is encountered. The criteria also state that the system must consider the airplane's available performance and the system's propensity for nuisance alerts due to turbulence.The FAA evaluates compliance with these criteria based upon the system's ability to issue timely warnings in all reasonably expected conditions. The FAA finds that encountering windshear during flap transition is a reasonably expected condition. This finding is based, in part, on the data obtained from the flight data recorder retrieved from the airplane involved in the accident in which windshear was encountered while the airplane was executing a missed approach. Second, the FAA has determined that conducting missed approaches, prior to encountering windshear, is a reasonably probable scenario. In such a scenario, the pilot would rely on prior knowledge attained in FAA-required training to recognize and recover from a windshear encounter, such as that provided in "Windshear Training Aid," Revision 1, dated February 1990. Therefore, the pilot would likely determine that windshear has been encountered before the detection system actually detects the phenomenon, since the WSS isintended to be strictly an adjunct system, not a sole or primary system. The windshear training that pilots receive instructs them not to retract the airplane's flaps in this scenario. However, if the pilot does not believe that windshear has been encountered, the pilot may execute a normal go-around and retract the flaps, due to what the pilot perceives to be an unstable approach. Therefore, the FAA considers any delay in windshear detection to be unacceptable while the airplane's flaps are in transition. Consequently, the FAA finds that any improvement in warning time for the pilot will enhance safety for the affected airplanes. Third, the FAA does not concur with the commenter's assertion that installation of a modified LRU, and consequently, removal of the windshear warning delay during flap transition, would result in an increase in nuisance alerts. The FAA has reviewed all available data and cannot substantiate that elimination of the sensitivity reduction factor duringflap transition would result in an increase in nuisance alerts. The FAA finds that the flaps are usually extended at altitudes higher than the altitude at which the system is armed. Furthermore, the FAA considers conducting a go-around with strong turbulence (excluding actual windshear conditions) to be a highly unlikely combination of events. In addition, the FAA will evaluate the modified Honeywell windshear computer, once it is developed, to determine compliance with the nuisance alert criteria, discussed above. Request to Reconsider Compliance Time for Replacement This same commenter requests that the FAA reconsider the proposed compliance time of 30 months for replacement of the LRU with a modified unit. The commenter points out that Honeywell has neither developed an appropriate modification nor released service bulletins to provide the procedural methods for complying with the requirements of the proposed AD. The commenter notes that the same is true for compliance with AD 96-02-06, amendment 39-9494 (61 FR 2095, January 25, 1996), which requires identical actions as those proposed, but applicable to certain other transport category airplanes. This commenter also points out that AD 96-02-06 provides for a compliance time of 36 months for the replacement; the AD also states that, as of 18 months after February 26, 1996 (the effective date of that AD), no unmodified LRU can be installed on any airplane. The proposed AD's compliance times are 30 months for replacement, and 12 months before installation of unmodified units is prohibited. Although this commenter did not request any specific changes to the proposed rule, the FAA infers from these comments that the commenter is concerned that there will be a problem with parts availability within the compliance time. At the time that AD 96-02-06 was issued in January 1996, the FAA had verified with the manufacturer that the lead time for developing the required LRU and making it available to operators was expected to be longer than 24 months, but not longer than 36 months. Since then, the manufacturer has given the FAA no new information that would change this schedule for availability of the required units; therefore, the FAA finds that the compliance times, as proposed, are appropriate. Conclusion After careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule as proposed. Cost Impact There are approximately 200 airplanes of the affected design in the worldwide fleet. The FAA estimates that 100 airplanes of U.S. registry will be affected by this AD. It will take approximately 1 work hour per airplane to accomplish the required AFM revision, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the AFM revision required by this AD on U.S. operators is estimated to be $6,000, or $60 per airplane. It willtake approximately 10 work hours per airplane to accomplish the required replacement, at an average labor rate of $60 per work hour. Required parts will be supplied by Honeywell at no cost to the operators. Based on these figures, the cost impact of the AD on U.S. operators is estimated to be $60,000, or $600 per airplane. The cost impact figures discussed above are based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted. Regulatory Impact 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 thepreparation of a Federalism Assessment. For the reasons discussed above, I certify that this action (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. A final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it 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, 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. § 39.13 - (Amended) 2. Section 39.13 is amended by adding the following new airworthiness directive: ## Affected data sheets (3) (OpenAirDocs) The type certificate data sheets whose models the AD names. - [TCDS A49EU](https://openairdocs.org/tcds/A49EU): BAE Systems (Operations) Limited; names 3 of 6 models: Avro 146-RJ85A, Avro 146-RJ70A, Avro 146-RJ100A - [TCDS A22WE](https://openairdocs.org/tcds/A22WE): The Boeing Company; names 2 of 11 models: MD-11, MD-11F - [TCDS A3WE](https://openairdocs.org/tcds/A3WE): The Boeing Company; names 1 of 6 models: 727-200 Series ## 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: 146 (146 by airframe model, 0 by engine model) - Makers: Mcdonnell Douglas 104, Boeing 28, British Aerospace 12, BAE Systems 2 Models with the most aircraft: - [Mcdonnell Douglas MD-11F](https://openairdocs.org/model/mcdonnell-douglas-md-11f): 100 aircraft (airframe model) - [British Aerospace AVRO 146-RJ85A](https://openairdocs.org/model/british-aerospace-avro-146-rj85a): 12 aircraft (airframe model) - [Boeing 727-223](https://openairdocs.org/model/boeing-727-223): 9 aircraft (airframe model) - [Boeing 727-227](https://openairdocs.org/model/boeing-727-227): 4 aircraft (airframe model) - [Mcdonnell Douglas MD-11](https://openairdocs.org/model/mcdonnell-douglas-md-11): 4 aircraft (airframe model) - [Boeing MD-11F](https://openairdocs.org/model/boeing-md-11f): 4 aircraft (airframe model) - [Boeing 727-225](https://openairdocs.org/model/boeing-727-225): 2 aircraft (airframe model) - [BAE Systems AVRO 146-RJ85A](https://openairdocs.org/model/bae-systems-avro-146-rj85a): 2 aircraft (airframe model) - [Boeing 727-200](https://openairdocs.org/model/boeing-727-200): 1 aircraft (airframe model) - [Boeing 727-212](https://openairdocs.org/model/boeing-727-212): 1 aircraft (airframe model) - [Boeing 727-230](https://openairdocs.org/model/boeing-727-230): 1 aircraft (airframe model) - [Boeing 727-232](https://openairdocs.org/model/boeing-727-232): 1 aircraft (airframe model) - [Boeing 727-243](https://openairdocs.org/model/boeing-727-243): 1 aircraft (airframe model) - [Boeing 727-247](https://openairdocs.org/model/boeing-727-247): 1 aircraft (airframe model) - [Boeing 727-264](https://openairdocs.org/model/boeing-727-264): 1 aircraft (airframe model) - [Boeing 727-281](https://openairdocs.org/model/boeing-727-281): 1 aircraft (airframe model) - [Boeing 727-277](https://openairdocs.org/model/boeing-727-277): 1 aircraft (airframe model) All 17 models: https://openairdocs.org/ad/96-25-15/models.md Every aircraft: https://openairdocs.org/ad/96-25-15/aircraft.md ## Related documents - [Proposed rule 96-NM-121-AD](https://openairdocs.org/proposed/96-NM-121-AD): Notice of proposed rulemaking (NPRM), published Sep 13, 1996 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.