AD 2000-07-27

Effective May 3, 2000.

The incorporation by reference of certain publications listed in the regulations is approved by the Director of the Federal Register as of May 3, 2000.

Comments for inclusion in the Rules Docket must be received on or before June 19, 2000.

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2000-NM-83-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

The service information referenced in this AD may be obtained from Honeywell, Publications, P.O. Box 21111, Mail Stop DV-10, Phoenix, Arizona 85036. This information may be examined at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the FAA, Chicago Aircraft Certification Office, 2350 East Devon Avenue, Room 323, Des Plaines, Illinois; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

Wess Rouse, Aerospace Engineer, Systems and Flight Test Branch, ACE-117C, FAA, Chicago Aircraft Certification Office, 2350 East Devon Avenue, Room 323, Des Plaines, Illinois 60018; telephone (847) 294-8113; fax (847) 294-7834.

The FAA has recently received three reports of dual inertial reference (IR) critical faults of the air data inertial reference system comprising two or more air data inertial reference units (ADIRU) on transport category airplanes during flight. Three days prior to one of the dual IR critical fault incidents, one of those ADIRU's had an IR critical fault in flight. During the subsequent ground check, the failed ADIRU passed the built-in test and aligned, functioning normally.

The subject ADIRU's are subject to IR critical faults related to the power supply margin. The demand for voltage increases as operating hours and temperature increase. Once the demand for voltage exceeds the capability of the power supply, the inertial reference portion of the ADIRU will exhibit an IR critical fault, while the air data portion of the ADIRU will continue to function normally. It may be possible to reset the failed inertial reference unit on the ground after the temperature of the ADIRU decreases; however, the risk of the dual critical fault increases when an ADIRU with a failed inertial reference power supply is returned to service. If two inertial reference units fail, the airplane is left with only one functioning source of attitude data. This condition could result in loss of the main sources of attitude data, consequent high pilot workload, and a significant increase in the likelihood of pilot error.

The FAA has reviewed and approved Honeywell Alert Service Bulletins HG2030AD-34-A0009, and HG2050AC-34-A0008, both dated March 9, 2000, which describe procedures for determining the modification status of the ADIRU. For any ADIRU part number (P/N) HG2050AC not marked as modification 2 or 3 and any ADIRU P/N HG2030AD not marked as modification 3 or 6, the alert service bulletins also describe procedures for replacement of the ADIRU with a serviceable ADIRU.

Since an unsafe condition has been identified that is likely to exist or develop on other products of the same type design, this AD is being issued to prevent loss of the main sources of attitude data, consequent high pilot workload, and a significant increase in the likelihood of pilot error. This AD requires inspection of a failed ADIRU to determine its modification status, and replacement of any unmodified failed ADIRU with a serviceable ADIRU. This AD also provides for optional terminating action for the requirements of the AD. The actions are required to be accomplished in accordance with the alert service bulletins 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.

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 shall 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 rule must submit a self-addressed, stamped postcard on which the following statement is made: “Comments to Docket Number 2000-NM-83-AD.” The postcard will be date stamped and returned to the commenter.

The regulations adopted herein 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. Therefore, it is determined that this final rule does not have federalism implications under Executive Order 13132.

The FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and that it 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.

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:

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

2. Section 39.13 is amended by adding the following new airworthiness directive: