On April 15, 2003, we issued emergency AD 2003-08-52, that is applicable to GEAE CT7-9B turbofan engines. That emergency AD requires rigging the compressor VG to VG schedule N. That action was prompted by reports of 12 compressor stall events that occurred over a six-month period. This is in contrast to recent historical experience of four to six stall events per year. The stall events have occurred on deceleration when transitioning from takeoff power to climb power. Of the 10 events under investigation, nine had the compressor VG rigged to the VG schedule N1. The manufacturer's maintenance manuals and related service bulletins permit the compressor VG to be rigged to either the VG schedule N or the VG schedule N1. The VG schedule N provides a higher stall margin at the expense of a small reduction of engine performance margin as compared to the VG schedule N1. Since 1992, the manufacturer has recommended that overhaul shops use the VG schedule N only. VG schedule N provides more stall margin on used engines, which inherently have a lower stall margin due to wear or deterioration. Other factors that contribute to lower stall margins include dirty compressors and the increased compressor clearances that occur during the first takeoff of the day. This condition, if not corrected, could result in a dual-engine in-flight shutdown or power loss due to a compressor stall during deceleration from takeoff power to climb power.
Relevant Service Information
We have reviewed and approved the technical contents of GEAE Alert Service Bulletin (ASB) No. CT7-TP S/B 72-A0328, Revision 1, dated April 8, 2003. That ASB describes procedures for rigging the compressor VG to the VG schedule N.
FAA's Determination and Requirements of This AD
The unsafe condition described previously is likely to exist or develop on other GEAE CT7-9B turboprop engines of the same type design. Therefore, we are issuing this AD to prevent a dual-engine in-flightshutdown or power loss due to a compressor stall during deceleration from takeoff power to climb power. This AD requires:
If both engines on the airplane are rigged to VG schedule N1, rigging the compressor VG on one engine to VG schedule N within 30 flight hours (FH) or 3 days after the effective date of this AD, whichever occurs later and,
Rigging the remaining engine compressor VG to VG schedule N within 100 FH or 10 days after the effective date of this AD, whichever occurs earlier.
If only one engine is rigged to VG schedule N1, rigging the compressor VG to VG schedule N within 100 FH or 10 days after the effective date of this AD, whichever occurs earlier.
You must do the actions per GEAE ASB No. CT7-TP S/B 72-A0328, Revision 1, dated April 8, 2003, described previously.
FAA's Determination of the Effective Date
Since it was found that immediate corrective action was required, notice and opportunity for prior public comment were impracticable and contraryto the public interest and that good cause existed to make the AD effective immediately on April 15, 2003, to all known U.S. owners and operators of GEAE CT7-9B turboprop engines. These conditions still exist, and we are publishing the AD in the Federal Register as an amendment to section 39.13 of part 39 of the Federal Aviation Regulations (14 CFR part 39) to make it effective to all persons.
Changes to 14 CFR Part 39--Effect on the AD
On July 10, 2002, we issued a new version of 14 CFR part 39 (67 FR 47997, July 22, 2002), which governs our AD system. This regulation now includes material that relates to special flight permits, alternative methods of compliance, and altered products. This material previously was included in each individual AD. Since this material is included in 14 CFR part 39, we will not include it in future AD actions.
Interim Action
The investigation to determine the root causes of the decel stall events is ongoing. We may take further rulemakingaction when we have identified the root causes.
Comments Invited
This AD is a final rule that involves requirements affecting flight safety and was not preceded by notice and an opportunity for public comment; however, we invite you to submit any written relevant data, views, or arguments regarding this AD. Send your comments to an address listed under ADDRESSES. Include "AD Docket No. 2003-NE-16-AD" in the subject line of your comments. If you want us to acknowledge receipt of your mailed comments, send us a self-addressed, stamped postcard with the docket number written on it; we will date-stamp your postcard and mail it back to you. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify it. If a person contacts us through a nonwritten communication, and that contact relates to a substantive part of this AD, we will summarize the contact and place the summary in the docket. We will consider all comments received by the closing date and may amend the AD in light of those comments.
We are reviewing the writing style we currently use in regulatory documents. We are interested in your comments on whether the style of this document is clear, and your suggestions to improve the clarity of our communications with you. You may get more information about plain language at http://www.plainlanguage.gov.
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 the regulation:
1. Is not a "significant regulatory action" under Executive Order 12866;
2. Is not a "significant rule" under the 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-16-AD" in your request.
List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.
Adoption of the Amendment
Accordingly, under 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. The FAA amends 39.13 by adding the following new airworthiness directive: