AD 98-26-06

This document publishes in the Federal Register an amendment adopting Airworthiness Directive (AD) 98-26-06 which was sent previously to all known U.S. owners and operators of Schweizer Aircraft Corporation (Schweizer) Model 269D helicopters by individual letters. This AD requires removing the main rotor drive shaft (shaft) and inspecting it for cracks. If a crack is found, replacing the shaft with an airworthy shaft is required. This AD also requires periodically verifying the torque of the main rotor hub (hub) bolts. This amendment is prompted by four reports of cracking in the shaft of helicopters with a large diameter hub. Wear patterns indicate cracking was caused by loss of clamping torque on the hub and shaft assembly due to the use of grease between the hub and shaft. This condition, if not corrected, could result in failure of the shaft and subsequent loss of control of the helicopter.

Final rule; request for comments

98-26-06 SCHWEIZER AIRCRAFT CORPORATION: Amendment 39-11002. Docket No. 98-SW-13-AD.

Applicability: Model 269D helicopters with a large diameter main rotor hub (hub), part number (P/N) 269A1002-11, and main rotor drive shaft (shaft), P/N 269A5305-139, -143, -145, or -147, installed, certificated in any category.

NOTE 1: This AD applies to each helicopter 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 helicopters that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must use the authority provided in paragraph (c) to request approval from the FAA. This approval may address either no action, if the current configuration eliminates the unsafe condition, or different actions necessary to address the unsafe condition described in this AD. Such a request should includean assessment of the effect of the changed configuration on the unsafe condition addressed by this AD. In no case does the presence of any modification, alteration, or repair remove any helicopter from the applicability of this AD.

Compliance: Required as indicated, unless accomplished previously.

To prevent failure of the shaft and subsequent loss of control of the helicopter, accomplish the following:

(a) Prior to 200 hours time-in-service (TIS) since the assembly of the hub and a shaft having zero hours TIS, and thereafter at intervals not to exceed 100 hours TIS,

(1) Remove the shaft from the power train system.

(2) Clean and inspect the shaft for a crack in the area of the six hub attach bolt (bolt) holes using a 10-power or higher magnifying glass and bright light.

(3) If no crack is found, inspect the shaft using a direct or indirect magnetic particle inspection method in accordance with ASTM Standard No. E1444 as follows:

(i) For directmagnetization, use an AC, DC, or AC/DC wet continuous method with fluorescent or nonfluorescent particles.

(A) Circular (Head Shot) - 1,100 amperes
Look for a longitudinal crack.

(B) Longitudinal (Coil Shot) - Because of variations in coil design, only the length-to-diameter ratio based on effective diameter and inspection region is provided.
Effective diameter - 1.279 inches
Length - 6.00 inches
L/D Ratio - 5
Look for a circumferential crack.

(C) Demagnetize and clean the inspection areas with solvent to remove residual particles.

(ii) For indirect magnetization, use an AC electromagnetic yoke (Magnaflux product No. Y-6 or equivalent). Set the spacing and the angle to suit the external diameter of the shaft.

(A) Magnetize each of the six hole areas by applying the AC electromagnetic yoke (yoke) circumferentially across the hole.

(B) During each magnetization, apply dry color contrasting particles to the inspection area and look for a circumferential crack propagating from any hole.

(C) Demagnetize and repeat the inspections with the poles of the yoke positioned longitudinally across each hole group looking for a circumferential crack.

(D) Demagnetize and clean the inspection areas with solvent to remove residual particles.

(iii) If no crack is found as a result of the magnetic particle inspection, reassemble the hub and shaft.

NOTE 2: Procedures in Model 269D Handbook of Maintenance Instructions (HMI) revised on June 12, 1998, include installing a three-piece retention fitting, applying a higher torque to each bolt, assembling with no lubricant, and applying zinc chromate primer between the hub and the shaft.

(4) If a crack is found, replace the shaft with an airworthy shaft.

(b) At intervals not to exceed 50 hours TIS after accomplishing paragraph (a),

(1) Unsafety and clean the exterior of the bolts.

(2) Unsafety and loosen the droopstop nut.

(3) Apply 390 in-lbs of torque to each of the six bolts. If any bolt rotates, accomplish the requirements of paragraph (a).

(4) Apply 390 to 410 in-lbs of torque to each of the six bolts and resafety.

(5) Torque and safety the droop stop nut.

(6) Seal the exterior of the bolts and washers with a corrosion preventative compound.

(c) 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, New York Aircraft Certification Office, FAA. Operators shall submit their requests through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, New York Aircraft Certification Office.

NOTE 3: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the New York Aircraft Certification Office.

(d) 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 helicopter to a location where the requirements of this AD can be accomplished.

(e) This amendment becomes effective on February 3, 1999, to all persons except those persons to whom it was made immediately effective by Priority Letter AD 98-26-06, issued December 9, 1998, which contained the requirements of this amendment.

On December 9, 1998, the FAA issued Priority Letter AD 98-26-06, applicable to Schweizer Model 269D helicopters, which requires removing the shaft and inspecting it for cracks. If a crack is found, replacing the shaft with an airworthy shaft is required. That AD also requires periodically verifying the torque of the hub bolts. That action was prompted by four reports of cracking in the shaft of helicopters with a large diameter hub. Wear patterns indicate cracking was caused by loss of clamping torque on the hub and shaft assembly due to the use of grease between the hub and shaft. A pilot reported excessive vibration in one incident. An inspection following that incident revealed a 2.5-inch horizontal crack in the shaft. The crack started from one of the three lower bolt holes, propagated to an adjacent bolt hole, and then propagated from the second bolt hole in a downward direction. This condition, if not corrected, could result in failure ofthe shaft and subsequent loss of control of the helicopter.

Since the unsafe condition described is likely to exist or develop on other Schweizer Model 269D helicopters of the same type design, the FAA issued Priority Letter AD 98-26-06 to prevent failure of the shaft and subsequent loss of control of the helicopter. The AD requires, prior to 200 hours time-in-service (TIS), and thereafter at intervals not to exceed 100 hours TIS, inspecting the shaft for cracks in the area of the six hub attach bolts using a 10-power or higher magnifying glass and bright light. If no crack is found as a result of the visual inspection, the AD requires inspecting the shaft using a magnetic particle inspection method. If a crack is found, the AD requires replacing the shaft with an airworthy shaft. The AD also requires periodically verifying the torque of the hub bolts. The short compliance time involved is required because the previously described critical unsafe condition can adversely affect the controllability of the helicopter. Therefore, the inspections and replacement, if necessary, are required prior to further flight, and this AD must be issued immediately.

Since it was found that immediate corrective action was required, notice and opportunity for prior public comment thereon were impracticable and contrary to the public interest, and good cause existed to make the AD effective immediately by individual letters issued on December 9, 1998, to all known U.S. owners and operators of Schweizer Model 269D helicopters. These conditions still exist, and the AD is hereby published in the Federal Register as an amendment to section 39.13 of the Federal Aviation Regulations (14 CFR 39.13) to make it effective to all persons.

The FAA estimates that 6 helicopters of U.S. registry will be affected by this AD, that it will take approximately 2 work hours for the periodic inspections and 22 work hours to replace the shaft, if necessary, per helicopter, and the average labor rate is $60 per work hour. Required parts will cost approximately $12,000 per replacement shaft. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $80,640 to replace the shafts in all the helicopters, and $7,200 a year for 10 inspections per year on each helicopter.

Comments Invited
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 should 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 No. 98-SW-13-AD." The postcard will be date stamped and returned to the commenter.

The regulations adopted herein will not havesubstantial 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 the preparation of a Federalism Assessment.

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."

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 a new airworthiness directive to read as follows: