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###### Department of Transportation

###### Federal Aviation Administration 

          - 14 CFR Part 39 
          - [Docket No. 2001-SW-39-AD] 
          - RIN 2120-AA64 

# AGENCY:

Federal Aviation Administration, DOT. 

# ACTION:

Notice of proposed rulemaking (NPRM). 

# SUMMARY:

This document proposes superseding an existing airworthiness directive (AD) for MD Helicopters Inc. Model MD-900 helicopters. That AD currently requires inspecting the main rotor upper hub assembly drive plate attachment flange (flange), determining the torque of each flange nut (nut), and if a crack is found, before further flight, replacing the hub assembly. In addition to the current requirements, this action would require visually inspecting the outer surface of the flange at specified intervals and removing the drive plate and visually inspecting the flange for a crack at specified intervals and replacing any unairworthy hub assembly. This proposal is prompted by reports that cracks starting at the drive plate attachment holes were found in the main rotor hub. The actions specified by the proposed AD are intended to detect a crack in the flange and to prevent failure of the hub assembly, loss of drive to the main rotor, and subsequent loss of control of the helicopter. 

# DATES:

Comments must be received on or before February 15, 2002. 

# ADDRESSES:

                        Submit comments in triplicate to the Federal Aviation Administration (FAA), Office of the Regional Counsel, Southwest Region, Attention: Rules Docket No. 2001-SW-39-AD, 2601 Meacham Blvd., Room 663, Fort Worth, Texas 76137. You may also send comments electronically to the Rules Docket at the following address:                         *9-asw-adcomments@faa.gov*. Comments may be inspected at the Office of the Regional Counsel between 9 a.m. and 3 p.m., Monday through Friday, except Federal holidays.                     

# FOR FURTHER INFORMATION CONTACT:

Jon Mowery, Aviation Safety Engineer, FAA, Los Angeles Aircraft Certification Office, Airframe Branch, 3960 Paramount Blvd., Lakewood, California 90712, telephone (562) 627-5322, fax (562) 627-5210. 

# SUPPLEMENTARY INFORMATION:

## Comments Invited 

Interested persons are invited to participate in the making of the proposed 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 above. All communications received on or before the closing date for comments, will be considered before taking action on the proposed rule. The proposals contained in this document may be changed in light of the comments received. 

Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the proposed 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 summarizing each FAA-public contact concerned with the substance of this proposal will be filed in the Rules Docket. 

Commenters wishing the FAA to acknowledge receipt of their mailed comments submitted in response to this proposal must submit a self-addressed, stamped postcard on which the following statement is made: “Comments to Docket No. 2001-SW-39-AD.” The postcard will be date stamped and returned to the commenter. 

## Availability of NPRMs 

Any person may obtain a copy of this NPRM by submitting a request to the FAA, Office of the Regional Counsel, Southwest Region, Attention: Rules Docket No. 2001-SW-39-AD, 2601 Meacham Blvd., Room 663, Fort Worth, Texas 76137. 

## Discussion 

On December 17, 1999, the FAA issued Emergency AD 99-26-20 to require certain inspections of the hub assembly for a crack, ensuring the correct torque of each nut, and replacing any cracked hub assembly with an airworthy hub assembly. That action was prompted by three occurrences of cracked hub assemblies. The FAA discovered errors after issuing Emergency AD 99-26-20 and corrected those errors by superseding that Emergency AD with AD 2001-07-09, Amendment 39-12175 (66 FR 19383, April 16, 2001). The requirements of that AD were intended to prevent failure of the hub assembly, loss of drive to the main rotor, and subsequent loss of control of the helicopter. 

Since the issuance of that AD, the FAA has received reports indicating that additional cracks have been found in the main rotor hub emanating from the drive plate attachment holes. 

This unsafe condition is likely to exist or develop on other MD Helicopters Inc. Model MD-900 helicopters of the same type design. Therefore, the proposed AD would supersede AD 2001-07-09 to contain the current requirements and to also require the following: 
    - Visually inspect the outer surface of the flange using a light and a 10x or higher magnifying glass at intervals not to exceed 100 hours TIS.
    - Remove the drive plate and visually inspect the flange for a crack at intervals not to exceed 300 hours TIS.
    - Replace any unairworthy hub assembly before further flight.

                    The FAA estimates 28 helicopters of U.S. registry would be affected by this proposed AD. It would take approximately 1 work hour per helicopter to verify the torque, 3 work hours per helicopter to perform the inspection, and 10 work hours per helicopter to replace the hub assembly,                           ( print page 64932)                        if necessary. The proposed actions would require approximately 1 work hour for a 100-hour TIS inspection, and 3 work hours for a 300-hour TIS inspection, at an average labor rate of $60 per work hour. Required parts to replace the hub assembly, if necessary, would cost approximately $21,610 per helicopter. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $159,770 for the first year, assuming 5 hub assembly replacements and assuming each helicopter has 6 torque verifications, 6 inspections, two 100-hour inspections, and one 300-hour inspection.                 

The regulations proposed herein would 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 proposal would not have federalism implications under Executive Order 13132. 

                    For the reasons discussed above, I certify that this proposed 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) if promulgated, 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 copy of the draft regulatory evaluation prepared for this action is contained in the Rules Docket. A copy of it may be obtained by contacting 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

## The Proposed Amendment 

Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration proposes to amend 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 

2. Section 39.13 is amended by removing Amendment 39-12175 (66 FR 19383, April 16, 2001), and by adding a new airworthiness directive (AD), to read as follows: 

**MD Helicopters, Inc.:**                                 Docket No. 2001-SW-39-AD. Supersedes AD 2001-07-09, Amendment 39-12175, Docket No. 2000-SW-15-AD.                             

*Applicability:*                                 Model MD-900 helicopters, with main rotor upper hub (hub) assembly, part number (P/N) 900R2101006-105 or 900R2101006-107, 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 otherwise 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 request approval for an alternative method of compliance in accordance with paragraph (e) 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 failure of the hub assembly, loss of drive to the main rotor, and subsequent loss of control of the helicopter, accomplish the following: 

(a) For the hub assembly, P/N 900R2101006-107, 

(1) Within 6 hours time-in-service (TIS), visually inspect the main rotor upper hub assembly drive plate attach flange (flange) for a crack and determine the torque of each flange attach nut (nut) in accordance with the Accomplishment Instructions, Part I, paragraph 2.A., steps (1) through (7) of MD Helicopter Inc. Service Bulletin SB 900-072, dated December 10, 1999 (SB). If a crack is found, before further flight, remove and replace the hub assembly with an airworthy hub assembly. 

(2) Within 25 hours TIS, accomplish Part II, of the Accomplishment Instructions, paragraph 2.B., steps (1) through (6), (8), and (9) of the SB. If a crack is found, before further flight, remove and replace the hub assembly with an airworthy hub assembly. 

(b) For the hub assembly, P/N 900R2101006-105, 

(1) Within 6 hours TIS, visually inspect the flange for a crack and determine the torque of each nut in accordance with the Accomplishment Instructions, Part I, paragraph 2.A., steps (1) through (7) of the SB. 

# Note 2:

The SB effectivity does not include hub assembly, P/N 900R2101006-105; however, certain provisions of this AD do apply to this P/N.

(2) If any nut has less than 180 inch pounds (20.34 Nm) of torque, before further flight, remove the drive plate and fretting buffer and inspect the flange in accordance with the procedures in paragraph (b)(3) of this AD. If a crack is detected, before further flight, remove and replace the hub assembly with an airworthy hub assembly. Reassemble in accordance with the procedures in paragraph (b)(3) of this AD. 

(3) Within 25 hours TIS, remove the main rotor drive plate assembly and anti-fretting ring and visually inspect the main rotor hub assembly as follows: 

(i) If present, remove sealant from the drive plate attachment to the hub assembly. 

(ii) Mark the main rotor hub holes to correspond with the drive plate hole numbers (see Figure 1 of this AD). 

(iii) Remove the main rotor drive plate (drive plate) assembly and anti-fretting ring (fretting buffer). 

(iv) Inspect drive plate to rotor hub assembly mating surfaces and the fretting buffer for fretting. 

(v) Using paint stripper (Consumable Item List C313 or equivalent) and cleaning solvent (C420 or equivalent), remove the paint from the upper mating surface of the hub assembly to enable an accurate visual inspection of each drive plate attachment bolt hole (bolt hole) area for cracking (Figure 1). Ensure the paint stripper and solvent DO NOT contaminate the upper bearing and upper grease seal areas. 

(vi) Using a 10 × or higher magnifying glass and light, inspect the mating surface area and the area around and inside the 10 boltholes of the hub assembly for a crack. If a crack is found, prior to further flight, replace the hub assembly with an airworthy hub assembly. 

(vii) If no crack is found, remove fretting debris from the mating surfaces of the hub assembly and the drive plate assembly, reassemble, fillet seal (C211 or equivalent) the surface of the drive plate to fretting buffer to hub assembly mating lines, and seal all exposed unpainted upper surfaces of the hub assembly. 

(viii) Reinstall the main rotor drive plate using 10 new sets of replacement attachment hardware. Torque the nuts to 160 inch pounds above locknut locking/run-on torque in the sequence shown (Figure 1). Record in the rotorcraft logbook, or equivalent record, the locknut locking/run-on torque for each nut. 

(ix) After the next flight, verify that the torque on each of the 10 nuts is at least 160 inch pounds above the locknut locking/run-on torque (minimum torque). Retorque as required without loosening nuts. 

(x) Thereafter, at intervals of at least 4 hours TIS, not to exceed 6 hours TIS, verify that the torque of each of the 10 nuts is at least the minimum torque. Retorque as required without loosening nuts. This torque verification is no longer required after the torque on each of the 10 nuts has stabilized at a torque value of 160 or more inch pounds for each nut during two successive torque verifications. 
      ( print page 64933)    
(c) Within 100 hours TIS and thereafter at intervals not to exceed 100 hours TIS, visually inspect the outer surface of the flange for a crack using a light and a 10 × or higher magnifying glass. If a crack is detected, replace the unairworthy hub assembly with an airworthy hub assembly before further flight. 

(d) At intervals not to exceed 300 hours TIS, remove the drive plate and visually inspect the flange for a crack using a light and a 10 × or higher magnifying glass. If a crack is detected, replace the unairworthy hub assembly with an airworthy hub assembly before further flight. 

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

# Note 3:

Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the LAACO.

                                (f) If any nut torque is below minimum torque and no hub assembly crack is found before disassembly inspection, after retorque                                       ( print page 64934)                                    in accordance with the applicable Maintenance Manual, a special flight permit for one flight below 100 knots indicated airspeed may be issued in accordance with 14 CFR 21.197 and 21.199 to operate the helicopter to a location where the requirements of this AD can be accomplished.                            

Issued in Fort Worth, Texas, on December 11, 2001. 

David A. Downey, 

Manager, Rotorcraft Directorate, Aircraft Certification Service. 

BILLING CODE 4910-13-P

BILLING CODE 4913-10-C

[FR Doc. 01-31042 Filed 12-14-01; 8:45 am]