Airworthiness Directives; McDonnell Douglas Helicopter Systems Model MD-900 Helicopters

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-SW-24-AD; Amendment 39-10989; AD 98-12-30]

RIN 2120-AA64

Airworthiness Directives; McDonnell Douglas Helicopter Systems

Model MD-900 Helicopters

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule; request for comments.

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SUMMARY: This document publishes in the Federal Register an amendment

adopting Airworthiness Directive (AD) 98-12-30 which was sent

previously to all known U.S. owners and operators of McDonnell Douglas

Helicopter Systems (MDHS) Model MD-900 helicopters by individual

letters. This AD requires inspecting the main rotor upper hub assembly

(hub assembly) for cracks, and if a crack is found, replacing the hub

assembly. The AD also requires verifying attachment nut torque values

and a repetitive inspection at intervals not to exceed 150 hours time-

in-service. This amendment is prompted by the discovery of cracks in 6

main rotor upper hub assemblies. This condition, if not corrected,

could result in failure of the hub assembly, loss of drive to the main

rotor, and subsequent loss of control of the helicopter.

DATES: Effective February 3, 1999, to all persons except those persons

to whom it was made immediately effective by priority letter AD 98-12-

30, issued on June 4, 1998, which contained the requirements of this

amendment.

Comments for inclusion in the Rules Docket must be received on or

before March 22, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

Administration (FAA), Office of the Regional Counsel, Southwest Region,

Attention: Rules Docket No. 98-SW-24-AD, 2601 Meacham Blvd., Room 663,

Fort Worth, Texas 76137.

FOR FURTHER INFORMATION CONTACT: Greg DiLibero, Aerospace Engineer,

FAA, Los Angeles Aircraft Certification Office, 3960 Paramount Blvd.,

Lakewood, California 90712, telephone (562) 627-5231, fax (562) 627-

5210.

SUPPLEMENTARY INFORMATION: On June 4, 1998, the FAA issued priority

letter AD 98-12-30, applicable to MDHS Model MD-900 helicopters, which

requires inspecting the hub assembly, part number 900R2101006-101 or -

103, for cracks, and if a crack is found, replacing the hub assembly.

The AD also requires verifying attachment nut torque values and a

repetitive inspection at intervals not to exceed 150 hours time-in-

service. That action was prompted by the discovery of cracks in 6 hub

assemblies. This condition, if not corrected, could result in failure

of the hub assembly, loss of drive to the main rotor, and subsequent

loss of control of the helicopter.

Since the unsafe condition described is likely to exist or develop

on other MDHS Model MD-900 helicopters of the same type design, the FAA

issued priority letter AD 98-12-30 to prevent failure of the hub

assembly, loss of drive to the main rotor, and subsequent loss of

control of the helicopter. The AD requires inspecting the hub assembly,

part number 900R2101006-101 or -103, for cracks, and if a crack is

found, replacing the hub assembly. The AD

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also requires verifying attachment nut torque values and a repetitive

inspection at intervals not to exceed 150 hours time-in-service. Due to

the criticality of the hub assembly, the short compliance time is

required. The previously described unsafe condition can adversely

affect the controllability of the helicopter 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 June 4, 1998 to all known U.S. owners and operators of MDHS

Model MD-900 helicopters. These conditions still exist, and the AD is

hereby published in the Federal Register as an amendment to Sec. 39.13

of the Federal Aviation Regulations (14 CFR 39.13) to make it effective

to all persons.

The FAA estimates that 26 helicopters of U.S. registry will be

affected by this AD, that it will take approximately 14 work hours per

helicopter to accomplish the required actions, and that the average

labor rate is $60 per work hour. Required parts will 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 $583,700 to accomplish

the required actions and replace the hub assemblies on all the fleet,

if necessary.

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-24-AD.'' The postcard will be date stamped and

returned to the commenter.

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 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.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by adding a new airworthiness directive

to read as follows:

AD 98-12-30 McDonnell Douglas Helicopter Systems: Amendment 39-

10989. Docket No. 98-SW-24-AD.

Applicability: Model MD-900 helicopters, with main rotor upper

hub assembly (hub assembly), part number (P/N) 900R2101006-101 or -

103, 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 (f) 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 include an 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 hub assembly, loss of drive to the

main rotor assembly, and subsequent loss of control of the

helicopter, accomplish the following:

(a) For a hub assembly that has accumulated 300 or more hours

time-in-service (TIS), accomplish the inspection procedures in

paragraph (b) of this AD before further flight. For a hub assembly

that has accumulated less than 300 hours TIS, accomplish the

inspection procedures in paragraph (b) of this AD within the next 25

hours TIS.

(b) Inspect and reassemble the hub assembly as follows:

(1) If present, remove sealant from the drive plate attachment

to the main rotor assembly.

(2) Using an indelible marker, number the main rotor drive plate

attachment fastener torque sequence on the drive plate (Figure 1).

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(3) Remove the main rotor drive plate assembly (drive plate

assembly) and fretting buffer. Discard the 10 bolts and nuts and 20

washers.

(4) Using paint stripper (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 the 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.

(5) Using a 10-power or higher magnifying glass, inspect the

area around the 10 bolt holes of the hub assembly for cracks. If a

crack is found, replace the hub assembly with an airworthy hub

assembly.

(6) Remove any fretting from the mating surfaces of the hub

assembly and the drive plate assembly.

Note 2: Boeing McDonnell Douglas Helicopter Systems Service

Letter SL900-039, dated May 20, 1998, pertains to the subject of

this AD.

(7) Reinstall the main rotor drive plate using 10 new sets of

replacement attachment hardware. Torque the nuts to 160-180 in.-lbs.

above locknut locking/run-on torque in the sequence shown (Figure

1). Record in the rotorcraft log book the locknut locking/run-on

torque for each nut.

(c) After the next flight, verify that the torque on each of the

10 nuts is at least 160 in.-lbs. above the locknut locking/run-on

torque (minimum torque). Re-torque as required without loosening

nuts. Fillet surface seal main rotor drive plate to fretting buffer

to hub assembly mating lines, and seal all exposed unpainted upper

surfaces of the hub assembly.

(d) 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. Re-torque as required without loosening

nuts. This torque verification is no longer required after the

torque on each of the 10 nuts has stabilized at the minimum torque

for each nut during two successive torque verifications.

(e) Repeat the requirements specified in this AD at intervals

not to exceed 150 hours TIS.

Note 3: Rotorcraft Maintenance Manual, CSP-900RMM-2, Section 62-

20-00 and 63-10-00, pertain to the subject of this AD.

(f) 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, FAA. Operators shall submit their requests through an FAA

Principal Maintenance Inspector, who may concur or comment and then

send it to the Manager, Los Angeles Aircraft Certification Office.

Note 4: Information concerning the existence of approved

alternative methods of compliance with this AD, if any, may be

obtained from the Los Angeles Aircraft Certification Office.

(g) 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.

(h) 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 98-12-30, issued June 4, 1998, which

contained the requirements of this amendment.

Issued in Fort Worth, Texas, on January 4, 1999.

Henry A. Armstrong,

Manager, Rotorcraft Directorate, Aircraft Certification Service.

[FR Doc. 99-683 Filed 1-15-99; 8:45 am]

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