Airworthiness Directives; Robinson Helicopter Company Model R22 Helicopters

DEPARTMENT OF TRANSPORTATION

14 CFR Part 39

[Docket No. 94-SW-27-AD; Amendment 39-9276; AD 95-06-03]

Airworthiness Directives; Robinson Helicopter Company Model R22

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) 95-06-03 which was sent

previously to all known U.S. owners and operators of Robinson

Helicopter Company (Robinson) Model R22 helicopters by individual

letters. This AD requires an inspection and modification of the main

rotor (M/R) gearbox. This amendment is prompted by a report of an

incident involving a Model R22 helicopter in which the two M/R mast

spanner nuts (nuts) became loose, resulting in failure of the M/R mast

support structure. The actions specified by this AD are intended to

prevent M/R separation and subsequent loss of control of the

helicopter.

DATES: Effective on June 29, 1995, to all persons except those persons

to whom it was made immediately effective by priority letter AD 95-06-

03, issued on March 8, 1995, which contained the requirements of this

amendment.

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

before August 14, 1995.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

Administration (FAA), Office of the Assistant Chief Counsel, Attention:

Rules Docket No. 94-SW-27-AD, 2601 Meacham Blvd., Room 663, Fort Worth,

Texas 76137.

FOR FURTHER INFORMATION CONTACT: Ms. Elizabeth Bumann, Aerospace

Engineer, FAA, Los Angeles Aircraft Certification Office, 3960

Paramount Blvd., Lakewood, California 90712, telephone (310) 627-5265,

fax (310) 627-5210.

SUPPLEMENTARY INFORMATION: On March 8, 1995, the FAA issued priority

letter AD 95-06-03, applicable to Robinson R22 helicopters, which

requires, within 25 hours time-in-service (TIS) after the effective

date of this AD, removal and disassembly of the M/R gearbox;

measurement of the break-loose torque value of the upper spanner nut;

replacement of the lock washers; increasing the torque values of the

two spanner nuts; reassembly and reinstallation of the M/R gearbox; and

verification of the M/R balance in accordance with the applicable

maintenance manual. That action was prompted by an incident reported by

the Civil Aviation Authority (CAA) of New Zealand involving failure of

the main rotor (M/R) mast support structure. An investigation revealed

that the two M/R mast spanner nuts (nuts) became loose and allowed the

M/R shaft to pull through the retention bearing in the

M/R gearbox. As the loads transferred from the M/R gearbox bearing to

the top of the mast, the rivets that attach the mast bearing outer

housing to the M/R shaft sheared, resulting in failure of the M/R mast

support structure.

Prior to June 15, 1992, the M/R gearbox assembly, P/N A006-1

Revisions A through Z, may have been assembled with paint on the

clamping surface of the M/R shaft, preventing a good clamping surface

for the nuts. Two earlier incidents in Australia prompted the

Commonwealth of Australia CAA to issue CAA AD/R22/35, dated September

1992, to inspect the nuts for looseness and increase the nut torque

values. The FAA did not issue an AD at that time due to inconclusive

information from the two isolated incidents. The compliance procedure

of this AD differs from CAA AD/R22/35 by requiring replacement of the

lock washer, part number (P/N) A269-1, located between the mast bearing

and the upper nut, with a different lock washer, P/N A269-2. The torque

values on both nuts have also been increased. The FAA has determined

that under-torqued nuts may become loose and create an unsafe

condition. Due to the criticality of ensuring that the nuts are

properly torqued, this AD is being issued immediately to correct an

unsafe condition. That condition, if not corrected, could result in M/R

separation and subsequent loss of control of the helicopter.

Since the unsafe condition described is likely to exist or develop

on other Robinson Model R22 helicopters of the same type design, the

FAA issued priority letter AD 95-06-03 to prevent M/R separation and

subsequent loss of control of the helicopter. The AD requires, within

25 hours time-in-service (TIS), removal and disassembly of the M/R

gearbox; measurement of the break-loose torque value of the upper

spanner nut; replacement of the lock washers; increasing the torque

values of the two spanner nuts; reassembly and reinstallation of the M/

R gearbox; and verification of the M/R balance in accordance with the

applicable maintenance manual.

Since the issuance of that AD, the FAA has received information

that Robinson Helicopter Company may not

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be providing to all individuals the MT-124 tool required to remove and

install the nuts. The relevant AD Note has been revised to state that

individuals may request an alternative method of compliance to use a

different nut socket in lieu of the MT-124 tool. Also, Note 1 has been

added to the AD clarifying the applicability to helicopters that have

been modified, altered, or repaired in the area subject to the

requirements of this AD. The addition of this note changed the

numbering of the subsequent notes. Paragraph (a) of the AD has also

been changed to allow use of an unserviceable M/R hub bolt or \5/8\-

inch diameter bolt to counteract torque when removing the nuts.

Finally, nomenclature and part numbers have been added throughout the

AD for clarification. The FAA has determined that these minor changes

will neither change the meaning or scope of the AD nor increase any

burden on any operator.

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 March 8, 1995, to all known U.S. owners and operators of

Robinson Model R22 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.

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. 94-SW-27-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. App. 1354(a), 1421 and 1423; 49 U.S.C.

106(g); and 14 CFR 11.89.

Sec. 39.13 [Amended]

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

to read as follows:

95-06-03 Robinson Helicopter Company:

Amendment 39-9276. Docket No. 94-SW-27-AD.

Applicability: Model R22 helicopters with main rotor gearbox

(gearbox), part number (P/N) A006-1, Revisions A through Z,

manufactured or overhauled prior to June 15, 1992, 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 (b) 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.

Note 2: The revision level (revision letter) of the gearbox can

be found on the data plate next to the sight glass.

Compliance: Required as indicated, unless accomplished

previously. To prevent main rotor (M/R) separation and subsequent

loss of control of the helicopter, accomplish the following:

(a) Within 25 hours time-in-service after the effective date of

this AD, inspect and modify the gearbox in accordance with the

following:

(1) Remove the gearbox in accordance with the applicable

maintenance manual.

(2) Drain the gearbox by removing the chip detector housing.

(3) Perform the following inspection and torquing of the shaft

retaining nuts.

Note 3: A special tool, a spanner nut socket, P/N MT124-1, may

be obtained from Robinson Helicopter Company. If that tool is not

available, individuals may propose using a different nut socket in

accordance with paragraph (b) of this AD.

(i) Lay the gearbox on its side using care to prevent damage to

the slider tube. Remove the eight NAS1291-4 nuts and two MS20074-04-

10 hex head cap screws holding the sump in place.

(ii) Gently remove the sump and discard the O-ring, using care

to keep all washer-shims on their respective bolts. With the bolts

still attached to the sump, replace the sump nuts on the bolts to

retain the washer-shims (the washer-shim stack is the same at each

location). Hand-tighten the nuts.

(iii) Bend back the two lock washer tabs locking the lower nut,

P/N A153-1. Insert an

[[Page 31238]]

unserviceable M/R hub bolt or a \5/8\-inch diameter bolt through the

teeter hinge bolt hole in the M/R shaft to counteract torque. Clamp

the unserviceable M/R hub bolt or the \5/8\-inch diameter bolt in a

vise or otherwise fasten it to a workbench. Do not clamp the M/R

shaft. Remove the lower nut from the

M/R shaft using a socket, P/N MT124-1, or an FAA-approved equivalent

tool. Remove and discard the lower lock washer, P/N A269-1.

(iv) Bend back the two lock washer tabs locking the upper nut,

P/N A153-1. Remove the upper nut, measuring the torque required to

break the nut loose. Remove and discard the upper lock washer, P/N

A269-1.

(v) If the upper nut required more than 10 ft.-lb. torque to

break loose, proceed to paragraph (a)(3)(vi). If the upper nut

required 10 ft.-lb. torque or less to break loose, report within 5

days the M/R gearbox P/N and break-loose torque value to the

Propulsion Manager, Los Angeles Aircraft Certification Office, 3960

Paramount Blvd., Lakewood, California 90712. Reporting requirements

have been approved by the Office of Management and Budget and

assigned OMB control number 2120-0056. Remove the gear carrier from

the M/R shaft. Inspect the splines and clamping surfaces on both the

shaft and gear carrier for pitting, galling, or scoring of surfaces.

Replace any unairworthy parts. If the inspection revealed no

pitting, galling, or scoring of surfaces, remove any paint from the

clamping surface on the shaft using either paint remover or a

plastic or wooden scraper, and ensure the surface is smooth and

clean. Reassemble the gear carrier to the shaft.

(vi) Inspect the two dowels or roll pins in the gear carrier for

damaged surfaces. Dowels or roll pins must protrude 0.045 to 0.055

inches for proper engagement with the lock washer, P/N A269-2. Also

clean the nuts, M/R shaft threads, and sump, using methyl-ethyl-

ketone (MEK) or Trichlorethane (1,1,1, TCE) before reassembly.

(vii) Install a lock washer, P/N A269-2. Apply anti-seize

(Loctite Anti-seize 767), P/N A257-9, to the M/R shaft threads and

to the chamfered-side face and threads of one nut and install the

nut with the chamfered side against the lock washer. Verify that the

dowels or roll pins are aligned with the holes in the lock washer.

Torque the nut to between 170 and 200 ft.-lb., as required to align

two lock washer tabs (tabs) with the nut. Do not untorque the nut to

align the lock washer tabs with the nut. For the two tabs that are

aligned with the recessed areas, bend down the tabs into the

recessed areas of the nut and inspect the edges of the bent tabs for

cracks.

(viii) Before installing the lock washer,

P/N A269-1, note that the edges are sharp on one side and rounded on

the other. De-burr the sharp edges on two opposite tabs (see figure

1). This will reduce the chance of cracking when these tabs are bent

up. Install the lock washer with the rounded edges toward the

installed nut.

(ix) Apply anti-seize, P/N A257-9, to the chamfered-side face

and threads of the lower nut. Align the two de-burred tabs with the

upper nut and install the lower nut with the chamfered side against

the lock washer. Hand-tighten the nut to hold the washer in place.

Bend the two de-burred tabs up to lock with the upper nut. Torque

the lower nut to between 90 and 120 ft.-lb., as required to align

the two additional tabs. Do not untorque the nut to align the lock

washer tabs with the nut. For the two tabs that are aligned with the

recessed areas, bend down the tabs into the recessed areas of the

nut to lock the lower nut.

(x) Verify that all six bent tabs properly engage the nuts (four

tabs to the upper nut and two to the lower nut), and inspect the

edges of the bent tabs for cracks. Replace any cracked lock washers.

Remove excess anti-seize compound.

(xi) Lubricate the O-ring, P/N A215-271, with oil, P/N A257-2,

and install the O-ring on the sump. Clean and inspect the sealing

surface of the gearbox housing for smoothness. Lightly lubricate the

sealing surface with oil, P/N A257-2.

(xii) Reinstall the sump onto the gearbox housing using the same

washer-shim stacks that were removed in accordance with paragraph

(a)(3)(ii) of this AD. Torque the sump bolts and chip detector as

follows:

(A) For the eight NAS1291-4 nuts on the AN4 bolts for the sump:

90 in.-lb. of torque (includes nut self-locking torque);

(B) For the two cap screws, P/N MS20074: 60 in.-lb. of torque

and install safety wire;

(C) For the chip detector, P/N A7260, (large nut): 150 in.-lb.

of torque and install safety wire;

(D) For the chip detector, P/N A7260, (small nut): 75 in.-lb. of

torque and install safety wire.

Note 4: Be sure to install ground wires under the nut located

aft of the forward right-hand mount.

(4) Reinstall the gearbox in accordance with the applicable

maintenance manual.

(5) Fill the gearbox with oil, P/N A257-2, to the middle of the

sight glass.

(6) Verify the M/R balance in accordance with the applicable

maintenance manual.

(b) An alternative method of compliance or adjustment of the

compliance time that provides an acceptable level of safety may be

used when 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 5: 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.

(c) 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.

(d) This amendment becomes effective on June 29, 1995, to all

persons except those persons to whom it was made immediately

effective by Priority Letter AD 95-06-03, issued March 8, 1995,

which contained the requirements of this amendment.

BILLING CODE 4910-13-P

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[GRAPHIC][TIFF OMITTED]TR14JN95.000

BILLING CODE 4910-13-C

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Issued in Fort Worth, Texas, on June 7, 1995.

Mark R. Schilling,

Acting Manager, Rotorcraft Directorate, Aircraft Certification Service.

[FR Doc. 95-14445 Filed 6-13-95; 8:45 am]

BILLING CODE 4910-13-P