Airworthiness Directives; Sikorsky Aircraft-Manufactured Model CH-54B Helicopters

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 97-SW-59-AD; Amendment 39-11235; AD 99-15-14]

RIN 2120-AA64

Airworthiness Directives; Sikorsky Aircraft-Manufactured Model

CH-54B Helicopters

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment adopts a new airworthiness directive (AD),

applicable to Sikorsky Aircraft-manufactured Model CH-54B helicopters,

that requires initial and recurring inspections and rework or

replacement, if necessary, of the second stage lower planetary plate

(plate). This amendment is prompted by two reports of cracked plates

that have been found during overhaul and inspections. The actions

specified by this AD are intended to prevent failure of the main

gearbox plate due to fatigue cracking, which could lead to failure of

the main gearbox and subsequent loss of control of the helicopter.

EFFECTIVE DATE: August 26, 1999.

FOR FURTHER INFORMATION CONTACT: Uday Garadi, Aerospace Engineer, FAA,

Rotorcraft Directorate, Rotorcraft Certification Office, Fort Worth,

Texas 76193-0170, telephone (817) 222-5157, fax (817) 222-5959.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal

Aviation Regulations (14 CFR part 39) to include an airworthiness

directive (AD) that is applicable to Sikorsky Aircraft-manufactured

Model CH-54B helicopters was published in the Federal Register on April

16, 1999 (64 FR 18835). That action proposed to require initial and

recurring inspections, and rework or replacement, if necessary, of the

plate.

Interested persons have been afforded an opportunity to participate

in the making of this amendment. No comments were received on the

proposal or the FAA's determination of the cost to the public. The FAA

has determined that air safety and the public interest require the

adoption of the rule as proposed.

The FAA estimates that 4 helicopters of U.S. registry will be

affected by this AD, that it will take approximately 8 work hours per

helicopter to accomplish the borescope inspection, 1 work hour to

inspect the main gearbox oil filter pack, 140 work hours to remove and

replace the main gearbox assembly, if necessary, and 20 work hours to

rework the plate, and that the average labor rate is $60 per work hour.

Required parts will cost approximately $8,000 per helicopter. Based on

these figures, the total cost impact of the AD on U.S. operators is

estimated to be $67,760; $2,160 to accomplish the initial inspections

and $65,600 to replace the plate in the main gearbox assembly in all 4

helicopters, if necessary. Daily preflight inspections of the main

gearbox oil filter pack will cost $60 per helicopter for each day

flight is conducted.

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.

For the reasons discussed above, I certify that this action (1) is

not a ``significant regulatory action'' under Executive Order 12866;

(2) is not a ``significant rule'' under 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. A final evaluation has been prepared for this action

and it is contained in the Rules Docket. A copy of it may be obtained

from the Rules Docket at the Office of the Regional Counsel, Southwest

Region, 2601 Meacham Blvd., Room 663, Fort Worth, Texas 76137.

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

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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 99-15-14 Blue Bird Helicopters: Amendment 39-11235. Docket No.

97-SW-59-AD.

Applicability: CH-54B helicopters with main gearbox second stage

lower planetary plate (plate), part number (P/N) 6435-20516-101,

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 (c) 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 plate due to fatigue cracking, which

could lead to failure of the main gearbox and subsequent loss of

control of the helicopter, accomplish the following:

(a) For main gearbox assemblies containing plate, part number

(P/N) 6435-20516-101, with 1,600 or more hours time-in-service

(TIS):

Note 2: If the TIS hours of the plate is not known, use the main

gearbox assembly's total operating time.

(1) Prior to the first flight of each day, inspect the main oil

filter for magnesium contamination. If magnesium contamination is

discovered, replace the main gearbox assembly.

(2) Within the next 100 hours TIS after the effective date of

this AD, and thereafter at intervals not to exceed 200 hours TIS,

conduct a borescope inspection of the plate for cracks in the area

of the nine lightening holes (see Figure 1). If a crack is found,

replace the plate with an airworthy plate. The plate, P/N 6435-

20516-101, is part of the main gearbox second stage planetary set

(P/N 6435-20514-041), which is a serialized matched set, and must be

replaced as a set.

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(b) At the next overhaul of the main gearbox assembly, inspect

and rework the plate, P/N 6435-20516-101, as follows:

(1) Fluorescent magnetic particle inspect the plate per ASTM

E1444 in circumferential and longitudinal directions using a wet

continuous method. Pay particular attention to the area around the

nine 1.750-inch diameter lightening holes.

(2) If a crack is found, the plate is unairworthy. Replace it

with an airworthy plate.

(3) If no crack is found, rework the plate as follows, ensuring

that all plate surfaces are free of any crack, scratch, dent, or

corrosion.

(i) Measuring from the center of each 1.750-inch diameter

lightening hole, machine 0.015/0.020 inch from the radius of the

hole (see Figure 2). Machined surface roughness shall not exceed 63

microinches AA rating.

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(ii) Apply a 0.030/0.050-inch radius on the top and bottom edge

of each hole.

(4) Fluorescent magnetic particle inspect the reworked areas per

ASTM E1444 in circumferential and longitudinal directions using a

wet continuous method.

(5) If a crack is found, the plate is unairworthy. Replace it

with an airworthy plate.

(6) If no crack is found, rework the plate as follows:

(i) Remove the protective finish from the specified areas on the

top and bottom of the plate as follows:

(A) Mask the top and bottom of the plate leaving exposed a 3.20-

inch minimum circumferential band centered on 13.75-inch diameter of

plate (see Figure 2). Mask the area to protect the thrust washer and

the surrounding areas from vapor blast.

(B) Using a vapor blast machine, remove the protective finish

from the exposed circumferential band on the top and bottom of the

plate. Use No. 220 aluminum oxide grit at a pressure of 80-90 pounds

per square inch.

(ii) Shot peen the specified areas on the plate by remasking the

top and bottom of the plate leaving exposed the 3.20-inch minimum

circumferential band centered on 13.75-inch diameter of the plate.

Mask the area to protect the thrust washer and the surrounding areas

from the shot peening process.

(iii) Shot peen the inside diameter of the lightening holes and

the upper and lower surfaces of the plate in the 3.20-inch minimum

circumferential band to 0.008 to 0.012A intensity, ensuring 200%

coverage per MIL-S-13165C or latest revision. Use cast steel shot,

size 170. Use a tracer dye inspection method.

Note 3: Overspray is permitted to allow a feathering application

during the peening process from the peened surface to the non-peened

surface.

(iv) Finish the reworked surfaces as follows:

(A) Clean the surfaces thoroughly with acetone (Fed. Spec O-A-

51, or equivalent).

(B) Apply Presto black or blueing touchup solution to the

reworked surfaces with cotton swabs. The solution temperature must

be between 21 deg. C and 49 deg. C (70 deg. F to 120 deg. F). Keep

the surfaces wet for about three minutes to get a uniform dark

color.

(C) Rinse the surface in cold running water and dry with forced

air.

Note 4: A hot water rinse may be used after the cold water rinse

to speed up drying time.

(D) Using steel wool, Grade 00 or finer, rub the surfaces

lightly. Polish with a soft cloth and then coat with a preservative

oil (MIL-C-15074).

(v) Identify the reworked plate by stamping the number of this

AD after the part number. Use a low-stress depth-controlled

impression-stamp with full fillet depth of no more than 0.003 inch

(see Figure 2). Marking must be such that it cannot be construed as

part of the part number.

(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, Rotorcraft Certification Office,

FAA, Rotorcraft Directorate. Operators shall submit their requests

through an FAA Principal Maintenance Inspector, who may concur or

comment and then send it to the Manager, Rotorcraft Certification

Office.

Note 5: Information concerning the existence of approved

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

obtained from the Rotorcraft 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 August 26, 1999.

Issued in Fort Worth, Texas, on July 15, 1999.

Henry A. Armstrong,

Manager, Rotorcraft Directorate, Aircraft Certification Service.

[FR Doc. 99-18683 Filed 7-21-99; 8:45 am]

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