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Disposition Comments

Docket No: 2010-0720 SNPRM

Directorate ID: 2010-SW-050-AD

Originating Office Tracking No.: SP1415B)-R

 NO COMMENTS RECEIVED – If this box is checked, no signatures are required.

No Has the referenced service information been revised since the NPRM was issued? If yes, 

list latest revision and attach a copy. Note that changes beyond the scope of the previously 

published NPRM will require a new notice. Contact the Directorate focal point for guidance.

Instructions: Summarize all comments by issue (not by commenter) and provide your recommended resolution of 

each issue. All comments relating to the same issue should be discussed together. Do not list all of the issues 

from one commenter together. If changes to the AD are required based on the comments received, explain why and 

describe in detail what change(s) you recommend. Reference FAA-IR-M-8040.1C Chapter 9.

ISSUE 1: Select one of the following: service info

If other, explain: 

Commenter(s): Sikorsky

What change to the AD action is requested? Summary Section;The second sentence of this section 

states “This proposal would require revising the airworthiness limitations section of the 

Instructions for Continued Airworthiness (ICA) to reduce the life limit of the main gearbox 

housing and replacing any main gearbox housing that exceeds the life limit.” Sikorsky presents 

the Airworthiness Limitations in Chapter 4 of ICA SA S92A-AWL-000. These limitations are 

expressed in terms of Replacement Intervals. Sikorsky proposes that the term “life limit” be 

replaced with “replacement interval” (2 instances).

Why is the change requested or how is it justified? 

Do we agree? 

If YES, we agree because Make the following changes to the AD: 

If PARTIALLY AGREE, we agree with because We disagree with because

Make the following changes to the AD: 

If NO, we don’t agree because when the main gearbox housing has reached its life limit it has 

reached the end of its useful life. The phase “replacement interval” is not as specific.

ISSUE 2: Select one of the following: service info

If other, explain: 

Commenter(s): Sikorsky

What change to the AD action is requested? Summary Section;Also within the second sentence of 

this section the phrase “replacing any main gearbox” exceeds the scope of this NPRM. While 

the applicability section denotes the specific main gearbox housing part numbers, the invocation 

of the term “any” in the Summary section may invite confusion and should be clarified. 
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Sikorsky proposes that the phrase “... replacing any applicable main gearbox housing...” be 

used instead.

Why is the change requested or how is it justified? 

Do we agree? 

If YES, we agree because Make the following changes to the AD: 

If PARTIALLY AGREE, we agree with because We disagree with because 

Make the following changes to the AD:

If NO, we don’t agree because in the context of the sentence, the word “applicable” does not 

add to the clarification.

ISSUE 3: Select one of the following: Service Info

If other, explain: 

Commenter(s): Sikorsky

What change to the AD action is requested? Summary Section; The third sentence of this section states 

“This proposal is prompted by a fatigue analysis conducted after a helicopter was found with a severed 

main gearbox mounting foot pad (foot pad) that failed due to fatigue”. Crack mode was determined to be 

surface corrosion cracking with fatigue as possible secondary contributor. Sikorsky proposes that this 

sentence should read that the foot pad failed due to corrosion/fatigue.

Why is the change requested or how is it justified? 

Do we agree? 

If YES, we agree because Make the following changes to the AD: 

If PARTIALLY AGREE, we agree with because We disagree with because 

Make the following changes to the AD: 

If NO, we don't agree because the surface corrosion cracking reduced the fatigue life of the main gearbox 

mounting foot pad. The fatigue analysis was performed to determine the life of the foot pad should 

surface corrosion cracking exist.

ISSUE 4: Select one of the following: Service Info

If other, explain: 

Commenter(s): Sikorsky

What change to the AD action is requested? Summary Section; Also within the third sentence of this 

section, the investigation is comprised of many elements and the resultant decrease in replacement 

interval is not attributed exclusively to a fatigue analysis. Accordingly, Sikorsky proposes that the phrase 

“a fatigue analysis” be replaced with “an evaluation”.

Why is the change requested or how is it justified? 
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Do we agree? 

If YES, we agree because Make the following changes to the AD: 

If PARTIALLY AGREE, we agree with because We disagree with because 

Make the following changes to the AD: 

If NO, we don't agree because although many elements are part of the investigation, the fatigue analysis is 

the primary source for determining the residual life of the part.

ISSUE 5: Select one of the following: Service Info

If other, explain: 

Commenter(s): Sikorsky

What change to the AD action is requested? Discussion Section; The second sentence of this 

section cites two instances of “life limit”. For the reason described in issue 1 above, Sikorsky proposes 

that these two entries should be replaced with “replacement interval”.

Why is the change requested or how is it justified? 

Do we agree? 

If YES, we agree because Make the following changes to the AD: 

If PARTIALLY AGREE, we agree with because We disagree with because 

Make the following changes to the AD: 

If NO, we don't agree because when the main gearbox housing has reached its life limit it has reached the 

end of its useful life. The phase “replacement interval” is not as specific. 

ISSUE 6: Select one of the following: Service Info

If other, explain: 

Commenter(s): Sikorsky

What change to the AD action is requested? Discussion Section; Also within the second sentence 

of this section, Sikorsky proposes that the phrase “... replace any main gearbox housing... ” should read 

“... replace any applicable main gearbox housing...”, for the reason specified in issue 2 above.

Why is the change requested or how is it justified? 

Do we agree? 

If YES, we agree because Make the following changes to the AD: 

If PARTIALLY AGREE, we agree with because We disagree with because 

Make the following changes to the AD: 

If NO, we don't agree because in the context of the sentence, the word “applicable” does not add to the 

clarification.

ISSUE 7: Select one of the following: Service Info
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If other, explain: 

Commenter(s): Sikorsky

What change to the AD action is requested? Discussion Section; The third sentence of this section 

iterates that this “proposal is prompted by a review of a fatigue analysis conducted after a helicopter was 

found with a severed foot pad due to the effect of fatigue of the main gearbox housing.” For the reason 

cited in issue 3 above, Sikorsky proposes that this sentence should read that the foot pad failed due to 

corrosion/fatigue.

Why is the change requested or how is it justified? 

Do we agree? 

If YES, we agree because Make the following changes to the AD: 

If PARTIALLY AGREE, we agree with because We disagree with because 

Make the following changes to the AD: 

If NO, we don't agree because the surface corrosion cracking reduced the fatigue life of the main gearbox 

mounting foot pad. The fatigue analysis was performed to determine the life of the foot pad should 

surface corrosion cracking exist.

ISSUE 8: Select one of the following: Service Info

If other, explain: 

Commenter(s): Sikorsky

What change to the AD action is requested? Discussion Section; Also within the third sentence of this 

section, and for the reason cited in issue 4 above, Sikorsky proposes that the phrase “a fatigue analysis” 

be replaced with “an evaluation”. 

Why is the change requested or how is it justified? 

Do we agree? 

If YES, we agree because Make the following changes to the AD: 

If PARTIALLY AGREE, we agree with because We disagree with because 

Make the following changes to the AD: 

If NO, we don't agree because although many elements are part of the investigation, the fatigue analysis is 

the primary source for determining the residual life of the part.

ISSUE 9: Select one of the following: Service Info

If other, explain: 

Commenter(s): Sikorsky

What change to the AD action is requested? Discussion Section; The second sentence of the second 

paragraph of this section proposes, within 60 days, revising the airworthiness limitations section of the 

ICA “to reduce the life limit of the main gearbox of the main gearbox housing from 2700 hours TIS to 
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1000 hours TIS and replacing, before further flight, any main gearbox housing that has exceeded the 

1000-hour TIS life limit”. For the reason described in issue 1 above, Sikorsky proposes that these two 

entries should be replaced with “replacement interval”.

Why is the change requested or how is it justified? 

Do we agree? 

If YES, we agree because Make the following changes to the AD: 

If PARTIALLY AGREE, we agree with because We disagree with because 

Make the following changes to the AD: 

If NO, we don't agree because when the main gearbox housing has reached its life limit it has reached the 

end of its useful life. The phase “replacement interval” is not as specific. 

ISSUE 10: Select one of the following: Service Info

If other, explain: 

Commenter(s): Sikorsky

What change to the AD action is requested? Compliance Section; Compliance item (a) specifies 

reducing the life limit of the affected main gearbox housing. For the reason described in issue 1 above, 

Sikorsky proposes that the term “life limit” be replaced with “replacement interval”.

Why is the change requested or how is it justified? 

Do we agree? 

If YES, we agree because Make the following changes to the AD: 

If PARTIALLY AGREE, we agree with because We disagree with because 

Make the following changes to the AD: 

If NO, we don't agree because when the main gearbox housing has reached its life limit it has reached the 

end of its useful life. The phase “replacement interval” is not as specific. 

For additional issues, double-click here
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Signature Section

Signature indicates concurrence with this action.

Originating Office Tracking No.: ANE-150

ASE Date

Branch Manager Date