09/06/2011 23:35 7149981365 HD NEUBERT PAGE 01 

H.O.NEUBERT & ASSOCIATES, INC. 

:;j:,iT?€NTOF' 

ADVANCED COMPOSITE APPUCATIONS ^'- ' ^^O^rfAT'O'^ 

MATEfllALS, DESIGN fiSTI^UCTURAL ANALYSIS. ^ ^ ' - ' ^•' '^' ' "•• ' "' 

PftOTOTVPE FABRICATION DEVELOPMENT. 

CdMPOStre ANALYSIS SOFTWARE ., , .. ^ ^ 

7 August 2011 

U.S. Department of Transportation 

Docket Operations, M-30> West Building Ground Floor, Room W12-140 

1200 New Jersey Avenue SE 

Washingtoh, DC 20950 

Re: Docl<etlvio. FAA-20il-0639, Directorate Identifier 2011-CE-016-AD 

This Submission is one part of two parts furnished by the International 

Comanche Society (ICiS) in response to the NPRM. 

ICS has 5 Technical Directors to support membership questions and 

concerns about the maintenance of thejr airplanes. In addition, there is a 

Fleet Airworthiness Corhmlttee, of which there are two Co-chairmen. The 

undersigned is one of the two co-chairmen. 

At my suggestion, the response to the NPRM would be in two parts. Part 1 

would be Organized byDave Fitzgerald, the other co-chairmen, using 4 of 

the Technical Directors, focusing on practical aspects of Comanche 

maintenance and the effects of the proposed AD, and Part 2 focusing on the 

more technical aspects. 

Please find Attachment A to this letter for the submitted comments. 

Hans D. Neubert 

DERT 605393-NI 

Fieet Airworthiness Committee Co-Chairmah 

6051 PRAPO STREET^ ANAHEIM HILLS, CA 92607 RES: (714) 9a8'Z504 

OPFICE: (714) 996-1365 
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Attachmen t A 

Comments to Docket No. FAA-2011-0639r Directorate 

Identifier 2011-CE-016-AD 

Comment 1 : ICS agrees with the need for a one time inspection of the 

stabilator horn, torque tube, bearings and mounting hardware. There is a 

high probability that the AN175 bolts holding the horn to the torque tube will 

be corroded. 

Comment 2: The reason that the torque tube assembly/control horn have 

not been previously inspected for cracks is due to the fact there is no prior 

Piper requirement to do so (Ref l : Piper Service Manual, 10th Rev., Part No. 

753-516, Chapter III , Table III-I , Section E). 

Comment 3: The NPRM references Piper Service Bulletin 1189 and quotes 

Piper's recommended inspection intervals. The preliminary copy of SB 1189 

has a file date of 21 May 2009, while the final release copy is dated 29 

March 2010. The two copies are identical. 

ICS believes the preliminary (and final version) copy was written based on a 

magazine article without substantiating data, field service history, or 

engineering evaluation. 

ICS recommends that the FAA evaluate Piper's SB 1189 as advisory only, at 

best. 

Commen t 4 : The NPRM references the stabilator horn generically. The 

correct part is number P/N 20397-00, and should be so stated in the AD. 

Comment 5: ICS has conducted an extensive owner survey of horn 

inspections (Ref. 3). Early copies of those results were submitted to the FAA 

for review. We are finding that more and more owners are performing the 

complete disassembly and inspection in anticipation of the AD. With over 

800 inspection reports now, those owners which have completed a valid 

inspection should be given specific credit within the wording of the AD so an 

unnecessary re-inspection will not be required. 

Comment 6: Stress corrosion of aluminum alloys is a calendar time-stress 

state-environment condition problem. Total time-in-service or flight hours 

flown are not valid measures of when cracking will occur (Ref. 5). ICS 

recommends that xxx hours TIS inspection Intervals be stricken from 
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wording within the AD. Calendar time is the only valid inspection interval 

period. 

Comment 7; It has been shown by test, measurement and detailed 

analysis (Refs: 2 and 4) that the key parameter causing SCC is excessive 

bolt torque holding the horn to the torque tube. These bolts are AN 175-33A 

close tolerance bolts. The application of these bolts Is in bolt shear, not bolt 

tension. From Reference 1, 5/16 bolts in shear should be torqued between 

60/85 inch- pounds, not the tension value of 100/140 inch-pounds (plus nut 

friction). 

ICS strongly believes this torque requirement change alone will cease SCC 

horn cracking in the future. 

Comment 8: Reference 6 provides a survivability chart (Figure 11), which 

shows that 100% survivability of C-ring short transverse test specimens 

when exposed to a 3.5% NaCI solution when tension stress Is less than 35 

ksi stress. The alloys plotted are 7075-T65 and 2219-T87. ICS believes 

that 2014-T6 will behave similarly. Required inspection intervals should be 

based on specimen survival rate based on horn stress. ICS has already 

demonstrated that critical horn stress is 1/5 of the critical stress shown in 

the Figure 11 of Reference 6. 

ICS strongly recommends that the FAA Instruct NIAR to conduct C-ring 

testing per Reference 6 to determine stress state threshold for SCC to occur. 

ICS further recommends that inspection intervals be based on these test 

results, not irrational TIS values based on speculation. 

Comment 9: Within the wording of the AD, ICS recommends that a 

terminating action be stated. ICS has determined that a number of 

180/250/260 Comanches came from the factory with thick walled tubes. 

Clearly, these are not conforming to the TC. Piper refuses to acknowledge 

this fact. A thick walled torque tube Is considered terminating action. 

Piper refuses to produce thick walled torque tubes, stating that it does not 

have the resources or engineering time to develop these Items. They claim 

that flutter and flight testing would be required. Installation of these thick 

torque tubes on the singles could not have been authorized without 

engineering disposition, therefore their installation has been Piper approved. 

With these four examples, over 14,000 trouble free flight hours have shown 

that the incorporation of the thick walled torque tubes is a safe condition and 

meets the equivalent safety of the 30/39 and 24-400 models. 
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If Piper chooses not to produce thick walled torque tubes, ICS has identified 

PMA qualified fabricators that would. 

REPORTS OF PA-24-180/250/260 AIRCRAFT 

WITH THICK-WALLED TORQUE TUBES 

# 

I 

2 

3 

4 

MODEL 

PA-24-180 

PA-24-250 

PA-24-250 

PA-24-180 

SERIAL # 

24-868 

24-950 

24-226 

24-703 

N# 

N5789P 

N5867P 

N5203P 

N5633P 

YEAR 

1959 

1959 

1958 

1959 

T.T. 

4200 

3600 

estimate 

2846 

3200 

Person Reporting 

Kristin Winter (707) 477-4727 

kristin winteifa)comcast.net 

Owner - Daniel Katz 

Chris Kuyoth 

5203P (COF) - Steven Fischer 

Larry 180 (COF) Lawrence 

Price 
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Comment 10: ICS recommends that the AD should contain a survey form 

that owners/inspectors submit to both the FAA and ICS when a cracked horn 

or a thick walled torque tube is found. 

References 

1. Piper Service Manual, 10th Revision, 1 April 2009, P/N 753-516. 

2. "Piper Comanche Horn Cracking", letter dated 17 April 2011, Eric Paul & 

Denny Haskins to Gregory (Keith) Noles, Atlanta ACQ. 
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3. "Cracked Torque Tube Horn Survey Results_Rev A", PowerPoint 

Presentation, Updated 20 Nov 2009. 

4. "Comanche Stabilator Horn Cracking Investigation - Final Analysis 

Report", PowerPoint Presentation, 17 May 2011. 

5. "Stress-Corrosion and Corrosion-Fatigue Susceptibility of High-Strength 

Aluminum Alloys", AFML-TR-70-259, WPAFB, Ohio, November 1970. 

6. "Time Exposure Studies on Stress Corrosion Cracking of Aluminum 2014-

T6, 2219-T87, 2014-T651, 7075-T651, and Titanium 6AI-4V", Final Report, 1 

June 1973, Grambling College, Dept. of Physics, Grambling, Louisiana.