Federal Register / Vol. 75, No. 12 / Wednesday, January 20, 2010 / Rules and Regulations 3127 

TABLE 1—STRUCTURAL REPAIR MANUALS ACCEPTABLE BEFORE THE EFFECTIVE DATE OF THIS AD 

Document Revision Date 

Airbus A330 Structural Repair Manual ................................................................................................................ 60 October 1, 2008. 

Airbus A330 Structural Repair Manual ................................................................................................................ 61 January 1, 2009. 

Airbus A340–200/–300 Structural Repair Manual ............................................................................................... 64 October 1, 2008. 

Airbus A340–200/–300 Structural Repair Manual ............................................................................................... 65 January 1, 2009. 

(4) As of the effective date of this AD, no 

person may replace a movable flap track 

fairing No. 3 on that airplane, unless the 

replacement fairing has been modified or 

repaired in accordance with the requirements 

of this AD. 

FAA AD Differences 

Note 1: This AD differs from the MCAI 

and/or service information as follows: The 

MCAI prohibits replacement of the affected 

part after modification, but this AD prohibits 

replacing the affected part as of the effective 

date of this AD. 

Other FAA AD Provisions 

(g) The following provisions also apply to 

this AD: 

(1) Alternative Methods of Compliance 

(AMOCs): The Manager, International 

Branch, ANM–116, FAA, has the authority to 

approve AMOCs for this AD, if requested 

using the procedures found in 14 CFR 39.19. 

Send information to ATTN: Vladimir 

Ulyanov, Aerospace Engineer, International 

Branch, ANM–116, Transport Airplane 

Directorate, FAA, 1601 Lind Avenue, SW., 

Renton, Washington 98057–3356; telephone 

(425) 227–1138; fax (425) 227–1320. Before 

using any approved AMOC on any airplane 

to which the AMOC applies, notify your 

principal maintenance inspector (PMI) or 

principal avionics inspector (PAI), as 

appropriate, or lacking a principal inspector, 

your local Flight Standards District Office. 

(2) Airworthy Product: For any requirement 

in this AD to obtain corrective actions from 

a manufacturer or other source, use these 

actions if they are FAA-approved. Corrective 

actions are considered FAA-approved if they 

are approved by the State of Design Authority 

(or their delegated agent). You are required 

to assure the product is airworthy before it 

is returned to service. 

(3) Reporting Requirements: For any 

reporting requirement in this AD, under the 

provisions of the Paperwork Reduction Act, 

the Office of Management and Budget (OMB) 

has approved the information collection 

requirements and has assigned OMB Control 

Number 2120–0056. 

Related Information 

(h) Refer to MCAI European Aviation 

Safety Agency Airworthiness Directive 2008– 

0153, dated August 8, 2008; and Airbus 

Mandatory Service BulletinsA330–57–3095, 

Revision 02, and A340–57–4103, Revision 

01, both dated April 3, 2008; for related 

information. 

Material Incorporated by Reference 

(i) You must use Airbus Mandatory Service 

Bulletin A330–57–3095, Revision 02, dated 

April 3, 2008; or Airbus Mandatory Service 

Bulletin A340–57–4103, Revision 01, dated 

April 3, 2008; as applicable; to do the actions 

required by this AD, unless the AD specifies 

otherwise. 

(1) The Director of the Federal Register 

approved the incorporation by reference of 

this service information under 5 U.S.C. 

552(a) and 1 CFR part 51. 

(2) For service information identified in 

this AD, contact Airbus SAS—Airworthiness 

Office—EAL, 1 Rond Point Maurice Bellonte, 

31707 Blagnac Cedex, France; fax +33 5 61 

93 45 80, e-mail airworthiness.A330– 

A340@airbus.com; Internet http:// 

www.airbus.com. 

(3) You may review copies of the service 

information at the FAA, Transport Airplane 

Directorate, 1601 Lind Avenue, SW., Renton, 

Washington. For information on the 

availability of this material at the FAA, call 

425–227–1221 or 425–227–1152. 

(4) You may also review copies of the 

service information that is incorporated by 

reference at the National Archives and 

Records Administration (NARA). For 

information on the availability of this 

material at NARA, call 202–741–6030, or go 

to: http://www.archives.gov/federal_register/ 

code_of_federal_regulations/ 

ibr_locations.html. 

Issued in Renton, Washington, on 

December 16, 2009. 

Stephen P. Boyd, 

Acting Manager, 

Transport Airplane Directorate, Aircraft 

Certification Service. 

[FR Doc. 2010–487 Filed 1–19–10; 8:45 am] 

BILLING CODE 4910–13–P 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 39 

[Docket No. FAA–2007–27862; Directorate 

Identifier 2007–CE–036–AD; Amendment 

39–16150; AD 2009–26–11] 

RIN 2120–AA64 

Airworthiness Directives; Thrush 

Aircraft, Inc. Model 600 S2D and S2R 

Series Airplanes 

AGENCY: Federal Aviation 

Administration (FAA), DOT. 

ACTION: Final rule. 

SUMMARY: We are adopting a new 

airworthiness directive (AD) to 

supersede AD (AD) 2006–07–15, which 

applies to Thrush Aircraft, Inc. Model 

600 S2D and S2R (S–2R) series airplanes 

(type certificate previously held by 

Quality Aerospace, Inc. and Ayres 

Corporation). AD 2006–07–15 currently 

requires repetitive inspections of the 

1/4-inch and 5/16-inch bolt hole areas 

on the wing front lower spar caps for 

fatigue cracking; replacement or repair 

of any wing front lower spar cap where 

fatigue cracks are found; and reporting 

of any fatigue cracks found to the FAA. 

AD 2006–07–15 also puts the affected 

airplanes into groups for compliance 

time and applicability purposes. Since 

we issued AD 2006–07–15, FAA 

analysis reveals that inspections are not 

detecting all existing cracks and shows 

the incidences of undetected cracks will 

increase as the airplanes age. 

Consequently, this AD retains the 

actions of AD 2006–07–15 and imposes 

a life limit on the wing front lower spar 

caps that requires replacement of the 

wing front lower spar caps when the life 

limit is reached. This AD also changes 

the requirements and applicability of 

the groups discussed above and removes 

the ultrasonic inspection method. We 

are issuing this AD to prevent wing 

front lower spar cap failure caused by 

undetected fatigue cracks. Such failure 

could result in loss of a wing in flight. 

DATES: This AD becomes effective on 

February 24, 2010. 

On February 24, 2010, the Director of 

the Federal Register approved the 

incorporation by reference of Thrush 

Aircraft, Inc. Custom Kit No. CK–AG– 

41, Revision A, dated March 8, 2007, 

listed in this AD. 

As of May 20, 2003 (68 FR 15653), the 

Director of the Federal Register 

approved the incorporation by reference 

of Quality Aerospace, Inc. Custom Kit 

No. CK–AG–30, dated December 6, 

2001, listed in this AD. 

As of July 25, 2000 (65 FR 36055), the 

Director of the Federal Register 

approved the incorporation by reference 

of Ayres Corporation Service Bulletin 

No. SB–AG–39, dated September 17, 

1996; and Ayres Corporation Custom Kit 

No. CK–AG–29, dated December 23, 

1997, listed in this AD. 

ADDRESSES: To get the service 

information identified in this AD, 

contact Thrush Aircraft, Inc., 300 Old 

Pretoria Road, P.O. Box 3149, Albany, 

Georgia 31706–3149. The service 


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information is also available on the 

Internet at http:// 

www.thrushaircraft.com. 

To view the AD docket, go to U.S. 

Department of Transportation, Docket 

Operations, M–30, West Building 

Ground Floor, Room W12–140, 1200 

New Jersey Avenue, SE., Washington, 

DC 20590, or on the Internet at http:// 

www.regulations.gov. The docket 

number is FAA–2007–27862; 

Directorate Identifier 2007–CE–036–AD. 

FOR FURTHER INFORMATION CONTACT: 

—Cindy Lorenzen, Aerospace Engineer, 

ACE–115A, Atlanta Aircraft 

Certification Office, 1701 Columbia 

Avenue, College Park, Georgia 30337; 

telephone: (404) 474–5524; facsimile: 

(404) 474–5606; e-mail: 

cindy.lorenzen@faa.gov; or 

—William O. Herderich, Aerospace 

Engineer, ACE–117A, Atlanta Aircraft 

Certification Office, 1701 Columbia 

Avenue, College Park, Georgia 30337; 

telephone: (404) 474–5547; facsimile: 

(404) 474–5606; e-mail: 

william.o.herderich@faa.gov. 

SUPPLEMENTARY INFORMATION: 

Discussion 

On April 27, 2009, we issued a 

proposal to amend part 39 of the Federal 

Aviation Regulations (14 CFR part 39) to 

include an AD that would apply to 

certain Thrush Aircraft, Inc. Model 600 

S2D and S2R (S–2R) series airplanes 

(type certificate previously held by 

Quality Aerospace, Inc. and Ayres 

Corporation). This proposal was 

published in the Federal Register as a 

notice of proposed rulemaking (NPRM) 

on May 4, 2009 (74 FR 20431). The 

NPRM proposed to supersede AD 2006– 

07–15, Amendment 39–14542 (71 FR 

19788, April 17, 2006) with a new AD 

that would: 

• Retain the actions of AD 2006–07– 

15; 

• Add life limits for the wing front 

lower spar caps; 

• Lower the initial and repetitive 

inspection times for Group 5 airplanes; 

• Correct some airplane Group 

classifications; 

• Add an airplane to the 

Applicability section; and 

• Remove the use of ultrasonic 

inspection methods. 

For replacement of the wing front 

lower spar caps, the initial compliance 

time for all airplanes will be at least an 

additional 500 hours time-in-service 

(TIS) after the effective date of this AD. 

Calculated from actual flight hour data 

from 285 S2R series airplanes, 500 

hours TIS equates to the average yearly 

operational time. The compliance 

schedules should give owner/operators 

enough time to schedule the 

replacement of the wing front lower 

spar caps. 

Although not required in this AD, we 

recommend installing ‘‘big butterfly’’ 

and lower splice plates, P/N 20211–09 

and P/N 20211–11, or Thrush Aircraft, 

Inc. Custom Kit No. CK–AG–41, 

Revision A, since they increase the 

strength of the wing beyond the 

minimum safety standards. 

Comments 

We provided the public the 

opportunity to participate in developing 

this AD. The following presents the 

comments received on the proposal and 

FAA’s response to each comment: 

Comment Issue No. 1: Extend 

Compliance Time To Replace the Spar 

Caps 

Marc Fries states that a large portion 

of the affected airplanes will need to 

address a spar replacement within a 

very short period of time, overwhelming 

a limited number of repair facilities. Mr. 

Fries also states that most operators 

have a short ‘‘down time’’ during their 

season in which to do this type of 

repair, and many operators will run out 

of flying hours before a repair facility 

can do the work or even get the kits 

from the factory. 

Mr. Fries requests an extension of the 

compliance time because there are a 

limited number of repair facilities, and 

the replacement parts may not be 

available immediately. Mr. Fries also 

requests to insert into the AD an 

allowance for an extension of the 

compliance time while continuing the 

spar cap inspections. 

We do not agree with the commenter. 

As stated in the NPRM, allowance for 

the compliance time based on the 

limited number of repair facilities and 

the limited availability of replacement 

parts has already been made. For 

airplanes that have already exceeded the 

life limit replacement time for the wing 

front lower spar caps, the minimum 

compliance time for those with the 

highest hours TIS, which are the 

airplanes with the highest risk of spar 

cap failure, is 500 hours TIS. Five 

hundred hours TIS equates to an 

average year of operation for these 

airplanes. Airplanes that have exceeded 

the life limit replacement time, but are 

not at the highest level of risk, will be 

allowed an even longer compliance time 

of 1,000 hours TIS, 1,500 hours TIS, or 

2,000 hours TIS based on the current 

number of hours TIS on the wing front 

lower spar caps. Airplanes that have not 

yet reached the life limit replacement 

time are allowed a minimum of 2,000 

hours TIS to comply with the AD. These 

compliance times result in an average 

operator having at least one year to 

comply with the AD; however, most 

operators will have much longer than 

one year to replace the wing front lower 

spar caps. These graduated compliance 

times should allow enough time for 

adequate supply of parts and repair 

facility availability. 

We are not changing the final rule AD 

action based on this comment. 

Comment Issue No. 2: Withdraw the AD 

Charles Brumley states that the pilot 

should be allowed to make his own 

decision whether a new spar cap is 

needed and requests an alternative to 

this AD. 

Mr. Brumley further states that he 

believes the AD is unnecessary for the 

following reasons: 

• If the pilot is involved in the 

maintenance of the airplane, then the 

pilot can make an informed decision 

about whether or not to install a new 

spar cap and whether or not the aircraft 

is in a condition for safe operation; 

• The AD will cause undue economic 

hardship on the airplane operators and 

the farms that use aerial application 

services; 

• There have only been a few cracks 

found, i.e., that there is not enough 

service history to support issuance of an 

AD; and 

• The large butterfly plates are 

adequate to ensure safety of the pilot 

until a spar cap crack is found. 

We infer this as a request for the FAA 

to withdraw the AD. 

We do not agree with the commenter. 

While the commenter may have 

maintained his airplane adequately, the 

formation of fatigue cracks mainly 

relates to the airplane’s design and 

operation. Replacement of the wing 

front lower spar caps when they have 

reached their life limits is currently the 

only means known to the FAA to 

address the unsafe condition. 

We have extensive crack data that 

currently shows 176 wings on 123 

airplanes had cracks in the wing front 

lower spar caps. As the incidences of 

cracking increase, which has occurred 

in the Thrush airplanes, the chance of 

an existing crack not being detected 

during an inspection increases. 

Airplanes with cracks in the wing front 

lower spar caps are unable to meet 

ultimate strength requirements, which 

could lead to a wing failure. The only 

known way of mitigating this risk is to 

replace the wing front lower spar caps. 

There are already procedures in place 

for owner/operators to request an 

alternative to any AD. Use the 

alternative method of compliance 

(AMOC) procedures provided in this AD 


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to request an AMOC. The request for an 

AMOC must include any substantiating 

information, such as stress and fatigue 

data. The AMOC will be approved if we 

find it provides an acceptable level of 

safety. 

We are not changing the final rule AD 

action based on this comment. 

Comment Issue No. 3: Adjusted Life 

Limits Based on Environmental 

Conditions 

Avenger Aircraft and Services 

(Avenger) states the life limits for the 

wing front lower spar caps should be 

adjusted if environmental conditions 

were not taken into account when 

determining the life limits. The 

commenter states that metal fatigue is 

influenced by environmental 

conditions. 

We do not agree with the commenter’s 

request to adjust the life limits. We did 

take environmental conditions into 

consideration during our analysis for 

determining the life limits. The riskbased analysis used by the FAA used 

actual reported crack data from inservice airplanes. These in-service data 

came from airplanes operated in a 

variety of environments; therefore, the 

raw data used in the FAA’s analysis 

include the effects caused by 

environmental conditions. 

We are not changing the final rule AD 

action based on this comment. 

Comment Issue No. 4: Adjust Life 

Limits Based on Crack Sizes 

Avenger states that the life limit of the 

wing front lower spar cap could be 

much shorter if crack sizes are taken 

into account during the risk assessment. 

Avenger also states that this can be 

particularly significant when some fleet 

crack sizes may have exceeded the 

critical size without failing due to the 

airplane not exceeding limit load at that 

particular time. 

We do not agree with the commenter’s 

request. Although we did not include 

the crack size in our analysis, we did 

use a statistical approach and took into 

account the TIS on the wing front lower 

spar cap when the crack was found and 

reported to the FAA. There are other 

factors in place in the AD to mitigate the 

risk associated with not using crack size 

to determine the life limit of the wing 

front lower spar caps. We determined a 

life limit for continued operational 

safety of the S2R fleet and did not 

propose a life limit as defined in FAA 

guidance for type certification of newly 

certificated airplanes. Our analysis of 

the crack data, which includes 

allowances for both the statistically 

significant amount of crack data on the 

Thrush fleet and the existence of an 

inspection program for the wing front 

lower spar caps, yielded the life limits 

times for the wing front lower spar caps 

shown in the NPRM. 

We are not changing the final rule AD 

action based on this comment. 

Comment Issue No. 5: Remove Magnetic 

Particle Inspection Method 

Avenger states that the flaw size that 

can be detected by the magnetic particle 

inspection method is 0.69 inches, which 

is in excess of the flaw size that would 

allow the wing front lower spar cap to 

continue to carry limit load. 

Avenger states, therefore, magnetic 

particle inspections should not be 

utilized as a valid inspection method 

and should be removed from the AD. 

We do not agree with the commenter. 

The magnetic particle inspection 

interval was originally set at 500 hours 

TIS by AD 2000–11–16 and was based 

on crack growth analysis provided by 

Ayres Corporation (Ayres). We accepted 

Ayres’ proposed usage of U.S. Air Force 

data from Report AFWAL 3–5–852, 

which showed a reliably detectable 

crack size (90 percent probability/95 

percent confidence) of 0.12 inch when 

using magnetic particle inspection 

methods. Using this detectable crack 

size with a repetitive inspection of 500 

hours TIS allowed for at least two 

inspections to occur after crack 

initiation and prior to a crack reaching 

its critical size. As the fleet aged and as 

more cracks occurred in-service, the risk 

to the fleet increased. To help mitigate 

this risk, we doubled the frequency of 

the inspections required in AD 2006– 

07–15. In this AD we are requiring 

inspections every 250 hours TIS, which 

allows for four chances of detecting a 

crack based on the data originally used 

by Ayres. This same 250-hour TIS 

inspection interval, along with imposing 

a wing front lower spar cap life limit to 

further mitigate risk, was included in 

the proposed AD. The detectable crack 

size of 0.12 inch used by Ayres is very 

near the values of detectable size 

currently suggested for use by the FAA 

(Ref. Website sponsored by the FAA in 

conjunction with Iowa State University 

http://www.cnde.iastate.edu/faa-casr/ 

engineers/index.html) of 0.13 to 0.15 

inch. With the added conservatism of 

four inspections to detect cracks before 

reaching a critical crack size, when two 

inspections are what is normally 

required in a more ideal environment, 

the inspection interval in this AD is 

well within the current guidelines. 

We are not changing the final rule AD 

action based on this comment. 

Comment Issue No. 6: Require 

Calibration Standards and Level 2 NDT 

Personnel To Perform Eddy Current 

Inspections 

Avenger states that calibration 

standards and Level 2 Non-destructive 

Testing (NDT) personnel are necessary 

to achieve reliability and repeatability 

in the inspections. These calibration 

standards are designed to replicate the 

structure being inspected with 

simulated flaws and are used every time 

as a setup tool by the inspector prior to 

conducting the on-aircraft inspection. 

Utilization of these standards is the 

current practice by all major aircraft 

manufacturers and should be required 

for the Thrush inspections in order to 

ensure a 90 percent probability of 

detection. In addition, the inspectors 

should be fully certified Level 2 NDT 

personnel with bolt hole eddy current 

qualifications. 

We do not agree with the commenter’s 

request that a change is needed to the 

AD. This AD and the ADs that this AD 

supersedes allow for eddy current 

inspection procedures to be approved 

only through the FAA’s Aircraft 

Certification Office (ACO). The FAA 

ACO already requires each procedure to 

have the correct type of calibration 

standard as this is a basic requirement 

for ensuring a good inspection. The 

FAA ACO has not and will not approve 

an eddy current inspection procedure 

that does not include a requirement to 

use only Level 2, or even more qualified 

Level 3, certified NDT inspectors for 

these eddy current inspections. 

We are not changing the final rule AD 

action based on this comment. 

Comment Issue No. 7: Allow Installing 

Supplemental Type Certificate (STC) 

SA03654AT as a Terminating Action in 

This AD 

Avenger states that a solution that was 

not available at the time the proposed 

AD was written is now currently on the 

market. Avenger requests that the 

following information be included in 

the AD. This solution is the Avenger 

STC SA03654AT Avenger Extended 

Performance Front Spar Enhancement 

Kit. 

STC SA03654AT installs FAAapproved replacement wing front lower 

spar caps for all airplanes that are the 

subject of this AD, except for Model S2D 

airplanes. The replacement spars have a 

life limit of 40,000 hours TIS with a 

parts cost of $40,000 and an installation 

cost of $25,500. 

Avenger’s FAA STC replacement kit 

includes the following: 

• 2 lower wing front lower spar caps 

(made from stainless steel, not 4000 

series steel); 


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• 2 front spar web doublers; 

• 1 large butterfly plate (redesigned); 

• 2 larger splice blocks (redesigned); 

and 

• All associated hardware for 

installation. 

Avenger requests that the AD be 

amended to include the installation of 

the Avenger Extended Performance 

(AXP) kit as a terminating action to this 

AD. 

We agree with the commenter. The 

replacement wing front lower spar caps 

and other modification parts that are 

approved by STC SA03654AT, 

Installation of Avenger Extended 

Performance Front Spar Enhancement 

Kit (new wing front spar lower caps, 

center splice and doublers), in 

accordance with Part II of Avenger 

Master Data List AAS–MDL–08–001, 

Revision B, dated November 26, 2008, 

or later FAA-approved revision, are a 

viable terminating action to this AD. 

The installation of STC SA03654AT is 

an alternative to replacing the wing 

front lower spar caps with Ayres/ 

Thrush wing front lower spar caps. 

We will change the final rule AD 

action to allow installing STC 

SA03654AT as a terminating action for 

this AD. 

Comment Issue No. 8: Require Reaming 

Bolt Hole Before Cold Working 

Avenger states it is their opinion that 

the cold working process accomplished 

as part of the Ayres Corporation Service 

Bulletin No. SB–AG–39, dated 

September 17, 1996, is not being 

conducted correctly, and fatigue damage 

is being introduced and made more 

critical than if cold working was not 

accomplished at all. In order to utilize 

mandrel expansion in a safe manner, the 

hole in question must first be reamed to 

remove any corrosion or existing cracks 

that are too small to be detected. This 

‘‘insurance cut’’ is required to remove 

any anomaly in the hole that may cause 

an issue during the cold working 

process. 

Avenger requests the AD be amended 

to explicitly state that prior to mandrel 

expansion, an insurance ream, capable 

of cleaning up a .03 inch undetected 

crack followed by a bolt hole eddy 

current inspection using a calibration 

standard, be accomplished prior to the 

mandrel expansion process. 

We do not agree with the commenter. 

The AD already requires using the cold 

working procedure found in Ayres 

Service Bulletin SB–AG–39, dated 

September 17, 1996. Steps 7 and 8 in 

the Rework section of this service 

bulletin require the bolt holes to be 

reamed before cold working of the 

holes. These procedures must be 

accomplished in order to be in 

compliance with this AD. 

We are not changing the final rule AD 

based on this comment. 

Comment Issue No. 9: Require 

Installing Big Butterfly Plates 

Michael Morris and Mr. Brumley state 

that instead of mandating the 

replacement of the wing lower spar 

caps, they would like the FAA to 

require installing big butterfly plates. In 

addition to installing the big butterfly 

plates, Mr. Morris also requests to keep 

the current inspection intervals for 

magnetic particle and eddy current 

inspections, and add a visual inspection 

every 100 hours TIS. 

Mr. Morris states that he believes 

replacing the spar cap is unnecessary for 

the following reasons: 

• The inspection program will 

continue to work; 

• The economic impact is too great; 

and 

• Some operators do not fly as 

aggressively as others and should not be 

penalized for the actions of the other 

pilots. 

We do not agree with the commenters. 

The ‘‘big butterfly’’ plate does not have 

enough strength to carry all of the 

possible flight loads in the event the 

wing spar cap is severed. This plate 

cannot be solely relied upon to ensure 

the safety of the airplane. 

Even if the spar cap is not completely 

severed but has a crack that is large 

enough to see when performing the 

commenter’s proposed 100-hour TIS 

visual inspection, the remaining 

strength in the wing spar joint is not 

enough to carry all of the possible flight 

loads. As explained in the proposed AD, 

inspection reliability for any type of 

inspection method is not 100 percent; 

therefore, over time the probability of an 

inspection failing to detect a crack 

increases and something more needs to 

be done to ensure the safety of the 

airplanes. 

As shown in the Initial Regulatory 

Flexibility Analysis section of the 

proposed AD, the economic impact was 

extensively studied. While we agree the 

AD will have a significant economic 

impact on small businesses, the only 

known way to ensure the safety of the 

airplane is to replace the wing front 

lower spar caps. 

We also agree that there are many 

variables affecting the life limit of the 

wing front lower spar caps, including 

the operating weights and operating G 

loads. Higher weights and higher G 

loads reduce the life limit of the wing 

front lower spar caps. The only way to 

consider giving credit to those who 

operate at lower weights and lower G 

loads would be if each individual 

airplane had recorded data for every 

flight since the wings were installed 

showing the weights and G loads. Each 

individual airplane owner would then 

need to have fatigue analysis and tests 

done by a qualified engineer to 

determine the life limit for that 

particular set of wings based on that 

recorded data. The expense of 

conducting this type of study for each 

airplane may be higher than the cost of 

replacement wing front lower spar caps; 

therefore, it may not be an economically 

viable alternative. 

We are not changing the final rule AD 

action based on this comment. 

Conclusion 

We have carefully reviewed the 

available data and determined that air 

safety and the public interest require 

adopting the AD as proposed except for 

the changes previously discussed and 

minor editorial corrections. We have 

determined that these minor 

corrections: 

• Are consistent with the intent that 

was proposed in the NPRM for 

correcting the unsafe condition; and 

• Do not add any additional burden 

upon the public than was already 

proposed in the NPRM. 

Costs of Compliance 

We estimate that this AD will affect 

808 airplanes in the U.S. registry, 

including those airplanes affected by 

AD 2006–07–15. 

We estimate the following costs to do 

each inspection: 

Labor cost Parts cost Total cost per 

airplane 

Total cost on 

U.S. operators 

3 work-hours × $80 = $240 ......................................................................................................... $525 $765 $618,120 


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We estimate the following costs to do 

cold work of bolt holes for the repair 

that may be required based on the 

results of the inspection. We have no 

way of determining the number of 

airplanes that may need such repair: 

Labor cost Parts cost Total cost per 

airplane 

1 work-hour × $80 = $80 ................................................................................................................................. $100 $180 

We estimate the following costs to do 

any reaming of outer holes to 5/16-inch 

diameter for the repair that may be 

required based on the results of the 

inspection. We have no way of 

determining the number of airplanes 

that may need such repair: 

Labor cost Parts cost Total cost per 

airplane 

1 work-hour × $80 = $80 .................................................................................................................................... None ............... $80 

We estimate the following costs to do 

any drilling and reaming of outer holes 

and adding three holes to install a 

Kaplan splice block for the repair that 

may be required based on the results of 

the inspection. We have no way of 

determining the number of airplanes 

that may need such modification: 

Labor cost Parts cost Total cost per 

airplane 

65 work-hours × $80 = $5,200 ................................................... $4,400 for splice block and $600 for hardware ......................... $10,200 

We estimate the following costs to do 

any necessary wing front lower spar cap 

replacement with the optional Ayres or 

Thrush part numbers (P/Ns) 20207–1, 

20207–2, 20207–11, 20207–12, 20207– 

13, 20207–14, 20207–15, or 20207–16 

that will be required based on the 

results of the inspection or by the wing 

front lower spar cap reaching the life 

limit: 

Labor cost per wing front lower spar cap 

Parts cost per 

wing front 

lower spar cap 

Total cost per airplane 

200 work-hours × $80 = $16,000 ............................................... $8,000 Each spar cap replacement = $24,000 

Two wing front lower spar caps per airplane = $48,000. 

However, the supply of individual 

wing front lower spar caps (new or 

used) is very limited. 

We estimate the following costs to do 

the optional installation of Thrush 

Aircraft, Inc. Custom Kit No. CK–AG– 

41, Revision A, dated March 8, 2007. 

This kit may be used to do any 

necessary wing front lower spar cap 

replacements that will be required based 

on the results of the inspection or that 

will be required based on reaching the 

life limit: 

Labor cost Parts cost Total cost per 

airplane 

300 work-hours × $80 = $24,000 .................................................................................................................... $40,000 $64,000 

We estimate the following costs to do 

the optional installation of Avenger 

Aircraft and Services STC SA03654AT 

for Avenger Extended Performance 

Front Spar Enhancement Kit. This kit 

may be used to do any necessary wing 

front lower spar cap replacements that 

will be required based on the results of 

the inspection or that will be required 

based on reaching the life limit: 

Labor cost Parts cost Total cost per 

airplane 

319 work-hours × $80 = $25,520 .................................................................................................................... $40,000 $65,500 

The FAA estimates that 501 airplanes 

affected by this AD will retire before 

their wing front lower spar cap life 

limits are reached. 

Authority for This Rulemaking 

Title 49 of the United States Code 

specifies the FAA’s authority to issue 

rules on aviation safety. Subtitle I, 

Section 106 describes the authority of 

the FAA Administrator. Subtitle VII, 

Aviation Programs, describes in more 

detail the scope of the agency’s 

authority. 


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1 Individual replacement of the two original 

equipment spars is cheaper (for one installation) 

than installing the Ayres/Thrush kit or the Avenger 

kit, but as noted in the ‘‘Cost of Compliance’’ 

section, the supply of these spar caps is very 

limited. Accordingly, total cost is overestimated, 

but only slightly, by our assumption that all 

operators would comply by installing a kit (NPRM: 

Ayres/Thrush kit, final rule: Avenger kit). 

We are issuing this rulemaking under 

the authority described in Subtitle VII, 

Part A, Subpart III, Section 44701, 

‘‘General requirements.’’ Under that 

section, Congress charges the FAA with 

promoting safe flight of civil aircraft in 

air commerce by prescribing regulations 

for practices, methods, and procedures 

the Administrator finds necessary for 

safety in air commerce. This regulation 

is within the scope of that authority 

because it addresses an unsafe condition 

that is likely to exist or develop on 

products identified in this AD. 

Final Regulatory Flexibility Analysis 

Introduction and Purpose of This 

Analysis 

The Regulatory Flexibility Act of 1980 

(Pub. L. 96–354) (RFA) establishes ‘‘as a 

principle of regulatory issuance that 

agencies shall endeavor, consistent with 

the objectives of the rule and of 

applicable statutes, to fit regulatory and 

informational requirements to the scale 

of the businesses, organizations, and 

governmental jurisdictions subject to 

regulation.’’ To achieve this principle, 

the RFA requires agencies to solicit and 

consider flexible regulatory proposals 

and to explain the rationale for their 

actions to assure that such proposals are 

seriously considered. The RFA covers a 

wide-range of small entities, including 

small businesses, not-for-profit 

organizations, and small governmental 

jurisdictions. 

Agencies must perform a review to 

determine whether a rule will have 

significant economic impact on a 

substantial number of small entities. If 

the agency determines that it will, the 

agency must prepare a regulatory 

flexibility analysis as described in the 

RFA. 

We determined that this final rule 

will have a significant economic impact 

on a substantial number of small entities 

and, accordingly, as required by section 

603(a) of the RFA, we prepared and 

published an initial regulatory 

flexibility analysis (IRFA) as part of the 

NPRM for this final rule (74 FR 20431, 

May 4, 2009). Section 604 of the RFA 

also requires an agency to publish a 

final regulatory flexibility analysis 

(FRFA) in the Federal Register when 

issuing a final rule. Section 604(a) 

requires that each FRFA contain: 

• A succinct statement of the need 

for, and objectives of, the final rule; 

• A summary of the significant issues 

raised by the public comments in 

response to the IRFA, a summary of 

agency’s assessment of such issues, and 

a statement of any changes made to the 

proposed final rule resulting from such 

comments; 

• A description of the steps the 

agency has taken to minimize the 

significant economic impact on small 

entities consistent with the stated 

objectives of applicable statues, 

including a statement of the factual, 

policy, and legal reasons for selecting 

the alternative adopted in the final rule 

and why each one of the other 

significant alternatives to the final rule 

considered by the agency that affect the 

impact on small entities was rejected. 

• A description of and an estimate of 

the number of small entities for which 

the final rule will apply; and 

• A description of the projected 

reporting, recordkeeping, and other 

compliance requirements of the final 

rule, including an estimate of the classes 

of small entities that will be subject to 

the requirement and the type of 

professional skills necessary for 

preparation of the report or record. 

Need for, and Objectives of Final Rule 

A series of ADs, beginning in 1997 

and culminating in AD 2006–07–15 in 

2006, addressed the issue of fatigue 

cracking of the wing front lower spar 

caps in Thrush Aircraft, Inc. Model 600 

S2D and S2R (S–2R) series airplanes 

(type certificate previously held by 

Quality Aerospace, Inc. and Ayres 

Corporation). This type of fatigue 

cracking, if not addressed, could result 

in catastrophic wing failure. The 

original 1997 AD was issued after an 

accident on an S2R series airplane in 

which the wing separated from the 

airplane in flight. Requirements of 

inspection and possible replacement 

were changed in 2000 to repetitive 

inspections and possible replacement. 

In 2006, the inspection rate was doubled 

after a completely severed wing front 

lower spar cap was found on one of the 

affected airplanes and the FAA noted 

that it was working with Thrush 

Aircraft, Inc. to develop a future 

terminating action. Analysis indicated 

that an undetected crack had existed 

during the previous two repetitive 

inspections of that wing front lower spar 

cap. 

Subsequent FAA analysis has shown 

that wing front lower spar cap fatigue 

cracking has increased as the fleet has 

aged and will continue to increase. 

Consequently, the incidences of 

undetected cracks will increase, 

increasing the probability of 

catastrophic wing failure. The FAA has 

concluded that repetitive inspections, as 

required since the 2000 AD, are 

insufficient by themselves to ensure the 

safety of these airplanes and, 

accordingly, in this final rule the FAA 

is requiring wing front lower spar cap 

life limits to address this safety issue. 

Summary of Significant Issues Raised by 

the Public in Response to the IRFA, 

Summary of FAA’s Assessment of Such 

Issues, Statement of Changes Made to 

the Final Rule as a Result of Such 

Issues, Description of the Steps the 

Agency Has Taken To Minimize a 

Significant Economic Impact on Small 

Entities, and Why Other Significant 

Alternatives to the Final Rule That 

Affect Small Entities Were Rejected 

There were no public comments to 

the IRFA, but there were public 

comments to the proposed rule, which 

have relevance for small and large 

entities alike. 

As noted in the preamble to the final 

rule, Avenger commented that it has 

developed a wing front lower spar 

replacement kit, which was not 

available when the proposed rule was 

issued. The FAA has approved their kit 

for a 40,000-hour TIS life limit. Avenger 

requested that the FAA approve the 

installation of its kit as a terminating 

action to the AD. As noted in the 

preamble, the FAA agrees with Avenger 

that installation of its kit is a viable 

terminating action to this AD. 

Accordingly, it is an alternative to 

replacing the wing front lower spar caps 

with Ayres/Thrush spar caps; and the 

FAA has incorporated this change in the 

final rule. This is a significant issue 

because the Ayres/Thrush kit, although 

priced slightly lower than the Avenger 

kit, has a lower life limit (ranging from 

5,400 to 28,800 hours TIS.) Many of the 

affected airplanes with the Ayres/ 

Thrush kit installed will require 

multiple replacements over their 

lifetimes and installation of the Ayres/ 

Thrush kit does not eliminate the 

requirement of repetitive inspections 

and reporting requirements. 

Consequently, the estimated cost of the 

final rule is lower given the availability 

of the Avenger kit as a terminating 

action. In the cost analysis for the 

proposed rule, we estimated the total 

cost to be $37.1 million. In the final 

rule, we estimate total cost to be $20.1 

million.1

As an alternative to replacing the 

wing front lower spar caps, two 

commenters suggested that the FAA 

require installation of ‘‘big butterfly’’ 

plates. But, as the FAA noted in the 

preamble, the ‘‘big butterfly plate’’ does 

not have enough strength to carry all the 


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2FAA Registry, http://www.faa.gov/ 

licenses_certificates/aircraft_certification/ 

aircraft_registry/releasable_aircraft_download/. 

Data downloaded on 4/14/08. 

possible flight loads if the wing front 

lower spar caps were severed. 

Accordingly, this plate cannot be solely 

relied upon to ensure the safety of the 

airplane and is not an acceptable 

alternative method of compliance to 

replacing the wing front lower spar 

caps. 

Additionally, one commenter 

suggested 100-hour TIS visual 

inspections. As discussed in the 

preamble, even if the wing front lower 

spar cap is not completely severed, but 

has a crack that is large enough to see 

when performing the 100-hour TIS 

visual inspection, the remaining 

strength in the wing spar joint is not 

enough to carry all possible flight loads. 

Therefore, the 100-hour TIS visual 

inspection alone is not a sufficient 

alternative method of compliance. 

The FAA believes there are currently 

no other available alternative methods 

of compliance to the final rule that will 

allow the safety objectives of the final 

rule to be achieved. The FAA, however, 

has allowed a generous compliance 

period that will significantly reduce the 

economic impact on small and large 

entities alike. As already noted in the 

preamble, airplanes that have already 

exceeded the life limit on their wing 

front lower spar caps are allowed 500, 

1,000, 1,500, or 2,000 hours TIS to 

comply with the final rule, depending 

on the current number of accumulated 

hours TIS. Since the average usage rate 

for the affected airplanes is about 500 

hours TIS per year, these allowances are 

equivalent, on average, to 1, 2, 3, and 4 

years to comply with the final rule. 

Airplanes that have not yet reached 

their wing front lower spar cap life limit 

are allowed a minimum of 2,000 hours 

TIS or, on average, 4 years to comply 

with the final rule. 

For a complete summary of public 

comments and the FAA’s responses, 

please see the Comments section in the 

preamble above. 

A Description of and an Estimate of the 

Number of Small Entities for Which the 

Final Rule Will Apply 

This final rule will affect 808 U.S.- 

registered and -operated Thrush 

Aircraft, Inc. Model 600S2D and S2R 

(S–2R) series airplanes. 2 In conducting 

this analysis, the FAA reviewed data 

from the FAA Registry to ascertain how 

many Thrush Aircraft, Inc. were 

registered and operated by small 

entities. The FAA Registry indicates that 

these 808 airplanes are owned by 546 

separate entities in agricultural aviation. 

All but one of these entities are small 

entities as defined by the Small 

Business Administration (SBA). 

Although the FAA Registry does not 

record financial or business data about 

the registered owners of aircraft, and 

such data for these entities are not 

readily available elsewhere, it appears 

that most, if not all, of the 546 entities 

are engaged in crop dusting, spraying, 

and seeding operations. These activities 

are classified in North American 

Industry Classification System (NAICS) 

industry, NAICS 115112—Soil 

Preparation, Planting, and Cultivating 

(including Crop Dusting, Crop 

Spraying). The concentration of these 

entities in a single NAICS industry 

reflects the specialized nature of 

agricultural airplanes with restricted 

airworthiness certificates. Furthermore, 

several of these entities were classified 

in the Standard Industrial Classification 

(SIC) equivalent of NAICS 115112 by 

http://www.manta.com. Although a few 

of these entities may also be engaged in 

firefighting, which is classified in 

NAICS 115310—Support Activities for 

Forestry (including Forest Fire 

Suppression), the FAA is unable to 

identify any of these entities as being 

principally engaged in firefighting. The 

SBA small business classification for 

NAICS 115112 is a maximum of $6.5 

million in business receipts, and for 

NAICS 115310 it is a maximum of $16.5 

million in business receipts. Only one 

entity in this sample appears to have 

business receipts over $6.5 million, and 

no entity has business receipts in excess 

of $16.5 million. Using the total number 

of airplanes owned as a size criterion, 

the FAA selected a sample of 41 of the 

largest affected entities and found 

median sales shown by http:// 

www.manta.com to be just $250,000 

annually. Firms in agricultural aviation 

appear to be inherently of small size. 

Accordingly, the FAA estimates that 545 

small entities will be affected by this 

final rule. 

Reporting, Record Keeping, and Other 

Compliance Requirements 

Small entities will incur no new 

reporting and record-keeping 

requirements as a result of this final 

rule. In fact, such requirements, for 

small and large firms alike, will be 

greatly reduced since installation of the 

Avenger kit has been incorporated as an 

alternative terminating action to this 

final rule. 

This final rule will affect U.S. 

operators of Thrush Aircraft, Inc. Model 

600S2D and S2R (S–2R) series 

agricultural airplanes airplanes. The 

affected airplanes were produced by 

Thrush Aircraft, Inc. predecessor firms 

over the period 1965–2000. This final 

rule largely retains the requirements of 

superseded AD 2006–07–15 to inspect/ 

repair/replace the currently installed 

Ayres/Thrush wing front lower spar 

caps. The new requirements set life 

limits on the Ayres/Thrush wing front 

lower spar caps and requires replacing 

of these wing front lower spar caps 

when the life limits are reached. 

Economic Impact on Small Entities 

Replacing the wing front lower spar 

caps is expensive and, consequently, as 

we show below, the final rule will have 

a significant economic impact on the 

substantial number of small firms we 

identified above. 

The total compliance cost 

(undiscounted) is $65,520 for an 

affected airplane for which the wing 

front lower spar caps are replaced before 

retirement, or zero for an affected 

airplane that will retire before its 

compliance date. Individual airplane 

compliance costs will result in costs to 

the small entities that own these 

airplanes and will vary depending on 

the number of affected airplanes owned 

by the entity. The ownership table 

below shows the variation in the 

number of owners with particular 

numbers of airplanes. The table shows 

that almost 75 percent of the 546 

individual owners have only one 

affected airplane, and more than 90 

percent of owners have no more than 

two affected airplanes. The average 

(mean) number of affected airplanes 

held is 1.48, while the median number 

held is just 1.00, so the median airplane 

cost is equivalent to the median owner 

cost. 


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3Small Business Administration, Office of 

Advocacy. http://www.sba.gov/advo/research/ 

us_rec02.txt. 

NUMBER OF THRUSH AIRCRAFT, INC. OWNERS HAVING PARTICULAR NUMBERS OF AFFECTED AIRPLANES

Number of 

affected airplanes held by 

single owner 

Number of 

owners 

Cumulative 

% 

1 406 74.4 

2 86 90.1 

3 26 94.9 

4 13 97.3 

5 7 98.5 

6 2 98.9 

7 2 99.3 

8 1 99.5 

9 2 99.8 

13 1 100.0 

Total ............................................................................................................................................. ........................ 546 ........................

Mean ............................................................................................................................................ 1.48 ........................ ........................

Median ......................................................................................................................................... 1.00 ........................ ........................

Source: FAA Registry. Data downloaded on 4/18/08. 

In the ‘‘Cost of Compliance’’ section of 

this final rule, we estimate total cost 

(undiscounted) to be $20.1 million and 

the present value cost to be $18.2 

million. As noted above, the FAA 

estimates that 545 of the 546 affected by 

this final rule are small firms, and, in 

fact, 99.7 percent of the final rule’s 

estimated cost is attributed to small 

entities. The following document 

analyzes the impact of this cost on the 

substantial number of small firms 

identified above. 

Because the FAA Registry does not 

collect financial or business data on 

these entities, and such data are not 

readily available elsewhere, the FAA 

also used Census Bureau size 

distribution data to assess the economic 

impact on small firms. The FAA used 

data from the 2002 Census since this is 

the latest census for which size 

distribution by business receipts is 

readily available. These data are 

available in a special census 

compilation for the SBA.3 The FAA 

used the data for NAICS 115112—Soil 

Preparation, Planting, and Cultivating 

(including Crop Dusting, Crop 

Spraying), but did not use the data for 

NAICS 115310—Support Activities for 

Forestry (including Forest Fire 

Suppression) since, as noted above, a 

very high percentage of the affected 

small firms, if not all, meet the 

classification standard of NAICS 

115112. Moreover, the size distribution 

of NAICS 115310 appears to be similar 

to that of NAICS 115112. The 

concentration of the affected airplanes 

in one NAICS industry, noted above, 

makes the use of census data feasible 

and appropriate. 

The relevant census data are provided 

in the table below: 

2002 CENSUS DATA FOR NAICS 115112—SOIL PREPARATION, PLANTING, AND CULTIVATING (INCL. CROP DUSTING, 

CROP SPRAYING)—SMALL SIZE CLASSES

Measure Total $0–100 

thousand 

$100–500 

thousand 

$500 

thousand– 

1 million 

$1–5 million $5–10 million 

Firms ........................................................ 2336 509 992 412 394 29 

Percentage of firms .................................. ........................ 21.8% 42.5% 17.6% 16.9% 1.2% 

Upper bound percentile ........................... ........................ 21.8% 64.3% 81.9% 98.8% 100.0% 

Est. Receipts ($000) ................................ $1,531,004 $25,681 $257,447 $286,462 $772,401 $189,013 

Receipts/Firm ($) ..................................... $655,396 $50,454 $259,523 $695,296 $1,960,409 $6,517,690 

Source: ‘‘Firms’’ and ‘‘Est. Receipts’’ from Small Business Administration, Office of Advocacy. http://www.sba.gov/advo/research/us_rec02.txt. 

The table above shows the number of 

firms and business receipt data for the 

five smallest size classes of NAICS 

115112 that encompass the size range of 

the firms affected by this final rule. In 

the ‘‘Percentage of firms’’ row, for each 

size class, the FAA calculates that 

class’s number of firms as a percentage 

of the total number of firms in the five 

size classes. Cumulating this percentage 

from the smallest to largest size class 

establishes the ‘‘Upper bound 

percentile’’—the cumulated percentage 

of firms of business receipt size ranging 

up to the upper bound of the size class. 

The final rule’s cost for the firms at the 

upper bound percentiles is then 

estimated as the corresponding 

percentiles in the estimated firm-level 

compliance cost data. In order to assess 

the economic impact of the final rule, 

these costs are calculated as a 

percentage of the census data upper 

bounds. 

For example, the upper bound 

percentile for the $100–500 thousand 

size class is 64.3 percent, so we estimate 

the NAICS 115112 firms at that 

percentile to have business receipts of 

$500,000. As shown in the table below, 

the FAA then determined the estimated 

compliance cost of firms at the same 

percentile in the compliance cost data to 

be $57,584. The FAA assumes these 

firms are the same, so the percentage 

cost impact (AD Cost/Firm Size) is 11.5 

percent. This procedure assumes the 

size distribution of the 808 firms 

affected by the final rule has a 


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distribution similar to the overall 

distribution of the small firms in NAICS 

115112. It also assumes there is a perfect 

rank correlation between the size of the 

affected firms and the firms’ present 

value compliance cost. While the latter 

assumption is certainly not the case, any 

deviation from such perfect correlation 

can only increase the impact of the final 

rule because smaller firms will have 

larger costs. Accordingly, the FAA’s 

determination that the final rule will 

have a significant impact on a 

substantial number of small entities is 

unaffected. 

ECONOMIC IMPACT OF AD ON SMALL FIRMS

AD cost to firm Firm percentile 

Estimated firm 

size (Census 

Bureau’s 

receipts upper 

bound) 

AD cost/firm 

size 

Cumulative 

number of 

firms 

$0 ........................................................................ 21.8 percentile .................................................... $100,000 0.0% 119.2 

$57,584 ............................................................... 64.3 percentile .................................................... $500,000 11.5% 351.5 

$63,220 ............................................................... 81.9 percentile .................................................... $1,000,000 6.3% 447.9 

$203,502 ............................................................. 98.8 percentile .................................................... $5,000,000 4.1% 540.2 

The table above shows a zero-cost 

impact on a firm at the 21.8 percentile. 

This result reflects the estimate in the 

FRFA cost analysis (see docket) that 

more than 500 older airplanes will retire 

before their wing front lower spar cap 

life limits are reached. As already 

mentioned, the AD cost for a firm at the 

64.3 percentile is $61,754, which as a 

percentage of estimated firm size (size 

class upper bound) is 11.5 percent of 

annual business receipts. This impact 

declines to 6.3 percent for a firm at the 

81.9 percentile and to 4.1 percent for a 

firm at the 98.8 percentile. The overall 

pattern is zero impact for the smallest of 

the small firms owners of the oldest 

airplanes, but a highly positive impact 

for the medium-sized small firms. In 

percentage terms, this impact falls for 

the largest small firms, but remains at a 

substantial level. While the FAA can 

make no definitive inference on the 

impact of the final rule on firms 

between the 21.8 and 64.3 percentiles, 

the FAA notes the cost varies from 6.3 

percent up to 11.5 percent of annual 

business receipts for 96 firms between 

the 81.9 and 64.3 percentiles and from 

4.1 percent to 6.3 percent of annual 

business receipts for 92 firms between 

the 98.8 and 81.9 percentiles. These 

estimated percentage impacts are 

substantial. Therefore, the FAA 

concludes that this final rule will have 

a significant impact on a substantial 

number of small entities. 

International Trade Impact Analysis 

The Trade Agreement Act of 1979 

prohibits Federal agencies from 

establishing any standards or engaging 

in related activities that create 

unnecessary obstacles to the foreign 

commerce of the United States. The 

statute does not consider legitimate 

domestic objectives, such as safety, as 

unnecessary. The statute also requires 

consideration of international standards 

and, where appropriate, that they be the 

basis for U.S. standards. The FAA is 

issuing this final rule because of a 

known safety problem. Therefore, this 

final rule AD action applies only to U.S. 

registered airplanes and is not 

considered an unnecessary obstacle to 

international trade. 

Unfunded Mandates Reform Act 

Assessment 

Title II of the Unfunded Mandates 

Reform Act of 1995 (Pub. L. 104–4) 

requires each Federal agency to prepare 

a written statement assessing the effects 

of any Federal mandate in a proposed or 

final agency rule that may result in an 

expenditure of $100 million or more 

(adjusted annually for inflation with the 

base year 1995) in any one year by State, 

local, and Tribal governments in the 

aggregate, or by the private sector. The 

Act deems such a mandate to be a 

‘‘significant regulatory action.’’ The FAA 

currently uses an inflation-adjusted 

value of $136.1 million. This rule does 

not contain such a mandate. 

Regulatory Findings 

We have determined that this AD will 

not have federalism implications under 

Executive Order 13132. This AD will 

not have a substantial direct effect 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. 

For the reasons discussed above, I 

certify that this AD: 

1. Is not a ‘‘significant regulatory 

action’’ under Executive Order 12866; 

2. Is not a ‘‘significant rule’’ under the 

DOT Regulatory Policies and Procedures 

(44 FR 11034, February 26, 1979); and 

3. Will have a significant economic 

impact, positive or negative, on a 

substantial number of small entities 

under the criteria of the Regulatory 

Flexibility Act. 

We prepared a summary of the costs 

to comply with this AD (and other 

information as included in the 

Regulatory Evaluation) and placed it in 

the AD Docket. You may get a copy of 

this summary by sending a request to us 

at the address listed under ADDRESSES. 

Include ‘‘Docket No. FAA–2007–27862; 

Directorate Identifier 2007–CE–036–AD’’ 

in your request. 

List of Subjects in 14 CFR Part 39 

Air transportation, Aircraft, Aviation 

safety, Incorporation by reference, 

Safety. 

Adoption of the Amendment 

■ Accordingly, under 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. 

§ 39.13 [Amended] 

■ 2. The FAA amends § 39.13 by 

removing Airworthiness Directive (AD) 

2006–07–15, Amendment 39–14542 (71 

FR 16691, April 4, 2006), and adding 

the following new AD: 

2009–26–11 Thrush Aircraft, Inc. (Type 

Certificate Previously Held by Quality 

Aerospace, Inc. and Ayres Corporation): 

Amendment 39–16150; Docket No. 

FAA–2007–27862; Directorate Identifier 

2007–CE–036–AD. 

Effective Date 

(a) This AD becomes effective on February 

24, 2010. 

Affected ADs 

(b) The following lists a history of the ADs 

affected by this AD action: 

(1) This AD supersedes AD 2006–07–15, 

Amendment 39–14542; 


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(2) AD 2006–07–15 superseded AD 2003– 

07–01, Amendment 39–13097; 

(3) AD 2003–07–01 superseded AD 2000– 

11–16, Amendment 39–11764; 

(4) AD 2000–11–16 superseded AD 97–17– 

03, Amendment 39–10195; and 

(5) AD 97–17–03 superseded AD 97–13–11, 

Amendment 39–10071. 

Applicability 

(c) This AD affects the following airplane 

models and serial numbers (S/Ns) in Table 1 

that are certificated in any category when 

wing front lower spar cap part numbers (P/ 

Ns) 20207–1, 20207–2, 20207–11, 20207–12, 

20207–13, 20207–14, 20207–15, or 20207–16 

are installed. This AD applies to the S/Ns in 

Table 1 with or without a ‘‘DC’’ suffix. This 

AD does not affect airplanes with any other 

wing front lower spar cap part number, e.g. 

Thrush P/N 22507 (any dash number) or 

Supplemental Type Certificate (STC) 

SA03654AT parts. The table also identifies 

the group that each airplane belongs in when 

determining inspection compliance times 

and life limit times for the parts: 

TABLE 1—APPLICABILITY AND AIRPLANE GROUPS

Model S/Ns Group 

(1) S–2R ....................................................... 5000R through 5100R, except 5010R, 5031R, 5038R, 5047R, and 5085R ..................... 1 

(2) S2R–G1 .................................................. G1–101 through G1–106 .................................................................................................... 1 

(3) S2R–R1820 ............................................. R1820–001 through R1820–035 ........................................................................................ 1 

(4) S2R–T15 ................................................. T15–001 through T15–033 (also see paragraph (d) of this AD) ....................................... 1 

(5) S2R–T34 ................................................. 6000R through 6049R, T34–001 through ..........................................................................

T34–143, T34–145, T34–171, T34-180, and .....................................................................

T34–181 (also see paragraph (e) of this AD) ....................................................................

1 

(6) S2R–G10 ................................................ G10–101 through G10–138, G10–140, and ......................................................................

G10–141 .............................................................................................................................

2 

(7) S2R–G5 .................................................. G5–101 through G5–105 .................................................................................................... 2 

(8) S2R–G6 .................................................. G6–101 through G6–147 .................................................................................................... 2 

(9) S2RHG–T65 ............................................ T65–002 through T65–018 ................................................................................................. 2 

(10) S2R–R1820 ........................................... R1820–036 ......................................................................................................................... 2 

(11) S2R–T34 ............................................... T34–144, T34–146 through T34–170, T34–172 through T34–179, and T34–189 

through T34–234 (also see paragraph (e) of this AD).

2 

(12) S2R–T45 ............................................... T45–001 through T45–014 ................................................................................................. 2 

(13) S2R–T65 ............................................... T65–001 through T65–018 ................................................................................................. 2 

(14) 600 S2D ................................................ All serial numbers beginning with 600–1311D ................................................................... 3 

(15) S–2R ..................................................... 1380R, 1416R through 2592R, 3000R, and 3002R .......................................................... 3 

(16) S2R–R1340 ........................................... R1340–001 through R1340–035 ........................................................................................ 3 

(17) S2R–R3S .............................................. R3S–001 through R3S–011 ............................................................................................... 3 

(18) S2R–T11 ............................................... T11–001 through T11–005 ................................................................................................. 3 

(19) S2R–G1 ................................................ G1–107 through G1–115 .................................................................................................... 5 

(20) S2R–G10 .............................................. G10–139, G10–142 through G10–165 ............................................................................... 5 

(21) S2R–G6 ................................................ G6–148 through G6–155 .................................................................................................... 5 

(22) S2RHG–T34 .......................................... T34HG–102 ........................................................................................................................ 5 

(23) S2R–T15 ............................................... T15–034 through T15–040 (also see paragraph (d) of this AD) ....................................... 5 

(24) S2R–T34 ............................................... T34–236 through T34–270 (also see paragraph (e) of this AD) ....................................... 5 

(25) S2R–T45 ............................................... T45–015 .............................................................................................................................. 5 

(26) S–2R ..................................................... 5010R, 5031R, 5038R, 5047R, and 5085R ....................................................................... 6 

(d) The S/Ns of Model S2R–T15 airplanes 

could incorporate T15-xxx and T27-xxx (xxx 

is the variable for any of the S/Ns beginning 

with T15- and T27-). This AD applies to both 

of these S/N designations as they are both 

Model S2R–T15 airplanes. 

(e) The S/Ns of Model S2R–T34 airplanes 

could incorporate T34-xxx, T36-xxx, T41- 

xxx, or T42-xxx (xxx is the variable for any 

of the S/Ns beginning with T34-, T36-, 

T41-, and T42-). This AD applies to all of 

these S/N designations as they are all Model 

S2R–T34 airplanes. 

(f) Any Group 3 airplane that has been 

modified with a hopper of a capacity more 

than 410 gallons, a piston engine greater than 

600 horsepower, or a gas turbine engine 

greater than 600 horsepower, is a Group 1 

airplane for the purposes of this AD. Inspect 

the airplane at the Group 1 compliance time 

specified in this AD. Replace the wing front 

lower spar caps in accordance with the 

formulas given in paragraph (k) of this AD. 

(g) Group 6 airplanes were originally 

manufactured with higher horsepower radial 

engines, but were converted to lower 

horsepower radial engines. They are now 

configured identically to Group 3 airplanes. 

Unsafe Condition 

(h) This AD is the result of the analysis of 

data from 117 wing front lower spar cap 

fatigue cracks found on similar design Model 

600 S2D and S2R (S–2R) series airplanes and 

the FAA’s determination that the 

replacement of high time wing front lower 

spar caps is necessary to address the unsafe 

condition for certain airplanes. Since we 

issued AD 2006–07–15, analysis reveals that 

inspections are not detecting all existing 

cracks, and incidences of undetected cracks 

are increasing. This AD retains the actions of 

AD 2006–07–15 and imposes a life limit on 

the wing front lower spar caps that requires 

you to replace the wing front lower spar caps 

when the life limit is reached. This AD also 

changes the requirements and applicability of 

the groups discussed above and removes the 

ultrasonic inspection method. We are issuing 

this AD to prevent wing front lower spar cap 

failure caused by undetected fatigue cracks. 

Such failure could result in loss of a wing. 

Compliance 

(i) To address the problem, do the 

following, unless already done: 

(1) If you have already done an inspection 

required by AD 2006–07–15, within the next 

30 days after February 24, 2010 (the effective 

date of this AD), identify the number of hours 

time-in-service (TIS) since your last 

inspection required by AD 2006–07–15. You 

will need this to establish the inspection 

interval for the next inspection required by 

this AD. 

(2) Inspect the two outboard bolt hole areas 

(whether 1⁄4-inch and 5⁄16-inch diameter bolt 

holes or both 5⁄16-inch diameter bolt holes) on 

each wing front lower spar cap for fatigue 

cracking using magnetic particle or eddy 

current procedures. If Kaplan splice blocks, 

P/N 22515–1/–3 or P/N 88–251, are installed 

following Quality Aerospace, Inc. Custom Kit 

No. CK–AG–30, dated December 6, 2001, 

inspect the three outboard bolt hole areas on 

each wing front lower spar cap for fatigue 

cracking using magnetic particle or eddy 

current procedures. Use the compliance 

times listed in paragraph (i)(3) of this AD for 

the initial inspection and the compliance 

time listed in paragraphs (i)(5), (i)(6), or (i)(7) 

of this AD for the repetitive inspections. The 

cracks may emanate from the bolt hole on the 

face of the wing front lower spar cap or they 

may occur in the shaft of the hole. Inspect 

both of those areas. 


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(i) If using the magnetic particle method, 

inspect using the ‘‘Inspection’’ portion of the 

‘‘Accomplishment Instructions’’ and ‘‘Lower 

Splice Fitting Removal and Installation 

Instructions’’ in Ayres Corporation Service 

Bulletin No. SB–AG–39, dated September 17, 

1996. Do the inspection following FAA 

Advisory Circular (AC) 43.13–1B, Chapter 5, 

Section 4, Magnetic Particle Inspection, using 

the wet particle method. You may obtain a 

copy of AC 43.13–1B at http://www.faa.gov/ 

regulations_policies/. Caution: Firmly 

support the wings during the inspection to 

prevent movement of the wing front lower 

spar caps when the splice blocks are 

removed. This will allow easier realignment 

of the splice block holes and the holes in the 

wing front lower spar cap for bolt insertion 

and prevent damage to the bolt hole. Damage 

to the bolt hole inner surface or edge of the 

bolt hole can cause cracks to begin 

prematurely. 

(ii) The inspection must be done by or 

supervised by a Level 2 or Level 3 inspector 

certified following the guidelines in FAA AC 

65–31A. You may obtain a copy of AC 65– 

31A at http://www.faa.gov/ 

regulations_policies/. 

(iii) If using eddy current methods, a 

procedure must be sent to the FAA, Atlanta 

Aircraft Certification Office (ACO), for 

approval before doing the inspection. Send 

your proposed procedure to the FAA, Atlanta 

ACO, Attn: Cindy Lorenzen, 1701 Columbia 

Avenue, College Park, Georgia 30337. You 

are not required to remove the splice block 

for the eddy current inspections, unless 

corrosion is visible. Eddy current inspection 

procedures previously approved under AD 

2006–07–15, AD 2003–07–01, AD 2000–11– 

16, AD 97–13–11, and/or AD 97–17–03 

remain valid for this AD. 

(iv) If you change the inspection method 

used (magnetic particle or eddy current), the 

TIS intervals for repetitive inspections are 

based on the method used for the last 

inspection. 

(3) If airplanes have not yet reached the 

threshold for the initial inspection required 

in AD 2006–07–15, initially inspect 

following the wing front lower spar cap 

hours total TIS schedule below or within the 

next 50 hours TIS after February 24, 2010 

(the effective date of this AD), whichever 

occurs later: 

TABLE 2—INITIAL INSPECTION TIMES

Airplane group 

Initially inspect upon accumulating 

the following hours total TIS on 

the wing front lower spar cap 

(i) Group 1 ........................................................................................................................................................... 2,000 hours TIS. 

(ii) Group 2 .......................................................................................................................................................... 1,400 hours TIS. 

(iii) Group 3 .......................................................................................................................................................... 6,400 hours TIS. 

(iv) Group 5 ......................................................................................................................................................... 1,000 hours TIS. 

(v) Group 6 .......................................................................................................................................................... (A) S/N 5010R: 5,530 hours TIS. 

(B) S/N 5038R: 5,900 hours TIS. 

(C) S/N 5031R: 6,400 hours TIS. 

(D) S/N 5047R: 6,400 hours TIS. 

(E) S/N 5085R: 6,290 hours TIS. 

(vi) Any airplane with the entire Custom Kit CK–AG–41 installed ...................................................................... 2,000 hours TIS. 

(4) Airplanes in all groups must meet the 

following conditions before doing the 

repetitive inspections required in paragraphs 

(i)(5), (i)(6), or (i)(7) of this AD: 

(i) No cracks have been found previously 

on wing front lower spar cap; or 

(ii) Small cracks have been repaired 

through cold work (or done as an option if 

never cracked) following Ayres Corporation 

Service Bulletin No. SB–AG–39, dated 

September 17, 1996; or 

(iii) Small cracks have been repaired by 

reaming the 1⁄4-inch bolt hole to 5⁄16 inches 

diameter (or done as an option if never 

cracked) following Ayres Corporation 

Custom Kit No. CK–AG–29, Part I, dated 

December 23, 1997; or 

(iv) Small cracks have been repaired 

through previous alternative methods of 

compliance (AMOC); or 

(v) Small cracks have been repaired by 

installing Kaplan splice blocks, P/N 22515– 

1/–3 or P/N 88–251 (or done as an option if 

never cracked) following Quality Aerospace, 

Inc. Custom Kit No. CK–AG–30, dated 

December 6, 2001. 

(5) Repetitively inspect Groups 1, 2, 3, and 

6 airplanes that do not have ‘‘big butterfly’’ 

plates and lower splice plates, P/Ns 20211– 

09 and 20211–11, installed following Ayres 

Corporation Custom Kit No. CK–AG–29, Part 

II, dated December 23, 1997; or that do not 

have ‘‘big butterfly’’ plates and lower splice 

plates, P/Ns 94418–5 and 94418–7 or P/Ns 

94418–13 and 94418–15, installed following 

Thrush Aircraft, Inc. Custom Kit No. CK– 

AG–41, Revision A, dated March 8, 2007; and 

meet the conditions in paragraph (i)(4) of this 

AD. Follow the wing front lower spar cap 

hours TIS compliance schedule below: 

TABLE 3—REPETITIVE INSPECTION TIMES FOR AIRPLANE GROUPS 1, 2, 3, AND 6 WITHOUT ‘‘BIG BUTTERFLY’’ PLATES AND

LOWER SPLICE PLATES

When airplanes accumulate the following hours TIS on the wing front lower 

spar cap since the last inspection required in AD 2006-07-15, 

Inspect within the following hours TIS 

after the effective date of this AD, 

Inspect thereafter at 

intervals not to 

exceed . . . 

(i) Magnetic Particle inspection: ........................................................................... ............................................................... 250 hours TIS. 

(A) 350 or more hours TIS ............................................................................ (A) 50 hours TIS.

(B) 175 through 349 hours TIS ..................................................................... (B) 75 hours TIS.

(C) Less than 175 hours TIS ........................................................................ (C) upon accumulating 250 hours TIS.

(ii) Eddy Current inspection: ................................................................................. ............................................................... 350 hours TIS. 

(A) 500 or more hours TIS ............................................................................ (A) 50 hours TIS.

(B) 275 through 499 hours TIS ..................................................................... (B) 75 hours TIS.

(C) Less than 275 hours TIS ........................................................................ (C) upon accumulating 350 hours TIS.

(6) Repetitively inspect Groups 1, 2, 3, 5, 

and 6 airplanes that have ‘‘big butterfly’’ 

plates and lower splice plates, P/Ns 20211– 

09 and 20211–11, installed following Ayres 

Corporation Custom Kit No. CK–AG–29, Part 

II, dated December 23, 1997; or that have ‘‘big 

butterfly’’ plates and lower splice plates, 

P/Ns 94418–5 and 94418–7, or P/Ns 94418– 

13 and 94418–15, installed following Thrush 

Aircraft, Inc. Custom Kit No. CK–AG–41, 

Revision A, dated March 8, 2007; and meet 

the conditions in paragraph (i)(4) of this AD. 

Follow the wing front lower spar cap hours 

TIS compliance schedule below: 


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TABLE 4—REPETITIVE INSPECTIONS TIMES FOR AIRPLANE GROUPS 1, 2, 3, 5, AND 6 WITH ‘‘BIG BUTTERFLY’’ PLATES AND

LOWER SPLICE PLATES

When airplanes accumulate the following hours TIS on the wing front lower 

spar cap since the last inspection required in AD 2006-07-15, 

Inspect within the following hours TIS 

after the effective date of this AD, 

Inspect thereafter at 

intervals not to 

exceed . . . 

(i) Magnetic particle inspection: ........................................................................... ............................................................... 450 hours TIS. 

(A) 650 or more hours TIS ............................................................................ (A) 50 hours TIS.

(B) 375 through 649 hours TIS ..................................................................... (B) 75 hours TIS.

(C) Less than 375 hours TIS ........................................................................ (C) upon accumulating 450 hours TIS.

(ii) Eddy Current inspection: ................................................................................. ............................................................... 625 hours TIS. 

(A) 900 or more hours TIS ............................................................................ (A) 50 hours TIS.

(B) 550 through 899 hours TIS ..................................................................... (B) 75 hours TIS.

(C) Less than 550 hours TIS ........................................................................ (C) upon accumulating 625 hours TIS.

Note 1: Group 5 airplanes had P/Ns 20211– 

09 and 20211–11 installed at the factory. 

(7) Repetitively inspect airplanes that 

incorporate Thrush Aircraft, Inc. Custom Kit 

No. CK–AG–41, Revision A, dated March 8, 

2007, in its entirety that meet the conditions 

in paragraph (i)(4) of this AD. Follow the 

wing front lower spar cap hours TIS 

compliance schedule below: 

TABLE 5—REPETITIVE INSPECTION TIMES FOR AIRPLANES WITH THRUSH AIRCRAFT, INC. CUSTOM KIT NO. CK–AG–41, 

REVISION A, INCORPORATED IN ITS ENTIRETY

When using the following inspection methods, Repetitively inspect at intervals not 

to exceed . . . 

(i) Magnetic particle inspection ............................................................................................................................ 900 hours TIS. 

(ii) Eddy current inspection .................................................................................................................................. 1,250 hours TIS. 

(j) Initially replace the wing front lower 

spar caps, P/Ns 20207–1, 20207–2, 20207–11, 

20207–12, 20207–13, 20207–14, 20207–15, or 

20207–16, at the times specified in Table 6 

of this AD. Repetitively replace thereafter at 

the life limit times specified in Table 7 of this 

AD. Do the replacements as specified in 

paragraph (l)(4) of this AD. 

TABLE 6—INITIAL COMPLIANCE TIME FOR WING FRONT LOWER SPAR CAP REPLACEMENT

Total hours TIS on the wing front lower spar cap 

Replace the wing front lower spar 

cap upon accumulating the 

following hours TIS on the spar 

cap after the effective date of this 

AD 

(i) Group 1 with a radial engine and more than 15,000 hours TIS .................................................................... 500 hours. 

(ii) Group 1 with a radial engine and 12,000 to 15,000 hours TIS ..................................................................... 1,000 hours. 

(iii) Group 1 with a radial engine and 9,000 to 11,999 hours TIS ...................................................................... 1,500 hours. 

(iv) Group 1 with a radial engine and 7,400 to 8,999 hours TIS ........................................................................ 2,000 hours. 

(v) Group 1 with a radial engine and less than 7,400 hours TIS ....................................................................... Use Table 7(xxii). 

(vi) Group 1 with a turbine engine and more than 14,000 hours TIS ................................................................ 500 hours. 

(vii) Group 1 with a turbine engine and 11,000 to 14,000 hours TIS ................................................................. 1,000 hours. 

(viii) Group 1 with a turbine engine and 8,000 to 10,999 hours TIS .................................................................. 1,500 hours. 

(ix) Group 1 with a turbine engine and 4,200 to 7,999 hours TIS ...................................................................... 2,000 hours. 

(x) Group 1 with a turbine engine and less than 4,200 hours TIS ..................................................................... Use Table 7(xxiii). 

(xi) Group 2 with more than 9,000 hours TIS ..................................................................................................... 500 hours. 

(xii) Group 2 with 6,000 to 9,000 hours TIS ....................................................................................................... 1,000 hours. 

(xiii) Group 2 with 3,900 hours to 5,999 hours TIS ............................................................................................ 1,500 hours. 

(xiv) Group 2 with less than 3,900 hours TIS ..................................................................................................... Use Table 7(xxiv). 

(xv) Group 3 and 6 with more than 28,800 hours TIS ........................................................................................ 500 hours. 

(xvi) Group 3 and 6 with 27,800 to 28,799 hours TIS ........................................................................................ 1,000 hours. 

(xvii) Group 3 and 6 with less than 27,800 hours TIS ........................................................................................ Use Table 7(xxv). 

(xviii) Group 5 with more than 8,000 hours TIS .................................................................................................. 500 hours. 

(xix) Group 5 with 5,000 to 7,999 hours TIS ...................................................................................................... 1,000 hours. 

(xx) Group 5 with 2,400 to 4,999 hours TIS ....................................................................................................... 1,500 hours. 

(xxi) Group 5 with less than 2,400 hours TIS ..................................................................................................... Use Table 7(xxvi). 

TABLE 7—WING FRONT LOWER SPAR CAP LIFE LIMITS

Airplane group 

Replace wing front lower spar cap 

upon the accumulation of the 

following hours TIS on the spar 

cap: 

(xxii) Group 1 with a radial engine ...................................................................................................................... 9,400 hours TIS. 


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TABLE 7—WING FRONT LOWER SPAR CAP LIFE LIMITS—Continued 

Airplane group 

Replace wing front lower spar cap 

upon the accumulation of the 

following hours TIS on the spar 

cap: 

(xxiii) Group 1 with a turbine engine ................................................................................................................... 6,200 hours TIS. 

(xxiv) Group 2 ...................................................................................................................................................... 5,400 hours TIS. 

(xxv) Groups 3 and 6 .......................................................................................................................................... 28,800 hours TIS. 

(xxvi) Group 5 ...................................................................................................................................................... 3,900 hours TIS with original wing 

front lower spar cap P/N 20207– 

11 or P/N 20207–12. 

5,400 hours TIS after original wing 

front lower spar cap has been 

replaced with any P/N 20207-xx 

wing front lower spar cap. 

Note 2: There is evidence of sharp, uneven 

edges on the spar cap bolt holes that resulted 

from the manufacturing process in Group 5 

airplanes. Once the original wing front lower 

spar caps are replaced, the life limit 

increases. 

(k) As previously stated in paragraph (f) of 

this AD, any Group 3 airplane that has been 

modified with a hopper of a capacity more 

than 410 gallons, a piston engine greater than 

600 horsepower, or a gas turbine engine 

greater than 600 horsepower, is a Group 1 

airplane for the purposes of this AD. Replace 

the wing front lower spar caps using the 

following formulas. 

(1) For airplanes that were originally Group 

3 airplanes and later modified by installing 

a piston engine of greater than 600 

horsepower and/or a hopper capacity of 

greater than 410 gallons, calculate the 

equivalent Group 1 hours TIS on each spar 

cap as follows: 

(i) Usage factor Total hrs. on cap pre-mod. Addition = +

28 800 ,

al hrs. on cap post-mod.

9 400 ,

(ii) Equivalent Group 1 hours TIS = 9,400 

× Usage Factor 

(2) For airplanes that were originally Group 

3 airplanes and later modified by installing 

a turbine engine of greater than 600 

horsepower, with or without installing a 

hopper with greater than 410 gallon capacity, 

calculate the equivalent Group 1 hours TIS 

on each spar cap as follows: 

(i) Usage factor Total hrs. on cap pre-mod. Addition = +

28 800 ,

al hrs. on cap post-mod.

6 200 ,

(ii) Equivalent Group 1 hours TIS = 6,200 

× Usage Factor 

(3) When the equivalent Group 1 hours TIS 

on the wing front lower spar cap equals the 

life limit of 9,400 hours TIS if a radial piston 

engine is installed or reaches 6,200 hours TIS 

if a turbine engine is installed, the wing front 

lower spar cap must be replaced. Use Table 

6 if over the life limit. 

(4) See the appendix to this AD for 

examples of how to calculate the applicable 

life limit. 

(l) If any cracks are found during any 

inspection required by this AD, you must 

repair the cracks or replace the wing front 

lower spar cap before further flight. 

(1) Use the cold work process to ream out 

small cracks as defined in Ayres Corporation 

Service Bulletin No. SB–AG–39, dated 

September 17, 1996, and deburr the bolt hole 

edges with the splice blocks removed after 

cold work is performed; or 

(2) If the crack is found in a 1⁄4-inch bolt 

hole, ream the 1⁄4-inch bolt hole to 5⁄16 inches 

diameter as defined in Part I of Ayres 

Corporation Custom Kit No. CK–AG–29, 

dated December 23, 1997; or 

(3) Install Kaplan splice blocks, P/N 

22515–1/3 or P/N 88–251, following Quality 

Aerospace, Inc. Custom Kit No. CK–AG–30, 

dated December 6, 2001; or 

(4) Replace the affected wing front lower 

spar cap following an FAA-approved 

procedure. Contact the FAA at the address in 

paragraph (t) of this AD to obtain an FAAapproved replacement procedure unless 

previously provided by the manufacturer at 

delivery of the airplanes. An alternative to 

replacing just the affected wing front lower 

spar cap is to replace both wing front lower 

spar caps and the surrounding structure 

following Thrush Aircraft, Inc. Custom Kit 

No. CK–AG–41, Revision A, dated March 8, 

2007. Another alternative to replacing just 

the affected wing front lower spar cap is to 

replace both wing front lower spar caps and 

the surrounding structure following Avenger 

Aircraft and Services FAA STC SA03654AT 

for Avenger Extended Performance Front 

Spar Enhancement Kit. You may obtain a 

copy of FAA STC SA03654AT at http:// 

www.faa.gov/aircraft/air_cert/ 

design_approvals/stc/. If you chose to install 

Thrush Custom Kit No. CK–AG–41, the FAA 

recommends installing Custom Kit No. CK– 

AG–41, Revision A, in its entirety although 

this is not mandatory. The additional 

structure provided in Thrush Aircraft, Inc. 

Custom Kit No. CK–AG–41, Revision A, 

dated March 8, 2007, will provide a greater 

level of safety than the minimum acceptable 

level of safety provided by replacing just the 

wing front lower spar cap. If choosing to 

install the Avenger FAA STC kit, it is 

mandatory to install the entire FAA STC kit. 

(m) If a crack is found, the reaming 

associated with the cold work process may 

remove a crack if it is small enough. Some 

aircraft owners/operators were issued 

AMOCs with AD 97–17–03 to ream the 1⁄4- 

inch bolt hole to 5⁄16 inches diameter to 

remove small cracks. Ayres Corporation 

Custom Kit No. CK–AG–29, Part I, dated 

December 23, 1997, also provides procedures 

to ream the 1⁄4-inch bolt hole to 5⁄16 inches 

diameter, which may remove a small crack. 

Resizing the holes to the required size to 

install a Kaplan splice block may also remove 

small cracks. If you use any of these methods 

to remove cracks and the airplane is reinspected before further flight and no cracks 

are found, you may continue to follow the 

repetitive inspection intervals for your 

airplane listed in paragraphs (i)(5), (i)(6), or 

(i)(7) of this AD. 

(n) For all inspection methods (magnetic 

particle or eddy current), hours TIS for initial 

and repetitive inspection intervals and wing 

front lower spar cap life limit start over when 


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the wing front lower spar cap is replaced 

with a new P/N 20207–1, 20207–2, 20207– 

11, 20207–12, 20207–13, 20207–14, 20207– 

15, or 20207–16. These wing front lower spar 

caps must be inspected as specified in 

paragraphs (i)(3), (i)(5), (i)(6), and (i)(7) of 

this AD. 

(1) If the wings or wing front lower spar 

caps were replaced with new or used wings 

or wing front lower spar caps during the life 

of the airplane and the logbook records 

positively show the hours TIS of the 

replacement wings or wing front lower spar 

caps, then initially inspect at applicable 

times specified in paragraph (i)(3) of this AD. 

Repetitively inspect thereafter at intervals 

specified paragraphs (i)(5), (i)(6), or (i)(7) of 

this AD. Replace the wing front lower spar 

caps upon reaching the life limit specified in 

Table 7 of this AD. 

(2) If the wings or wing front lower spar 

caps were replaced with new or used wings 

or wing front lower spar caps during the life 

of the airplane and logbook records do not 

positively show the hours TIS of the 

replacement wings or wing front lower spar 

caps, then inspect within 50 hours TIS after 

February 24, 2010 (the effective date of this 

AD), unless already done. Repetitively 

inspect thereafter at intervals specified in 

paragraphs (i)(5), (i)(6), or (i)(7) of this AD. 

Replace the wing front lower spar caps 

within 500 hours TIS after February 24, 2010 

(the effective date of this AD). 

(3) If both wing front lower spar caps are 

replaced by installing the entire Thrush 

Aircraft, Inc. Custom Kit No. CK–AG–41, 

Revision A, dated March 8, 2007, then 

initially inspect at 2,000 hours TIS as shown 

in paragraph (i)(3) of this AD. Repetitively 

inspect thereafter at intervals specified in 

paragraph (i)(7) of this AD. Replace the wing 

front lower spar caps at times specified in 

paragraph (i)(8) of this AD. 

(o) Any wing front lower spar cap that is 

removed and is at or beyond the replacement 

time specified in this AD must be disposed 

of following the procedures in 14 CFR Part 

43.10. 

(p) Replacement times start over when the 

wing front lower spar cap is replaced with a 

new P/N 20207–1, 20207–2, 20207–11, 

20207–12, 20207–13, 20207–14, 20207–15, or 

20207–16. These wing front lower spar caps 

are now life-limited parts and must be 

replaced upon the accumulation of the hours 

TIS specified in Table 7 of this AD. 

(q) Report any cracks you find within 10 

days after the cracks are found or within 10 

days after February 24, 2010 (the effective 

date of this AD), whichever occurs later. 

Send your report to Cindy Lorenzen, 

Aerospace Engineer, ACE–115A, Atlanta 

ACO, 1701 Columbia Avenue, College Park, 

Georgia 30337; telephone: (404) 474–5524; 

facsimile: (404) 474–5606; e-mail: 

cindy.lorenzen@faa.gov. The Office of 

Management and Budget (OMB) approved 

the information collection requirements 

contained in this regulation under the 

provisions of the Paperwork Reduction Act 

and assigned OMB Control Number 2120– 

0056. Include in your report the following 

information: 

(1) Aircraft model and serial number; 

(2) Engine model; 

(3) Aircraft hours TIS; 

(4) Left and right wing front lower spar cap 

hours TIS; 

(5) Hours TIS on the spar cap since last 

inspection; 

(6) Crack location and size; 

(7) Procedure (magnetic particle, 

ultrasonic, or eddy current) used for the last 

inspection; 

(8) Description of any previous 

modifications and hours TIS when the 

modification was done, such as engine model 

change, installation of winglets, hopper 

capacity increase, cold working procedure 

done on bolt holes, installation of butterfly 

plates, or installation of Thrush Aircraft, Inc. 

Custom Kit No. CK–AG–41. 

(r) Installation of the replacement wing 

front lower spar caps and other modification 

parts that are approved by FAA STC 

SA03654AT, Installation of Avenger 

Extended Performance Front Spar 

Enhancement Kit (new wing front spar lower 

caps, center splice and doublers), in 

accordance with Part II of Avenger Master 

Data List AAS–MDL–08–001, Revision B, 

dated November 26, 2008, terminates the 

actions required by this AD. The installation 

of FAA STC SA03654AT is an alternative to 

replacing the wing front lower spar caps with 

Ayres/Thrush wing front lower spar caps. 

Special Flight Permits 

(s) Under 14 CFR part 39.23, we are 

limiting the special flight permits for this AD 

by the following conditions: 

(1) The hopper is empty; 

(2) Vne is reduced to 126 miles per hour 

(109 knots) indicated airspeed (IAS); and 

(3) Flight into known turbulence is 

prohibited. 

Alternative Methods of Compliance 

(AMOCs) 

(t) The Manager, Atlanta Aircraft 

Certification Office, (ACO) FAA, ATTN: 

Cindy Lorenzen, Aerospace Engineer, ACE– 

115A, Atlanta ACO, 1701 Columbia Avenue, 

College Park, Georgia 30337; telephone: (404) 

474–5524; facsimile: (404) 474–5606; e-mail: 

cindy.lorenzen@faa.gov; or William O. 

Herderich, Aerospace Engineer, ACE–117A, 

Atlanta ACO, 1701 Columbia Avenue, 

College Park, Georgia 30337; telephone: (404) 

474–5547; facsimile: (404) 474–5606; e-mail: 

william.o.herderich@faa.gov, has the 

authority to approve AMOCs for this AD, if 

requested using the procedures found in 14 

CFR 39.19. Before using any approved AMOC 

on any airplane to which the AMOC applies, 

notify your appropriate principal inspector 

(PI) in the FAA Flight Standards District 

Office (FSDO), or lacking a PI, your local 

FSDO. 

(u) AMOCs approved for AD 2006–07–15, 

AD 2003–07–01, AD 2000–11–16, AD 97–13– 

11, and/or AD 97–17–03 are approved as 

AMOCs for this AD except for those 

pertaining to ultrasonic inspection methods. 

Material Incorporated by Reference 

(v) You must use Ayres Corporation 

Service Bulletin No. SB–AG–39, dated 

September 17, 1996; Ayres Corporation 

Custom Kit No. CK–AG–29, dated December 

23, 1997; Quality Aerospace, Inc. Custom Kit 

No. CK–AG–30, dated December 6, 2001; 

Thrush Aircraft, Inc. Custom Kit No. CK– 

AG–41, Revision A, dated March 8, 2007; and 

Part II of Avenger Master Data List AAS– 

MDL–08–001, Revision B, dated November 

26, 2008, to do the actions required by this 

AD, unless the AD specifies otherwise. 

(1) The Director of the Federal Register 

approved the incorporation by reference of 

Thrush Aircraft, Inc. Custom Kit No. CK– 

AG–41, Revision A, dated March 8, 2007, and 

Part II of Avenger Master Data List AAS– 

MDL–08–001, Revision B, dated November 

26, 2008, under 5 U.S.C. 552(a) and 1 CFR 

part 51. 

(2) On May 20, 2003 (68 FR 15653), the 

Director of the Federal Register approved the 

incorporation by reference of Quality 

Aerospace, Inc. Custom Kit No. CK–AG–30, 

dated December 6, 2001. 

(3) On July 25, 2000 (65 FR 36055), the 

Director of the Federal Register approved the 

incorporation by reference of Ayres 

Corporation Service Bulletin No. SB–AG–39, 

dated September 17, 1996; and Ayres 

Corporation Custom Kit No. CK–AG–29, 

dated December 23, 1997. 

(4) For service information identified in 

this AD, contact Thrush Aircraft, Inc., 300 

Old Pretoria Road, P.O. Box 3149, Albany, 

Georgia 31706–3149, Internet: http:// 

www.thrushaircraft.com. To obtain 

information about Avenger Master Data List 

AAS–MDL–08–001 and the optional 

installation of FAA STC SA03654AT, contact 

Avenger Aircraft and Services, 103 N. Main 

Street, Suite 106, Greenville, South Carolina 

29601, Internet: http:// 

www.avengeraircraft.com. 

(5) You may review copies of the service 

information incorporated by reference for 

this AD at the FAA, Central Region, Office of 

the Regional Counsel, 901 Locust, Kansas 

City, Missouri 64106. For information on the 

availability of this material at the Central 

Region, call (816) 329–3768. 

(6) You may also review copies of the 

service information incorporated by reference 

for this AD at the National Archives and 

Records Administration (NARA). For 

information on the availability of this 

material at NARA, call (202) 741–6030, or go 

to: http://www.archives.gov/federal_register/

code_of_federal_regulations/

ibr_locations.html. 

Appendix to AD 2009–26–11 

The following are examples of calculating 

equivalent Group 1 hours. 

Example 1: S/N xxx was originally a Group 

3 airplane; later it was modified with a 

Wright R–1820–71, 1200 horsepower, radial 

engine when the wing front lower spar caps 

had 15,700 hours TIS on them. The wing 

front lower spar caps have accumulated an 

additional 8,200 hours since the engine 

conversion for a total of 23,900 hours TIS on 

the wing front lower spar caps. 

Usage Factor = 15,700 hours/28,800 + 8,200 

hours/9,400 = 1.417 

Equivalent Group 1 hours = 9,400 × 1.417 = 

13,320 hours. 

The wing front lower spar caps will need 

to be replaced within the next 1,000 hours 

TIS after the effective date of this AD as 

determined by Table 6 for a Group 1 airplane 


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Federal Register / Vol. 75, No. 12 / Wednesday, January 20, 2010 / Rules and Regulations 3141 

with a radial engine with between 12,000 and 

15,000 hours TIS. 

Example 2: S/N yyy was originally a Group 

3 airplane; later it was modified with a 

PT6A–34, 750 horsepower, turbine engine 

when the wing front lower spar caps had 

5,300 hours TIS on them. The wing front 

lower spar caps now have 7,700 hours TIS. 

Usage Factor = 5,300 hours/28,800 + (7,700 

¥ 5,300)/6,200 = 0.571 

Equivalent Group 1 hours = 6,200 × 0.571 = 

3,540 hours. 

The wing front lower spar caps will need 

to be replaced at 6,200 equivalent Group 1 

total hours TIS, which is within the next 

2,660 hours TIS (6,200 ¥ 3,540 = 2,660). 

Issued in Kansas City, Missouri, on January 

8, 2010. 

Margaret Kline, 

Acting Manager, Small Airplane Directorate, 

Aircraft Certification Service. 

[FR Doc. 2010–594 Filed 1–19–10; 8:45 am] 

BILLING CODE 4910–13–P 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 39 

[Docket No. FAA–2010–0029; Directorate 

Identifier 2009–NM–262–AD; Amendment 

39–16179; AD 2009–21–10 R1] 

RIN 2120–AA64 

Airworthiness Directives; AVOX 

Systems and B/E Aerospace Oxygen 

Cylinder Assemblies, as Installed on 

Various Transport Airplanes 

AGENCY: Federal Aviation 

Administration (FAA), Department of 

Transportation (DOT). 

ACTION: Final rule; request for 

comments. 

SUMMARY: The FAA is revising an 

existing airworthiness directive (AD), 

which applies to certain AVOX Systems 

and B/E Aerospace oxygen cylinder 

assemblies, as installed on various 

transport airplanes. That AD currently 

requires removing certain oxygen 

cylinder assemblies from the airplane. 

This AD removes certain oxygen 

cylinder part numbers from the 

applicability. This AD was prompted by 

the reported rupture of a high-pressure 

gaseous oxygen cylinder, which had 

insufficient strength characteristics due 

to improper heat treatment. We are 

issuing this AD to prevent an oxygen 

cylinder from rupturing, which, 

depending on the location, could result 

in structural damage and rapid 

decompression of the airplane, damage 

to adjacent essential flight equipment, 

deprivation of the necessary oxygen 

supply for the flightcrew, and injury to 

cabin occupants or maintenance or 

other support personnel. 

DATES: This AD is effective February 4, 

2010. 

We must receive any comments on 

this AD by March 8, 2010. 

ADDRESSES: You may send comments by 

any of the following methods: 

• Federal eRulemaking Portal: Go to 

http://www.regulations.gov. Follow the 

instructions for submitting comments. 

• Fax: 202–493–2251. 

• Mail: U.S. Department of 

Transportation, Docket Operations, M– 

30, West Building Ground Floor, Room 

W12–140, 1200 New Jersey Avenue, SE., 

Washington, DC 20590. 

• Hand Delivery: U.S. Department of 

Transportation, Docket Operations, M– 

30, West Building Ground Floor, Room 

W12–140, 1200 New Jersey Avenue, SE., 

Washington, DC 20590, between 9 a.m. 

and 5 p.m., Monday through Friday, 

except Federal holidays. 

Examining the AD Docket 

You may examine the AD docket on 

the Internet at http:// 

www.regulations.gov; or in person at the 

Docket Management Facility between 9 

a.m. and 5 p.m., Monday through 

Friday, except Federal holidays. The AD 

docket contains this AD, the regulatory 

evaluation, any comments received, and 

other information. The street address for 

the Docket Office (telephone 800–647– 

5527) is in the ADDRESSES section. 

Comments will be available in the AD 

docket shortly after receipt. 

FOR FURTHER INFORMATION CONTACT: 

Nicholas Wilson, Aerospace Engineer, 

Cabin Safety and Environmental 

Systems Branch, ANM–150S, Seattle 

Aircraft Certification Office, FAA, 1601 

Lind Avenue, SW., Renton, Washington 

98057–3356; telephone (425) 917–6476; 

fax (425) 917–6590. 

SUPPLEMENTARY INFORMATION: 

Discussion 

On November 25, 2009, we issued AD 

2009–21–10, amendment 39–16049 (74 

FR 63063, December 2, 2009). That AD 

applies to certain AVOX Systems and B/ 

E Aerospace oxygen cylinder 

assemblies, as installed on various 

transport airplanes. That AD requires 

removing certain oxygen cylinder 

assemblies from the airplane. That AD 

was prompted by the reported rupture 

of a high-pressure gaseous oxygen 

cylinder, which had insufficient 

strength characteristics due to improper 

heat treatment. The actions specified in 

that AD are intended to prevent an 

oxygen cylinder from rupturing, which, 

depending on the location, could result 

in structural damage and rapid 

decompression of the airplane, damage 

to adjacent essential flight equipment, 

deprivation of the necessary oxygen 

supply for the flightcrew, and injury to 

cabin occupants or maintenance or 

other support personnel. 

Actions Since AD Was Issued 

Since we issued AD 2009–21–10, we 

have been notified that its applicability 

(in paragraph (c)) erroneously includes 

oxygen cylinder assemblies having part 

numbers B43570–3 and B43570–5. 

Those oxygen cylinder assemblies are 

manufactured from composite material, 

instead of steel, and the erroneous part 

numbers do not correspond to any serial 

numbers listed in the AD. Composite 

oxygen tanks are not subject to the 

identified unsafe condition. These part 

numbers have been removed from Table 

1 of this AD. 

We have also been notified that serial 

numbers K617383 through K617423 

inclusive and K757064 through 

K757066 inclusive have been 

withdrawn from service. These serial 

numbers have been removed from Table 

3 of this AD. 

FAA’s Determination and Requirements 

of This AD 

Certain affected airplanes have been 

approved by the aviation authorities of 

other countries, and are approved for 

operation in the United States. 

The unsafe condition described 

previously is likely to exist or develop 

in other products of these same type 

designs. For this reason, we are issuing 

this AD to revise AD 2009–21–10. This 

new AD retains the requirements of the 

existing AD, but removes part numbers 

B43570–3 and B43570–5 from the 

applicability of this AD, and removes 

certain serial numbers from Table 3 of 

this AD. 

Additional Change to AD 

We have revised this AD to identify 

the legal name of certain manufacturers 

as published in the most recent type 

certificate data sheet for the affected 

airplane models. 

FAA’s Justification and Determination 

of the Effective Date 

This AD addresses the consequences 

of the potential rupture of certain 

oxygen cylinder assemblies. Because of 

our requirement to promote safe flight of 

civil aircraft and thus the critical need 

to ensure the proper functioning of the 

oxygen cylinders and the short 

compliance time involved with this 

action, this AD must be issued 

immediately. 

Because an unsafe condition exists 

that requires the immediate adoption of 


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