CUBCRA~TERS ""' 

cu bcra Fters.com 

U.S. Department of Transportation 

Docket Operations 

West Building Ground Floor 

Room W12-140 

1200 New Jersey Avenue, SE. 

Washington, DC 20590 

Re: Petition for Exemption from 14 CFR 23.629 

To Whom It May Concern: 

1 4 v l j -· !. ~!\ ' D 1 ~ I _, 

April 28, 2014 

In May of 1998, the Gavilan model EL-1 was awarded its type certificate, A00002NY. It was certified as a day, VFR 

airplane with a 4,200 MTOW and a VNE of 155 knots. In March of 2008, the Type Certificate was revoked due to the 

then-current holder's inability to comply with 14 CFR 21.99(a). Ownership of the airplane and its relevant engineering 

and manufacturing data was purchased by Cub Crafters of Yakima Washington in 2012. Cub Crafters is in the process of 

re-establishing the type certificate for the Gavilan model EL-1 under Project Number TC6535NY-A. The project was 

started with the New York Aircraft Certification Office and is in the process of being transferred to the Seattle Aircraft 

The original certification basis was 14 CFR Part 23 amendments 23-1 through 23-46 and 14 CFR Part 36 Appendix G, 

including amendments36-1 through 36-20. The certification basis for the current project to re-establish the Type 

Certificate has been agreed on and includes all amendments up to 23-59. Cub Crafters is working with the Seattle ACO 

to show compliance through that amendment. By agreement with the FAA, all of the original data that was approved is 

valid and applicable under the new application. As such, compliance has effectively been shown for any regulation 

which has not been amended since 23-46, or any regulation that has been amended in a manner that will not impact the 

Gavilan EL-1. 

The purpose of this letter is to petition the FAA to exempt the Gavilan model EL-l from the revised requirement of 14 

CFR 23.629 amendments 23-48 and 23-62. These amendments specifically require the airplane to have additional flight 

testing that was not required under its original certification. Cub Crafters requests exemption from both amendments 

because: 

1. The change between amendment 23-48 and 23-62 is not applicable to the Gavilan EL-1, so for the purpose of 

this project, exemption to amendment 23-62 is equivalent to amendment 23-48. 

2. The current determined certification basis to re-establish the Type Certificate for the Gavilan EL-1 is amendment 

23-59. This basis will expire on August 8, 2014, a date which may arrive before a final position on this exemption 

request becomes effective. In case the certification basis changes, an exemption to both amendments will save 

Cub Crafters and the FAA the burden of reapplying and reconsidering this exemption request. 

The Gavilan EL-i is a two-occupant, day, VFR airplane with a maximum gross weight of 4,200 lb. It is a slow airplane with 

a maximum cruise speed of 123 knots and a never exceed speed of only 155 knots. 

Cub Crafters is petitioning for this exemption in accordance with 14 CFR 11.81 under Petitions for Rulemaking. Cub 

Crafters only requests exemption from the requirement to flight test the airplane in 23.629(a) and asserts that the 

original compliance (by analysis) shall suffice. 

Cub Grafters, Inc. 1 1918 South 161

h Avenue 1 Yakima, Washington 98903 1 p 509.248.9491 1 cubcrafters.com 
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Rationale 

Cub Crafters proposes the following as mitigating factors regarding safety in support of this exemption request: 

1. Design cruise speed (Vc) is 140 knots, never exceed speed (VNd is 155 knots, and the demonstrated dive speed 

(V0F} is 180 knots. Therefore, it is a slow airplane. 

2. The design has high drag. The aircraft was designed to haul large volumes of cargo. It has a large square section 

fuselage. The landing gear is fixed and the wings are supported by external struts. 

3. The fuselage uses proven and predictable construction of a steel tube frame with aluminum skin. The wings and 

tails both use thick airfoils (12% thickness to chord ratio). The wings use a NACA 4412 airfoil and the vertical and 

horizontal tails use a NACA 0012 airfoil. The wings and tails are constructed of aluminum with two spars, ribs, 

stringers and skins. The structure is very stiff. 

4. In its original certification, compliance was demonstrated by performing a ground vibration survey and by 

analysis. This was carried out by John Baker, a Flutter DER who had over 35 years of experience when he did this 

analysis. This conservative analysis had ample margins and it was accepted for type certification. 

5. The EL-l is of a group of airplanes for which compliance by analyses for freedom from flutter is applicable due to 

its methods of construction, high drag, and slow speed. The examples used in the preamble for amendment 48 

to justify the requirement for flight tests differ significantly from this case. 

6. 23.629(i) (amendment 48) states (emphasis added): "For modifications to the type design that could affect the 

flutter characteristics, compliance with paragraph (a) of this section must be shown, except that analysis based 

on previously approved data may be used alone to show freedom from flutter, control reversal and divergence, 

for all speeds up to the speed specified for the selected method". This application for type certification of the ELl is unique in the sense that it is a Type Certificate that had been issued previously and then revoked for the 

reasons mentioned above. It is, strictly speaking, not a modification of an existing design, but rather a new 

application based on a design which has not been modified since it was issued a Type Certificate. Therefore, 

while not applicable according to the letter of the law, Cub Crafters posits that the intent of the law is met and 

23.629(i) provides technical justification for not having to conduct a flight test. 

7. The airplane was designed and built for a maximum gross weight of 4,800 lbs and all certification analyses and 

ground tests were performed using this weight. In flight test, with the exception of the Part 36 noise 

certification, the airplane was flown at a maximum weight of 4,500 lbs. The noise certification was done at 

4,200 lbs and hence the limitation on the type certificate. 

8. In flight tests, the airplane was safely flown at speeds up to VoF = 180 kts. At this speed, the pilot performed 

controllability and maneuverability checks. There was no trend towards control reversal and no tendency of 

divergent behavior. Furthermore, while flutter exciters were not employed, the pilot did perform "stick raps" -

sharply striking the elevator, aileron, and rudder pilot controls- in an attempt to excite flutter. In all three axes 

the airplane demonstrated adequate structural damping and no flutter tendency. 

9. Cub Crafters intends to recertify the airplane to the same speed, altitude, and weight envelope as the original 

Type Certificate. 

10. The test article was manufactured over 15 years ago for the original certification. It was not outfitted to 

accommodate flutter exciters and retrofitting it now would be a significant (and prohibitive) burden on Cub 

Crafters. As discussed in 6, above, this burden would not be placed on Cub Crafters (or other manufacturer) if 

this were a modification. For commercial reasons, such a retrofit may not make sense for Cub Crafters and 

could terminate the program. 

11. The Type Certificate was revoked per the letter dated March 7, 2008 (Case number 2007EA580002). The reason 

for the action was that the holder demonstrated that it lacked the qualifications necessary to hold the Type 

Cub Grafters, Inc. 1 1918 South 1611' Avenue 1 Yak1ma, Washington 98903 1 p 509.248.9491 I cubcrafters.com 
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certificate. It was not due to an airworthiness issue. Had that not occurred, this airplane would be grandfathered 

and still eligible for production and commercial sale today. 

Public Interest 

Granting this exemption for the Gavilan EL-1 will serve the public interest for the following reasons: 

1. It will provide a path for safely establishing compliance with 14 CFR 23 at a cost which makes the project viable. 

2. As a single-engine, non-turbine cargo airplane, this airplane serves an important niche that is not well 

represented in the market. It will have lower acquisition and operating costs than a turbo-prop cargo plane. 

Some communities i~ our country (and other parts of the world) depend upon airplanes as a sole or primary 

means to transport goods and supplies. This airplane will enable operators to cost-effective-ly serve those 

communities. 

3. This airplane has a sizeable payload and fuel capacity. As such, it is an excellent platform for missions that may 

require long durations with some specialized equipment, such as search & rescue missions and law enforcement 

patrol missions. It is clearly in the public's interest that these missions can be conducted cost effectively. 

4. The manufacture, sales, and operation of this airplane will provide jobs for many people. Skilled laborers will 

manufacture the airplanes. Salespeople will broker deals to buy and sell these airplanes. The EL-1 is intended 

for small commercial operators in rural communities where ground transport is difficult, such as Alaska. 

Therefore, it has the potential to bring significant economic benefit to these areas. Pilots and A&P mechanics 

will be needed to operate the aircraft. And owners will no doubt create additional jobs in the support and 

conduct of their business activities. These jobs and income will enhance the local, state, and national 

economies. 

Exercise of Exemption Outside of the United States 

Regarding the desire of Cub Crafters to exercise the privileges of the exemption outside the United States, we wish to 

reserve the right to market and export the Gavilan EL-1 to customers in countries outside the United States. We 

understand that the exemption to a Part 23 regulation is a certification issue (not an operational issue) and that it will be 

listed on the Gavilan EL-l's Type Certificate and Data Sheet, which will be reviewed by other Civil Aviation Authorities in 

their validation of the EL-l's certification basis. 

Daniel Glaser 

Certification Manager 

Cub Crafters Gavilan EL-1 Project 

Cub Crafters, Inc. 1 1918 South 16111 Avenue 1 Yakima, Washington 98903 I p 509.248.9491 I cubcrafters.com