U.S. Department
of Transportation

Federal Aviation

St. Louis
Flight Standards District Office

10801 Pear Tree Lane
Suite 200
St. Ann, Missouri 63074


May 2002 




Thought for the month....
If you are feeling froggy, then jump.

The Project... I am working with a group of people who are restoring a Piper J-5A. This airplane was involved in a landing accident that resulted in a less than airworthy wing and landing gear. The restoration was undertaken by an eager group of guys who wanted to tackle something that would be an educational project. Because I have never worked on fabric covered airplane repairs I thought that this was a perfect chance to broaden my knowledge in this area of airplane construction and repair.

Early on in the project, inspection of the damage showed that a fair number of the wing ribs needed changing. At $70 or so for each rib replaced it was calculated that a minimum of $1000 in ribs alone would have to be spent. One inquisitive project member asked me if the ribs could be constructed out of wood instead of purchased. This would have resulted in a change of materials, as the original ribs are made of aluminum. A material substitution like this would constitute a major alteration to the type design of the airplane.

To find out if this was a reasonable solution I contacted the FAA manufacturing office that has certification responsibility for the airplane. The inspector who oversees Piper's manufacturing explained to me that at a minimum the construction of the replacement ribs would have to satisfy the load testing limits that the airplane was certified to. A rib had to be made based on the original airfoil shape and tested to CAR 4a requirements that specify structural loading conditions and meet or exceed the minimum criteria of the certifying rule. The next step in the process was to obtain approval from the FAA to make the alteration. This is accomplished by one of two methods. The first method is to apply for a Supplemental Type Certificate (STC) to replace the aluminum ribs with wood ribs. The process is similar to applying for a type certificate and it is a drawn out process. The other method is to request a field approval.

The field approval is a fast track version of a change to a type certificate, or to make major alterations to the type certificate of a product or a component part. It is issued by an FAA Airworhiness Inspector. Should the Inspector feel that he or she is not knowledgeable enough to approve a request for a field approval the Inspector can pass the request and supporting data to an FAA engineering office for review. If the engineering office accepts the data as sound the Inspector then can grant the field approval.

Before a field approval is issued all requests for approvals are required to include instructions for continued airworthiness, commonly referred to as ICA's. This procedure parallels a similar procedure for a Supplemental Type Certificate application. In 1981 all STC's applied for were required to include instructions for continued airworthiness. To some people the need for including the ICA's constitutes nothing more that additional bureaucratic red tape. But is it really?

How is the person you ask to perform an annual inspection supposed to determine the airworthiness of an alteration granted under a field approval? What if the alteration becomes defective or inoperative, how would it be repaired? Maintenance regulations require the mechanic to perform repairs using the manufacturers maintenance instructions, instructions for continued airworthiness, or data acceptable to the FAA. Additionally, the repair is supposed to return the airplane to its original or properly altered condition. If your mechanic doesn't have written instructions to maintain an alteration, then by the rule work cannot be performed on that alteration. This includes performing annual, 100 hour or other required inspections because by definition an inspection is maintenance.

The process of developing instructions for continued airworthiness varies with the complexity of the alteration. In some cases it can be as simple as referencing a document already published. After they are developed the ICA's are entered on the back side of an FAA Form 337, Major Repair and Alteration record. These instructions are not to be considered as approved data even though they are made part of the FAA Field Approved document. The instructions are given the status of "FAA Acceptable Data". A person abiding by those instructions in the exercise of maintaining the alteration is in compliance with the regulations on maintaining aircraft or their components.

Anybody can come up with the data or produce the design specifications not just the mechanic or authorized inspector. Many times it is the owner of the aircraft who provides the data to the person who is going to make the alteration. It is important to remember that copying a previously approved supplemental type certificate and submitting that data for field approval not only won't get a favorable response from the FAA, but may cause legal troubles from the original holder of the STC. If you want to make an alteration and have or can develop the fabrication and installation data I would say to you "If you're feeling froggy...then jump!"

Upcoming Events

May 23rd
Working CFI Safety Seminar
Meramec Community College
Lecture Hall 101
6:30 to 9:30 PM

Steven Long
Airworthiness Safety Program Manager
1-800-322-8876 extension 4830