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Everything You Wanted To Know About Field Approvals
But Were Afraid To Ask...
Courtesy of Jim Montague

What is a Field Approval?

A Field Approval is the granting, by an FAA airworthiness inspector, of FAA "approval" for a major repair or major alteration. The approval is given only after conducting a physical inspection and/or after reviewing data.There are three different kinds of Field Approvals for which the local FAA inspector can sign off:

EXAMINATION of data only:
This is the most common form of Field Approval. The mechanic or repairman submits "acceptable" data to the local FAA office for approval. The "approved data" can be used to perform a major repair or major alteration. Once the data has been approved under this procedure it can be used only for that one aircraft (described in Block 1 of FAA Form 337). However, if you want to do the exact same repair or alteration to another like make or model aircraft you can use the original Form 337 as the basis for obtaining a new Field Approval for the second aircraft.

PHYSICAL INSPECTION, demonstration or testing of the repair or alteration:
This is rarely done except in cases where technicians find unapproved engine or components installed on aircraft, which apparently have been installed for some time. Since the aircraft has flown successfully for many hours, and FAA inspector can, if satisfied with the installation, approve the installation. He does so by signing a new Form 337.

EXAMINATION of data only for duplication on identical make and model aircraft by the original modifier:
This is a procedure that saves the maintenance technician and the FAA a lot of time. For example, one technician wants to install duplicate avionics packages on as many Cessna 501s as possible; or maybe he wants to install duplicate installations of tundra tires on Beech 18s. The technician can submit the data to be approved along with a request that the data approval be extended to other identical aircraft. The FAA inspector, if satisfied, signs Block 3 that grants duplication of the data for the original Form 337. When the technician finishes a duplicate alteration on other aircraft, he sends the FAA a regular Form 337 , properly filled out listing the "approved data" on the back and making references to the Field Approval. To avoid problems, attach a duplicate copy of the original Field Approval Form 337.

WHAT A FIELD APPROVAL IS NOT
A Field Approval is not a regulation, it is a policy. Because it is a procedure and not a rule, a mechanic is not automatically entitled to a Field Approval - even if he submits a "perfect" FAA Form 337 to the FAA. Why? Because the authority to grant a Field Approval and the great burden of responsibility that goes with signing Block 3 of the Form 337 has been delegated only to the local FAA district office airworthiness inspector.The responsibility for data approval is so monumental that no one, not even the FAA administrator, may force the inspector to approve a major repair or major alteration against his or her better judgment. Since it is the inspector who makes the final decision and is held accountable by the FAA for that decision, most inspectors are overly cautious when it comes to signing off a Field Approval.

WHY DO YOU NEED A FIELD APPROVAL?
Four regulations, FAR 65.95, FAR 121.379, FAR 135.437, and FAR 145.51 all require "approved" data for major repairs and major alterations. Approved data can be;
Type Certificate Data Sheets (TCDS)
Airworthiness Directives (AD)
Designated Engineering Representative (DER) data
Designated Alteration Station (DAS) data
FAA-Approved data
FAA-Approved Manufacturer’s data
Supplemental Type Certificates (STC) and
Appliance manufacturers manuals.

If you can’t find approved data of this type, your only chance for getting data approved is to apply to the FAA for an STC or to ask a local FAA inspector for a Field Approval.

WHAT CANNOT BE APPROVED WITHOUT ENGINEERING APPROVAL:
Some repairs and alterations are so complex they are actually design changes and require an STC. The following alterations are examples of alterations that cannot be Field Approved.
(1) Increase in gross weight and/or changes in center of gravity range
(2) Installation, changes, or relocation of equipment and systems that may adversely affect the structural integrity, flight, or ground handling characteristics of the aircraft
(3) Any change (alteration) of movable control surfaces that may adversely disturb the dynamic and static balance, alter the contour, or make any difference (plus or minus) in the weight distribution
(4) Change in control surface travel outside approved limits, control system mechanical advantage, location of control system component parts, or direction of motion of controls
(5) Changes in basic dimensions or external configuration of the aircraft, such as wing and tail platform or incidence angles, canopy, cowlings, contour or radii, or location of wing and tail fairings
(6) Changes to landing gear, such as internal parts of shock struts, length, geometry of members, or brakes and brake systems(7) Any change to manifolding, engine cowling, and/or baffling that may adversely affect the flow of cooling air
(8) Changes to primary structure that may adversely affect strength or flutter and vibration characteristics or damage the tolerance design philosophy
(9) Changes to systems that may adversely affect aircraft airworthiness, such as:
---Relocation of exterior fuel vents
---Use of new type or different hydraulic components
---Tube material and fittings not previously approved
(10) Changes to oil and fuel lines or systems that may adversely affect their operation, such as: ---New types of hose and/or hose fittings
---Changes in fuel dump valves
---New fuel cell sealant's
---New fuel or oil line materials
---New fuel or oil system components
(11) Any change to the basic engine or propeller design controls, operating limitations, and/or unapproved changes to engine adjustments and settings having an affect on power output
(12) Changes in a fixed fire extinguisher or detector system that may adversely affect the system effectiveness or reliability, such as:
---Relocation of discharge nozzle or detector units
---Use of new or different detector components in new circuit arrangements
---Decreasing amount or different type of extinguishing agent
(13) Changes that do not meet the minimum standards established in a Technical Standard Order (TSO) under which a particular aircraft component or appliance is manufactured
(14) Modifications to approved type (TSO) radio communications and navigational equipment that may adversely affect reliability or airworthiness, such as:
---Changes that deviate from the vacuum tube or semiconductor manufacturer’s operating limitations
---Any changes to IF frequency
---Extension of receiver frequency range above or below the manufacturerâ™s extreme design limits
---Major changes to the basic design of low approach aids
---Changes that deviate from the design environmental performance
(15) Changes to aircraft structure or cabin interior of aircraft that may adversely affect evacuation of occupants in any manner

HELPFUL HINTS FOR FIELD APPROVALS
First, do not cut metal, splice wire or install equipment until you receive the approval. The only thing worse than not getting a Field Approval is telling your customer the expensive equipment you installed in his aircraft has to be removed.

Determine if the repair or alteration is major as defined by FAR 1. If it is major, go to the next step.

Do not set unreasonable goals. Allow a reasonable time, at least 30 days for the Field Approval.

Research all sources for "approved data" to make the repair or alterations.

Find out what kind of data the inspector wants to see, then assemble it in a reasonable and understandable format. The data must be current, accurate and must support as well as describe the alteration or repair. Data can be in the form of drawings, sketches or photographs. References to AC 43.13-1B and 2A. manufacturer’s maintenance manuals, kits, bulletins, and service letters may be helpful.

A cover letter for the Form 337 describing in detail how you are going to accomplish the repair or alteration is also helpful. Vague or useless technical references are unprofessional and should be avoided because it destroys your credibility.

With your research completed, send the FAA inspector duplicate copies of the Form 337 along with the data you want approved. If you did your homework carefully and followed these helpful hints, you will have an excellent chance of getting your repair or alteration approved on the first attempt. If you do not, find out what is wrong and try again.

Don't forget?? ICA's ; HBAW 98-18 , FSAW 98-03
The purpose of the ICA is to provide instructions on how to maintain aircraft which are altered and appliances which are installed in accordance with a field approved major alteration. The ICA checklist is a guide for both the applicant who creates the ICA and the FAA Flight Standards inspector who accepts the ICA. The ICA developed in accordance with this guidance constitutes methods, techniques and practices "acceptable" to the Administrator.

REFERENCES
From FAA Order 8300.10
CHAPTER 1. PERFORM FIELD APPROVAL OF MAJOR REPAIRS AND MAJOR ALTERATIONS
CHAPTER 2. ISSUE SFAR 36 AUTHORIZATION
CHAPTER 79. REVIEW FAR PART 121/135.411(a)(2) ENGINEERING CHANGE AUTHORIZATION
CHAPTER 235. INTRODUCTION TO AVIONICS
CHAPTER 237. EVALUATE AVIONICS EQUIPMENT APPROVAL
CHAPTER 241. APPROVE AREA NAVIGATIONAL SYSTEMS
CHAPTER 136. APPROVAL OF PARACHUTE ALTERATIONS
CHAPTER 7. POWERPLANT REPAIRS
HBAW 98-18: Checklist for Instructions for Continued Airworthiness for Major
Alterations Approved Under the Field Approval Process.