We help Organizations quickly Conceptualize, Design, Develop, and Implement Innovative Cost-Effective Solutions for Avionics, Aircraft, and Flight Guidance-Navigation-Control Systems.

What We Can Do
What We Have Done
On Learjets
ASTECH's Founder
Expert's Corner
- FAA STC Process
In Closing











a. Data submitted to the FAA should demonstrate that the modification to a TC aircraft, engine, or propeller complies with the appropriate regulations. This data should be obtained, organized, and submitted by the applicant or the applicant's representative to the FAA for review and approval.

b. Required design data can be divided into two major categories: descriptive, and compliance or substantiation data. Descriptive data defines the design of the modification, while compliance data substantiates that the design meets the applicable regulations.

c. A copy of all data will remain on file with the FAA. However, this data is treated as the applicant's property and cannot be released outside the FAA without the applicant's consent.

d. All data submitted must be identified. This includes title, drawing or report number, revision level, date, and applicant's name. Each page of a report should contain enough of this information for complete identification. The FAA project number should also be identified.

e. Descriptive data requirements (for "one-only" versus "multiple" STC's) are different. However, the SAME LEVEL OF SAFETY IS REQUIRED for either application.

f. Data to be submitted to the FAA should have the following tasks accomplished in accordance with 14 CFR part 21, section 21.21 and 21.33(b) before submittal:

(1) All descriptive and substantiation data is checked for completeness and correctness of information.

(2) The design data and the modified aircraft complies with the applicable regulations; (FAA verifies this finding.)

(3) The descriptive data conforms with the actual configuration of the modification, and all stress analyses, test proposals, and test results are based on the descriptive data.

(4) The data describing and substantiating the modification is properly identified, presented in an orderly fashion, and clearly states the manner in which it contributes to the findings of compliance.


a. In general, descriptive data should completely define, or describe, a given design. It may include drawings, sketches, marked photographs, process specifications, etc. The data will be verified by the FAA for compliance with the applicable airworthiness regulations.

b. A "one-only" STC descriptive data package is applicable to only one installation/modification. The package may consist of marked-up photographs, sketches, written descriptions, marked-up excerpts from manufacturers' parts catalogs and maintenance manuals, and similar document excerpts. If descriptive data other than drawings is submitted, such data must be of sufficient quantity and quality to properly ascertain the nature of the modification. This includes defining all critical equipment, parts, and attachments, and identifying any components of the original aircraft that have been removed.

NOTE: Since parts catalogs are not FAA- approved documents, excerpts from parts catalogs alone are not sufficient.

c. A "multiple" STC descriptive data package should completely and accurately describe the fabrication, assembly, and installation of all portions of the modification. This includes: engineering drawings; material and manufacturing processes, specifications and tolerances; data necessary for fabrication of all parts and assemblies; and installation drawings and/or instructions. See appendix 2. In addition, the descriptive data must be adequate for reproduction of parts and/or installation of subsequent modifications on other serial numbers of the same model TC product.

d. Technical information should include the following when applicable:

(1) Identification (title, drawing or report number, aircraft applicability, revision level, date, and applicant's name).

NOTE: When purchased Original Equipment Manufacture/Supplier parts, accessories and equipment are involved, whether new or used, provide purchase orders of other acceptable traceable documentation, including any name plate identification, part number, revision letter, serial number, etc.

(2) Materials used (and identified by material specification).

(3) Material test criteria and procedures.

(4) Fasteners used and location. (Each rivet, bolt, nut, screw, or other fasteners identified by specification - standard part numbers, such as Air Force - Navy Aeronautical Standard (AN), National Aerospace Standard (NAS), and Military Standard (MS), are acceptable.)

(5) Dimensions (with tolerances included).

(6) Manufacturer and part number of purchased parts (i.e. vendor data).

(7) Process specifications.

(8) Ratings and power requirements of electrical equipment.

(9) Electrical load analysis for the installation.

(10) Weight and balance data of assemblies and equipment items to be installed, and/or the complete modification. A complete list of parts added and/or removed. Updated aircraft equipment list.

(11) Installed placards.

(12) Instrument markings.

(13) Flight manual/supplement changes.

(14) Continued airworthiness instructions.

(15) EMI test report.

(16) Qualification test procedures and report.

(17) Software documents.

(18) Analysis reports.

(19) Test plans.

(20) Test reports.

e. Design of equipment or components to be installed, purchased and/or furnished, should be completely defined. If the item is TSO approved, the nameplate data may be adequate. Other equipment may require a source-control drawing identifying the equipment by manufacturer, part number, drawing number, revision level, or any other necessary data. Installation instructions for the modification should include all pertinent information provided by the equipment's manufacturer.

NOTE: When a multiple STC kit is sold, it should contain an inventory of ALL parts and installation instructions. Details of the parts manufacturing data that is proprietary will not be included in the kit.

f. Process specifications necessary for production of parts should be included in the descriptive data package. These specifications should include all materials, fabrication, and assembly procedures.

(1) Industry standards and specifications include those of Civil Aeronautics Manual (CAM) 18; the latest versions of AC 43.13-1A, Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair; and AC 43.13-2A, Acceptable Methods, Techniques, and Practices Aircraft Alterations; various Society of Automotive Engineers Aerospace standards; AN; MS; and NAS specifications; and various military handbooks. A copy of each standard and specification (except CAM 18, AC 43.13-1, AN, MS, and NAS) should be supplied as part of the descriptive data package. Certain industry standard specifications may be used, or specifications may be developed.

(2) Nonstandard specifications should include a complete and unambiguous definition of the materials to be used, detailed procedures, critical processes (e.g. temperatures, times, etc.), inspection criteria, rework limits, etc. The FAA will review any nonstandard specification.

g. Installation instructions should be adequately identified with a document number and an original issue/revision date, and should be complete enough to allow the installer to duplicate the installation. Each page of the instructions should be dated.

h. A Flight Manual Supplement should be provided to the pilot if required by the modification (refer to 14 CFR part 21, section 21.5), regardless of the method used to provide operating instructions on the original aircraft.


a. In general, substantiating and/or compliance data is intended to show compliance with the applicable regulations. This data may include: compliance checklists; analyses; test proposals and reports; and instructions for continued airworthiness and operations. Data from an existing STC may be used, provided a letter of authorization from the STC holder is obtained. A copy of this data and authorization letter should be submitted to the FAA if used.

NOTE: If the ACO engineer has relevant tests or other engineering data available from previous approvals, he/she may waive the requirement for an applicant to conduct such tests or submit duplicate data for a current STC application. The ACO engineer may use the relevant data for comparison purposes, but shall not disclose the data or its source to the current applicant.

b. The compliance checklist specifies each applicable certification rule and the method by which compliance will be shown (e.g., analysis, structural test, ground test, flight test, etc.). It provides a concise, easily reviewed program outline which assures that all pertinent certification rules and their means of compliance are addressed. The compliance checklist should be prepared by the applicant after the certification basis is identified. See chapter 3. Each rule should be examined and identified for applicability to the proposed modification along with a method of showing compliance. The checklist can be updated later to identify the report, letter, test, etc. used to show compliance. For a sample format, see figure 2-5. Identification of appropriate certification rules may require the assistance from the FAA project team.

c. A basic loads analysis is necessary when the structure is modified or structural loads are changed. This establishes the applied loads (flight, ground, landing, etc.) which are determined from weight, center of gravity, power, and aircraft aerodynamic characteristics using design speeds, and load and safety factors specified in the certification basis. These loads, with the structural analysis and/or tests, form the foundation used to provide the required structural substantiation only if experience has shown this method to be reliable. Ultimate load testing may be required in cases where limit load tests may be inadequate.

NOTE: All structural loads should be approved by the ACO prior to stress or test. The ACO may have a DER recommend approval.

d. Structural analyses establish mathematically that the appropriate structural strength requirements have been met. These analyses build on the basic loads and material allowable data and may include: static stress, fatigue, fail safe, damage tolerance, etc. The applicant should assure that the analytical methods and assumptions used are applicable, that all pertinent loading conditions have been addressed, and that appropriate margins of safety have been shown for all structural elements.

e. Allowable material strength properties are established for the materials used in substantiating primary aircraft structure and the properties must be FAA approved. For metallic materials, the use of MIL-HDBK-5, Metallic Materials and Elements for Flight Vehicles Structures, data is recommended (but other data may be acceptable). Nonmetallic materials may require the development of allowable data.

f. Numerical analysis of structures may be accomplished, with FAA approval, by using computer programs that define and validate each structure computer model through analysis routines and limited load tests.

NOTE: All computer programs used in any tests or analysis should be validated or previously approved by the FAA. Both stress and deflection results should match. Other validation methods may be possible when agreed to by the FAA.

g. Safety assessments evaluate the effects of foreseeable failures of the aircraft structure and/or systems. The depth and level of the detail is dependent on the severity of the failure conditions, functions performed, and the complexity and novelty of the aircraft. Faults that are undetectable are presumed to exist at the same time as each other single fault. Any necessary actions should be taken (system redesign, aircraft flight manual procedure changes, etc.) to correct unsafe conditions found as a result of an assessment. A safety assessment may also be required for aircraft systems.

h. Test plans and reports should be prepared for each required structural, component, ground test, and flight test. Test plans should include conformity inspection requirements and should be submitted to the FAA for approval PRIOR TO assembly and testing of test articles.

i. Instructions for continued airworthiness describe any maintenance requirements necessary to maintain aircraft airworthiness and are provided in accordance with the applicable regulations, (e.g., 14 CFR part 23, section 23.1529; part 25, section 25.1529; part 27, section 27.1529; part 29, section 29.1529; part 31, section 31.82; part 33, section 33.4, or part 35, section 35.4). See appendix 5.

NOTE: For any STC application submitted after January 28, 1981, the applicant shall furnish at least one set of complete Instructions for Continued Airworthiness to the owner. See 14 CFR part 21, section 21.50.

j. The weight and balance manual, or Airplane/Rotorcraft Flight Manual (AFM/RFM) for the original type design, should be revised accordingly when modifications change the aircraft weight and balance and/or the operating limitations, procedures, performance, or loading instructions for the modified aircraft. The applicable weight and balance data is FAA approved and documented in a supplement to the original weight and balance report. Update aircraft equipment list.

k. Structural life limits are established based on fatigue test data with adequate factors of safety applied. New structural life limits may be required when modifications change an aircraft designed with safe - life structures.



The drawing package describes the manufacture and installation of all parts necessary for the modification. All part contours, materials, manufacturing operations, dimensions, finish specifications, etc., are identified either directly on the face of the drawing or by reference to a process specification or other appropriate material.

NOTE: Drawings are a major portion of the descriptive data required for a multiple STC. All drawings must be DER or FAA approved prior to FAA acceptance and conformity inspection. See 14 CFR part 21, section 21.33.


Drawing numbers should follow a logical pattern. For instance:

a. 60000, Final Installation.
b. 60100, Major Assembly.
c. 60101, Detail.
d. 60102, Detail.
e. 60200, Major Assembly, etc.


a. Each revision level should identify the changes and approval dates on the drawing. These items should be reflected in the drawing list submitted with the drawing package for FAA approval.

b. Minor design changes (refer to 14 CFR Part 21, section 21.93 and 21.95), and major design changes (refer to 14 CFR part 21, section 21.93 and 21.97) to drawings and specifications should be submitted in a manner as determined by the ACO.

NOTE: After approval and issuance of the STC any change to the drawings should be submitted with the revised drawing list to the FAA for approval.


Thoroughly checking drawings for accuracy and completeness prior to FAA submittal for review should reduce potential drawing returns and resubmittals due to unacceptable errors. See section 3.


a. Standard manufacturing tolerances should be noted on the drawing, such as: XX.XXX inches ± .010; XX.XX inches ± .03; XX X/X inches ± 1/16; with tolerances which differ from these standards called out on the face of the drawing, (i.e., .625 + .001, - .000).

b. The magnitude of tolerances is critical. Unnecessary narrow and/or broad tolerances should be avoided, as manufactured parts are rejected if tolerances are not met. See ANSI Specification Y14.5.


A drawing list, or Master Drawing List (MDL), should be prepared and submitted with the drawings. This list should include installation instructions, any process specifications, drawing or document number, revision level, any engineering change orders in effect, the date prepared, and the approval dates of all material. See appendix 2.


a. A drawing list and several sample drawings for the Acme Aircraft Corporation flap hinge bracket installation are located in appendix 2, demonstrating one way of meeting drawing package requirements. Process specifications for plating and inspection, as well as the installation instructions, are included in the drawing list, and they are divided into installation and manufacturing data. A revision control page is shown, but may not be needed on a very short drawing list.

b. Drawing examples showing a detail part, a subassembly, and an installation are also included in appendix 2. They illustrate the type of information required on drawings of various types and an acceptable way of organizing a drawing system.


5-11. GENERAL.

Prior to FAA submittal, completed working drawings should be reviewed, via a guide or a system, by someone OTHER THAN the person responsible for drafting the drawings. In the case of descriptive data, the first such check may be performed by the engineer. The following is an example of a drawing checklist.


a. The perspective of whether an accurate and complete design is portrayed should be realized before reviewing the contents of the drawing.

b. Each part should be correctly designed and illustrated with all necessary views of the part shown on the drawing.

c. Dimensions.

(1) Accuracy of all dimensions should be checked by scaling and, where advisable, also by calculation.

NOTE: All calculations should be preserved.

(2) Completeness of the dimensions should be checked to verify no adding or subtracting is required for a needed dimension.

d. Tolerances should not be too "fine" or too "coarse," which might impact the duplication accuracy or operation.

NOTE: Each production part should meet or exceed the established tolerances.

e. Finishes should be checked for proper specification on each part and assembly drawing.

f. Material specifications should be checked to verify that every specification is correct and that all necessary information is given.

g. Part compatibility.

(1) Interference, or compatibility of each adjacent part, should be checked in the final assembly to assure proper clearances. The "worst case" tolerance limits should be used.

(2) Mechanical movement clearances should be laid out to scale and checked for interference (and considering tolerances) in all positions at the extreme limits of travel.

h. Detail parts should be checked to verify all screws, bolts, pins, rivets, etc., are standard aircraft quality parts and that, where applicable, stock sizes have been utilized.

i. The Title block should present the following information:

(1) A drawing number to identify the print for filing purposes and to prevent confusing it with other prints.

(2) The name of the part or assembly.

(3) The scale to which it is drawn.

(4) The date.

(5) The name and address of the applicant and firm.

(6) The name of the draftsmen, checker, and person approving the drawing.

(7) The aircraft model, detail or assembly it is to be used on.

(8) The drawing number of the next higher assembly.

j. The Bill of material block should present the following information:

(1) The number of the part or assembly.

(2) The name of the part of assembly.

(3) The material from which the part is to be constructed.

(4) The quantity required.

(5) The source of the part or material.

k. The Revision block should present the following information:

(1) The identification symbol.

(2) The listing of the numbered or lettered changes (A through Z is followed by AA through ZZ; I, O, Q, and X are never used).

(3) The date.

(4) The nature of the revision.

(5) The authority for the change.

(6) The name of the draftsman who made the change.

NOTE: To distinguish the corrected drawing from its previous version, the Title block may contain a space for entering the appropriate symbol to designate that the drawing has been changed or revised.

l. Other details should be reviewed:

(1) The border around the drawing defining the work area should be 7/8 inch to _ inch from the edge.

(2) The dimensions and views should be sufficient in describing the part or assembly, including a full sectional view of assembled parts. Decimal dimensions are desirable. Views with hidden lines should be avoided when possible, and dimensions to hidden lines should not to be used.

(3) Tolerances on the drawing should be noted when different form those called out in the title block.

(4) Parts should be indicated by a noun, followed by a description of what they do, and where they are located on the aircraft.

(5) The finish operation/process should be indicated, such as: cadmium plate, zinc chromate coat, anodize, shot peen, tumble, sand blast, vinyl wash, epoxy, etc.

NOTE: Zinc chromate and vinyl wash denote primers; final finishes should be specified as well (e.g. enamel, epoxy, lacquer, dope, etc.). A complete designation of a finish process/operation should include a reference to a specification.

(6) Standard tolerances specified by applicant/designer should be indicated.

(7) General notes are not referenced from the field of the drawing but apply "Unless Otherwise Noted".

(8) Specific notes (also listed under the general notes column) apply to particular parts, areas or operations, and are usually referenced from the field of the drawing by the note number enclosed within a triangle.

m. The drawing should be reviewed in its entirety, adding explanatory notes (as needed) that will increase its utility.

n. Sources. French & Vierck, Fundamentals of Engineering Drawing, pp. 365-6, McGraw-Hill, Inc., 1960; Drawing Requirements Manual, and Airframe and Power Mechanics General Handbook, Chapter 2, -- U.S. Government Printing Office; and Global Engineering Documentation Services, Santa Anna, California.

For more information on how ASTECH Engineering may be able to help you, please contact Jeff Wilson at or call 316-304-6157.

© Copyright 1996 ASTECH Engineering. All rights reserved. No part of this document may be reproduced in any form without the expressed written consent of the author.

Keywords: Concept Research Development Integration Integrated Aviation Avionics Aircraft Flight Controls
Autopilots Navigation Guidance Analysis Simulation Software Algorithms Hardware Interfaces
Requirements Engineers HITL FCS GPS FMS UAV Systems