March 1, 2018

Bringing New Technology in our Cockpit: Understanding Minor Mods


The findings of the US General Aviation Joint Steering Committee (GAJSC) has identified that the Angle-Of-Attack (AOA) indicator is a key safety enhancement to reduce fatal Loss-Of-Control – In flight (LOC-I) accidents in general aviation (GA).  The joint Transport Canada Civil Aviation (TCCA) and COPA General Aviation Safety Campaign (GASC) launched in June 2017 has reached the same conclusion with its review of recent Canadian statistics. In fact, the GASC strongly believes that the installation of an AOA indicator system is one of the best investments one could perform to enhance the safety of his or her GA airplane.  As a responsible and safety conscious pilot, you are might be considering the installation of an AOA indicator system in your type certified airplane, but are probably thinking that the cost and complexity of installing such a system is daunting.  In this case, please keep on reading…

The aviation industry, particularly with electronics, offers us an extensive selection of aviation products using modern technology. The current Canadian Aviation Regulations (CAR) appeared before this new technology arrived. These regulations, in many cases, have made it more time consuming and expensive to incorporate this new technology in the cockpit than may be desirable, even when the safety benefits that this new technology can offer would seem to be obvious. The COPA staff reviewed this situation with TCCA staff to determine possible ways forward. TCCA staff have advised that, for several of the latest “lifesaving technologies” that have been identified for GA, including AOA indicators, that the number of regulatory approvals required, with their associated time and cost, may be less than we expected. The appropriate TCCA staff has reviewed and accepted this article. We publish it for your information as well as to support you when discussing a potential new installation with your AME.

CAR 571 – Aircraft Maintenance Requirements provides regulations in respect of maintenance and elementary work performed on aircraft.  CAR 571.06 provides that each modification on an aeronautical product shall conform to the requirements of the relevant technical data. Aircraft modifications are classified as: either “major” modifications, which must be done in accordance with “approved data” or “specified data” as defined in CAR Standard 571.06; or “minor” modifications, which may be done in accordance with “acceptable data” as also defined in CAR Standard 571.06.  The definition of “major modification” is provided under CAR 101.01 as an alteration that has other than a “negligible effect on the weight and center-of-gravity limits, structural strength, performance, power plant operation, flight characteristics or other qualities affecting its airworthiness or environmental characteristics.”  The decision as to whether any particular modification proposed for a particular aircraft is classified as “major” or “minor” is up to the aircraft maintenance engineer (AME) that will need to sign the maintenance release, pursuant to CAR 571, following incorporation of the modification. The AME should refer to CAR 571 Appendix A for clear and easy guidance with respect to determining if the modification is major or minor.

The installation of some models of AOA indicator onto some general aviation airplanes may be found by an AME to be no more than a minor modification.  In these cases, the AME may accomplish the minor modification using an appropriate set of “acceptable data”, such as the AOA indicator manufacturer’s recommended installation instructions, Federal Aviation Administration (FAA) Advisory Circular (AC) 43.13-2B Acceptable Techniques and Practices or as otherwise specified in CAR Standard 571.06(1).

Where a particular modification is deemed to be a major modification, the AME requires “approved data” as defined in CAR Standard 571.06(1).  Typically, approved data takes the form of a service bulletin from the aircraft manufacturer or a third party Supplemental Type Certificate (STC).  Where approved data does not exist for your particular airplane model and proposed AOA indicator combination, it may be time consuming and more expensive to have this data developed (by the aircraft manufacturer or a third party aircraft design engineering service) and approved by Transport Canada or its appropriately authorized aircraft certification delegate (e.g. Design Approval Representative (DAR)).

On March 31, 2016, the Federal Aviation Administration (FAA) issued Policy Statement PS-AIR-21.8-1602 – Approval of Non-Required Safety Enhancing Equipment (NORSEE). This policy was intended to support the FAA’s objective “to encourage and enable voluntary safety enhancements” of the GA and rotorcraft fleets.  The policy provided criteria under which NORSEE could obtain a production approval under Title 14, Code of Federal Regulations (14 CFR), para. 21.8(d), without a corresponding specific installation approval (e.g. under an STC). Equipment approved as NORSEE may have a variety of uses including—

1. Increasing overall situation awareness;
2. Providing additional information other than the aircraft primary system;
3. Providing independent warning, cautionary, or advisory indications; and/or
4. Providing additional occupant safety protection.

Most NORSEE categories fall under the avionics, electronic instrument, and display categories.  AOA indicators may be manufactured further to the NORSEE policy so long as they are determined to be a minor change to a type design and whose failure condition is minor. It is further to this policy that many AOA indicator system kits are in production and are currently available for sale to owners and operators of GA airplanes.

In the absence of the FAA policy, manufacture of articles under 14 CFR part 21 is only permitted where a design approval has already been obtained, whether together with a Technical Standard Order Authorization (TSOA) or Parts Manufacture Approval (PMA), or through a type certification process. The policy alleviates both real and perceived challenges to incorporating safety advancements in the general aviation (GA) and rotorcraft fleets. The NORSEE policy was intended to reduce equipment costs by allowing applicants the flexibility to select various industry standards that suit their product, as long as it meets the minimum design requirements established by the FAA.  TCCA staff confirm that the installation of some of these products into a type certified GA aircraft in Canada can be done as a minor modification under existing regulations, and therefore may not require an STC or manufacturer’s service bulletin.

The FAA policy was aimed at supporting the objectives of the FAA-led international efforts to overhaul the airworthiness standards for GA airplanes through reorganizing 14 CFR part 23, EASA’s Certification Specifications CS-23, Transport Canada’s Airworthiness Manual (AWM) Chapter 523, and equivalent other foreign airworthiness authority standards. By restructuring 14 CFR part 23 and replacing the prescriptive design requirements with performance-based standards, these design standard amendments are intended to help get safety enhancing technologies into the marketplace quickly while reducing costs.  TCCA participated actively in the FAA Part 23 Reorganization Aviation Rulemaking Committee (ARC) that lead to the amendments and is in the process of amending the AWM to align with the FAA’s amendment 23-64 to 14 CFR part 23. To view a short video on these internationally supported efforts to revitalize GA, please visit

The installation of an AOA indicator system in your certified aircraft could be an example of a minor modification. Searching the internet for AOA’s takes us to a well-known (at least to Amateur Builders) aircraft parts supplier. Their selection of AOA systems includes some STC’d AOA’s, but most are not STC’d. Be aware that an STC has applicability to only those aircraft models identified on the STC, so be sure that your aircraft is covered by the STC before you buy it.  Should you purchase an AOA for which installation on your aircraft model is approved by an STC, your AME should have no issue with the installation and maintenance release of your aircraft. If you choose an AOA that is not approved for your aircraft by an STC, then your AME will have to decide if this installation is a minor modification or a major modification. The factors affecting his decision will include the level of details and the quality of the installation instructions provided by the manufacturer; does your chosen AOA system interface with other systems on the aircraft and to what extent; does it have an FAA Approval Letter or Form, etc. The products offered by that supplier typically indicate what documentation accompanies the item; some even indicate that their product may be installed as a minor modification (always confirm with your AME) requiring only a Log Book Entry.

TCCA does recognize the installation of several products as minor modifications and intends on publishing an AC to clarify the regulation in respect of installation of NORSEE articles in GA aircraft. Pending the publication of such an AC, TCCA recognizes the accuracy and validity of the information provided in this article for the purpose of assisting aircraft owners in working with their AME’s in these circumstances. Mr. Blake T. Cheney, Chief, Aircraft Certification Standards at TCCA, has reviewed and significantly improved the content and accuracy of the information published here. We sincerely appreciate his contribution to this important aspect of aircraft operations.