Every Two Years

Every Two Years FAR 91.411 and 91.413 testing requirements By Jim Sparks May/June 2001 It comes with the same surefootedness as the tax collector, but with a somewhat reduced frequency, it sneaks up with all the stealth characteristics...


Every Two Years

FAR 91.411 and 91.413 testing requirements

By Jim Sparks

May/June 2001

Connecting Air Data test equipment.It comes with the same surefootedness as the tax collector, but with a somewhat reduced frequency, it sneaks up with all the stealth characteristics of the most advanced tactical fighter and the consequence of oversight can be every bit as deadly. In most cases, its presence is anticipated and dealt with in stride. Such are the dealings with Air Data Indicating and Reporting systems.

Regulations for reporting systems
91-144 in progress using computerized tester.Most Airworthiness Agencies throughout the world realize the importance of proper operation of the devices that inform the flight crew as well as advise ground based air traffic controllers or other aircraft of altitude and position. This realization comes in the form of Airworthiness Regulations. The United States Federal Aviation Regulation (FAR) 91-411 addresses the certification of barometric altimeter systems and FAR 91-413 is concerned with guaranteeing that the Transponder system is operating within specification.
Most Airworthiness Agencies throughout the world require similar tests. In addition, anytime an aircraft is accepted for registration in a specific country, the authorities must be assured of continuing airworthiness and will require a plan outlining normal maintenance actions. Most often, these maintenance plans are derived by the airframe manufacturer and then customized for each unit as needed and finally approved by local airworthiness authorities. It is then up to the aircraft operator to make sure the maintenance and inspection program is followed and documented. Some aircraft manufacturers have already included the testing of the air data and reporting systems in their recommended maintenance programs.

Customized tests
Normal Altimeter and Standby undergoing test.Certain customizations may also be included such as, testing Mode S Transponder and verification of Reduced Vertical Separation Minimum (RVSM) qualification. The tests developed by the manufacturer often includes testing Altitude Alerts, Over-speed Detection, and possibly the testing of airframe systems that require air data input. The ways and means of testing also will be a variable. In some cases, Altitude indicators or Air Data Computers are removed from the aircraft and shipped to an appropriately rated facility where testing and certification is accomplished. In other cases, all components are tested and qualified while still installed in the aircraft by using calibrated test equipment. Many times, the aircraft manufacturer will stipulate how the equipment should be checked.

Guidelines for operation
Airworthiness regulations provide a guideline for insuring a minimum standard for equipment operation. Frequently, equipment manufacturer’s tolerances are more restrictive than federal regulations and for this equipment to remain in service, the most restrictive calibration limits are observed.
Equipment that requires certification can include everything from the most basic pneumatic altimeter to the most advanced air data computer.
United States Federal Aviation Regulation 91-411 states "No person may operate an airplane or helicopter in controlled airspace under IFR conditions unless within the preceding 24 months, each static pressure system, each altimeter instrument and each automatic pressure altitude reporting system has been tested and inspected and found to comply with FAR Part 43 Appendix E." The regulation goes on to read that with the exception of moisture drains, any opening of the system will also require inspection and test in accordance with both Appendix E and F of Part 43.
Another stipulation of 91-411 addresses the qualification of those performing the tests. The aircraft manufacturer is of course granted this authority, but so are Certificated Repair Stations possessing a Class 1 Instrument rating and the equipment needed to carry out the assessment. A limited instrument rating appropriate to the make and model of the equipment to be tested or a limited rating pertaining to the test to be carried out. A repair station with a specific model aircraft rating can also be considered qualified. A U.S. government certificated Airframe Mechanic is authorized to perform static system checks and inspections only.
Altimeters and Altitude reporting equipment approved under Technical Standard Orders (TSO) are considered to be tested and in compliance as of their date of manufacture. This can often be a factor when calculating future testing.
It is also stated that no person may operate an aircraft in controlled airspace under Instrument Flight Rules (IFR) above the maximum altitude where the altimeters and altitude reporting systems have been tested.
The certification of Altitude Reporting Systems has similar requirements to Altimeters. United States Federal Aviation Regulation 91-413 states, "No one may use a Transponder unless within the preceding 24 months, the system was tested and inspected in accordance with Appendix F of FAR Part 43." Testing is also required following any installation or maintenance where data correspondence error could be introduced. Those authorized to conduct the evaluation of the equipment include a certificated repair station properly equipped to perform the functions necessary and holding a Class III Radio Rating.

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