About TSO'd Radios and Instruments

First what actually is a TSO?

Technical Standard Orders (TSO)

A TSO is a minimum performance standard for specified materials, parts, and appliances used on civil aircraft. When authorized to manufacture a material, part, or appliances to a TSO standard, this is referred to as TSO authorization. Receiving a TSO authorization is both design and production approval.

Receiving a TSO Authorization is not an approval to install and use the article in the aircraft. It means that the article meets the specific TSO and the applicant is authorized to manufacture it.

source: https://www.faa.gov/aircraft/air_cert/design_approvals/tso/

OK. So it is a minimum!! performance standard. It means that a certain part meets that standard and went through the extra loop of FAA approval.

It does not mean that parts without the TSO approval are below that standard, they might be even above it and are aircraft parts that can be proven to match the TSO if needed. Meaning, the approval process can be done by the manufacturer, or by you, the aircraft owner. (https://www.valavionics.com/installation-in-type-certificated-aircraft.html)

TSO required?

The question is whether your aircraft radios or instruments have to meet that Standard. In the contrary to common believe, certified planes do not have to use TSO'd instruments per se, it rather all depends on how the aircraft was initially certified.

The reasoning that TSO'd radios and instruments are for certified aicraft and non-TSO'd are for Experimentals only is without any sense making logic. Any safety argument is without basis; after all, experimental aircraft participate in the air space system in the same way as your certified aircraft. It rather gives the installer a convenient way to proof conformity with FAA regs if needed.

But are they needed? A quick search of part 91 shows that only some of the equipment must meet a TSO. For 121/135 ops the list expands IIRC

  • 91.207 - ELT
  • 91.215 - Transponder
  • 91.217 - Encoder
  • 91.223 - TAWS
  • 91.225 - ADS-B
  • 91.609 - FDR
  • 91 Appendix G - RVSM

For VFR operations only ELTs and Transponders + ADS-B are on the list, regardless of certification basis.

The pecking order to check whether your VFR aircraft needs a TSO'd radio or instrument is:

  1. Check its certification basis. For Ercoupes, this is CAR 3, effective December 15, 1946 with no amendments, no exemptions. (In CAR 3 we read: RADIO EQUIPMENT- INSTALLATION § 3.721 General. Radio equipment and installations in the airplane shall be free from hazards in themselves, in their method of operation, and in their effects on their components of the airplane). Instruments are mentioned a few times, altimeters are just listed, no further requirements and for ASI we read: FLIGHT AND NAVIGATIONAL INSTRUMENTS § 3.663 Air-speed indicating system. This system shall be so installed that the air-speed indicator shall indicate true air speed at sea level under standard conditions to within an allowable installational error of not more than plus or minus 3 percent of the calibrated air speed or 5 miles per hour, whichever is greater, throughout the operating range of the airplane
  2. Check its Type Certificate. For Ercoupes, we read: Approval for the installation of all items of equipment listed herein has been obtained by the aircraft manufacturer except those items preceded by an asterisk (*). The asterisk denotes that approval has been obtained by someone other than the aircraft manufacturer. An item marked with an asterisk may not have been manufactured under an FAA monitored or approved quality control system, and therefore conformity must be determined if the item is not identified by a Form FAA-186, PMA or other evidence of FAA production approval. This CAN be by using TSO'd material, STC, technical data.
  3. Check the general FAA & FCC Regs. Joe Norris at EAA says NOTHING in FAA regs says a radio needs to be TSO'd, or even "meet requirements of TSO'd", so long as it is legal per FCC to operate as an aviation radio, then it's legal to install in any aircraft, even certificated aircraft. Repeating: there ARE NO requirements in the FARs for RADIOs for VFR use to be TSO'd. Joe says he has read the regs thoroughly and says if someone tells you to the contrary, get them to state where in FARs it says so.
  4. Caveat: some radio installation shops may THINK you need to have TSO'd radios because their own internal repair station manual may only allow the shop to put in TSO'd radios, so the shop folks assume it's because there's FAA regs requiring it, when it's only their own shop internal requirements.