FAR 23.2520 — HIRF Protection
FAR 23.2520 requires Part 23 airplane electrical and electronic systems to be protected from High-Intensity Radiated Fields (HIRF) for safe flight and IFR ops.
FAR 23.2520 is a Part 23 airworthiness design standard that protects airplanes from High-Intensity Radiated Fields (HIRF) — the strong electromagnetic energy radiated by sources like high-power radar, broadcast transmitters, and military emitters. The concern is that this energy can disrupt avionics and electronic flight controls.
The rule applies to electrical and electronic systems based on how critical they are:
- Safety-critical systems (those whose failure would prevent continued safe flight and landing) must be designed and installed so that:
- The function is not adversely affected during or after HIRF exposure, and
- The system recovers normal operation in a timely manner after exposure, unless recovery would conflict with other operational requirements.
- IFR-approved airplanes have an additional requirement: any system whose failure would significantly reduce airplane capability or the crew's ability to handle an adverse condition must also recover normal operation in a timely manner after HIRF exposure.
Operationally, this is why your certified avionics keep working when you fly past a radar site or broadcast tower — the certification standard required the manufacturer to prove HIRF tolerance.