Special Conditions: Learjet Model 55 and 55B Airplanes; High-Intensity Radiated Fields (HIRF)

These special conditions are issued for Learjet Model 55 and 55B airplanes modified by JetCorp. These modified airplanes will have novel and unusual design features when compared to the state of technology envisioned in the airworthiness standards for transport category airplanes. The modification incorporates the installation of dual Attitude Heading Reference Systems (ARHS) that provide air data input to both pilot and copilot flight instruments displaying critical flight parameters (attitude) to the flightcrew. The applicable airworthiness standards do not contain adequate or appropriate safety standards for the protection of these systems from the effects of high- intensity radiated fields. The special conditions contain the additional safety standards that the Administrator considers necessary to establish a level of safety equivalent to that provided by the existing airworthiness standards.