QUALIFICATION OF AIR TAXI INTERCONNECT SYSTEMS [CONTINUED]
Lightning Protection UAMs operating in the 5,000-foot envelope must incorporate design features that mitigate the potentially harmful effects of lightning strike. Being a smaller vehicle equates to significantly larger energy levels that will need to be managed to prevent electrical system issues that could result in a flight safety event. As the UAM market transitions from the developmental phase and becomes integrated into the daily routines of the commuter, safety and reliability must be addressed in the system design. The following Title 14 Code of Federal Regulations 25.1316 and Advisory Circular 20-136 cover general lightning strike and HIRF requirements for grounding and shielding in aircraft systems. Summary of DOT/FAA/AR-04/13, General Aviation Lightning Strike Report and Protection Level Study • Data in the database revealed that aircraft were most vulnerable to a lightning strike when flying in clouds and rain. • The study found that the amount of lightning and HIRF protection in an aircraft had a significant impact on reducing the extent of damage resulting from a lightning strike. • Compared to lesser or unprotected aircraft, lightning and HIRF-protected aircraft had a significantly lower percentage of electrical failures or electrical interferences due to lightning strikes. • The percentage of electrical failures due to lightning strikes on HIRF-protected systems (2%) was much less than unprotected systems
(20%), thus indicating the effectiveness of HIRF protection. A survey of U.S. commercial jets showed the majority of lightning strikes occur between altitudes of 5,000 feet (1,524 meters) and 15,000 feet (4,572 meters). With its lower proposed maximum operating altitude of 5,000 feet, UAM vehicles will nevertheless be required to design a robust shielding and grounding system to mitigate the damaging effects of lightning occurring even at this altitude. The Federal Aviation Regulations for lightning strike are documented in the following parts which are dependent on the vehicle classification. Aircraft –
Aircraft - Transport
Rotorcraft - Transport
General Aviation
Airframe
23.867 23.954 23.1309
25.581 25.954 25.1309
29.610 29.954
Fuel Systems Other Systems
27.1309H
FAR 25.581 defines the requirements associated with lightning protection as follows: (a) The airplane must be protected against catastrophic effects from lightning. (b) For metallic components, compliance with paragraph (a) of this section may be shown by: (1) Bonding the components properly to the airframe; or (2) Designing the components so that a strike will not endanger the airplane. (c) For nonmetallic components, compliance with paragraph (a) of this section may be shown by:
(1) Designing the components to minimize the effect of a strike; or (2) Incorporating acceptable means of diverting the resulting electrical current so as not to endanger the airplane. EWIS design to meet lightning strike requirements IAW commercial transport systems will likely follow these guidelines: • Wire bundle shielding – From traditional copper-plated strands to metallized polymer-core options to hybrid solutions, the
QwikConnect • July 2021
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