Aircraft lightning strikes occur more frequently than you might think. It’s estimated that on average, commercial aircraft lightning strikes occur every 1,000 hours of flight time.
When a strike happens, lightning attaches itself to an extremity, such as the nose, leading edge of the wing, or wing-tip, travels along the exterior of the airplane, exits at another aircraft extremity, and continues on to hit the ground.
Up to 1 million volts can be delivered in a single lightning strike. The damage inflicted to the aircraft can vary depending on the duration of the lightning strike, the amount of lightning energy dissipated by the aircraft, and the lightning attachment and exit locations on the aircraft.
Lightning strike protection
Today’s aircraft incorporate state-of-the-art composite materials, specialized computer systems, and components that are lighter in weight, and offer better reliability and longevity, but can also make them more susceptible to damage by lightning. These technological advances are prompting regular updates to strict lightning safety regulations, underscoring the priority placed on lightning protection equipment.
Aircraft manufacturers design and continually test their airplanes for lightning strike protection to keep passengers safe and protect sensitive equipment from damage.
A broad array of components and systems designed to withstand, direct, and dissipate the powerful discharge of a lightning strike are required for lightning protection. This equipment must be tested and verified by the manufacturers to meet the stringent lightning protection regulations.
Lightning protection testing
Key lightning protection tests that should be conducted by manufacturers include:
- Direct effects lightning testing meeting military and commercial requirements: MIL-STD-464; FAA AC-20-53A, RTCA/D0-160, ARP 5416
- Up to 200 kiloamperes oscillatory current waveform (components A, Ah, and D)
- Up to 3,000 amperes unipolar current waveform (component B)
- Photographic and explosive mixture ignition detection
- Over 2,500 μF at 5kV
- Over 60 μF at 45 kV
Flame arrestor testing
Flame arrestor technology must be addressed carefully as well. Standards to be met include SFAR88 requirements with flame arrestor technology. Other flame arrestor tests include:
- Testing per AC 25-975
- Flame propagation/flame holding
- Vaporized hexane or jet fuel testing
- Heated air/fuel mixtures up to 165°F +20/-10
- Air and mixture flow as high as 18 SCFM
- Data acquisition software that monitors and collects data requirements
Innovative protection for the life of the aircraft
Parker Aerospace has recently introduced the unique-to-market, lightweight, high-pressure isolator (highly resistive union) that protects fuel system components from carrying the high current load of direct lightning strikes, yet allows safe relaxation of static charge developed through the refueling process.
- Engineered to provide exceptional insulation resistance without reducing flow rates or requiring special adaptors or modifications
- Patented manufacturing process for light weight and compact design
- Compatible with multiple tube material options, Parker highly resistive unions give aerospace fluid systems application flexibility and ease of maintenance
- Available with or without bulkhead flanges
Selecting a lightning protection equipment supplier
When selecting lightning protection equipment and components, aircraft design engineers should consider partnering with a supplier that offers:
- Years of experience in delivering engineered solutions to the aerospace industry
- A broad range of safety-certified products
- On-site testing for lightning, fire, and flammability
Parker Aerospace has been patenting, testing and manufacturing a comprehensive array of lightning-safe components and equipment for more than 70 years. Thousands of active and certified products have been designed to meet, and in many cases, exceed the stringent lightning safety requirements of the aircraft industry.
Parker’s technology is grounded on decades of proven on-wing time and durability through more than 100 million flight hours on most products. Parker’s engineered solutions include:
- Fuel caps and mating adapters
- Anti-siphon adapters and fuel stainers
- Flame arrestors
- Sump drain valves
- Positive/negative pressure relief valves
- Gravity fillers
- Lightning isolation/static dissipation fuel tubes
- Magnetic fuel level indicators
Parker Aerospace’s lightning test laboratory offers unique and specialized capabilities that ensure our products provide the ultimate lightning protection, certified to the most stringent commercial and military regulations for lightning, fire, and flammability. Engineers are active members of the SAE A-2 Lightning Safety Committee.
Now, watch this video to learn about Parker's extensive on-site testing capabilities for lightning and fire:
This blog was contributed by the Glen Kukla, engineering site leader, Parker Fluid Systems Division.