Lightning striking an airplane might sound like a terrifying scenario, but modern aircraft are designed to handle the impact with minimal consequences. Although passengers and crew may witness a flash and hear a loud noise when lightning strikes, the careful engineering of lightning protection systems ensures that nothing serious happens to the aircraft or its sensitive components. So, what exactly happens when lightning strikes an airplane? Let's find out.
Lightning and Airplanes
It is estimated that on average, each airplane in the U.S. commercial fleet is struck lightly by lightning more than once each year. Interestingly, airplanes can actually trigger lightning when they fly through heavily charged regions of clouds. In these cases, the lightning flash originates from the airplane and extends in opposite directions. Smaller business and private airplanes are thought to be struck less frequently due to their small size and ability to avoid weather conditions that are conducive to lightning strikes.
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Lightning Protection
Over the years, much has been learned about how lightning can affect airplanes, leading to significant improvements in protection techniques. Today, airplanes undergo rigorous lightning certification tests to verify the safety of their designs. The last confirmed commercial plane crash in the U.S. directly attributed to lightning occurred in 1967 when lightning caused a catastrophic fuel tank explosion. Since then, advancements in lightning protection systems have made air travel even safer.
How Aircraft Withstand Lightning
When lightning strikes an airplane, it initially attaches to an extremity such as the nose or wing tip. As the aircraft continues flying through the lightning flash, the lightning reattaches itself to the fuselage at other locations. The current then travels through the conductive exterior skin and structures of the aircraft and exits through another extremity, such as the tail. Occasionally, pilots may experience temporary flickering of lights or short-lived interference with instruments. However, these instances are generally harmless.
Most aircraft are primarily made of aluminum, which conducts electricity well. Ensuring that no gaps exist in the conductive path allows most of the lightning current to remain on the exterior of the aircraft. Some modern aircraft made of advanced composite materials contain embedded layers of conductive fibers or screens designed to carry the lightning current effectively.
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Protecting Sensitive Equipment
Modern passenger jets have complex electrical systems, including miles of wires and dozens of computers and instruments. To protect these sensitive components from power surges, lightning protection engineers must not only safeguard the aircraft's exterior but also ensure that damaging surges or transients cannot reach the equipment inside the aircraft. Lightning traveling on the exterior skin can induce transients into wires or equipment beneath the skin. Engineers employ careful shielding, grounding, and the application of surge suppression devices to prevent problems caused by these indirect effects. Every circuit and critical equipment must be verified to be protected against lightning according to regulations set by aviation authorities.
Fuel System Considerations
One of the major concerns during a lightning strike is the aircraft's fuel system. Even a tiny spark in this area could have disastrous consequences. Engineers take extreme precautions to prevent lightning currents from causing sparks in any part of the fuel system. This involves ensuring the thickness of the aircraft skin around the fuel tanks, tight structural joints and fasteners, and designing access doors, caps, vents, pipes, and fuel lines to withstand lightning. Additionally, the use of new fuels with reduced explosive vapors has become widespread.
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Lightning Protection for Radar Instruments
The aircraft's radome, which houses radar and other flight instruments, requires special attention from lightning protection engineers. To function properly, radar cannot be confined within a conductive enclosure. Lightning diverter strips, consisting of solid metal bars or a series of closely spaced buttons of conductive material, are applied along the outer surface of the radome. These strips protect the radar instruments by redirecting lightning strikes away from the sensitive equipment, much like a lightning rod on a building.
Concerns for Private and Kit-Built Aircraft
Private general aviation planes and kit-built composite aircraft have their own considerations when it comes to lightning protection. Private planes should avoid flying through or near thunderstorms due to the severe turbulence found in storm cells. The FAA has specific lightning protection regulations for private aircraft that do not transport passengers, providing a basic level of protection for the airframe, fuel system, and engines. Kit-built composite aircraft, which are considered "experimental" by the FAA, are not subject to lightning protection regulations. It has been found that lightning can damage inadequately protected composites, so pilots of such aircraft should avoid flying near lightning storms or certain types of clouds.
Frequently Asked Questions
Q: Can lightning cause a commercial airplane to crash?
A: The last confirmed commercial plane crash directly attributed to lightning occurred in 1967. Since then, extensive improvements in lightning protection systems have made air travel safer, and lightning strikes generally do not pose a significant risk to commercial airplanes.
Q: Do passengers feel anything when lightning strikes an airplane?
A: Passengers may see a flash and hear a loud noise if lightning strikes their airplane. However, due to the careful engineering of lightning protection systems, nothing serious should happen to the aircraft or its passengers.
Q: Are private planes more or less susceptible to lightning strikes?
A: Generally, private planes are thought to be struck less frequently than commercial planes due to their smaller size and ability to avoid weather conditions conducive to lightning strikes. However, it is still important for private pilots to exercise caution and avoid flying near thunderstorms.
Q: What precautions are taken to protect the fuel system during a lightning strike?
A: Engineers take extreme precautions to ensure that lightning currents cannot cause sparks in any portion of an aircraft's fuel system. This includes designing the aircraft skin around the fuel tanks to be thick enough to withstand burn through and ensuring tight structural joints and fasteners to prevent sparks.
Q: How does lightning protection differ for radar instruments on an airplane?
A: The aircraft's radome, which contains radar and other flight instruments, is protected by lightning diverter strips. These strips, made of conductive material, redirect lightning strikes away from the sensitive equipment, similar to how a lightning rod works on a building.
Remember, although lightning strikes on airplanes may seem concerning, extensive precautions and engineering advancements ensure that air travel remains safe even during thunderstorms.