What if lightning strikes an airplane

Samara Cokinos , Meteorologist. Lightning strikes commercial aircraft on average once every 1, flight hours. A shocking statistic but luckily the aircraft can usually handle it.

The flight had just flown from San Juan, Puerto Rico to Baltimore and was to finish the last leg to Philly with 73 passenger and 8 crew on board. There was a cold front moving into Philadelphia with thunderstorm and lightning potential in the flight path. According to the aircraft accident report by the Civil Aeronautics Board, the aircraft was in a holding pattern when it was struck by lightning.

These consist of an embedded layer of conductive fibers, such as mesh constructed from copper foil, to direct the current. The lightning exits another extremity of the aircraft, such as the tip of the tail. It will then continue to the opposite polarity in the cloud structure. However, if it cannot find an opposite polarity, it will hit a point on earth instead. If the aircraft becomes part of the cloud-to-ground lightning event in this way, passengers and crew may see a flash and hear a loud bang.

According to a Boeing essay on lightning strike maintenance best practices, pilots have occasionally reported a temporary flickering of the lights or brief instrument interference on such occasions. Therefore, every circuitry and equipment essential to the safe flight and landing of the plane must have specific protection in the form of shielding, grounding, and surge suppression.

Meanwhile, Boeing also says that a strike of unusually high intensity has the potential to damage components such as electrically controlled fuel valves, generators, power feeders, and electrical distribution systems. When dealing with any form of a spark, flammable substances such as fuel need to be heavily protected. The construction around aircraft fuel tanks must be thick enough to withstand a burn through from the lightning.

All vents, access doors, and caps must adhere to lighting protection certification standards. These were raised after the last severe lightning strike accident happened when a Pan Am Boeing exploded in flight after vapors in the fuel tank ignited.

New fuels with less hazardous vapors have also become the norm. The airplane then flies through the lightning flash, which reattaches itself to the fuselage at other locations while the airplane is in the electric "circuit" between the cloud regions of opposite polarity. The current will travel through the conductive exterior skin and structures of the aircraft and exit off some other extremity, such as the tail.

Pilots occasionally report temporary flickering of lights or short-lived interference with instruments. Most aircraft skins consist primarily of aluminum, which conducts electricity very well. By making sure that no gaps exist in this conductive path, the engineer can assure that most of the lightning current will remain on the exterior of the aircraft.

Some modern aircraft are made of advanced composite materials, which by themselves are significantly less conductive than aluminum. In this case, the composites contain an embedded layer of conductive fibers or screens designed to carry lightning currents. Modern passenger jets have miles of wires and dozens of computers and other instruments that control everything from the engines to the passengers' headsets.

These computers, like all computers, are sometimes susceptible to upset from power surges. So, in addition to safeguarding the aircraft's exterior, the lightning protection engineer must make sure that no damaging surges or transients can reach the sensitive equipment inside the aircraft.

Lightning traveling on the exterior skin of an aircraft has the potential to induce transients into wires or equipment beneath the skin. These transients are called lightning indirect effects. Careful shielding, grounding and the application of surge suppression devices avert problems caused by indirect effects in cables and equipment when necessary.

Every circuit and piece of equipment that is critical or essential to the safe flight and landing of an aircraft must be verified by the manufacturers to be protected against lightning in accordance with regulations set by the Federal Aviation Administration FAA or a similar authority in the country of the aircraft's origin. The other main area of concern is the fuel system, where even a tiny spark could be disastrous.

Engineers thus take extreme precautions to ensure that lightning currents cannot cause sparks in any portion of an aircraft's fuel system.

Occasionally, a static wick will be the victim of lightning exiting the airplane. I have been in airplanes that have sustained lightning strikes several times with very little damage. Q: When lightning strikes an airplane, are you safer in the air or on the ground?

A: In the air, airplanes are designed to dissipate the lightning quickly. I have been flying airplanes that were struck multiple times, and there was little or no damage sustained. All the surfaces are bonded, giving the lightning a pathway to pass back into the atmosphere.