I know that they certify airplanes for lightning strikes (at least some of them anyway), but does it cause any damage to the airplane or to the electronics? Are there any required inspections if an airplanes is struck by lightning?
The vast majority of aircraft require an inspection, from small Cessna singles to Boeing airliners. Usually, they require at the very least:
- A visual inspection of the aircraft for damage, particularly the nose, tail section and wingtips. Most of the time, the damage is easily visible as "burn" marks or erosion of parts of the skin.
- A check of the communication/navigation systems, both visually and functional testing
- A check of all avionics, including GPS systems
- Propeller should be removed and inspected by an A/P for damage
Engine should be inspected by a procedure similar to the following:
- Remove the engine from the aircraft and disassemble it.
- Inspect the engine for arcing and heat damage to the crankshaft, main bearings, counterweights, camshaft lobes, bearings, gear teeth and any other parts applicable to your engine. Any magnetic parts should be degaussed following the specific procedure in your manual.
- Measure each other part to make sure it is within tolerances for your engine.
- Reassemble, then install the engine.
(depends on company) Send in an lightning strike report to your manufacturer
- Confirmation of compass being within 10 degrees of another (stricter for transport low visibility operations) after completion of repair/inspection works
- Cessna 172R Maintenance Manual
- Aero Magazine -- Lightning Strikes: Protection, Inspection, and Repair (Boeing, Q4 2012)
- Continental Maintenance and Overhaul Manual: M-18
The one time that I was struck by lightning for sure (there with a couple of other times I wondered if I had) was in a Cessna 310. Everything was working after the strike. However, an inspection of the airplane afterward showed that the very aft end of the right tip tank had melted and then resolidified.
As I understand it, a lightning charge typically "flows" around the outside of a metal aircraft.
Airplanes are designed to withstand lightning strikes, since they are expected to experience this in service. The goal is to conduct the current through the airplane while minimizing any damage this will cause.
Metal parts are naturally conductive, but composites need a conductive layer such as a metal mesh added to conduct the current. The parts also need to be connected, or the current will arc across the gap, possibly damaging both parts or sparking a fire. This connection can either be through properly installed fasteners like bolts or rivets, or through the use of bonding jumpers.
Fuel and electical systems in the aircraft require special attention. In the fuel tanks, parts must be connected well without gaps to avoid sparks that could ignite fuel vapors. Electrical systems must be sufficiently isolated to prevent lightning current from damaging them.
As this Boeing information shows, the protection required also depends on the location in the airplane. Different parts generally experience lightning strikes in different ways, and need different approaches in design.
The Boeing page also includes a flowchart for deciding whether a system needs to be inspected after a lightning strike. If the system was not used after the strike, it should be checked. If the system was used after the strike, it only needs to be checked if the system had anomalies in flight or of there is damage near the antennas for that system.