Usually, nobody on the aircraft knows they were hit by lightning, including the pilots. Everyone may see the lightning flash, but not know if it hit the aircraft. It’s only obvious if somebody sees it hit.
When I greet the flight crew at the gate, they may say to me, “We flew through some lightning, and it looked like we might have been hit, but not sure”. So then, I will try to look for lightning strikes on the aircraft when I do my walk-around inspection.
We do mandatory walk-around inspections to every arrival, anyways. I’ve discovered lightning strikes when the flight crew didn’t know they were hit.
So, it usually doesn’t affect the aircraft. They are designed to be able to take lightning strikes.
Sometimes, when the aircraft gets hit with a lightning strike, the instruments will fluctuate somewhat, and give the pilots a hint that they may have been hit. That was reported to me on a few occasions.
When we do find evidence of a lightning strike, that aircraft is grounded until we do a comprehensive lightning strike inspection on the entire aircraft, at the hangar. Our paperwork for this inspection is about 70 pages long.
Sometimes there is only an entrance mark or an entrance and an exit mark. Other times, the lightning skips across the fuselage like when you skip a rock over the water surface. It kind of looks like a machine gun fired down the side of the plane.
Here is a lightning strike I found during my walk-around. This is on a 787 Dreamliner, which is made of carbonfiber:
The maintenance manual tells me that the dimensions I measured are within limits and all I have to do is clean it up, tape it off and apply a special epoxy coating made for the carbonfiber skin:
When it dries, I paint it. Unfortunately, the paint has metalic flakes in it and it won’t match the rest of the paintjob, because we are prohibited from spraying paint, per the EPA.
Only a certified paint facility can spray paint. So, I had to brush it on. The new paint sticks out like a sore thumb.