Lightning Strike!

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If you're based in Florida, summertime means either flying around thunderstorms or not flying at all. But even the most experienced hand dodging TRW will occasionally get more than was bargained for, as AVweb publisher Carl Marbach discovered when his Aerostar took a damaging lightning strike while flying in an area that his radar and Stormscope said were okay. Here's the story and the photos of what happened to Carl's airplane (he won't be flying it for awhile).

If you don't want to fly around thunderstorms in Florida in the summer months, don't fly. But I got more than I bargained for in my most recent flight from Lancaster, Pennsylvania to home base in Boca Raton Florida.

Friday, June 13, 1997

The usual clusters of storms over the Southern Florida peninsula were evident both on the radar picture I got with my weather briefing, my eyes in the cockpit and on the color radar in my Aerostar 601P, N6069N. There was one big storm over Daytona Beach which was easily circumnavigated by going about 5 miles west of the OMN VOR and then turning to intercept V3 southbound. Ahead looked more ominous. There was a line of storms starting about Melbourne, Florida that looked, at least to the eyes, solid. ATC suggested heading southeast where "everyone else" was going through. After consulting the radar and the WX-8 stormscope I headed about 120 degrees, about 30 degrees east of the normal V3 routing.

The cells stood out very well on the radar as large red blobs; there was on over land near Melbourne and one well out to sea, with very little precipitation in between. The cells were separated by about 50 miles, and it looked like a good plan. I began my descent from FL220 to 16000 feet about opposite Melbourne and soon entered the clouds. There were one or two small patches of level 1 (light) precipitation showing on the radar and there was some moderate turbulence as I flew through them. Each of these little areas was about 2 miles wide with light rain on the windshield. Somewhere in the continued descent I saw a lightning bolt off the left wing, at the same time I heard a "whoooosh" – nothing else. The avionics never wavered, no circuit breakers popped, in short nothing happened. I estimated the lightning bolt to be about 1 mile away. I was more occupied with flying the airplane in occasional moderate turbulence and studying the radar than thinking about a lightning bolt that I thought was more than a mile away.

About this time ATC suggested a turn back toward the airway. I declined based on the radar and flew another 10 miles before turning back towards the coast. After the turn, the clouds broke up and it was VFR the rest of the way to Boca.

On the ground I noticed that one corner of the left propeller looked chipped. A close inspection revealed a jagged break of about ¼ inch and the aluminum looked like it had melted where the piece broke off. There was a slight discoloring of the paint and I immediately thought that it had been hit by lightning. I walked around the left wing and saw the three pencil sized holes in the trailing edge of the flap. There was a slight discoloration in the paint here as well. Continuing around the tail appeared to be undamaged, nothing on the flap on the right wing….then I saw the large, fist sized burn on the top of the right wing outer panel near the trailing edge. The screw in that area had been melted and a small piece of melted aluminum was also visible near the trailing edge.

The airplane had flown perfectly, with no hint of any problems all the way to BCT. The avionics appear to be undamaged. The burn mark on the right wing was about 12 inches from the fuel tank in that wing which certainly makes me nervous and I guess makes me lucky- if anyone hit by lightning can be called lucky.

Monday June 16, 1997
What Now?

There are several service bulletins relating to what you have to do to engines, propellers and the airframe in the event of a lightning strike. Some, but not all of these are to protect the manufacturers against any liability from subsequent failures.

So far this is clear:

  • The left flap skin has to be repaired.

  • The right wing outer panel has to be inspected and repaired.

  • The left prop hub has to be taken apart and inspected.

  • The left prop blade that was struck may have to be replaced.

  • The wing structure must be thoroughly borescoped for internal damage caused by arcing.

  • The left engine must be torn down, inspected and demagnetized.

  • All the avionics must be checked for proper operation.

The good news is that my insurance company (USAIG) has agreed pay for all this.

Tuesday June 17, 1997

More damage was found on the clear plastic cover to the wingtip strobe and recognition light. One screw was burned and the washers all showed some heat damage. There was a small burn mark inside the plastic lens as well. No other external damage has been found.

Palm Beach Propeller shop examined the left engine with a gaussmeter and found that it has a significant amount of magnetism. The right engine showed none and this adds to the belief that it escaped any consequences of the strike.
Lycoming issued a service bulletin for lightning strikes on June 30, 1976. Here is the text of that bulletin:

Lycoming Service Bulletin Number 401

Date: June 30, 1976
Subject: Recommendations for aircraft struck by Lightning
Models affected:  All aircraft powered by Avco Lycoming engines
Time of compliance: Anytime aircraft is struck by lightning

Damage to an aircraft, which has been struck by lightning, is usually apparent and often confined to a specific area of the structure. In such instances where the engine and its accessories, controls, fuel or exhaust systems are involved it is necessary to evaluate and repair the damage before the aircraft is flown again.

Although the path of the lightning may appear to have been around the external housings of the engine components, it is nevertheless impossible to asses the internal damage that might have occurred by heat during the lightning discharge. Therefor, in the event the engine has been damaged by lightning, disassemble and inspect the component parts. Heat generated by the arcing effect of the electrical discharge can cause irreparable damage to the hardened surfaces of ball bearings, crankshaft bearing surfaces, camshaft lobes, gear teeth and other parts that are surface hardened; these should not be reused if discoloration, cracks or other indication of damage by lightning is evident.

The new flap skin is scheduled to arrive tomorrow.

I'll continue to update this as it happens.