The experience of a Twin Navion pilot provides an interesting story by which we can all benefit. On July 25, 1986 over Canmore, Alberta a Twin Navion was struck by lightning during a moderate rain shower while flying at 7,200 feet ASL. The lightning arrived in the form of a five foot diameter fire ball directly in front of the aircraft, accompanied by a deafening bang. More than $7,000 of damage was caused to the airframe and aircraft components.

The aircraft had left Calgary at noon on a trip to Salmon Arm, BC, and encountered virga and rain showers at 9,500 feet passing east of Banff over Canmore, Alberta. Tops of clouds appeared to be about 13,000. The Twin Navion was equipped with a WX-8 "Stormscope," which tested serviceable, and the unit showed no serious activity within the isolated showers in the area. There was no turbulence, but light rain and snow were present at an OAT of plus 4 degrees. There were significant CB build-ups in the region around Lake Louise, Alberta and Golden, BC. Calgary Flight Service advised that Golden had issued a special announcing 5/10 towering cumulus and CB just east of the town.

The pilot confirmed the extent of this CB and decided no to carry on through the continental divide at Golden, turning back towards Calgary. To stay below the base of the showers, which had lowered about 2,500 feet in less than 10 minutes, he descended to 7,000 feet. The "Stormscope" still showed nil activity in the rain ahead. Light to moderate rain was encountered, and then bang! - lightning struck.

The lightning passed from the nose through to the tail of the aircraft, exiting through the rudder trim tab and rear navigation light. The light was shattered, melted and refused exiting electrical charge. The lightning singed sleeping bags and pillows stowed in the nose, resulting in a strong burnt smell. The radios were still functional but the ADFs would not home.

After a safe landing in Calgary (engines and aircraft systems worked fine), an inspection revealed extensive damage. The two Collins 650A ADF loop antennae were destroyed - the amplifiers were burnt out in the solid unit. The rudder trim tab and trim tab cables were burnt, and there was skin damage to the aircraft nose. The spirit compass and carb air temperature gauges were demagnetized, and extensive areas of the cabin and nose were magnetized, including landing gear, heater, radios, radio racks, pilots' seats, control yoke and control columns as well as hoses, nuts and bolts.

The aircraft had to be demagnetized, all compasses and the RMI system had to be overhauled and reswung; the rudder trim tab and trim cables were replaced, as was the rear navigational light and the ADF loops. Of course, sheet metal repairs were necessary for the nose section. The ELT required recertification although it had just been signed off, and the WX-8 "Stormscope" was returned to the factory for a check and recalibration.

Recent lightning research has revealed that sometimes the presence of an aircraft can initiate a lightning discharge (see ASL 4/86, page 2). It has also been suggested that lightning will attach to the airframe at a point where insulating material and metal are touching - in this example, in the nose compartment where the sleeping bags were stored. Additionally, weather radar and "Stormscope" are excellent weather avoidance devices but, as the story shows, are not infallible in detecting every hazard.