I'd heard of this phenomenon before, but couldn't figure
out exactly how it happened.

I believe it occurs when the sun angle is parralel with the top of the open
canopy and the magnification is caused by rays passing through the plexiglass
at almost a zero angle. The fire is started on any object that is close to the
focus point, ie. instrument panels, head rest on K-21 or DG-300. I know of an
ASH-25 that was *totaled* after a cockpit fire caused by this phenomenon.
JJ Sinclair