I believe there's also been an occasion when an incident occurred, involving a biz-jet and an a/c of composite construction. IIRC, the latter's airframe did not provide a usable primary echo, whilst its single SSR aerial was shielded (from the ground interrogator) by the attitude of the a/c at the time. As usual, the 'holes lined up'. It may not be a common occurrence, but there's more and more of them out there.