That's a microswitch underneath the chair that checks for presence of that chair...

jacquesm on Nov 11, 2019 | parent | context | favorite | on: When His SR-71 Blackbird Disintegrated, This Pilot...

That's a microswitch underneath the chair that checks for presence of that chair. If the switch is no longer depressed the chair is gone or the switch is maladjusted, which can easily happen.

anonymousiam on Nov 11, 2019 [–]

Especially on a brand new aircraft during the maiden flight.