Jet engine removal bolt design failure

Stage-business case. Tom passes around a hardened steel bolt assembly used to dismount jet engines from aircraft wings. The bolt had two diameters with flats on the center shoulder for restraint; mechanics torqued only the outer nut, ignoring the shoulder, which over-torqued the assembly and initiated a crack. A 5-million-dollar engine dropped on the tarmac. Used to introduce load-path reasoning.

So far as that level of engineering, another bolted thing — we found this the other day when we were cleaning out some junk downstairs in the basement. [Tom produces a small hardened-steel bolt assembly.] We called this Tron air in the old days. This little bolt is part of a system to take a jet engine off the airplane wing. You have a sort of roll-up dolly that's about 15 feet tall, you roll it up to the wing, you put this bolt into the hanger for the thing that holds the turbine engine on the wing, and you torque it down. You torque it on this side, then you torque on this side, and then you pull it out. You release the bolts that held it on the wing, and now you have the jet engine that you can work on as a mechanic.