A couple points -
Not sure if I have this right.... You can check the integrity of the rigger's seal without pulling out the rigger's packing card? Is this correct?
The rigger's lead seal is on the endpoints of the thread which is tied around the last pin on the ripcord. The point is that when the ripcord is pulled the thread is broken and that means someone has opened the parachute. The integrity of the rigger's seal can be checked by opening the flap that covers the ripcord and the cones through which the ripcord pins are inserted. The rigger's packing card is a piece of paper that has its own small storage pocket somewhere on the harness or container and contains information regarding repacking and other items related to the parachute. To be legal for emergency use, the parachute must have been repacked within a specified time period and the rigger's lead seal must be intact.
R99 is correct on this. As for the difference of military vs civilian packing cards on backpack bailout rigs, I'm not 100% sure, but I can't see where they'd differ much if at all. Pretty basic information - the type of canopy inside, the repack dates (and if used vs normal 'cycle' repack), and any repairs or part changes made. R99 is also correct that the ejection systems for high performance military aircraft are a whole different matter. Those are usually integrated with the seat and designed for the specific aircraft.
Interesting to note, looking at the picture of the card for Hayden's returned chute, neither rigger wrote the 3-letter seal ID on the card. Not that I look at a lot of them, but most of the ones i see today do have it. I guess it's rigger's discretion.
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I talked to an older rigger, and according to him indeed it was a fairly common practice for an instructor to use a bailout rig to put out static line students instead of wearing a more cumbersome gutter gear sport rig. They wouldn't jump with it, but put out their students and ride the plane down. So Eric's assertion that Cossey may have used the DBC rig while instructing is feasible.
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Don't know what Hayden's plane was, but it would be aerobatic. The FAA requires a bailout rig for aerobatic flying, which is why he had them. According to RMB, Hayden was annoyed by this and had no intention of ever actually using it. I'm guessing that a structural failure or a fire may have convinced him otherwise.
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Per 377's post, my first reserve ride was also on a 26' Navy Conical. It was 4 years older than I was.