Re: TSFS Destruct Sequence: Why Chekov?
Chekov identifies himself as "acting Science Officer" to the computer. Perhaps that is the required position, along with Captain and Chief Engineer.
That's been my take on it too. It's also something that may vary from ship (on other vessels, it might be require the Security Chief or whoever was third in the chain-of-command).
"There's always someone wanting to ruin a good party..."