Star Trek: The Next Generation, Disaster. First aired Oct. 21, 1991.
When Trek isn't relying on its strong captain, it relies on its technology. After its writers painted themselves into a dramatic corner, Trek always had technological mumbo-jumbo to fall back on which means the characters sometimes found miraculous new devices that instantly solve their problems. This episode deprived the Enterprise bridge of both its captain, who gets stranded in a turbolift, and its technology, which is largely disabled when the ship runs into mysterious "quantum filaments" (like I said, there's often some mumbo-jumbo). Chaos ensues, and all the characters must effectively switch roles: Counselor Deanna Troi, the senior officer left on the bridge, must learn to be the tough captain; the captain, in a turbolift with a bunch of kids, must be a counselor; the ship's bar, Ten Forward, becomes a sickbay. Trek is a formula show that always knew it had to break the formula routinely to survive.