In the Gimli glider case the aircraft wasn't legally allowed to take off. The pilots also deferred the decision on whether to take off to the maintenance crew

In the Gimli glider case the aircraft wasn't legally allowed to take off. The pilots also deferred the decision on whether to take off to the maintenance crew who are not the ones authorized to make that decision. The pilots were initially demoted because of that but were restored due to public pressure. There was mitigating circumstances though, the procedures were frequently being revised (the 767 was brand new) and previously it had been permissible to take off without a fuel indicator. None of this takes away from the huge achievement of their landing. Simulator runs show the landing was near impossible. Had Captain Pearson not been an experienced glider pilot its likely they would have ditched in the river, and the historical survivability of water landings are not good.