A plane flies through the night. A winter storm howls as the pilot radios for meteorological information, trying to steer clear of the worst of it. All has gone well apart from the weather. The news that a heart was coming had reached the airport in plenty of time for the pilot to ready her plane for take off. By the time the ambulance arrived with sheriff escort, the engines were warm and ready to taxi onto the runway. The controller held air traffic as the two-engine craft sped down the runway and lifted into the air.

But now the weather: Will she be able to complete her route? "Continue ahead," comes the report, "but landing may be a problem." An hour and a half passes, more bad weather. The controller at the receiving airport decides to bring her in with the caution, "Low visibility, …