A computer glitch that caused passenger data to disappear off of United Airlines computer systems caused the airline to have to cancel several dozen flights Friday night, including some out of SFO, and delay about 105 more worldwide, leaving thousands stranded. At SFO, a few hundred people were affected, and the lack of working computer systems led in some cases to the issuing of charming handwritten boarding passes like this one.

Compounding the problem of so many canceled and delayed flights is the fact that airlines in general no longer keep as many empty seats on flights, thereby making it more difficult to accommodate stranded passengers when problems like this occur. In the 1970s, flights had an average of 40% vacant seats, and they now keep that down to about 20% or less.

Flights resumed Saturday, and United now says it has corrected the glitch.