Hi, On Christmas Day last Saturday, Comair Airlines had to completely stop flying all of its planes due to computer problems. Comair blamed the computer problems on their pilot scheduling software being overloaded after bad weather earlier in the week forced many flights to be rescheduled. Comair now hopes to have all of its 1,100 daily flights restored by tomorrow. An article which was published today at the Cincinnati Post Web site provides some interesting details of a software failure in Comair's pilot scheduling software: How it happened http://www.cincypost.com/2004/12/28/comp12-28-2004.html According to the article, Comair is running a 15-year old scheduling software package from SBS International (www.sbsint.com). The software has a hard limit of 32,000 schedule changes per month. With all of the bad weather last week, Comair apparently hit this limit and then was unable to assign pilots to planes. It sounds like 16-bit integers are being used in the SBS International scheduling software to identify transactions. Given that the software is 15 years old, this design decision perhaps was made to save on memory usage. In retrospect, 16-bit integers were probably not a good choice. An anonymous message posted to Slashdot the day after Christmas first described the software failure at Comair: http://slashdot.org/comments.pl?sid=134005&cid=11185556 Earlier this year, an overflow of a 32-bit counter in Windows shut down air traffic control over southern California for 3 hours: Microsoft server crash nearly causes 800-plane pile-up http://www.techworld.com/opsys/news/index.cfm?NewsID=2275 This problem occurred because of a known design flaw in older versions of Windows: http://tinyurl.com/5n9gc Richard M. Smith http://www.ComputerBytesMan.com
