Software Bug In Bombardier Airliner Made Planes Turn the Wrong Way

An anonymous reader quotes a report from The Register: A very specific software bug made airliners turn the wrong way if their pilots adjusted a pre-set altitude limit. The bug, discovered on Bombardier CRJ-200 aircraft fitted with Rockwell Collins Aerospace-made flight management systems (FMSes), led to airliners trying to follow certain missed approaches turning right instead of left -- or vice versa.

First discovered in 2017, the flaw was only apparent when pilots manually edited a pre-set "climb to" altitude programmed into a "missed approach" procedure following an Instrument Landing System approach. It also arose if pilots used the FMS's temperature compensation function in extremely cold weather. In theory the bug could have led to airliners crashing into the ground, though the presence of two trained and alert humans in the cockpit monitoring what the aircraft was doing made this a remote possibility. "The bug was first uncovered when a CRJ-200 crew flying into Canada's Fort St John airport used the FMS's temperature correction function," the report adds. "They discovered that the software turned their aeroplane in the wrong direction while it was following the published missed approach, something that generally does not happen. The fault was swiftly reported to the authorities and the relevant manufacturers."

Full details, including the maths, are available here. The U.S. Federal Aviation Authorities also published a Powerpoint presentation (PDF) about the bug.