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Montreal, Canda - A software bug, which has been recently discovered on Bombardier CRJ200s causes the aircraft to turn the wrong direction if pilots adjust a pre-set altitude limit.
The bug led to CRJ200 jets in some cases trying to follow certain missed approaches turning right instead of left – or vice versa. Missed approaches are used when pilots aren't confident that they're going to land safely. They are a published path that helps the pilot safely position the airplane for another attempt.

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 CRJ200 crew flying into Canada's Fort St John airport used the FMS's temperature correction function. They discovered that the software turned their airplane 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.

Temperature correction is a function of modern FMSes that helps keep airplanes at a safe height above the ground while following published approach paths under instrument flight rules (or the autopilot). Airport approaches are designed with a given set of atmospheric conditions, including a standard temperature, in mind. When real-world temperatures drop below certain limits, pilots must apply a correction to their altimeters in order to stay at a safe height above ground. Lower temperatures, for a given atmospheric pressure, introduce a progressively greater error in the altimeter reading.

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