Source: TheRegister

 – May 29th, 2020

 

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.
 
[…]
 
Rockwell Collins explained that “an error in the design of the Pro Line 4 FMC software causes changes to the procedure-defined turn direction, during a missed approach when the procedure has been significantly modified… The FMS may change the planned database turn direction to an incorrect turn direction when the altitude climb field is edited.”

The incorrect turn direction, said the company, “is dependent on leg types and geometries of the instrument departure procedure and missed approach procedures.” In other words, the bug only occurred rarely and under specific conditions.