The US FAA is alerting operators of some popular regional jets and turboprops that input errors on certain Honeywell-built flight management systems on the aircraft could cause an aircraft to unexpectedly alter its course.
Prompting the warning was an unidentified incident involving a flight crew performing a standard terminal arrival route (STAR) to the Salt Lake City International airport. Air traffic control uses STARs to help sequence aircraft for instrument approaches.
At some point during the area navigation (RNAV) arrival in question, the pilots reprogrammed the aircraft's flight management system (FMS) with a different landing runway, causing the aircraft's autopilot to reverse course back to the initial starting point for the STAR, a navigation facility more than 50nm behind the aircraft.
The special airworthiness information bulletin (SAIB), issued on 7 January, informs owners and operators of the ATR42 turboprop and Embraer ERJ and E-170/190 aircraft to "ensure that their flight crews are familiar with" a Honeywell service information letter published in October 2009, after the Salt Lake City incident.
The SAIB also targets operators of a large number of business jets with the Honeywell equipment.
Honeywell and FAA during the joint investigation of the incident determined that "due to pilot workload in [the approach] phase of flight, a more detailed explanation [in the FMS operating manual] was required to alert flight crews on how FMS software is designed to handle such changes".
In particular, crews are now instructed to place the autopilot in "heading" mode with the aircraft's current heading until the FMS flight plan has been modified to match the current aircraft position in the procedure.
FAA says the issue, at this time, is not "an unsafe condition" that would warrant an airworthiness directive.