The European Aviation Safety Agency has issued an airworthiness directive that will remove flight attitude restrictions for Honeywell Primus Apex-equipped PC-12NGs in lieu of a software upgrade or hardware change-out.
The regulator in early April had issued an emergency AD against the integrated avionics suite, alerting operators to the possibility that both primary flight displays could indicate an erroneous roll attitude offset of up to 10° in the same direction when the Apex-equipped aircraft were taxied on to the runway in an accelerated turn, with take-off immediately following.
Additionally, Honeywell had found that aircraft operating in high geographic latitudes with correspondingly low horizontal magnetic field components were susceptible to incorrect heading computations when operating in magnetometer mode on the ground.
Honeywell traced the problem to a software issue in Apex's air data, attitude and heading reference system (ADAHRS).
Interim ADs while Honeywell developed a fix called for pilots to hold in place for 60s before lining up on the runway for take-off, followed by a low-acceleration turn on to the runway, and waiting 15s once aligned with the runway centreline before departure. After departure, turns were limited to 30° maximum during the climb.
The final AD, published on 20 November, gives operators 180 days to install either a new software load for the ADAHRS or to replace the ADAHRS unit itself, actions that will remove all limitations.
Pilatus has begun installing the fix on its assembly line aircraft starting at serial number 1181.