The US Federal Aviation Administration has issued advice to US Pilatus PC-12 operators following a Swiss civil aviation authority emergency airworthiness directive on how to handle an approach anomaly reported by some pilots flying the turboprop single. The FAA says the type has suffered several events on final approach in which an abrupt nose-down pitch force immediately followed autopilot disconnection while the flaps were set at 40°.
A possible out-of-trim condition exists that could reduce controllability, says the FAA. Pilatus says the pitch-down is not abrupt, but occurs over a period of about 2s and says that it is not unusual for pilots to experience a slight trim imbalance when tripping out an autopilot. The manufacturer adds that the tendency has not caused any accidents or serious incidents. Pilatus engineers, however, are examining the situation to see if a remedy can be developed, the company says. Meanwhile, Swiss operators have been required to revise the operating manual to order pilots to disengage the autopilot before selecting 40° flap on approach, and the FAA is recommending the same temporary revision.
Source: Flight International
