PC-12
Flight Crew Multiengine; Flight Crew Flight Instructor
Flight Crew Last 90 Days 150; Flight Crew Total 7043; Flight Crew Type 35
Aircraft Equipment Problem Critical
Aircraft Aircraft Damaged; General Maintenance Action
Aircraft
En-route an abnormally low prop rpm was noted (below the normal; governed cruise rpm which is not controllable by the pilot). The emergency checklist was consulted. The problem could not be resolved but it was determined that the flight could be continued to destination. On approach; as the power was reduced the prop rpm continued to reduce. Because the possibility of other prop anomalies was anticipated; some power was kept in until just prior to touch down. After touchdown power was reduced to idle and beta was selected. Instead of braking action resulting; the aircraft was felt to surge forward. The power lever was returned to flight idle and the condition lever moved to ground idle. Heavy braking was applied; resulting in both tires being flat spotted and deflating. After slowing the aircraft was taxied clear of the runway onto a taxiway and shut down. No further damage resulted.
We allowed for a slightly longer landing with a bit more power. This resulted in a slightly longer float landing with more than 3500 ft of remaining runway. This amount of runway is well within the landing capabilities of the PC-12.It is known that the PC-12 is light and tires must be treated with care. Heavy braking can easily lead to flattened tires. At the time of landing the aircraft was accelerating when it was supposed to be slowing. The first reaction was to add heavy pressure to the brakes while trying to slow the plane by other means which included PL back to neutral; CL to ground idle; and flaps to O degrees. The perception at the time was that we were fast approaching the end of the runway thus increasing anxiety which resulted in braking heavily. This resulted in the flattening of the two main tires.There was no further damage to the aircraft or property. The passengers were deplaned.
When the PC-12 suffered abnormal propeller RPM response the flight was continued to destination where; upon landing; the prop failed to shift to Beta mode and the aircraft accelerated and demanding immediate and extreme braking to stop on the runway.  Both main gear tires were flatted and deflated as a result.  No injuries or other damage to the aircraft.