Date: 201606
Local time of day: 0601-1200
Location: ZZZ.Tower, US
Flight conditions: VMC
Light: Daylight
Aircraft: PC-12
Operating under: Part 91
Mission: Ferry / Re-Positioning
Flight phase: Climb
Airspace: Class D ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Stall Warning System
Component problem: Malfunctioning
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Distraction; Workload
Anomaly: Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Bird / Animal
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: We were cleared for the IFR takeoff; with visual conditions existing. My first officer rotated at the appropriate speed and started the climb out. Before I was even able to observe and call out a positive rate of climb for gear retraction; the amber 'PUSHER' CAS illuminated on the CAS panel; along with a red 'STALL' warning message on both PFDs; the aural 'STALL; STALL; STALL' warning; and constant shaker activation on both pilots' control yokes. In addition to this; the speed tape was red on both PFDs; and there was no longer a DSB [Dynamic Speed Bug] present on either airspeed tape. We were in agreement that the aircraft was not actually stalling; and quickly verbalized this to each other. In addition to this; we quickly determined that we were out of usable runway and would continue to climb to pattern altitude and return for landing. I contacted the air traffic controller to advise her of our intentions; but she did not get back to us due to a busy frequency. We continued climbing; keeping everything configured how it was. Once ATC told us to contact departure; I advised her of our intentions- that we needed to remain in the pattern and to return for landing. I asked for priority because the pattern was getting busy and did not want to extend our time airborne unnecessarily. The air traffic controller asked if we needed any assistance; I declined. Meanwhile; while turning crosswind; my first officer ensured to pull the power back enough to keep below the flap extension speed for flaps 15. We decided we would just keep the airplane configured as is since it would be a quick pattern - gear down and flaps 15 degrees. I looked to see what position my AOA probe was in to see if that could be a factor in causing the shaker activation. The LH AOA vane was in the up position when I looked; but we were also in a left turn at that point. My first officer noted that the RH AOA vane seemed to be in a normal position. The shaker continued the entire time while airborne; but there was no pusher activation at any time.I asked my first officer if he was comfortable continuing to fly and if he felt that he had positive control of aircraft. He said he yes to both; therefore I had him continue flying the airplane since I thought there could be more confusion caused by exchanging controls at that point. ATC cleared us onto a base once we had traffic on final in sight. My first officer called for flaps 30. I set them as called for and we completed the Before Landing and Prior to Landing checklists. We maintained a slightly faster airspeed on approach to landing since we most likely no longer had stall protection. As my first officer landed the airplane; there was a slight balloon; something not typical of his landings. He explained that the shaker was making it difficult to flare at that point; as it was causing the yoke to be very stiff. It was; however; still a completely safe landing.As soon as we touched down; everything seemed to go back to normal - the shaker was no longer activating; we no longer had the Amber PUSHER CAS; the red STALL warning message went away; the airspeed indicator returned to normal; and the aural 'STALL' warnings ceased. We taxied back and shut down. After shutdown; I did a post flight inspection of the airplane; looking closely at both AOA vanes to see if I could observe any defects or abnormalities. I did not notice anything out of the ordinary on either side. However; there was evidence that something had hit the leading edge of the RH wing; just a few inches away from the AOA plate; towards the wingtip. There did not seem to be any bird feathers; but the debris area was approximately 4 inches wide and was about 5.5 inches top to bottom; extending from the leading edge of the wing to underneath. My suspicion is perhaps a bird hit the AOA probe and then continued on to hit the leading edge of the wing- but this is just speculation. We did not experience any abnormal engine or propeller indications during flight; so I am comfortable in saying the bird did not interfere with our engine.I contacted [Operations] and informed them of the issue; and then spoke with Maintenance Control. We also noticed that on the ground with the batteries turned on; both shakers would activate for approximately 30 seconds and then settle down; even though both AOA probes were in the down position.We were then instructed by [Operations] to do a tail swap with another crew that had just finished their day. This would allow us to continue with our scheduled reposition flight. Lastly; Maintenance Control requested that I download and send them the aircraft's ACMF [Aircraft Condition Monitoring Function] and FHDB [Fault History Database] logs via the aircraft iPad and send them via email. Although this is clearly an aircraft malfunction that could not really be avoided; it was a scenario that I had never encountered before. Therefore; I was able to learn a few things. I found the aural 'STALL' warning to be very distracting while we were flying in the pattern to return for landing. As the pilot monitoring; I was responsible for radio calls; but I could barely hear ATC even with the volume turned all the way up because the aural warning system kept yelling 'STALL STALL STALL' the entire time. In addition to this; I found it difficult to communicate with my crewmember because I had to have ATC turned up to the max volume. We both found this distracting. I looked for an aural inhibit button on the FMS panel quickly; but could not see anything. In addition to this; my first officer mentioned that the yoke was rather stiff while flying with the shaker activated. We were both glad to get on the ground.Therefore; lessons that I learned include the following:1) I gained awareness that the yoke feels stiff while the shaker is activated. Therefore; I can be prepared for this if something similar to this happens in the future. Additionally; I will be aware that it may be more difficult to flare the aircraft properly when coming in for landing.2) I learned that I should remember that the Aural Warning Inhibit rocker switch is located on the Captain's side of the cockpit. During the hurry with everything going on; I unfortunately forgot this. If I had remembered this rocker switch; I could have activated it to mute the aural 'STALL' warnings; making it a much better flight environment. My thoughts go to 'out of sight; out of mind' in regards to why I forgot the switch was over there. Therefore; this is a good lesson learned for myself going into the future.




Synopsis: PC-12 pilot reported they returned to departure airport following false stall warnings shortly after takeoff that may have been related to a bird strike on an AOA vane.