Narrative:

I departed ZZZ on an IFR flight plan to ZZZ1. The planned route had been entered into the FMS after what I considered to be an unusually long period for the FMS to initialize. After departure I engaged the yd and shortly afterward; the ap; in heading mode; following assigned radar vectors until being cleared direct to the ZZZ VOR. After activating direct I switched to navigation mode and proceeded. I reached the cruise altitude of 15000 ft and continued. At this point I had not encountered any anomalies. Approximately 15-20 minutes into the flight the master caution alerted with following cas messages appearing simultaneously: unable FMS-GPS mon; GPS 1 fail following a few seconds later was: taws fail. Several seconds after the initial warnings the cas messages cleared and I reset the master caution. During this period the FMS and ap remained activated and engaged and seemed to be tracking the entered flight plan. At this point I believed this was an erroneous message and continued to monitor the track and flight attitude indications. This same sequence then repeated 2-3 minutes later and repeated at an average of a 2-3 minute intervals throughout the 45 minutes remaining of the flight. During the cruise portion of the flight I programmed the garmin 496 as a backup to the onboard GPS. During the descent and initial approach to ZZZ1 I began to encounter IMC conditions. The AWOS at ZZZ1 reported OVC021. Anticipating the need for an instrument approach I requested and received vectors to zzzzz intersection; an IAF on the GPS runway 35 approach. I estimated the timing of the GPS failures to arrive at the IAF with the GPS functioning while I began the approach; anticipating that I would be in VMC before beginning the final approach based on the reported weather. I checked the raim prediction and monitored the status of the GPS on the sensors page of the mfd. I then programmed the garmin 496 for the missed approach as a way to cross check the FMS and in the event of a complete failure; an emergency means of navigation since the missed approach procedure was GPS based. As I began the approach the FMS and GPS and all seemed to function properly. When I joined the approach at zzzzz intersection at 2000 ft MSL I was still in IMC with intermittent ground contact. The FMS lead the turn to final and once established I began the descent to the intermediate altitude of 1700 ft MSL. I broke out at approximately 1850 ft MSL prior to the FAF and began to look for the field. Unable to initially locate the runway I cross checked the position with the 496 and it indicated the airport to be at approximately 10 O'clock and 3 miles. Looking visually I immediately located the airport; disconnect the ap and continued the approach and landing visually. After landing I notified the owner of the situation and began the process of determining a course of action. After agreeing to return the plane to ZZZ; since the weather had improved to VMC. I flew utilizing the navigation radios as the primary navigation source and monitored the GPS. The GPS continued to operate intermittently though the failures became longer and longer finally reaching the point at which the FMS went into the dr (dead reckoning) mode. All other modes of the FMS and flight deck (heading; trk; speed; vs; bl and altitude) operated properly during the return flight. At one point I attempted to utilize the FMS in the dr mode and while it seemed to be leading direct to ZZZ1 VOR while cross checking on the garmin 496 we were not compensating for the crosswind and were heading approximately 100 right of course. The flight concluded in VMC conditions without other anomalies. The ferry flight for maintenance was conducted in VMC conditions. The GPS operated as described above; however; an even more disturbing failure occurred. Approximately 5 minutes into the flight while in straight and level cruise; the pilot's pfd display indicated a sudden shift of the horizon indicating an 8-100 turn to the left. This was followed almost immediately by a master warning indicating an autoplt failure and loss of the FD and yd. I looked at the copilot's side pfd display and it also showed the erroneous bank. Outside visual cues continued to indicate straight and level flight as did the esis (electronic standby instrument system). I continued the flight in VMC and utilized the esis as the eadi source. I reported the new failures to maintenance and was informed of a pending pilatus service letter regarding this issue. At this point I have serious concerns with operating this aircraft in IMC. The possibility of receiving conflicting information from incorrect pfd indications and a correct esis display could lead to pilot confusion while in IMC.

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Original NASA ASRS Text

Title: A PC-12 CAS ALERTED 'UNABLE FMS-GPS MON;' 'GPS 1 FAIL' AND 'TAWS FAIL.' THE PILOT BELIEVED THE INDICATIONS WERE ERRONEOUS; BUT ON A RETURN FERRY FLIGHT A MAP SHIFT OCCURRED ALONG WITH FAILURES OF THE AUTOPILOT; YAW DAMPENER; AND FLIGHT DIRECTOR.

Narrative: I DEPARTED ZZZ ON AN IFR FLIGHT PLAN TO ZZZ1. THE PLANNED ROUTE HAD BEEN ENTERED INTO THE FMS AFTER WHAT I CONSIDERED TO BE AN UNUSUALLY LONG PERIOD FOR THE FMS TO INITIALIZE. AFTER DEPARTURE I ENGAGED THE YD AND SHORTLY AFTERWARD; THE AP; IN HEADING MODE; FOLLOWING ASSIGNED RADAR VECTORS UNTIL BEING CLEARED DIRECT TO THE ZZZ VOR. AFTER ACTIVATING DIRECT I SWITCHED TO NAV MODE AND PROCEEDED. I REACHED THE CRUISE ALTITUDE OF 15000 FT AND CONTINUED. AT THIS POINT I HAD NOT ENCOUNTERED ANY ANOMALIES. APPROXIMATELY 15-20 MINUTES INTO THE FLIGHT THE MASTER CAUTION ALERTED WITH FOLLOWING CAS MESSAGES APPEARING SIMULTANEOUSLY: UNABLE FMS-GPS MON; GPS 1 FAIL FOLLOWING A FEW SECONDS LATER WAS: TAWS FAIL. SEVERAL SECONDS AFTER THE INITIAL WARNINGS THE CAS MESSAGES CLEARED AND I RESET THE MASTER CAUTION. DURING THIS PERIOD THE FMS AND AP REMAINED ACTIVATED AND ENGAGED AND SEEMED TO BE TRACKING THE ENTERED FLIGHT PLAN. AT THIS POINT I BELIEVED THIS WAS AN ERRONEOUS MESSAGE AND CONTINUED TO MONITOR THE TRACK AND FLIGHT ATTITUDE INDICATIONS. THIS SAME SEQUENCE THEN REPEATED 2-3 MINUTES LATER AND REPEATED AT AN AVERAGE OF A 2-3 MINUTE INTERVALS THROUGHOUT THE 45 MINUTES REMAINING OF THE FLIGHT. DURING THE CRUISE PORTION OF THE FLIGHT I PROGRAMMED THE GARMIN 496 AS A BACKUP TO THE ONBOARD GPS. DURING THE DESCENT AND INITIAL APPROACH TO ZZZ1 I BEGAN TO ENCOUNTER IMC CONDITIONS. THE AWOS AT ZZZ1 REPORTED OVC021. ANTICIPATING THE NEED FOR AN INSTRUMENT APPROACH I REQUESTED AND RECEIVED VECTORS TO ZZZZZ INTERSECTION; AN IAF ON THE GPS RUNWAY 35 APPROACH. I ESTIMATED THE TIMING OF THE GPS FAILURES TO ARRIVE AT THE IAF WITH THE GPS FUNCTIONING WHILE I BEGAN THE APPROACH; ANTICIPATING THAT I WOULD BE IN VMC BEFORE BEGINNING THE FINAL APPROACH BASED ON THE REPORTED WEATHER. I CHECKED THE RAIM PREDICTION AND MONITORED THE STATUS OF THE GPS ON THE SENSORS PAGE OF THE MFD. I THEN PROGRAMMED THE GARMIN 496 FOR THE MISSED APPROACH AS A WAY TO CROSS CHECK THE FMS AND IN THE EVENT OF A COMPLETE FAILURE; AN EMERGENCY MEANS OF NAVIGATION SINCE THE MISSED APPROACH PROCEDURE WAS GPS BASED. AS I BEGAN THE APPROACH THE FMS AND GPS AND ALL SEEMED TO FUNCTION PROPERLY. WHEN I JOINED THE APPROACH AT ZZZZZ INTERSECTION AT 2000 FT MSL I WAS STILL IN IMC WITH INTERMITTENT GROUND CONTACT. THE FMS LEAD THE TURN TO FINAL AND ONCE ESTABLISHED I BEGAN THE DESCENT TO THE INTERMEDIATE ALTITUDE OF 1700 FT MSL. I BROKE OUT AT APPROXIMATELY 1850 FT MSL PRIOR TO THE FAF AND BEGAN TO LOOK FOR THE FIELD. UNABLE TO INITIALLY LOCATE THE RUNWAY I CROSS CHECKED THE POSITION WITH THE 496 AND IT INDICATED THE AIRPORT TO BE AT APPROXIMATELY 10 O'CLOCK AND 3 MILES. LOOKING VISUALLY I IMMEDIATELY LOCATED THE AIRPORT; DISCONNECT THE AP AND CONTINUED THE APPROACH AND LANDING VISUALLY. AFTER LANDING I NOTIFIED THE OWNER OF THE SITUATION AND BEGAN THE PROCESS OF DETERMINING A COURSE OF ACTION. AFTER AGREEING TO RETURN THE PLANE TO ZZZ; SINCE THE WEATHER HAD IMPROVED TO VMC. I FLEW UTILIZING THE NAV RADIOS AS THE PRIMARY NAV SOURCE AND MONITORED THE GPS. THE GPS CONTINUED TO OPERATE INTERMITTENTLY THOUGH THE FAILURES BECAME LONGER AND LONGER FINALLY REACHING THE POINT AT WHICH THE FMS WENT INTO THE DR (DEAD RECKONING) MODE. ALL OTHER MODES OF THE FMS AND FLT DECK (HDG; TRK; SPD; VS; BL AND ALT) OPERATED PROPERLY DURING THE RETURN FLIGHT. AT ONE POINT I ATTEMPTED TO UTILIZE THE FMS IN THE DR MODE AND WHILE IT SEEMED TO BE LEADING DIRECT TO ZZZ1 VOR WHILE CROSS CHECKING ON THE GARMIN 496 WE WERE NOT COMPENSATING FOR THE CROSSWIND AND WERE HEADING APPROXIMATELY 100 RIGHT OF COURSE. THE FLIGHT CONCLUDED IN VMC CONDITIONS WITHOUT OTHER ANOMALIES. THE FERRY FLIGHT FOR MAINTENANCE WAS CONDUCTED IN VMC CONDITIONS. THE GPS OPERATED AS DESCRIBED ABOVE; HOWEVER; AN EVEN MORE DISTURBING FAILURE OCCURRED. APPROXIMATELY 5 MINUTES INTO THE FLIGHT WHILE IN STRAIGHT AND LEVEL CRUISE; THE PILOT'S PFD DISPLAY INDICATED A SUDDEN SHIFT OF THE HORIZON INDICATING AN 8-100 TURN TO THE LEFT. THIS WAS FOLLOWED ALMOST IMMEDIATELY BY A MASTER WARNING INDICATING AN AUTOPLT FAILURE AND LOSS OF THE FD AND YD. I LOOKED AT THE COPILOT'S SIDE PFD DISPLAY AND IT ALSO SHOWED THE ERRONEOUS BANK. OUTSIDE VISUAL CUES CONTINUED TO INDICATE STRAIGHT AND LEVEL FLIGHT AS DID THE ESIS (ELECTRONIC STANDBY INSTRUMENT SYSTEM). I CONTINUED THE FLIGHT IN VMC AND UTILIZED THE ESIS AS THE EADI SOURCE. I REPORTED THE NEW FAILURES TO MAINT AND WAS INFORMED OF A PENDING PILATUS SERVICE LETTER REGARDING THIS ISSUE. AT THIS POINT I HAVE SERIOUS CONCERNS WITH OPERATING THIS AIRCRAFT IN IMC. THE POSSIBILITY OF RECEIVING CONFLICTING INFORMATION FROM INCORRECT PFD INDICATIONS AND A CORRECT ESIS DISPLAY COULD LEAD TO PILOT CONFUSION WHILE IN IMC.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.