A CHALLENGER 300 DEPARTED WITH THE TAT PITOT COVER INSTALLED BECAUSE OF NUMEROUS DISTRACTIONS. ACFT RETURN TO LAND.

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I ARRIVED AT THE ACFT FIRST; AT ABOUT XA45 AM LCL. THERE WAS A TSTM IN PROGRESS WITH MODERATE RAIN AND LIGHTNING; CLOUD TO CLOUD. IT WAS STILL DARK OUTSIDE. I PARKED MY PVT VEHICLE NEAR THE PLANE AND UNLOADED MY LUGGAGE PLANE-SIDE. THE ACFT WAS OPENED AND ACFT PREPARATIONS FOR FLT WERE STARTED. I INSPECTED THE REAR EQUIP AREA IN PREPARATION FOR STARTING THE APU. THE ELECTRONIC COCKPIT CHKLIST WAS STARTED UP TO AND INCLUDING START OF APU. I THEN EXITED ACFT AND STARTED REMOVING STALL VANE COVERS AND PITOT PROBE COVERS. I OBSERVED TAT COVER; YET KNEW AT THAT TIME; I WOULD NEED TO GET A LADDER TO REACH IT. (THIS TAT COVER WAS NOT SECURED TO R PITOT PROBE COVER; AS IS NORMALLY THE CASE.) ABOUT THAT TIME; THE OTHER CREW MEMBER ARRIVED. WE GREETED EACH OTHER. AT THAT SAME TIME; THE LINE SVC EMPLOYEE PULLED UP THE FUEL TRUCK NEAR SINGLE POINT AREA IN PREPARATION FOR FUELING. I THEN WENT INTO THE MAINT BUILDING TO RETRIEVE COMPANY PAPERWORK (FLT PLANS; APG; TRIP SHEETS; WX PACK). AFTER RETURNING PAPERWORK TO ACFT; I MOVED MY VEHICLE TO EMPLOYEE PARKING LOT. UPON RETURNING TO ACFT; I LOCATED ACFT LOGBOOK AND CALLED DISPATCH TO OPEN-UP. MYSELF AND THE FO WERE STILL IN THE PROCESS OF COMPLETING INSIDE AND OUTSIDE PREFLT DUTIES. ACFT WAS THEN FUELED. FLT SVC WAS CONTACTED FOR A WX BRIEFING. A WALK TO THE FBO WAS MADE; SO THE WSI RADAR AND WX COULD BE CHKED. AT ALL OF THE ABOVE TIMES; MODERATE RAIN WAS IN PROGRESS; AND UMBRELLAS WERE NEEDED AND USED. THE FO AND MYSELF DECIDED THAT TSTMS IN THE AREA WERE TOO NUMEROUS AND SEVERE; AND A WX DELAY WOULD BE NECESSARY. THE COMPANY DISPATCH WAS IMMEDIATELY NOTIFIED OF THE REQUIRED WX DELAY. A 2 HR WX DELAY WAS NEEDED BEFORE A DEP COULD BE SAFELY MADE. UPON DEP (POS LEG); IT WAS QUICKLY OBSERVED BY BOTH PLTS THAT THE FLT DIRECTOR WAS ONLY AVAILABLE IN PITCH AND ROLL MODE; AND ALSO THE AUTOPLT WOULD NOT TURN ON. A MIN LATER; WE OBSERVED THAT THERE WAS NO SAT; ISA; TAS INFO DISPLAYED ON THE MFD'S AND PFD'S. A DELAY VECTOR WAS REQUESTED FROM ATC AND COMPANY MAINT; FIELD SVC WAS CALLED VIA FLT PHONE. ONBOARD MAINT DIAGNOSTICS AND CURRENT FAULTS WERE CHKED INFLT. A TAT PROBE; FAILED WIRING MESSAGE WAS OBSERVED. A DECISION WITH MAINT WAS MADE TO RETURN TO ZZZ ARPT. ENRTE BACK TO ZZZ; I REMEMBERED THE TAT COVER I SAW EARLIER AND ASKED MY PARTNER IF HE HAD SEEN OR REMOVED IT. HE SAID NO AND WE BOTH REALIZED IT MIGHT STILL BE ON AND WAS PROBABLY THE CAUSE OF THE SYS MALFUNCTIONS. A SAFE; UNEVENTFUL VISUAL APCH WAS MADE IN VMC CONDITIONS. AFTER PARKING AT FBO MAINT; WE (CREW) EXITED THE ACFT; AND OBSERVED THAT THE TAT PROBE COVER WAS STILL ON AND INTACT. (NO BURNED AREAS NOTED.) COVER WAS REMOVED; AND SAT; ISA; SAT DISPLAYS IN COCKPIT RETURNED IMMEDIATELY. MAINT WAS NOTIFIED IMMEDIATELY. NO CURRENT RELATED FAULTS WERE OBSERVED ON COPLT'S MFD MAINT. CAUSE: LINKS ON THE ERROR CHAIN STARTED BREAKING: 1) WX WAS POOR AND IT WAS STILL DARK; TSTMS WERE MODERATE TO OCCASIONALLY HVY RAIN; REQUIRING USE OF UMBRELLAS DURING PREFLT AND OUTSIDE OPS. UMBRELLAS OBSTRUCTED VIEW OF TOP PORTION OF ACFT. 2) TAT COVER IS UNSERVICEABLE CONDITION; NOT PROPERLY CONNECTED TO R PITOT PROBE COVER; UNABLE TO REACH WITHOUT LADDER. 3) NORMAL ROUTINES BROKEN; USE OF PROBE; STALL VANE; TAT COVERS RARELY USED IN DAY TO DAY OPS; EXCEPT FOR INCLEMENT WX. THEY ARE TYPICALLY ONLY OBSERVED 'ON' WHEN PICKING UP AN ACFT THAT HAS COME OUT OF MAINT AT ZZZ. 4) ALLOWING MULTIPLE DISTRS: FUELER; PERSONAL VEHICLE; MORNING GREETING; WX; ALL DURING PREFLT OPS. SUGGESTION: BE MUCH MORE AWARE OF THE ERROR CHAIN. FOCUS ON PREFLT AND TRY TO PREVENT DISTRS DURING THE PREFLT. BE MUCH MORE VIGILANT IN THESE WX CONDITIONS; AND MUCH MORE VIGILANT WHEN PICKING UP A PLANE OUT OF MAINT; WHICH MIGHT HAVE DIFFERENT ROUTINES THAN FLT CREW. EVEN THOUGH I DID FINAL CHK BEFORE BOARDING ACFT FOR DEP; REMEMBER TO LOOK UP AND SEE ALL OF THE FUSELAGE. ENCOURAGE OTHER CREW MEMBER TO DO THE SAME.