BE90 PLT EXPERIENCED LOSS OF PITOT STATIC INFO AFTER TKOF FROM DFW AND DIVERTED TO AN ALTERNATE ARPT.

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AFTER HAVING FILED AN IFR FLT PLAN TO ZZZ AND CHKING THE WX; I COMPLETED A COMPREHENSIVE ACFT PREFLT INSPECTION. WE STARTED UP; TAXIED OUT TO RWY 18 AND TOOK OFF; AFTER HAVING RECEIVED THE APPROPRIATE CLRNCS AND COMPLETING ALL CHKLISTS TO THIS POINT. EVERYTHING APPEARED TO BE NORMAL UNTIL LIFTOFF; WHEN BOTH L AND R AIRSPD INDICATORS AND ALTIMETERS BECAME VERY ERRATIC AND UNRELIABLE. I SELECTED PLT'S EMER STATIC AIR SOURCE AND ELECTED TO CONTINUE AS CLRED TO BURN OFF A LITTLE FUEL AND GET A LITTLE BETTER FEEL OF THE AIRPLANE BEFORE LNDG. WE WERE CLRED TO 6000 FT AND A HDG OF 190 DEGS. EVEN ON PLT'S EMER STATIC SOURCE AIR; THERE WERE STILL LARGE ERRORS IN BOTH ALT AND AIRSPD INDICATIONS; AND THE AUTOPLT PITCH AND ALT HOLD MODES WERE ERRATIC. THE SYMPTOMS WERE CLOSELY RESEMBLING THE BLOCKED PITOT STATIC SYS PROB WHICH I HAVE DONE ON NEARLY EVERY SIMULATOR RECURRENT TRAINING SESSION FOR SEVERAL YRS. WE WERE HAVING TO RELY ON APCH CTL AND ATC CTR FOR ALT ADVISORIES; SINCE OUR INDICATORS WERE SO INACCURATE. WE WERE ALSO NOT SURE THAT OUR MODE C ALT RPTING WAS CORRECT AND WE MAY HAVE BUSTED AN ALT IN THE PROCESS. BUT THE WX WAS CLR AND 10 SM VISIBILITY AND WE WERE KEEPING A VERY CLOSE TFC WATCH. AFTER 20 MINS; I DECIDED TO LAND AT ACT. THE LNDG WAS NORMAL IN EVERY RESPECT AND AFTER TAXIING TO THE RAMP AND SHUTTING DOWN; I DISCOVERED THAT THE CREW WHO HAD WASHED THE AIRPLANE HAD SEALED THE STATIC PORTS ON BOTH SIDES OF THE AIRPLANE WITH TRANSPARENT TAPE AND HAD FAILED TO REMOVE IT AFTERWARDS. THE TRANSPARENT TAPE WAS INVISIBLE ON MY ORIGINAL WALKAROUND PREFLT INSPECTION. INCIDENTALLY; ON A DIFFERENT AIRPLANE AND ARPT; THE SAME THING HAD HAPPENED LAST MONTH; BUT THEY USED MASKING TAPE AND I DISCOVERED IT DURING PREFLT. AFTER REMOVING THE TAPE; WE REFILED OUR FLT PLAN AND CONTINUED TO OUR ORIGINAL DEST; WITHOUT FURTHER INCIDENT. THE WASHING CREW AND THEIR SUPVR HAVE BEEN NOTIFIED OF THEIR ERROR IN PROC AND A FOLLOW-UP WILL BE MADE IN A FEW DAYS. IN THE FUTURE; I PLAN TO SEARCH MORE CLOSELY FOR TRANSPARENT TAPE ON THE STATIC PORTS DURING THE PREFLT INSPECTION. ALSO; I HAVE BEEN ASKING A LOT OF LINE CREWS WHAT THEIR PROC IS FOR WASHING AIRPLANES. SO FAR; I HAVEN'T FOUND ANYONE ELSE USING TRANSPARENT TAPE; BUT IF I DO I WILL STRONGLY DISCOURAGE IT.