AC69 PLT EXPERIENCES STATIC SYSTEM FAILURE AT FL250 AFTER DEPARTING FOLLOWING A HEAVY RAINSTORM.

Narrative

WE HAD TO WAIT 30 MINS FOR AN AREA OF HVY RAIN TO PASS THROUGH. WE DEPART SAT ABOUT XA00 LCT; ON THE ALAMO 6; LUFKEN TRANSITION; MY FINAL ALT WAS FL250. WE HAD TO LEVELOFF AT FL240 FOR ABOUT 10 MINS FOR TFC. (THERE WAS 1 HOLE THROUGH THE TSTM.) WHEN CLRED TO CLB FROM FL240 TO FL250; I ENGAGED THE ALT PRE-SELECT. AFTER CHANGING FREQ WHILE CLB; I NOTICED THE AIRSPD WAS DECREASING AS WE CLBED. WHEN THE ACFT LEVELED AT FL250 THE AIRSPD WAS ZERO. WE NEVER ENCOUNTERED ANY ICE AND THE PITOT HEAT WAS ON. SO I SELECT THE ALTERNATE STATIC SOURCE. THE ALTIMETER BEGAN TO CLB. I FINALLY SHUT IT OFF AND STOP THE CLB AT FL220. EVEN THOUGH I WAS AT FL250 THE GPS VERIFIED ME AT FL250. I NOTIFIED CTR OF MY PROB AND ASKED FOR AN ALT BELOW FL180 SO I COULD GO VFR. NOTE -- THE OAT WAS -10 DEGS C. WHEN REACHING 15000 FT; EVERYTHING INDICATED CORRECTLY. I COULD ONLY FIGURE WATER FROM THE HARD RAIN AT SAT; MUST HAVE ENTERED THE SYS AND FROZE WHILE AT FL240. WE HAD THE SYS CHKED THE NEXT DAY AND FOUND NOTHING WRONG.