C177 MAINTAINING 7000 FT ENCOUNTERED STRONG UPDRAFT IN IMC CONDITIONS. DEVIATED FROM ALT 280 FT. REQUESTED BLOCK ALT BUT CTR UNABLE ACCOUNT TFC AT 8000 FT. REGAINED ASSIGNED ALT 7000 FT.

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AT ABOUT XA00 ON MAY/XX/97; I WAS ON AN IFR FLT PLAN FROM SRB; TN; TO N99; PA. BEFORE REACHING THE FINAL CRUISE ALT OF 9000 FT; THE CTLR (I BELIEVE IT WAS TYS APCH) HELD ME AT 7000 FT DUE TO XING BARON TFC AT 8000 FT. I STOPPED THE CLB AND HELD 7000 FT AS INSTRUCTED. WHILE CRUISING IN IMC AT 7000 FT; I SUDDENLY ENCOUNTERED AN AREA OF HVY RAIN AND SIMULTANEOUSLY VERY STRONG UPDRAFTS. WITHIN A SECOND OR TWO; I REACTED BY PUSHING THE NOSE DOWN BUT WITH THE VERY STRONG UPDRAFTS THE AIRPLANE CONTINUED TO CLB AS THE AIRSPD INCREASED WHILE I CONTINUED TO PUSH THE NOSE DOWN. WITHIN 5-7 SECONDS AFTER ENTERING THE HVY RAIN THE ACFT HAD GAINED BTWN 250-280 FT AND INCREASED SPD BY 15-20 KTS. AROUND THIS TIME; I ASKED THE CTLR FOR A BLOCK ALT TO 8000 FT. OF COURSE; THE CTLR ADVISED ME THAT SHE COULD NOT PROVIDE THE CLRNC. WITHIN 10-15 SECONDS AFTER ENTERING THE AREA OF HVY RAIN; I WAS ABLE TO DSND BACK TO 7000 FT. DURING THIS TIME; PWR WAS REDUCED AND THE ACFT WAS TRIMMED NOSE DOWN. THINGS THAT COULD HAVE BEEN DONE DIFFERENTLY INCLUDE: 1) RATHER THAN ASK FOR THE IMPOSSIBLE CLRNC I SHOULD HAVE RESPONDED TO THE CTLR BY EXPLAINING THAT I WAS HAVING TROUBLE MAINTAINING ALT AND THAT I WAS TRYING TO CORRECT THE SIT. 2) WHILE THE AIRSPD AT THE TIME WAS TOO HIGH TO ALLOW LOWERING THE GEAR; A LOWER PWR SETTING WHEN ENTERING AREAS OF SUSPECT TURB WOULD PROVIDE A MARGIN OF SAFETY AND WOULD ALLOW LOWERING OF THE GEAR.