ALTDEV THEN A SPD DEV DURING ATTEMPT TO HOLD ALT.

Narrative

WE WERE IN CRUISE FLT. THE FO WAS FLYING - I WENT OFF FREQ TO COPY ATIS. CTR HANDED US OFF; THE FO ACKNOWLEDGED THE CALL AND CONTACTED APCH. (THERE WAS A SUBSTANTIAL PRESSURE GRADIENT FROM THE S VERSES THE N SIDE OF THE MOUNTAIN RANGE OVER WHICH WE WERE PASSING). A PORTION OF THE ATIS WAS GARBLED; SO IT WAS NECESSARY TO WAIT FOR THE TAPE TO PLAY AGAIN. WHILE I WAS OFF ATC FREQ; WE ENCOUNTERED A STRONG UPDRAFT WHILE IN LIGHT TO OCCASIONALLY MODERATE TURB. THE FO BROUGHT THE PWR BACK TO FLT IDLE; BUT WE WERE TAKEN OFF ALT BY NEARLY 300 FT. I CAME BACK ONTO COM #1 AS THE MOTION NOW TURNED INTO A STRONG DOWNDRAFT WITH ASSOCIATED (NOW MORE CONSISTENTLY) MODERATE TURB. AS THE FO BROUGHT THE ACFT LEVEL AGAIN I ADDED MAX PWR - WE WERE AT FULL PWR AS THE AIRSPD BLED OFF AND WE STRUGGLED TO MAINTAIN ALT. I CALLED ATC AND REQUESTED A BLOCK ALT STATING WE WERE HAVING DIFFICULTY MAINTAINING OUR ALT; AT WHICH TIME THEY GAVE US A PLT'S DISCRETION DSCNT. A PIREP WAS MADE TO THE ATC FACILITY REGARDING THE TURB; UP/DOWN DRAFTS AND MOUNTAIN WAVE ACTION. NO MOISTURE RETURNS WERE PAINTED ON OUR RADAR IN THE AREA OF THE UP/DOWN DRAFTS. UNFORTUNATELY WE WERE NOT BOTH ON ATC FREQ WHEN THE DRAFTS FIRST HIT. THE FO WAS BUSY FLYING AS I ATTEMPTED TO RETURN TO ATC FREQ TO ADVISE OF OUR STATUS. HAD WE BOTH BEEN ON ATC; PERHAPS THE CALL COULD HAVE COME SOONER. NONE-THE-LESS; WE DID OUR BEST TO ADVISE ASAP WHILE 'FLYING THE AIRPLANE FIRST.' MOTHER NATURE IS STRONG AND AT TIMES FLEXES HER MUSCLES AND SHOWS JUST HOW POWERFUL SHE CAN BE. ATC NEVER QUESTIONED OUR ALT AT ANY TIME.