OVERLY ANXIOUS PLT IN IMC CONDITIONS MAKES A PREMATURE DSCNT IN AN ALTDEV ALT EXCURSION.

Narrative

APCHING LWS VOR FROM LKT ON V-520; I WAS GIVEN THE FOLLOWING CLRNC FROM SEATTLE CTR: 'CLRED FOR THE LEWISTON TRANSITION TO PULLMAN' I ACKNOWLEDGED CLRED FOR THE TRANSITION.' MY LAST AMENDED ALT ASSIGNMENT WAS 8000. THE PUW VOR RWY 5 APCH HAS A PUBLISHED TRANSITION OFF OF THE LWS VOR: THE LWS R-277 TO INTERCEPT THE PUW R-212 FOR A NOPT APCH. THE PUBLISHED ALT FOR THE TRANSITION IS 4500. AT LWS; IN ADVERSE INFLT CONDITIONS; I BEGAN A DSCNT. THE CTR FREQ WAS BUSY; AND I DID NOT INFORM THEM OF VACATING 8000; AS I WAS ON 2 PUBLISHED TRANSITION. AT 7000 FT; CTR INFORMED ME I WAS TO BE MAINTAINING 8000 AND NOW TO MAINTAIN 7000. I ACKNOWLEDGED THE 7000 CLRNC BUT OFFERED THAT I WAS CLRED ON THE TRANSITION. CTR RESPONDED THAT I WAS CLRED TO FLY THE PROFILE ONLY OF THE TRANSITION AND HAD TO MAINTAIN ALT; I DIDN'T ARGUE THAT 'PROFILE' MEANS ALT. SINCE 'CLRED FOR THE TRANSITION' IS NOT IN THE PLT CTLR GLOSSARY; SAFETY WAS COMPROMISED. I BELIEVE THE CLRNC SHOULD HAVE BEEN 'FLY OUT BOUND ON LWS R-277 RADIAL; MAINTAIN 8000.'