AN SMT CREW WERE UNABLE TO MAINTAIN ALT BECAUSE OF VERY HIGH AIR TEMP.

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ON THE EVENING OF FEB/TUE/93; SMT JET WAS IN THE SALT LAKE CITY; UT; AIRSPACE. WE WERE GIVEN A CLRNC TO CLB TO FL410. THE PLANE CLBED TO FL410 WITH NO PROBS. WE LEVELED OFF AT FL410 AND THE PLANE WAS BEGINNING TO ACCELERATE. WE FLEW AT FL410 FOR APPROX 8 MINS; AND THE CONDITIONS AT THIS TIME WERE ISA PLUS 10. THE PLANE WAS FLYING WITHIN THE STEP-CLB WT OF 12200 LBS AND THE ISA PLUS 10 TEMP RANGE ACCORDING TO SMT FLT MANUAL. SUDDENLY; WE NOTICED A DECREASE IN AIRSPD; AND AN INCREASE IN THE AOA; AND A MAJOR CHANGE IN THE OUTSIDE AIR TEMP; ISA PLUS 18; WE HAD HIT WARMER AIR. ALSO; OUR VLF OMEGA SYS TOLD US WE WERE EXPERIENCING A 180 DEG WIND SHIFT. WE ALSO ENCOUNTERED SOME LIGHT TURB. ALL OF THESE CONDITIONS HAPPENED IN SECONDS AND CAUSED THE PLANE TO QUICKLY DECELERATE. THE CO-CAPT WAS THEN INSTRUCTED TO IMMEDIATELY GET A CLRNC FROM ZLC FOR LOWER ALT NEEDED IMMEDIATELY. DURING THE CALL TO CTR FOR IMMEDIATE LOWER ALT CLRNC; THE PLANE THEN BEGAN TO BUFFET. I; AS THE CAPT; QUICKLY LOWERED THE NOSE TO RECOVER AND TO AVOID A HIGH ALT STALL. WHILE RECOVERING THE PLANE; IT DRIFTED OUT OF THE LEGAL ALT BY 400 FT. THE RECOVERY WAS HANDLED WITH MINIMAL ALT LOSS. THE CTR WITHIN SECONDS GAVE US A HDG AND CLRNC FOR LOWER ALT DSCNT TO 37000 FT. THEY WERE QUICK TO RESPOND. THE CTR ASKED US IF WE HAD HAD A PROB WHEN WE WERE LEVELED OFF AT FL370. THEY WERE TOLD THAT WE HAD THE TEMP AND WT FOR FL410 BUT HAD LOST IT SUDDENLY AND THEY WERE TOLD OF THE CHANGES IN TEMP AND WIND SHIFT BY THE CAPT OF THE PLANE. ALSO; THEY WERE TOLD OF BEING UNABLE TO MAINTAIN ALT AT FL410. THEY WERE CONCERNED AND WERE TOLD ALL WAS NOW NORMAL. AT THAT TIME; THE CAPT AND CO-CAPT WERE NOT LED TO BELIEVE BY THE CTLRS THAT THERE WERE ANY PROBS FROM WHAT HAD OCCURRED. 20 MINS LATER; WHEN LEAVING THE AIRSPACE OF ZLC; THE HEAD SUPVR CALLED AND WANTED THE CAPT'S NAME; ADDRESS; PHONE NUMBER; AND CERTIFICATE NUMBER. IT WAS STATED AT THAT TIME THAT WE HAD LEFT ALT WITHOUT PERMISSION AND WE WERE TOLD WE WERE CLOSE TO ANOTHER PLANE IN OUR DSCNT. THEY WERE NONSPECIFIC AND NO INFO PROVIDED. AS THE CAPT; I PROVIDED HER WITH INFO REQUESTED FROM ME AND EXPLAINED TO HER WHAT HAD HAPPENED AND THAT WE HAD NOT LOST MORE THAN 400 FT AND HELD THE BEST ALT POSSIBLE FOR THE PERFORMANCE OF THE PLANE AND SAFETY OF ALL TILL GIVEN A CLRNC. MY CO-CAPT DID NOT DECLARE AN EMER AND AT THE TIME I WAS RECOVERING THE PLANE FROM THE BUFFET AND TRYING TO HOLD ALT AWAITING THE CLRNC. CONDITIONS WERE CLR; VISIBILITY 150 MI; NIGHT; NO TFC SIGHTED. IN RETROSPECT; AT FL370 FOR THE REST OF THE WX PATTERN WE ENTERED IT WAS ISA PLUS 20 WHICH I PERSONALLY HAVE NOT EVER SEEN AND THE WIND CONTINUALLY DID 180 DEG WIND SHIFTS.