A BAE146 IN CRUISE AT FL290 DECLARED AN EMER DUE TO #1 ENG ROLLBACK AND DSNDED TO FL260 WHERE ENGS #2 AND #4 ROLLED BACK TO SUB IDLE RPM. BTWN 12000 FT AND 11000 FT THE ENGS STARTED BACK TO NORMAL.

Narrative

WE WERE DIVERTING AROUND WX AND CLRED FROM SCOTT'S BLUFF DIRECT TO MEDICINE BOW. ABOUT 60 MI OUT WE WERE CLRED TO FL290 FROM FL310. AFTER WE LEVELED WE KEPT THE ENGS AT 82% N1 AND .62 MACH ANTICIPATING ROUGH AIR FROM THE TCU'S (TWRING CUMULUS CLOUDS) 40-45 MI TO OUR L SIDE. WE WERE IMC AND NOTICED #1 ENG N1 WAS 80% AND DECREASING AND TGT (TURBINE GAS TEMP) WAS 805 DEGS INCREASING. AT THIS POINT WE CALLED FOR FL260 AND COMPLETED THE EMER CHKLIST. WHILE DSNDING THROUGH FL260 (WE HAD REQUESTED AS LOW AS WE COULD GET) #2 AND #4 ENGS STARTED ROLLING BACK RAPIDLY. WE CALLED THE PURSER FORWARD AROUND FL220 AND TOLD HER TO PREPARE THE CABIN FOR AN EMER LNDG. THEN WE CALLED ATC AND DECLARED AN EMER; (WHICH WE LATER CANCELED). AT 14000 FT WE STARTED TO BECOME VISUAL TO THE E AND ATC GAVE US A HEADING OF 220 DEGS FOR VECTORS TO CHEYENNE WHICH WAS 25 MI AWAY. ONLY AT BTWN 12000 FT AND 11000 FT (5500 ABOVE GND) AND IN VISUAL CONDITIONS DID THE ENGS START TO COME BACK TO NORMAL. DURING DSCNT WE STARTED THE APU AT 14000 FT BECAUSE WE HAD NO PWR (GENERATORS CLICKING ON AND OFF) AND NO PRESSURIZATION. RADIOS WERE ALSO BEING SPIKED AND WE COULD ONLY HEAR HALF OF ATC'S INSTRUCTIONS. ONCE APU WAS ON AND ENGS APPEARED TO RUN NORMAL WE DECIDED TO CONTINUE TO DENVER FOR A NORMAL LNDG. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE ACFT HAD TEXTRON LYCOMING ALF 502R-5 ENGS AND THE ROLLBACK SIT HAS BEEN ONGOING FOR 12 YRS. THE RPTR SAID AFTER THIS INCIDENT THE FAA; HONEYWELL (THE PRESENT OWNER OF LYCOMING) AND ALL OTHER PARTIES CONCERNED MET TO ATTEMPT TO DETERMINE A POSITIVE FIX. THE RPTR STATED HONEYWELL MAINTAINS WITH THE AIRFOIL ANTI-ICE ON AND ENG ANTI-ICE ON THE ENG BLEED AIR IS NOT HOT ENOUGH TO DEICE THE ENG SPLITTER VANES. THE RPTR STATED SEVERAL OPERATING PROCS HAVE BEEN DEVELOPED FOR THE CONDITIONS PRESENT DURING THIS INCIDENT. THE RPTR SAID ONE FACTOR WAS THE SUDDEN OUTSIDE AIR TEMP DROP FROM 26 DEGS TO -7 DEGS IN 20 SECONDS. THE RPTR SAID 3 ENG ROLLBACKS WERE RPTED LAST YR WITH 1 ACFT DSNDING TO WITHIN 1000 FT OF THE GND BEFORE PWR WAS RECOVERED. THE RPTR STATED A MODIFICATION WAS ADOPTED AND ALL BAE146 ACFT ARE TO BE COMPLETED BY THE END OF 2002.