AN L1011-500 IN CRUISE AT FL370 EXPERIENCED A SLOW LOSS OF AIRSPD AND WAS REQUIRED TO DSND 2000 FT TO RECOVER; CAUSED BY AUTOTHROTTLE FAILURE.

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WHILE IN CRUISE AT FL370; THE CAPT LEFT THE FLT STATION TO RELIEVE HIMSELF. I WAS PERFORMING SOME FUEL XFEED ADJUSTMENTS AT THIS TIME AND THE FO WAS LOOKING AT THE FLT PLAN AT THE TIME TO THE BEST OF MY RECOLLECTION. THE ACFT WAS ON AUTOPLT AND AUTOTHROTTLE. ABOUT 2 MINS AFTER THE CAPT LEFT HIS SEAT; THE FO SUDDENLY ALERTED TO AIRSPD DETERIORATION. MY ATTN WAS IMMEDIATELY DIRECTED TO THE APPLICATION OF PWR AS WAS THE FO'S. I NOTED AIRSPD/MACH TO BE AT APPROX 210 KTS AND .650 MACH. IMMEDIATE APPLICATION OF PWR ARRESTED AIRSPD DETERIORATION AND AIRSPD BEGAN TO INCREASE IMMEDIATELY. HOWEVER; LEVEL FLT AT FL370 COULD NOT BE INITIALLY SUSTAINED WITHOUT THE ONSET OF LOW SPD BUFFET AND IT BECAME EVIDENT THAT SOME ALT WOULD HAVE TO BE TRADED FOR AIRSPD TO IMMEDIATELY RETURN AIRSPD TO DESIRED MINIMUMS. BY THIS TIME; THE CAPT HAD RETURNED TO THE FLT STATION. HE IMMEDIATELY RECOGNIZED THE SIT AND CHKED THE 360 DEG TCASII DISPLAY AND CONCURRED SOME DSCNT WAS REQUIRED TO RAPIDLY REGAIN AIRSPD. ALL POSSIBLE VISUAL CLRING WAS ALSO EXERCISED. THIS MANEUVER RESULTED IN THE SACRIFICE OF 2000 FT OF ALT AND CLB BACK TO FL370 WAS BEGUN IMMEDIATELY UPON ATTAINING SUFFICIENT CLB AIRSPD. TIME OF ALT WAS PROBABLY ABOUT 3 MINS. TOTAL TIME OF EVENT IS ESTIMATED TO BE 5 OR 6 MINS. THE SIT WAS FURTHER COMPLICATED BY THE FACT THAT ENG #1 TET (TOTAL ENG TEMP) GAUGE POINTER WAS NOTED TO BE OFF-SCALE HIGH AT THIS TIME AND SOME MOMENTARY DOUBT OF ENG CONDITION HAD TO BE RESOLVED. IT WAS NOTED THAT BOTH TET POINTER AND DRUM DIGITAL DISPLAY WERE ERRONEOUS AND HIGH LEVELS OF PWR WERE MANAGED WITH USE OF EPR AND RPM INSTS FOR ENG #1. DELAYED NOTICE OF THE FAILURE OF THE AUTOTHROTTLE SYS TO MAINTAIN DESIRED MACH AND THE VERY SLOW AND INSIDIOUS RETARDATION OF THE THROTTLES THUS RESULTING IN LOSS OF AIRSPD; WENT UNNOTICED BECAUSE THERE WAS NO AUTOTHROTTLE DISCONNECT OR OTHER VISUAL OR AURAL WARNING TO ALERT EITHER REMAINING CREW MEMBER TO THE PROB THAT BEGAN WHILE WE ALLOWED OURSELVES TO BE DISTR BY OTHER DUTIES WHICH COULD HAVE BEEN DELAYED FOR THE BRIEF TIME THE CAPT WAS OUT OF HIS DUTY STATION.