Narrative:

We had been in and out of clouds at FL310. We were using engine anti-ice when necessary. There was no evidence of any ice accumulation. The first officer left the cockpit to use the lavatory, then came back with my crew meal. After a few mins, we noticed the aft had slowed to about 220 KTS and the throttles were split. The right engine was not developing cruise thrust. It was apparent we would not be able to accelerate so I told center we wanted to descend to FL280. The controller gave us a frequency change, but the first officer had already started down at my request. The next controller approved FL280. Shortly after the descent, I turned on the ignition and anti-ice. The right engine indications returned to normal. We stayed at FL280 for a little while, then returned to FL310. I am going to be more aggressive using anti-ice in the future and much more vigilant monitoring the instruments during cruise.

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Original NASA ASRS Text

Title: AN MD83 FLC LEAVES THEIR ASSIGNED ALT PRIOR TO RECEIVING THEIR REQUESTED ALT ASSIGNMENT DURING A SPD BLEED AT FL310 WITH SIGNS OF ENG ICING WHILE ON FREQ WITH ZMP, MN.

Narrative: WE HAD BEEN IN AND OUT OF CLOUDS AT FL310. WE WERE USING ENG ANTI-ICE WHEN NECESSARY. THERE WAS NO EVIDENCE OF ANY ICE ACCUMULATION. THE FO LEFT THE COCKPIT TO USE THE LAVATORY, THEN CAME BACK WITH MY CREW MEAL. AFTER A FEW MINS, WE NOTICED THE AFT HAD SLOWED TO ABOUT 220 KTS AND THE THROTTLES WERE SPLIT. THE R ENG WAS NOT DEVELOPING CRUISE THRUST. IT WAS APPARENT WE WOULD NOT BE ABLE TO ACCELERATE SO I TOLD CTR WE WANTED TO DSND TO FL280. THE CTLR GAVE US A FREQ CHANGE, BUT THE FO HAD ALREADY STARTED DOWN AT MY REQUEST. THE NEXT CTLR APPROVED FL280. SHORTLY AFTER THE DSCNT, I TURNED ON THE IGNITION AND ANTI-ICE. THE R ENG INDICATIONS RETURNED TO NORMAL. WE STAYED AT FL280 FOR A LITTLE WHILE, THEN RETURNED TO FL310. I AM GOING TO BE MORE AGGRESSIVE USING ANTI-ICE IN THE FUTURE AND MUCH MORE VIGILANT MONITORING THE INSTS DURING CRUISE.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.