B737-800 CAPTAIN FEELS LIGHT BUFFET AT FL360 AND NOTES AIRSPEED IS IN THE MINIMUM MANEUVER SPEED YELLOW RANGE. THRUST IS INCREASED AND DESCENT IS INITIATED TO REGAIN AIRSPEED.

Narrative

DURING CRUISE FLT AT FL360; I FELT A SMALL BUFFET OF THE ACFT. I OBSERVED THE CURRENT AIRSPD WAS IN THE MINIMUM MANEUVER SPD YELLOW RANGE; I PUSHED THE THROTTLES UP. THE COPLT REQUESTED AND RECEIVED A LOWER ALT. I TOOK OVER CTL OF THE ACFT BY HAND AND PUSHED LIGHTLY ON THE YOKE TO LOWER THE NOSE OF THE ACFT. LOWERING THE NOSE OF THE ACFT CAUSED ANOTHER LARGER BUFFET. I RELEASED THE PRESSURE AND THE BUFFET STOPPED. I AGAIN PUSHED THE NOSE OVER AND THE BUFFET RETURNED. I THEN USED A VERY SMALL PITCH DOWN FORCE TO REGAIN SPD WITH JUST A LIGHT BUFFET. DURING THE PITCH DOWN; I NOTICED THE FMC/MCP COMMAND MAGENTA BUG WAS IN THE MINIMUM MANEUVER SPD YELLOW RANGE. THE COPLT HAD ENGAGED THE AUTOTHROTTLE. I DSNDED TO FL300. THE FLT RETURNED TO NORMAL. I RECONNECTED THE AUTOPLT AND AUTOTHROTTLE AND CLBED TO FL380. I DID NOT EXPERIENCE ANY OTHER PROBS. THE FMC EITHER COMMANDED A LOWER SPD OR I DID NOT TURN ON THE AUTOTHROTTLE 30 MINS EARLIER AFTER A TREND CHK OF THE ENGS. ALTHOUGH; I WOULD THINK IN 30 MINS THE ACFT WOULD HAVE GOTTEN LIGHTER AND THE AIRSPD WOULD HAVE INCREASED.