B737-800 captain feels light buffet at FL360 and notes airspeed is in the minimum maneuver speed yel...

Attributes
ACN	812881
Time
Date	200811
Place
Altitude	msl bound lower : 30000 msl bound upper : 38000
Aircraft 1
Controlling Facilities	artcc : zzz.artcc
Operator	common carrier : air carrier
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	812881
Events
Anomaly	aircraft equipment problem : less severe non adherence : company policies other anomaly
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance flight crew : exited adverse environment flight crew : regained aircraft control
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Flight Crew Human Performance

Narrative:

During cruise flight at FL360; I felt a small buffet of the aircraft. I observed the current airspeed was in the minimum maneuver speed yellow range; I pushed the throttles up. The copilot requested and received a lower altitude. I took over control of the aircraft by hand and pushed lightly on the yoke to lower the nose of the aircraft. Lowering the nose of the aircraft 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 speed with just a light buffet. During the pitch down; I noticed the FMC/MCP command magenta bug was in the minimum maneuver speed yellow range. The copilot had engaged the autothrottle. I descended to FL300. The flight returned to normal. I reconnected the autoplt and autothrottle and climbed to FL380. I did not experience any other problems. The FMC either commanded a lower speed or I did not turn on the autothrottle 30 mins earlier after a trend check of the engines. Although; I would think in 30 mins the aircraft would have gotten lighter and the airspeed would have increased.

Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of May 2009 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.

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.