B737-800 is unable to maintain airspeed at FL390 while maneuvering for WX.

Attributes
ACN	665181
Time
Date	200507
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : jax.airport
State Reference	FL
Altitude	msl single value : 39000
Environment
Weather Elements	Thunderstorm
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zjx.artcc
Operator	common carrier : air carrier
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 200 flight time total : 15000 flight time type : 2000
ASRS Report	665181
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : asi other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance flight crew : regained aircraft control other
Supplementary
Problem Areas	Weather Chart Or Publication Flight Crew Human Performance Aircraft Company Environmental Factor
Primary Problem	Ambiguous
Air Traffic Incident	Pilot Deviation

Narrative:

We slowed to .76 mach to work through thunderstorms. Autothrottles did not hold speed. We went to maximum continuous power -- still above minimum maneuvering speed. Speed would not recover. After several mins; it continued to deteriorate. Getting very near stick shaker; I ordered first officer to descend. Radio was very busy. We were at FL384 before getting clearance to FL370. The controller did not seem alarmed.

Original NASA ASRS Text

Title: B737-800 IS UNABLE TO MAINTAIN AIRSPD AT FL390 WHILE MANEUVERING FOR WX.

Narrative: WE SLOWED TO .76 MACH TO WORK THROUGH TSTMS. AUTOTHROTTLES DID NOT HOLD SPD. WE WENT TO MAX CONTINUOUS PWR -- STILL ABOVE MINIMUM MANEUVERING SPD. SPD WOULD NOT RECOVER. AFTER SEVERAL MINS; IT CONTINUED TO DETERIORATE. GETTING VERY NEAR STICK SHAKER; I ORDERED FO TO DSND. RADIO WAS VERY BUSY. WE WERE AT FL384 BEFORE GETTING CLRNC TO FL370. THE CTLR DID NOT SEEM ALARMED.

Data retrieved from NASA's ASRS site as of January 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.