MD80 flight crew reports 35 KT airspeed loss at FL310 after mountain wave encounter and autothrottle...

Attributes
ACN	747954
Time
Date	200707
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : den.vor
State Reference	CO
Altitude	msl single value : 31000
Environment
Weather Elements	Thunderstorm
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv.artcc
Operator	common carrier : air carrier
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
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
ASRS Report	747953
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
ASRS Report	747954
Events
Anomaly	aircraft equipment problem : less severe inflight encounter : turbulence inflight encounter : weather other anomaly
Independent Detector	other flight crewa
Consequence	other
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Aircraft

Narrative:

While navigating around WX in the den area; encountered mountain wave activity. Autothrottles retarded and were very slow to recover. Right throttle lagged by .30 EPR and left throttle never reached maximum EPR to recover loss of airspeed. Flight crew responded to large throttle split and resultant rapid loss of 35 KTS of airspeed during what appeared to be wave activity. First officer manually disengaged autothrottles and set 'cl EPR.' 'cl EPR' maintained for approximately 2 mins to recover airspeed. No altitude lost.

Original NASA ASRS Text

Title: MD80 FLT CREW RPTS 35 KT AIRSPD LOSS AT FL310 AFTER MOUNTAIN WAVE ENCOUNTER AND AUTOTHROTTLE MALFUNCTION.

Narrative: WHILE NAVING AROUND WX IN THE DEN AREA; ENCOUNTERED MOUNTAIN WAVE ACTIVITY. AUTOTHROTTLES RETARDED AND WERE VERY SLOW TO RECOVER. R THROTTLE LAGGED BY .30 EPR AND L THROTTLE NEVER REACHED MAX EPR TO RECOVER LOSS OF AIRSPD. FLT CREW RESPONDED TO LARGE THROTTLE SPLIT AND RESULTANT RAPID LOSS OF 35 KTS OF AIRSPD DURING WHAT APPEARED TO BE WAVE ACTIVITY. FO MANUALLY DISENGAGED AUTOTHROTTLES AND SET 'CL EPR.' 'CL EPR' MAINTAINED FOR APPROX 2 MINS TO RECOVER AIRSPD. NO ALT LOST.

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.

MD80 flight crew reports 35 KT airspeed loss at FL310 after mountain wave encounter and autothrottle malfunction.