MD80 crew used the FMC wind display to predict a mountain wave encounter.

Attributes
ACN	460618
Time
Date	200001
Day	Tue
Local Time Of Day	0601 To 1200
Place
State Reference	CO
Altitude	msl single value : 37000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv.artcc
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Navigation In Use	other other
Flight Phase	cruise : level
Route In Use	enroute airway : ns.airway
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	460618
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : multi engine
Events
Anomaly	inflight encounter : weather other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : flt management system other flight crewa
Resolutory Action	other
Supplementary
Problem Areas	Weather
Primary Problem	Weather

Narrative:

Mountain wave encounter. En route at FL370, mach .77 IMC. Occasional light chop. Light/moderate mountain wave activity had been reported. Noticed the 'wind arrow' on the FMS navigation display change from a steady 70 KT tailwind to 10 KTS of left cross and then fluctuate. Pointed this out to first officer and advanced power in anticipation of regaining the tailwind and losing IAS. Within 10 seconds wind arrow came back to a steady 60 KT tail and IAS decayed 20 KIAS. No loss of altitude. Convinced airspeed loss would have been worse without early warning from FMS. Suggest monitoring GPS GS/wind when mountain wave are reported, as I believe it can provide advance warning.

Original NASA ASRS Text

Title: MD80 CREW USED THE FMC WIND DISPLAY TO PREDICT A MOUNTAIN WAVE ENCOUNTER.

Narrative: MOUNTAIN WAVE ENCOUNTER. ENRTE AT FL370, MACH .77 IMC. OCCASIONAL LIGHT CHOP. LIGHT/MODERATE MOUNTAIN WAVE ACTIVITY HAD BEEN RPTED. NOTICED THE 'WIND ARROW' ON THE FMS NAV DISPLAY CHANGE FROM A STEADY 70 KT TAILWIND TO 10 KTS OF L CROSS AND THEN FLUCTUATE. POINTED THIS OUT TO FO AND ADVANCED PWR IN ANTICIPATION OF REGAINING THE TAILWIND AND LOSING IAS. WITHIN 10 SECONDS WIND ARROW CAME BACK TO A STEADY 60 KT TAIL AND IAS DECAYED 20 KIAS. NO LOSS OF ALT. CONVINCED AIRSPD LOSS WOULD HAVE BEEN WORSE WITHOUT EARLY WARNING FROM FMS. SUGGEST MONITORING GPS GS/WIND WHEN MOUNTAIN WAVE ARE RPTED, AS I BELIEVE IT CAN PROVIDE ADVANCE WARNING.

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.