A320 flight crew encounters turbulence jetstream activity at altitude. Airspeed deteriorates to the ...

Attributes
ACN	692284
Time
Date	200604
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : ddy.vortac
State Reference	WY
Altitude	msl single value : 37000
Environment
Weather Elements	Windshear
Aircraft 1
Controlling Facilities	artcc : zdv.artcc
Operator	common carrier : air carrier
Make Model Name	A320
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time last 90 days : 250 flight time total : 8300 flight time type : 2900
ASRS Report	692284
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	altitude deviation : excursion from assigned altitude other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : airspd indicator other flight crewa other flight crewb
Resolutory Action	controller : issued advisory flight crew : overrode automation flight crew : returned to assigned altitude flight crew : exited adverse environment
Supplementary
Problem Areas	Environmental Factor Flight Crew Human Performance Aircraft

Narrative:

At FL370 we were given a 070 degree heading for spacing to ord. There were a lot of PIREPS for light to moderate turbulence associated with the jetstream as well as mountain wave activity. We were also assigned a speed of mach .74; but the captain told center we could only give them mach .75. (Mach .74 would have been too close to V alpha prot). I looked at my pfd and noticed a drop of 20 KTS of airspeed which put our speed very close to V alpha prot. I disconnected the autoplt and began a shallow descent to build up speed. I told the captain to tell center we were descending. We were doing 200-300 FPM down. The captain responded 'wait just a min.' I then looked at the EPR on the upper ECAM display and the autothrust was already commanding the maximum EPR limit. The captain told me to disconnect the autothrottles. After doing so; I realized that we needed more thrust; so I went to toga; which yielded no further increase. I then set mct and had no other option but to continue to sacrifice altitude for airspeed at approximately FL365 ATC said that we were 500 ft low. The captain said 'stand by.' we were then given a direct clearance. We decided to stay on the heading because if we turned; that would have decreased V alpha prot enough to bring us closer to stall. After the airspeed recovered; I began a climb back to FL370. During this event there was only light chop. The airspeed decrease was due to windshear associated with the jetstream. The wind velocity decreased approximately 30 KTS in a short distance. After we reported the shear to ATC; an air carrier flight reported the same and said that they had to go to mct as well earlier. They did not report a PIREP during their occurrence; however. We also made a report to dispatch. We did not exceed any airspeed or engine limits to my knowledge and did not trigger V alpha prot.

Original NASA ASRS Text

Title: A320 FLT CREW ENCOUNTERS TURB JETSTREAM ACTIVITY AT ALT. AIRSPD DETERIORATES TO THE V ALPHA PROT RANGE (HIGH ANGLE OF ATTACK; STALL AREA). FLT CREW IS FORCED TO DSND TO GAIN AIRSPD BACK.

Narrative: AT FL370 WE WERE GIVEN A 070 DEG HDG FOR SPACING TO ORD. THERE WERE A LOT OF PIREPS FOR LIGHT TO MODERATE TURB ASSOCIATED WITH THE JETSTREAM AS WELL AS MOUNTAIN WAVE ACTIVITY. WE WERE ALSO ASSIGNED A SPD OF MACH .74; BUT THE CAPT TOLD CTR WE COULD ONLY GIVE THEM MACH .75. (MACH .74 WOULD HAVE BEEN TOO CLOSE TO V ALPHA PROT). I LOOKED AT MY PFD AND NOTICED A DROP OF 20 KTS OF AIRSPD WHICH PUT OUR SPD VERY CLOSE TO V ALPHA PROT. I DISCONNECTED THE AUTOPLT AND BEGAN A SHALLOW DSCNT TO BUILD UP SPD. I TOLD THE CAPT TO TELL CTR WE WERE DSNDING. WE WERE DOING 200-300 FPM DOWN. THE CAPT RESPONDED 'WAIT JUST A MIN.' I THEN LOOKED AT THE EPR ON THE UPPER ECAM DISPLAY AND THE AUTOTHRUST WAS ALREADY COMMANDING THE MAX EPR LIMIT. THE CAPT TOLD ME TO DISCONNECT THE AUTOTHROTTLES. AFTER DOING SO; I REALIZED THAT WE NEEDED MORE THRUST; SO I WENT TO TOGA; WHICH YIELDED NO FURTHER INCREASE. I THEN SET MCT AND HAD NO OTHER OPTION BUT TO CONTINUE TO SACRIFICE ALT FOR AIRSPD AT APPROX FL365 ATC SAID THAT WE WERE 500 FT LOW. THE CAPT SAID 'STAND BY.' WE WERE THEN GIVEN A DIRECT CLRNC. WE DECIDED TO STAY ON THE HDG BECAUSE IF WE TURNED; THAT WOULD HAVE DECREASED V ALPHA PROT ENOUGH TO BRING US CLOSER TO STALL. AFTER THE AIRSPD RECOVERED; I BEGAN A CLB BACK TO FL370. DURING THIS EVENT THERE WAS ONLY LIGHT CHOP. THE AIRSPD DECREASE WAS DUE TO WINDSHEAR ASSOCIATED WITH THE JETSTREAM. THE WIND VELOCITY DECREASED APPROX 30 KTS IN A SHORT DISTANCE. AFTER WE RPTED THE SHEAR TO ATC; AN ACR FLT RPTED THE SAME AND SAID THAT THEY HAD TO GO TO MCT AS WELL EARLIER. THEY DID NOT RPT A PIREP DURING THEIR OCCURRENCE; HOWEVER. WE ALSO MADE A RPT TO DISPATCH. WE DID NOT EXCEED ANY AIRSPD OR ENG LIMITS TO MY KNOWLEDGE AND DID NOT TRIGGER V ALPHA PROT.

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.

A320 flight crew encounters turbulence jetstream activity at altitude. Airspeed deteriorates to the V alpha prot range (high angle of attack; stall area). Flight crew is forced to descend to gain airspeed back.