A B737 flight crew experiences temporary loss of aircraft control while encountering moderate turbul...

Attributes
ACN	614438
Time
Date	200404
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : ink.vortac
State Reference	TX
Altitude	msl bound lower : 27000 msl bound upper : 41000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zhu.artcc
Operator	common carrier : air carrier
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : instrument pilot : commercial
Experience	flight time last 90 days : 60 flight time total : 3500 flight time type : 1500
ASRS Report	614438
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	inflight encounter : turbulence inflight encounter : weather inflight encounter other non adherence : published procedure other anomaly other anomaly
Independent Detector	aircraft equipment other aircraft equipment : hi speed stick shacker and clacker other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance flight crew : regained aircraft control flight crew : exited adverse environment other
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft Weather Environmental Factor
Primary Problem	Weather

Narrative:

We were cruising at FL410 (filed altitude). There were no bad ride reports up ahead, but ZHU did advise us of an area of building thunderstorms up ahead and gave us a slight rerte to avoid them. We could see the building storms ahead of us, but we were going to be above and to the north of them on our route of flight. Prior to the event, we computed our airspeed range (.73 - .80). Our optimum altitude in the FMC was FL400. The captain turned the seatbelt sign on and advised the flight attendants to be seated just in case the ride got rough. At what appeared to be about 20 NM north of the nearest storm, still in clear air, we encountered moderate turbulence. I immediately called ATC and requested lower and a deviation further north for WX. The controller told us to deviation as necessary and descend to FL270. We immediately started a descent, but about 15 seconds later, we seemingly got caught in an updraft as we were unable to continue descending and actually started climbing again. Our airspeed subsequently bled off to approximately .74 mach and we got the stick shaker for about 5 seconds, which surprised me at that airspeed. We were then able to continue the descent and the airspeed rapidly increased to approximately .82 mach where we got the clacker. We subsequently got the airspeed under control and continued our descent to FL270. The whole event lasted 5-10 mins. I called back to check on the flight attendants and passenger and they were all fine. I thought the captain did an absolutely outstanding job of controling the aircraft in this sudden unsuspected volatile situation. I believe we did everything right as a crew. It is very easy to get sucked into believe if you are above a storm or off to the side that turbulence will not be an issue. Also, cruising above opt altitude (FL400 in this case) does limit your options if you do encounter turbulence. We agreed that pilots should strongly consider in the future to not fly above optimum altitude if there is a chance to encounter this kind of turbulence, even if you are filed there.

Original NASA ASRS Text

Title: A B737 FLT CREW EXPERIENCES TEMPORARY LOSS OF ACFT CTL WHILE ENCOUNTERING MODERATE TURB NEAR TSTM ACTIVITY AT FL410 ON FREQ WITH ZHU, TX.

Narrative: WE WERE CRUISING AT FL410 (FILED ALT). THERE WERE NO BAD RIDE RPTS UP AHEAD, BUT ZHU DID ADVISE US OF AN AREA OF BUILDING TSTMS UP AHEAD AND GAVE US A SLIGHT RERTE TO AVOID THEM. WE COULD SEE THE BUILDING STORMS AHEAD OF US, BUT WE WERE GOING TO BE ABOVE AND TO THE N OF THEM ON OUR RTE OF FLT. PRIOR TO THE EVENT, WE COMPUTED OUR AIRSPD RANGE (.73 - .80). OUR OPTIMUM ALT IN THE FMC WAS FL400. THE CAPT TURNED THE SEATBELT SIGN ON AND ADVISED THE FLT ATTENDANTS TO BE SEATED JUST IN CASE THE RIDE GOT ROUGH. AT WHAT APPEARED TO BE ABOUT 20 NM N OF THE NEAREST STORM, STILL IN CLR AIR, WE ENCOUNTERED MODERATE TURB. I IMMEDIATELY CALLED ATC AND REQUESTED LOWER AND A DEV FURTHER N FOR WX. THE CTLR TOLD US TO DEV AS NECESSARY AND DSND TO FL270. WE IMMEDIATELY STARTED A DSCNT, BUT ABOUT 15 SECONDS LATER, WE SEEMINGLY GOT CAUGHT IN AN UPDRAFT AS WE WERE UNABLE TO CONTINUE DSNDING AND ACTUALLY STARTED CLBING AGAIN. OUR AIRSPD SUBSEQUENTLY BLED OFF TO APPROX .74 MACH AND WE GOT THE STICK SHAKER FOR ABOUT 5 SECONDS, WHICH SURPRISED ME AT THAT AIRSPD. WE WERE THEN ABLE TO CONTINUE THE DSCNT AND THE AIRSPD RAPIDLY INCREASED TO APPROX .82 MACH WHERE WE GOT THE CLACKER. WE SUBSEQUENTLY GOT THE AIRSPD UNDER CTL AND CONTINUED OUR DSCNT TO FL270. THE WHOLE EVENT LASTED 5-10 MINS. I CALLED BACK TO CHK ON THE FLT ATTENDANTS AND PAX AND THEY WERE ALL FINE. I THOUGHT THE CAPT DID AN ABSOLUTELY OUTSTANDING JOB OF CTLING THE ACFT IN THIS SUDDEN UNSUSPECTED VOLATILE SIT. I BELIEVE WE DID EVERYTHING RIGHT AS A CREW. IT IS VERY EASY TO GET SUCKED INTO BELIEVE IF YOU ARE ABOVE A STORM OR OFF TO THE SIDE THAT TURB WILL NOT BE AN ISSUE. ALSO, CRUISING ABOVE OPT ALT (FL400 IN THIS CASE) DOES LIMIT YOUR OPTIONS IF YOU DO ENCOUNTER TURB. WE AGREED THAT PLTS SHOULD STRONGLY CONSIDER IN THE FUTURE TO NOT FLY ABOVE OPTIMUM ALT IF THERE IS A CHANCE TO ENCOUNTER THIS KIND OF TURB, EVEN IF YOU ARE FILED THERE.

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.

A B737 flight crew experiences temporary loss of aircraft control while encountering moderate turbulence near thunderstorm activity at FL410 on frequency with ZHU, tx.