A beech jet 400 crew lost 600 ft during severe turbulence after an autoplt disconnect.

Attributes
ACN	641754
Time
Date	200412
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : zfw.artcc
State Reference	TX
Altitude	msl single value : 37000
Environment
Flight Conditions	VMC
Weather Elements	Windshear Turbulence
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zfw.artcc
Operator	general aviation : corporate
Make Model Name	Beechjet 400
Operating Under FAR Part	Part 91
Navigation In Use	other
Flight Phase	cruise : level cruise : enroute altitude change
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 50 flight time total : 11500 flight time type : 500
ASRS Report	641754
Person 2
Affiliation	company : corporate
Function	flight crew : first officer
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : turbulence non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance flight crew : returned to assigned altitude
Supplementary
Problem Areas	Environmental Factor Flight Crew Human Performance
Primary Problem	Environmental Factor

Narrative:

While in cruise flight at FL370 we had been encountering continuous very strong moderate turbulence. After enduring this for several mins, we requested a lower altitude. While awaiting clearance, the turbulence suddenly turned to severe. The autoplt disconnected and before I could recover, we had descended approximately 600 ft. The turbulence was so bad that I had a hard time making the aircraft respond to control inputs to climb. After getting the ok to continue our descent to FL330, where we again encountered heavy moderate to severe turbulence and once again the autoplt disconnected and this time while being ready for it took me 300 ft to recover. Obviously, there was a forecast of turbulence, but I have never in my flying career ever experienced turbulence of this magnitude in clear air conditions. I feel that if I and my first officer, who is new to flying high performance aircraft, were more diligent in monitoring the autoplt, we may have possibly avoided the excess altitude loss created by the autoplt disconnect. This should be a lesson for everyone who is going to operate in rvsm airspace.

Original NASA ASRS Text

Title: A BEECH JET 400 CREW LOST 600 FT DURING SEVERE TURB AFTER AN AUTOPLT DISCONNECT.

Narrative: WHILE IN CRUISE FLT AT FL370 WE HAD BEEN ENCOUNTERING CONTINUOUS VERY STRONG MODERATE TURB. AFTER ENDURING THIS FOR SEVERAL MINS, WE REQUESTED A LOWER ALT. WHILE AWAITING CLRNC, THE TURB SUDDENLY TURNED TO SEVERE. THE AUTOPLT DISCONNECTED AND BEFORE I COULD RECOVER, WE HAD DSNDED APPROX 600 FT. THE TURB WAS SO BAD THAT I HAD A HARD TIME MAKING THE ACFT RESPOND TO CTL INPUTS TO CLB. AFTER GETTING THE OK TO CONTINUE OUR DSCNT TO FL330, WHERE WE AGAIN ENCOUNTERED HVY MODERATE TO SEVERE TURB AND ONCE AGAIN THE AUTOPLT DISCONNECTED AND THIS TIME WHILE BEING READY FOR IT TOOK ME 300 FT TO RECOVER. OBVIOUSLY, THERE WAS A FORECAST OF TURB, BUT I HAVE NEVER IN MY FLYING CAREER EVER EXPERIENCED TURB OF THIS MAGNITUDE IN CLR AIR CONDITIONS. I FEEL THAT IF I AND MY FO, WHO IS NEW TO FLYING HIGH PERFORMANCE ACFT, WERE MORE DILIGENT IN MONITORING THE AUTOPLT, WE MAY HAVE POSSIBLY AVOIDED THE EXCESS ALT LOSS CREATED BY THE AUTOPLT DISCONNECT. THIS SHOULD BE A LESSON FOR EVERYONE WHO IS GOING TO OPERATE IN RVSM AIRSPACE.

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.