Clear air turbulence causes significant loss of altitude.

Attributes
ACN	101651
Time
Date	198901
Day	Tue
Local Time Of Day	0001 To 0600
Place
Locale Reference	atc facility : dfw
State Reference	TX
Altitude	msl bound lower : 20500 msl bound upper : 24000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	climbout : intermediate altitude
Route In Use	enroute airway : j25
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 160 flight time total : 10000 flight time type : 3500
ASRS Report	101651
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 200 flight time total : 4500
ASRS Report	101652
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather other anomaly
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course flight crew : regained aircraft control
Consequence	Other
Supplementary
Primary Problem	Weather
Air Traffic Incident	other

Narrative:

After leveling at FL230 and while on autoplt, we were cleared to climb to FL330. Out of approximately FL240 we entered severe turbulence which disengaged our autoplt and pitched the aircraft nose down 15 to 20 degrees. I took control of the aircraft, disengaging all autoflt equipment (automatic throttles, navigation, etc) and recovered the aircraft after a 3 to 4 thousand foot loss of altitude. Center was notified of CAT. Supplemental information from acn 101652. The turbulence kicked off the autoplt, it was of such intensity the instruments were difficult to read, I believe we were in a bank to the right and a pitch down nose attitude.

Original NASA ASRS Text

Title: CLEAR AIR TURBULENCE CAUSES SIGNIFICANT LOSS OF ALT.

Narrative: AFTER LEVELING AT FL230 AND WHILE ON AUTOPLT, WE WERE CLRED TO CLB TO FL330. OUT OF APPROX FL240 WE ENTERED SEVERE TURB WHICH DISENGAGED OUR AUTOPLT AND PITCHED THE ACFT NOSE DOWN 15 TO 20 DEGS. I TOOK CONTROL OF THE ACFT, DISENGAGING ALL AUTOFLT EQUIPMENT (AUTO THROTTLES, NAV, ETC) AND RECOVERED THE ACFT AFTER A 3 TO 4 THOUSAND FOOT LOSS OF ALT. CENTER WAS NOTIFIED OF CAT. SUPPLEMENTAL INFO FROM ACN 101652. THE TURB KICKED OFF THE AUTOPLT, IT WAS OF SUCH INTENSITY THE INSTRUMENTS WERE DIFFICULT TO READ, I BELIEVE WE WERE IN A BANK TO THE R AND A PITCH DOWN NOSE ATTITUDE.

Data retrieved from NASA's ASRS site as of August 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.