An air carrier MD80 lost 500 ft in turbulence in the top of a cumulo nimbus cloud.

Attributes
ACN	353769
Time
Date	199611
Day	Sat
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : dfw
State Reference	TX
Altitude	msl bound lower : 30500 msl bound upper : 31000
Environment
Flight Conditions	Mixed
Light	Night
Aircraft 1
Controlling Facilities	artcc : zfw tower : dfw
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	353769
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
ASRS Report	353770
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather other spatial deviation
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course flight crew : exited adverse environment flight crew : became reoriented
Consequence	Other
Supplementary
Primary Problem	Weather
Air Traffic Incident	other

Narrative:

We were just level at FL310 and had been deviating around WX at night. I had just turned the seat belt sign off and had talked to the passenger. My first officer and I both noticed a cumulo nimbus cloud with the tops at our altitude. I tried to steer around the cloud. We ended up in the tops with moderate turbulence and, as I was in a 30 degree turn, either I knocked the autoplt off or it kicked off due to turbulence. We lost about 500 ft before we corrected back to our assigned altitude. We checked with ATC and they only noted about a 150 ft deviation from altitude. No one was injured from the turbulence. Supplemental information from acn 353770: omega navigation showed us at manki when VHF navigation indicated we were off by about 2 mins, 10-12 mi or so. We both were double-checking our position when the captain saw some convective tops on the nose. We clipped the cell top, experiencing a sudden moderate jolt. The autoplt disengaged as the turbulence continued.

Original NASA ASRS Text

Title: AN ACR MD80 LOST 500 FT IN TURB IN THE TOP OF A CUMULO NIMBUS CLOUD.

Narrative: WE WERE JUST LEVEL AT FL310 AND HAD BEEN DEVIATING AROUND WX AT NIGHT. I HAD JUST TURNED THE SEAT BELT SIGN OFF AND HAD TALKED TO THE PAX. MY FO AND I BOTH NOTICED A CUMULO NIMBUS CLOUD WITH THE TOPS AT OUR ALT. I TRIED TO STEER AROUND THE CLOUD. WE ENDED UP IN THE TOPS WITH MODERATE TURB AND, AS I WAS IN A 30 DEG TURN, EITHER I KNOCKED THE AUTOPLT OFF OR IT KICKED OFF DUE TO TURB. WE LOST ABOUT 500 FT BEFORE WE CORRECTED BACK TO OUR ASSIGNED ALT. WE CHKED WITH ATC AND THEY ONLY NOTED ABOUT A 150 FT DEV FROM ALT. NO ONE WAS INJURED FROM THE TURB. SUPPLEMENTAL INFO FROM ACN 353770: OMEGA NAV SHOWED US AT MANKI WHEN VHF NAV INDICATED WE WERE OFF BY ABOUT 2 MINS, 10-12 MI OR SO. WE BOTH WERE DOUBLE-CHKING OUR POS WHEN THE CAPT SAW SOME CONVECTIVE TOPS ON THE NOSE. WE CLIPPED THE CELL TOP, EXPERIENCING A SUDDEN MODERATE JOLT. THE AUTOPLT DISENGAGED AS THE TURB CONTINUED.

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.