B757-200 deviates from cleared altitude at cruise in the vicinity of convective WX.

Attributes
ACN	717376
Time
Date	200611
Local Time Of Day	1201 To 1800
Place
Locale Reference	intersection : remis
State Reference	FL
Altitude	msl bound lower : 37000 msl bound upper : 37450
Environment
Weather Elements	Turbulence Windshear
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : zme.artcc
Operator	common carrier : air carrier
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
ASRS Report	717376
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : turbulence inflight encounter : weather non adherence : clearance other anomaly other anomaly
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : regained aircraft control flight crew : exited adverse environment
Supplementary
Problem Areas	Flight Crew Human Performance Environmental Factor Aircraft Weather
Primary Problem	Environmental Factor

Narrative:

While cruising in light chop at FL370 between redfn and remis in the vicinity of thunderstorm with the autoplt engaged; the aircraft climbed uncommanded to FL373 in approximately 5 seconds. The autoplt was disconnected; and while attempting to descend the aircraft climbed to FL374.5 and the airspeed decreased approximately 100 KTS in 3 seconds; then immediately returned to cruise speed and then decreased 30 KTS before being stabilized. The aircraft was manually flown to FL370 and a request was made and approved to descend to FL350. The flight continued uneventfully. ATC said that there was no traffic conflict and they did not request any postflt action. There were no injuries or damage to the aircraft; and dispatch was notified.

Original NASA ASRS Text

Title: B757-200 DEVIATES FROM CLRED ALT AT CRUISE IN THE VICINITY OF CONVECTIVE WX.

Narrative: WHILE CRUISING IN LIGHT CHOP AT FL370 BTWN REDFN AND REMIS IN THE VICINITY OF TSTM WITH THE AUTOPLT ENGAGED; THE ACFT CLBED UNCOMMANDED TO FL373 IN APPROX 5 SECONDS. THE AUTOPLT WAS DISCONNECTED; AND WHILE ATTEMPTING TO DSND THE ACFT CLBED TO FL374.5 AND THE AIRSPD DECREASED APPROX 100 KTS IN 3 SECONDS; THEN IMMEDIATELY RETURNED TO CRUISE SPD AND THEN DECREASED 30 KTS BEFORE BEING STABILIZED. THE ACFT WAS MANUALLY FLOWN TO FL370 AND A REQUEST WAS MADE AND APPROVED TO DSND TO FL350. THE FLT CONTINUED UNEVENTFULLY. ATC SAID THAT THERE WAS NO TFC CONFLICT AND THEY DID NOT REQUEST ANY POSTFLT ACTION. THERE WERE NO INJURIES OR DAMAGE TO THE ACFT; AND DISPATCH WAS NOTIFIED.

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.