Altitude deviation after in-flight encounter with moderate turbulence.

Attributes
ACN	259551
Time
Date	199312
Day	Tue
Local Time Of Day	0001 To 0600
Place
Locale Reference	atc facility : ord
State Reference	IL
Altitude	msl bound lower : 37000 msl bound upper : 37500
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zau
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 14350
ASRS Report	259551
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter other non adherence : clearance other anomaly
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera other flight crewa
Resolutory Action	flight crew : regained aircraft control flight crew : returned to intended course or assigned course
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Weather
Air Traffic Incident	Pilot Deviation

Narrative:

In cruise from las direct dtw, smooth air since east of den, cruise speed selected to .81M (hurry up flight plan, normal cruise is .78M). Encountered sudden and short duration moderate turbulence. Aircraft speed reached overspd threshold as we went into turbulence (.82M is maximum, but it might begin overspd protection just a little lower). When the medium large transport first officer overspd occurs, the autoplt disconnects and the nose pitches up (with neutral stick) to slow down. Control action must be quick in manual flight to smoothly push forward on the stick to stay within 300 ft of assigned altitude. Our aircraft climbed briefly to 37500 ft. The overspd was over very quickly (15 seconds?). The autoplt engaged again and we began descent to FL310. ZAU said altitude deviation was not a problem. This event occurred while I, as captain, was out of the cockpit briefly, in lavatory.

Original NASA ASRS Text

Title: ALTDEV AFTER INFLT ENCOUNTER WITH MODERATE TURB.

Narrative: IN CRUISE FROM LAS DIRECT DTW, SMOOTH AIR SINCE E OF DEN, CRUISE SPD SELECTED TO .81M (HURRY UP FLT PLAN, NORMAL CRUISE IS .78M). ENCOUNTERED SUDDEN AND SHORT DURATION MODERATE TURB. ACFT SPD REACHED OVERSPD THRESHOLD AS WE WENT INTO TURB (.82M IS MAX, BUT IT MIGHT BEGIN OVERSPD PROTECTION JUST A LITTLE LOWER). WHEN THE MLG FO OVERSPD OCCURS, THE AUTOPLT DISCONNECTS AND THE NOSE PITCHES UP (WITH NEUTRAL STICK) TO SLOW DOWN. CTL ACTION MUST BE QUICK IN MANUAL FLT TO SMOOTHLY PUSH FORWARD ON THE STICK TO STAY WITHIN 300 FT OF ASSIGNED ALT. OUR ACFT CLBED BRIEFLY TO 37500 FT. THE OVERSPD WAS OVER VERY QUICKLY (15 SECONDS?). THE AUTOPLT ENGAGED AGAIN AND WE BEGAN DSCNT TO FL310. ZAU SAID ALTDEV WAS NOT A PROB. THIS EVENT OCCURRED WHILE I, AS CAPT, WAS OUT OF THE COCKPIT BRIEFLY, IN LAVATORY.

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.