Altitude bust after autoplt trips off.

Attributes
ACN	291128
Time
Date	199412
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : zbw
State Reference	MA
Altitude	msl bound lower : 38000 msl bound upper : 39000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zbw
Operator	general aviation : corporate
Make Model Name	Learjet 36
Operating Under FAR Part	Part 91
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : commercial pilot : atp
Experience	flight time last 90 days : 150 flight time total : 6000 flight time type : 150
ASRS Report	291128
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude inflight encounter other non adherence : clearance other anomaly other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : regained aircraft control flight crew : returned to intended course or assigned course
Consequence	other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

While in a routing climb from FL350 to FL390 in a lear 36A I encountered moderate to severe clear air turbulence. I had just leveled at FL390 and had engaged the altitude hold of the autoplt, the turbulence was encountered at about this time. In the turbulence the autoplt disengaged and consequently we were placed in a nose down position. Our mach number was .78 and with this pitch down began to increase rapidly. In an effort to decrease our rate of descent I gently applied back pressure while decreasing the thrust to flight idle. At this point I immediately encountered aileron activity (buzz) and was forced to release back pressure. Slowly the rate of descent decreased and I was able to regain control. No damage was done to the aircraft, only a shaken flight crew and passenger. Possible ways to prevent this from happening again: cruise at lower mach numbers. In retrospect an emergency should have been declared when I realized that the rate of descent could not be stopped. Total altitude loss was about 1000 ft and recovery to FL390 was made as quickly as possible. In the activity I also neglected to forward the report of turbulence on to ATC which was also my error.

Original NASA ASRS Text

Title: ALT BUST AFTER AUTOPLT TRIPS OFF.

Narrative: WHILE IN A RTING CLB FROM FL350 TO FL390 IN A LEAR 36A I ENCOUNTERED MODERATE TO SEVERE CLR AIR TURB. I HAD JUST LEVELED AT FL390 AND HAD ENGAGED THE ALT HOLD OF THE AUTOPLT, THE TURB WAS ENCOUNTERED AT ABOUT THIS TIME. IN THE TURB THE AUTOPLT DISENGAGED AND CONSEQUENTLY WE WERE PLACED IN A NOSE DOWN POS. OUR MACH NUMBER WAS .78 AND WITH THIS PITCH DOWN BEGAN TO INCREASE RAPIDLY. IN AN EFFORT TO DECREASE OUR RATE OF DSCNT I GENTLY APPLIED BACK PRESSURE WHILE DECREASING THE THRUST TO FLT IDLE. AT THIS POINT I IMMEDIATELY ENCOUNTERED AILERON ACTIVITY (BUZZ) AND WAS FORCED TO RELEASE BACK PRESSURE. SLOWLY THE RATE OF DSCNT DECREASED AND I WAS ABLE TO REGAIN CTL. NO DAMAGE WAS DONE TO THE ACFT, ONLY A SHAKEN FLC AND PAX. POSSIBLE WAYS TO PREVENT THIS FROM HAPPENING AGAIN: CRUISE AT LOWER MACH NUMBERS. IN RETROSPECT AN EMER SHOULD HAVE BEEN DECLARED WHEN I REALIZED THAT THE RATE OF DSCNT COULD NOT BE STOPPED. TOTAL ALT LOSS WAS ABOUT 1000 FT AND RECOVERY TO FL390 WAS MADE AS QUICKLY AS POSSIBLE. IN THE ACTIVITY I ALSO NEGLECTED TO FORWARD THE RPT OF TURB ON TO ATC WHICH WAS ALSO MY ERROR.

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.