A lear 45 flight crew experience clear air turbulence at FL430.

Attributes
ACN	614101
Time
Date	200404
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : zid.artcc
State Reference	IN
Altitude	msl single value : 43000
Environment
Flight Conditions	VMC
Weather Elements	Turbulence Windshear
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid.artcc tower : ind.tower
Operator	general aviation : corporate
Make Model Name	Learjet 45
Operating Under FAR Part	Part 91
Flight Phase	cruise : enroute altitude change cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : multi engine pilot : atp
Experience	flight time last 90 days : 100 flight time total : 8000 flight time type : 1000
ASRS Report	614101
Person 2
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : turbulence other anomaly other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : took precautionary avoidance action flight crew : exited adverse environment flight crew : regained aircraft control
Supplementary
Problem Areas	Environmental Factor Flight Crew Human Performance Weather
Primary Problem	Weather

Narrative:

While established in level flight at FL430 over gez at about XA00Z, we experienced a sudden high altitude shear associated with the jetstream that resulted in a high speed excursion lasting about 30-45 seconds. The event began without much advanced warning as the flight had experienced nothing more than light turbulence up to that point. The airplane suddenly encountered a strong horizontal shear that resulted in the airplane very quickly exceeding mach .81. As the airspeed exceeded mach .81 and the overspd warning sounded, I pulled back the power. This had no effect on reducing the speed. I then deployed the spoilers. It took about another 15-20 seconds to slow the airplane back to below mach .81. This event began so suddenly that, with the autoplt on and with altitude hold engaged, the aircraft achieved a nose low attitude of about 3-4 degrees which resulted in an altitude loss of about 300 ft. Disconnecting the autoplt and hand flying the airplane immediately arrested this trend. It was very difficult to control the airplane at this point as I was contending with indicated airspeed fluctuations of about 40-45 KTS with the airspeed trend bar fluctuating wildly. I also observed the wind velocity on the pfd fluctuate from between 40-85 KTS. The airplane was also experiencing moderate turbulence which added to the handling difficulties. The turbulence was not a critical factor in terms of structural integrity as the dynamics of this event were more of a horizontal nature. The first officer made an immediate request for a lower altitude. The speed of the aircraft was eventually slowed and a descent to FL410 was initiated. Although I cannot be certain, it is my belief that suddenness in which this event occurred resulted in incipient mach tuck causing the nose to lower and altitude to be lost with altitude hold on the autoplt still on. It should also be reported that there was no convective activity present in the area.

Original NASA ASRS Text

Title: A LEAR 45 FLT CREW EXPERIENCE CLR AIR TURB AT FL430.

Narrative: WHILE ESTABLISHED IN LEVEL FLT AT FL430 OVER GEZ AT ABOUT XA00Z, WE EXPERIENCED A SUDDEN HIGH ALT SHEAR ASSOCIATED WITH THE JETSTREAM THAT RESULTED IN A HIGH SPD EXCURSION LASTING ABOUT 30-45 SECONDS. THE EVENT BEGAN WITHOUT MUCH ADVANCED WARNING AS THE FLT HAD EXPERIENCED NOTHING MORE THAN LIGHT TURB UP TO THAT POINT. THE AIRPLANE SUDDENLY ENCOUNTERED A STRONG HORIZ SHEAR THAT RESULTED IN THE AIRPLANE VERY QUICKLY EXCEEDING MACH .81. AS THE AIRSPD EXCEEDED MACH .81 AND THE OVERSPD WARNING SOUNDED, I PULLED BACK THE PWR. THIS HAD NO EFFECT ON REDUCING THE SPD. I THEN DEPLOYED THE SPOILERS. IT TOOK ABOUT ANOTHER 15-20 SECONDS TO SLOW THE AIRPLANE BACK TO BELOW MACH .81. THIS EVENT BEGAN SO SUDDENLY THAT, WITH THE AUTOPLT ON AND WITH ALT HOLD ENGAGED, THE ACFT ACHIEVED A NOSE LOW ATTITUDE OF ABOUT 3-4 DEGS WHICH RESULTED IN AN ALT LOSS OF ABOUT 300 FT. DISCONNECTING THE AUTOPLT AND HAND FLYING THE AIRPLANE IMMEDIATELY ARRESTED THIS TREND. IT WAS VERY DIFFICULT TO CTL THE AIRPLANE AT THIS POINT AS I WAS CONTENDING WITH INDICATED AIRSPD FLUCTUATIONS OF ABOUT 40-45 KTS WITH THE AIRSPD TREND BAR FLUCTUATING WILDLY. I ALSO OBSERVED THE WIND VELOCITY ON THE PFD FLUCTUATE FROM BTWN 40-85 KTS. THE AIRPLANE WAS ALSO EXPERIENCING MODERATE TURB WHICH ADDED TO THE HANDLING DIFFICULTIES. THE TURB WAS NOT A CRITICAL FACTOR IN TERMS OF STRUCTURAL INTEGRITY AS THE DYNAMICS OF THIS EVENT WERE MORE OF A HORIZ NATURE. THE FO MADE AN IMMEDIATE REQUEST FOR A LOWER ALT. THE SPD OF THE ACFT WAS EVENTUALLY SLOWED AND A DSCNT TO FL410 WAS INITIATED. ALTHOUGH I CANNOT BE CERTAIN, IT IS MY BELIEF THAT SUDDENNESS IN WHICH THIS EVENT OCCURRED RESULTED IN INCIPIENT MACH TUCK CAUSING THE NOSE TO LOWER AND ALT TO BE LOST WITH ALT HOLD ON THE AUTOPLT STILL ON. IT SHOULD ALSO BE RPTED THAT THERE WAS NO CONVECTIVE ACTIVITY PRESENT IN THE AREA.

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.