Astra crew was operating the aircraft too high for proper buffet margin.

Attributes
ACN	476164
Time
Date	200006
Day	Mon
Local Time Of Day	0601 To 1200
Place
State Reference	SD
Altitude	msl bound lower : 41000 msl bound upper : 45000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv.artcc tower : bjc.tower
Operator	general aviation : corporate
Make Model Name	IAI1125 (Astra)
Operating Under FAR Part	Part 91
Navigation In Use	other
Flight Phase	cruise : level cruise : enroute altitude change
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : cfi pilot : multi engine
Experience	flight time last 90 days : 150 flight time total : 12000 flight time type : 280
ASRS Report	476164
Person 2
Affiliation	company : corporate
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : multi engine
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather inflight encounter other non adherence : clearance non adherence : published procedure other anomaly other anomaly other
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : regained aircraft control other
Supplementary
Problem Areas	Weather Aircraft FAA Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

During cruise at FL450 en route from eugene, or, to south bend, in, in convective activity, a descent to FL410 was initiated due to an increased deck angle, decreased airspeed, and substantial depreciation in performance indicated by the angle of attack and was followed by a very noticeable tail buffet. This was due to an aggressive downdraft at the time, not a mechanical which was suggested to the NTSB by ATC. I felt a stall could happen with little or not notice due to the flight conditions we were experiencing. We requested a descent to a lower atl 3 times from ATC. The first time ATC told us to stand by. In the second attempt we told ATC we were experiencing tail buffet, and needed lower immediately. ATC told us again to stand by and they would try and coordinate it first. Due to my situation worsening, and after seeing no conflicting traffic on the TCASII, I felt I had no other choice but to advise ATC I was descending out of FL450 for lower. ATC then immediately cleared us to FL410. I did what I had to do because ATC was so obtuse to a growing critical situation. It takes a coordinated effort between ATC and the aircraft they control to keep traffic moving safely. After all, safety is paramount. Our environment can be very hostile and most unforgiving if necessary attention is not given to detail.

Original NASA ASRS Text

Title: ASTRA CREW WAS OPERATING THE ACFT TOO HIGH FOR PROPER BUFFET MARGIN.

Narrative: DURING CRUISE AT FL450 ENRTE FROM EUGENE, OR, TO SOUTH BEND, IN, IN CONVECTIVE ACTIVITY, A DSCNT TO FL410 WAS INITIATED DUE TO AN INCREASED DECK ANGLE, DECREASED AIRSPD, AND SUBSTANTIAL DEPRECIATION IN PERFORMANCE INDICATED BY THE ANGLE OF ATTACK AND WAS FOLLOWED BY A VERY NOTICEABLE TAIL BUFFET. THIS WAS DUE TO AN AGGRESSIVE DOWNDRAFT AT THE TIME, NOT A MECHANICAL WHICH WAS SUGGESTED TO THE NTSB BY ATC. I FELT A STALL COULD HAPPEN WITH LITTLE OR NOT NOTICE DUE TO THE FLT CONDITIONS WE WERE EXPERIENCING. WE REQUESTED A DSCNT TO A LOWER ATL 3 TIMES FROM ATC. THE FIRST TIME ATC TOLD US TO STAND BY. IN THE SECOND ATTEMPT WE TOLD ATC WE WERE EXPERIENCING TAIL BUFFET, AND NEEDED LOWER IMMEDIATELY. ATC TOLD US AGAIN TO STAND BY AND THEY WOULD TRY AND COORDINATE IT FIRST. DUE TO MY SIT WORSENING, AND AFTER SEEING NO CONFLICTING TFC ON THE TCASII, I FELT I HAD NO OTHER CHOICE BUT TO ADVISE ATC I WAS DSNDING OUT OF FL450 FOR LOWER. ATC THEN IMMEDIATELY CLRED US TO FL410. I DID WHAT I HAD TO DO BECAUSE ATC WAS SO OBTUSE TO A GROWING CRITICAL SIT. IT TAKES A COORDINATED EFFORT BTWN ATC AND THE ACFT THEY CTL TO KEEP TFC MOVING SAFELY. AFTER ALL, SAFETY IS PARAMOUNT. OUR ENVIRONMENT CAN BE VERY HOSTILE AND MOST UNFORGIVING IF NECESSARY ATTN IS NOT GIVEN TO DETAIL.

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.