Aircraft enters mach buffet at altitude due to performance limitation.

Attributes
ACN	552249
Time
Date	200206
Day	Sat
Local Time Of Day	1201 To 1800
Place
State Reference	FO
Altitude	msl bound lower : 42000 msl bound upper : 43000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : bird.artcc artcc : eggx.artcc tower : toa.tower
Operator	general aviation : corporate
Make Model Name	Falcon 2000
Operating Under FAR Part	Part 91
Navigation In Use	other
Flight Phase	cruise : level
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : eggx.artcc
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : atp pilot : commercial
Experience	flight time last 90 days : 80 flight time total : 3000 flight time type : 80
ASRS Report	552249
Person 2
Affiliation	company : corporate
Function	flight crew : first officer
Qualification	pilot : atp pilot : commercial pilot : instrument pilot : multi engine
Experience	flight time last 90 days : 90 flight time total : 6500 flight time type : 80
ASRS Report	552567
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other anomaly other anomaly other
Independent Detector	other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance flight crew : regained aircraft control
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Environmental Factor Flight Crew Human Performance Aircraft
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

During our flight we were filed to and received clearance to climb to FL430. At cruise FL430 the temperature was found to be warmer than forecasted and the aircraft would not gain speed as it leveled off in-flight. As the speed started to bleed off, we requested FL420 several times with shanwick oceanic cta and several times got a 'stand by' reply. As the flight continued west from eraka the temperature steadily got warmer till the aircraft's airspeed decreased to just above stall very quickly. At the same time shanwick ATC came back with a rerte clearance to copy, at which time the mach indicator tape on the pfd unit flipped from mach speed to the IAS tape and a buffet was felt in the flight controls of the aircraft. At this time, I nosed over the aircraft to gain speed back and leveled off at FL428 to maintain control of the aircraft. As PNF was still receiving the rerte clearance he demanded a descent to FL420, at which time I am not sure what was said because at the same time a secondary buffet was felt on the flight controls, which I responded to by nosing the aircraft over in a descent to FL420, again to maintain control of the aircraft. Shanwick control asked our altitude and we told them we were now at FL420 at which time they handed us over to iceland control, who informed us we were not to deviate from altitude without an ATC clearance. Our flight conditions at the time of this incident were VMC with a TCASII target at our south position 30 mi at FL350. The forecast temperature at FL430 was to be about static air temperature -51 degrees to -52 degrees, but was found to be about -47 degrees (isa +09) which was too warm for our aircraft to sustain flight at FL430 at our weight. I believe ATC was too slow in issuing us a clearance to a lower altitude and at the same time we did not strongly state our immediate concern to maintain flight at FL430 due to the situation happening so quickly. In hindsight, an emergency should have been declared and vacating from our assigned flight level should have been reported to ATC asa. The situation happened quickly and I was expecting to have the requested altitude. We did not get to report the deviation as soon as we would have liked while trying to insure control of the aircraft.

Original NASA ASRS Text

Title: ACFT ENTERS MACH BUFFET AT ALT DUE TO PERFORMANCE LIMITATION.

Narrative: DURING OUR FLT WE WERE FILED TO AND RECEIVED CLRNC TO CLB TO FL430. AT CRUISE FL430 THE TEMP WAS FOUND TO BE WARMER THAN FORECASTED AND THE ACFT WOULD NOT GAIN SPD AS IT LEVELED OFF INFLT. AS THE SPD STARTED TO BLEED OFF, WE REQUESTED FL420 SEVERAL TIMES WITH SHANWICK OCEANIC CTA AND SEVERAL TIMES GOT A 'STAND BY' REPLY. AS THE FLT CONTINUED W FROM ERAKA THE TEMP STEADILY GOT WARMER TILL THE ACFT'S AIRSPD DECREASED TO JUST ABOVE STALL VERY QUICKLY. AT THE SAME TIME SHANWICK ATC CAME BACK WITH A RERTE CLRNC TO COPY, AT WHICH TIME THE MACH INDICATOR TAPE ON THE PFD UNIT FLIPPED FROM MACH SPD TO THE IAS TAPE AND A BUFFET WAS FELT IN THE FLT CTLS OF THE ACFT. AT THIS TIME, I NOSED OVER THE ACFT TO GAIN SPD BACK AND LEVELED OFF AT FL428 TO MAINTAIN CTL OF THE ACFT. AS PNF WAS STILL RECEIVING THE RERTE CLRNC HE DEMANDED A DSCNT TO FL420, AT WHICH TIME I AM NOT SURE WHAT WAS SAID BECAUSE AT THE SAME TIME A SECONDARY BUFFET WAS FELT ON THE FLT CTLS, WHICH I RESPONDED TO BY NOSING THE ACFT OVER IN A DSCNT TO FL420, AGAIN TO MAINTAIN CTL OF THE ACFT. SHANWICK CTL ASKED OUR ALT AND WE TOLD THEM WE WERE NOW AT FL420 AT WHICH TIME THEY HANDED US OVER TO ICELAND CTL, WHO INFORMED US WE WERE NOT TO DEVIATE FROM ALT WITHOUT AN ATC CLRNC. OUR FLT CONDITIONS AT THE TIME OF THIS INCIDENT WERE VMC WITH A TCASII TARGET AT OUR S POS 30 MI AT FL350. THE FORECAST TEMP AT FL430 WAS TO BE ABOUT STATIC AIR TEMP -51 DEGS TO -52 DEGS, BUT WAS FOUND TO BE ABOUT -47 DEGS (ISA +09) WHICH WAS TOO WARM FOR OUR ACFT TO SUSTAIN FLT AT FL430 AT OUR WT. I BELIEVE ATC WAS TOO SLOW IN ISSUING US A CLRNC TO A LOWER ALT AND AT THE SAME TIME WE DID NOT STRONGLY STATE OUR IMMEDIATE CONCERN TO MAINTAIN FLT AT FL430 DUE TO THE SIT HAPPENING SO QUICKLY. IN HINDSIGHT, AN EMER SHOULD HAVE BEEN DECLARED AND VACATING FROM OUR ASSIGNED FLT LEVEL SHOULD HAVE BEEN RPTED TO ATC ASA. THE SIT HAPPENED QUICKLY AND I WAS EXPECTING TO HAVE THE REQUESTED ALT. WE DID NOT GET TO RPT THE DEV AS SOON AS WE WOULD HAVE LIKED WHILE TRYING TO INSURE CTL OF THE ACFT.

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.