Narrative:

We were at FL390 with indicated mach .798, isa -3. At that weight, we were 'by the book' safe. I anticipated the temperature (OAT) would rise per our computer flight plan printout. 1 hour and 15 mins into the flight, I told the copilot to watch outside air temperature, and that if it started to get warmer, he had the power to prevent a drop in mach and to keep the speed up. I excused myself to the lavatory to relieve myself as I had been in the seat for 2 hours. As I returned from the aft cabin, the passenger detained me for several mins. The copilot is a highly experienced pilot with multiple ratings in heavy corporate aircraft. While I was out of the cockpit, he accepted a clearance to FL410, and initiated the climb. I was unaware of this climb until I returned to the cockpit. I first noticed a problem as I approached the cockpit. The distinct noise of boundary layer separation became audible. I asked what was going on as he started a turn. As I plopped into the seat, the burble of deep separation manifested, and I saw our mach was .71 with OAT temperature isa +5. We were at FL410. I immediately disconnected the autoplt and allowed the nose to drop. We lost 600 ft down to 40400 ft MSL. After getting speed back, I slowly climbed to 41000 ft to attempt to comply with the clearance as the copilot explained center required a climb and a turn. He said the temperature was fine until he climbed past 39500 ft MSL, then it started to climb rapidly. During the drift-down, the copilot called ATC to say we could not maintain altitude. Naturally ATC had other traffic (an air carrier) that was at FL390 and we were as upset as ATC by the situation. We saw the air carrier well before it would have been unavoidable. We discussed this as we overcame our nervous ticks and I have vowed to let all who fly with me know we don't accept climb clrncs unless we both agree. I absolutely would not have accepted the climb with what I knew, nor would I have attempted a bank to conform with a heading change in that situation. We want to please, but there are absolute limits we cannot ignore. Supplemental information from acn 606850: upon reaching 41000 ft the temperature was now warming up rapidly. I advised ATC that we were not going to be able to maintain 41000 ft for very long. ATC said it would be about 8 mins before 39000 ft would be available. At this time the temperature warmed up to isa +7. This is way too warm for the aircraft to maintain 41000 ft. I advised ZME that we needed a lower altitude. They said they were unable to give us lower altitude at that time, but instead had us turn 40 degrees. By turning us to this new heading ATC said we would only have to wait 3 mins for the descent to 39000 ft. During the turn, with a bank angle of 15 degrees our margin above stall increased and we in turn, started to incur a low speed buffet. At that time I started to descend and gain airspeed and advised ZME. I can say that we as a crew will look closer at our performance charts before accepting a higher altitude. The other factor in this incident was the temperature increasing a total of 9 degrees C. Leaving the assigned altitude of 41000 ft was necessary to preserve safety of flight.

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Original NASA ASRS Text

Title: GLF200 FO CLBED THE ACFT TOO HIGH FOR THE ACFT GROSS WT, GOT ON THE BACK SIDE OF THE PWR CURVE, AND WITH SLOWING MACH, HAD TO DSND TO PREVENT A STALL IN ZME CLASS A RESULTING IN A CONFLICT WITH ANOTHER ACFT.

Narrative: WE WERE AT FL390 WITH INDICATED MACH .798, ISA -3. AT THAT WT, WE WERE 'BY THE BOOK' SAFE. I ANTICIPATED THE TEMP (OAT) WOULD RISE PER OUR COMPUTER FLT PLAN PRINTOUT. 1 HR AND 15 MINS INTO THE FLT, I TOLD THE COPLT TO WATCH OUTSIDE AIR TEMP, AND THAT IF IT STARTED TO GET WARMER, HE HAD THE PWR TO PREVENT A DROP IN MACH AND TO KEEP THE SPD UP. I EXCUSED MYSELF TO THE LAVATORY TO RELIEVE MYSELF AS I HAD BEEN IN THE SEAT FOR 2 HRS. AS I RETURNED FROM THE AFT CABIN, THE PAX DETAINED ME FOR SEVERAL MINS. THE COPLT IS A HIGHLY EXPERIENCED PLT WITH MULTIPLE RATINGS IN HVY CORPORATE ACFT. WHILE I WAS OUT OF THE COCKPIT, HE ACCEPTED A CLRNC TO FL410, AND INITIATED THE CLB. I WAS UNAWARE OF THIS CLB UNTIL I RETURNED TO THE COCKPIT. I FIRST NOTICED A PROB AS I APCHED THE COCKPIT. THE DISTINCT NOISE OF BOUNDARY LAYER SEPARATION BECAME AUDIBLE. I ASKED WHAT WAS GOING ON AS HE STARTED A TURN. AS I PLOPPED INTO THE SEAT, THE BURBLE OF DEEP SEPARATION MANIFESTED, AND I SAW OUR MACH WAS .71 WITH OAT TEMP ISA +5. WE WERE AT FL410. I IMMEDIATELY DISCONNECTED THE AUTOPLT AND ALLOWED THE NOSE TO DROP. WE LOST 600 FT DOWN TO 40400 FT MSL. AFTER GETTING SPD BACK, I SLOWLY CLBED TO 41000 FT TO ATTEMPT TO COMPLY WITH THE CLRNC AS THE COPLT EXPLAINED CTR REQUIRED A CLB AND A TURN. HE SAID THE TEMP WAS FINE UNTIL HE CLBED PAST 39500 FT MSL, THEN IT STARTED TO CLB RAPIDLY. DURING THE DRIFT-DOWN, THE COPLT CALLED ATC TO SAY WE COULD NOT MAINTAIN ALT. NATURALLY ATC HAD OTHER TFC (AN ACR) THAT WAS AT FL390 AND WE WERE AS UPSET AS ATC BY THE SIT. WE SAW THE ACR WELL BEFORE IT WOULD HAVE BEEN UNAVOIDABLE. WE DISCUSSED THIS AS WE OVERCAME OUR NERVOUS TICKS AND I HAVE VOWED TO LET ALL WHO FLY WITH ME KNOW WE DON'T ACCEPT CLB CLRNCS UNLESS WE BOTH AGREE. I ABSOLUTELY WOULD NOT HAVE ACCEPTED THE CLB WITH WHAT I KNEW, NOR WOULD I HAVE ATTEMPTED A BANK TO CONFORM WITH A HDG CHANGE IN THAT SIT. WE WANT TO PLEASE, BUT THERE ARE ABSOLUTE LIMITS WE CANNOT IGNORE. SUPPLEMENTAL INFO FROM ACN 606850: UPON REACHING 41000 FT THE TEMP WAS NOW WARMING UP RAPIDLY. I ADVISED ATC THAT WE WERE NOT GOING TO BE ABLE TO MAINTAIN 41000 FT FOR VERY LONG. ATC SAID IT WOULD BE ABOUT 8 MINS BEFORE 39000 FT WOULD BE AVAILABLE. AT THIS TIME THE TEMP WARMED UP TO ISA +7. THIS IS WAY TOO WARM FOR THE ACFT TO MAINTAIN 41000 FT. I ADVISED ZME THAT WE NEEDED A LOWER ALT. THEY SAID THEY WERE UNABLE TO GIVE US LOWER ALT AT THAT TIME, BUT INSTEAD HAD US TURN 40 DEGS. BY TURNING US TO THIS NEW HDG ATC SAID WE WOULD ONLY HAVE TO WAIT 3 MINS FOR THE DSCNT TO 39000 FT. DURING THE TURN, WITH A BANK ANGLE OF 15 DEGS OUR MARGIN ABOVE STALL INCREASED AND WE IN TURN, STARTED TO INCUR A LOW SPD BUFFET. AT THAT TIME I STARTED TO DSND AND GAIN AIRSPD AND ADVISED ZME. I CAN SAY THAT WE AS A CREW WILL LOOK CLOSER AT OUR PERFORMANCE CHARTS BEFORE ACCEPTING A HIGHER ALT. THE OTHER FACTOR IN THIS INCIDENT WAS THE TEMP INCREASING A TOTAL OF 9 DEGS C. LEAVING THE ASSIGNED ALT OF 41000 FT WAS NECESSARY TO PRESERVE SAFETY OF FLT.

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.