Narrative:

After takeoff and climbing through about 3000 ft, the PIC brought to my attention that our long range navigation unit was not processing the GPS signal correctly. He engaged the autoplt to troubleshoot the problem. After working with the problem he went to trim the nose down to maintain our proper climb speed and stated that his trim switch was not working properly. The other trim switch position worked properly and the copilot's switch worked in all position. He found that by pushing nose down with a sideward motion at the full nose down position it would make contact and work. Climb to FL390 was uneventful other than a slightly slower climb speed because of having to 'work with the nose down trim switch' and the navigation problem solved by turning off the unit and restarting it. When we leveled off at FL390 from the slower climb speed, we noticed that the airspeed was not increasing as it normally would for this combination of weight, altitude and temperature (forecast and actual) according to the aircraft performance charts. I asked ZKC for FL370 and they replied that they had to check with ZFW. While waiting for a call back our speed situation was getting worse and it was apparent we would not be able to stay at FL390. The PIC instructed me to tell ZKC that we needed to make an immediate descent and they replied it would be 3 mins. The PIC and I knew we couldn't wait that long as the airspeed was slowly retreating. Our TCASII showed the traffic 2000 ft below us that ATC was holding us for so I asked for a right turn so we could get out of FL390 as soon as possible as we were then at maximum power. We received our turn to 270 degrees and the PIC disengaged the autoplt, and started the turn to the right. The turn resulted in a loss of lift especially more pronounced due to our slow airspeed and our vvi showed a descent and ATC said we were not cleared out of FL390 and I replied we knew that but we were unable to maintain FL390 due to the temperature at altitude. The PIC maintained the altitude while just above stall speed until we were given a lower altitude. I heard ZKC tell the gulfstream to turn right to 180 degrees and descend to FL350 immediately. Once we got our airspeed back, the aircraft flew normally and we were passed to ZFW where they asked us to call an ATC phone number. Factors: 1) a long range navigation unit that was not processing the GPS signal properly. 2) an intermittent autoplt trim switch. 3) slow airspeed at leveloff and cruise. 4) loss of lift due to turn maneuver and low airspeed. 5) slow response of ATC in providing information on descent from FL390. 6) failure on my part not stating we could not maintain FL390 and asking for an immediate descent. Discovery: reviewing this flight I believe that the 2 minor problems resulted in our getting behind the power curve envelope. Instead of being able to accelerate once we leveled out and started our cruise at FL390. Another factor was conflicting traffic at FL370 and ATC's time delay in advising us on our request for a lower altitude. Corrective actions: 1) avoid the distrs of small maintenance problems. 2) avoid falling behind the power/airspeed flight envelope. 3) advise ATC at the earliest of potential areas of concern. 4) ATC advising air crews without delay according to workload. 5) air crew terminology in using immediate to get ATC's attention. Supplemental information from acn 538309: finally the combination of completing the turn, maximum power, and losing a few hundred ft of altitude was enough to let the aircraft pick up enough speed to reduce the drag that it would then hold the altitude.

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Original NASA ASRS Text

Title: LJ35 CREW WAS REQUIRED TO DSND FROM FL390 TO KEEP THE ACFT FROM STALLING.

Narrative: AFTER TKOF AND CLBING THROUGH ABOUT 3000 FT, THE PIC BROUGHT TO MY ATTN THAT OUR LONG RANGE NAV UNIT WAS NOT PROCESSING THE GPS SIGNAL CORRECTLY. HE ENGAGED THE AUTOPLT TO TROUBLESHOOT THE PROB. AFTER WORKING WITH THE PROB HE WENT TO TRIM THE NOSE DOWN TO MAINTAIN OUR PROPER CLB SPD AND STATED THAT HIS TRIM SWITCH WAS NOT WORKING PROPERLY. THE OTHER TRIM SWITCH POS WORKED PROPERLY AND THE COPLT'S SWITCH WORKED IN ALL POS. HE FOUND THAT BY PUSHING NOSE DOWN WITH A SIDEWARD MOTION AT THE FULL NOSE DOWN POS IT WOULD MAKE CONTACT AND WORK. CLB TO FL390 WAS UNEVENTFUL OTHER THAN A SLIGHTLY SLOWER CLB SPD BECAUSE OF HAVING TO 'WORK WITH THE NOSE DOWN TRIM SWITCH' AND THE NAV PROB SOLVED BY TURNING OFF THE UNIT AND RESTARTING IT. WHEN WE LEVELED OFF AT FL390 FROM THE SLOWER CLB SPD, WE NOTICED THAT THE AIRSPD WAS NOT INCREASING AS IT NORMALLY WOULD FOR THIS COMBINATION OF WT, ALT AND TEMP (FORECAST AND ACTUAL) ACCORDING TO THE ACFT PERFORMANCE CHARTS. I ASKED ZKC FOR FL370 AND THEY REPLIED THAT THEY HAD TO CHK WITH ZFW. WHILE WAITING FOR A CALL BACK OUR SPD SIT WAS GETTING WORSE AND IT WAS APPARENT WE WOULD NOT BE ABLE TO STAY AT FL390. THE PIC INSTRUCTED ME TO TELL ZKC THAT WE NEEDED TO MAKE AN IMMEDIATE DSCNT AND THEY REPLIED IT WOULD BE 3 MINS. THE PIC AND I KNEW WE COULDN'T WAIT THAT LONG AS THE AIRSPD WAS SLOWLY RETREATING. OUR TCASII SHOWED THE TFC 2000 FT BELOW US THAT ATC WAS HOLDING US FOR SO I ASKED FOR A R TURN SO WE COULD GET OUT OF FL390 ASAP AS WE WERE THEN AT MAX PWR. WE RECEIVED OUR TURN TO 270 DEGS AND THE PIC DISENGAGED THE AUTOPLT, AND STARTED THE TURN TO THE R. THE TURN RESULTED IN A LOSS OF LIFT ESPECIALLY MORE PRONOUNCED DUE TO OUR SLOW AIRSPD AND OUR VVI SHOWED A DSCNT AND ATC SAID WE WERE NOT CLRED OUT OF FL390 AND I REPLIED WE KNEW THAT BUT WE WERE UNABLE TO MAINTAIN FL390 DUE TO THE TEMP AT ALT. THE PIC MAINTAINED THE ALT WHILE JUST ABOVE STALL SPD UNTIL WE WERE GIVEN A LOWER ALT. I HEARD ZKC TELL THE GULFSTREAM TO TURN R TO 180 DEGS AND DSND TO FL350 IMMEDIATELY. ONCE WE GOT OUR AIRSPD BACK, THE ACFT FLEW NORMALLY AND WE WERE PASSED TO ZFW WHERE THEY ASKED US TO CALL AN ATC PHONE NUMBER. FACTORS: 1) A LONG RANGE NAV UNIT THAT WAS NOT PROCESSING THE GPS SIGNAL PROPERLY. 2) AN INTERMITTENT AUTOPLT TRIM SWITCH. 3) SLOW AIRSPD AT LEVELOFF AND CRUISE. 4) LOSS OF LIFT DUE TO TURN MANEUVER AND LOW AIRSPD. 5) SLOW RESPONSE OF ATC IN PROVIDING INFO ON DSCNT FROM FL390. 6) FAILURE ON MY PART NOT STATING WE COULD NOT MAINTAIN FL390 AND ASKING FOR AN IMMEDIATE DSCNT. DISCOVERY: REVIEWING THIS FLT I BELIEVE THAT THE 2 MINOR PROBS RESULTED IN OUR GETTING BEHIND THE PWR CURVE ENVELOPE. INSTEAD OF BEING ABLE TO ACCELERATE ONCE WE LEVELED OUT AND STARTED OUR CRUISE AT FL390. ANOTHER FACTOR WAS CONFLICTING TFC AT FL370 AND ATC'S TIME DELAY IN ADVISING US ON OUR REQUEST FOR A LOWER ALT. CORRECTIVE ACTIONS: 1) AVOID THE DISTRS OF SMALL MAINT PROBS. 2) AVOID FALLING BEHIND THE PWR/AIRSPD FLT ENVELOPE. 3) ADVISE ATC AT THE EARLIEST OF POTENTIAL AREAS OF CONCERN. 4) ATC ADVISING AIR CREWS WITHOUT DELAY ACCORDING TO WORKLOAD. 5) AIR CREW TERMINOLOGY IN USING IMMEDIATE TO GET ATC'S ATTN. SUPPLEMENTAL INFO FROM ACN 538309: FINALLY THE COMBINATION OF COMPLETING THE TURN, MAX PWR, AND LOSING A FEW HUNDRED FT OF ALT WAS ENOUGH TO LET THE ACFT PICK UP ENOUGH SPD TO REDUCE THE DRAG THAT IT WOULD THEN HOLD THE ALT.

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.