Narrative:

The incident occurred completing the last leg of our sck- den-las-sck trip. Both pilots were quite tired as our sck departure was at XO37 am and it was now close to XA00 am. Departing las airport on the oasis 8 departure/beatty transition, ZLA cleared us to FL350. The aircraft was light and was climbing through approximately FL260 at 2000-3000 FPM when ZLA instructed us to climb and maintain FL280 due to traffic: a B737 was at 12 O'clock at FL290. I acknowledged the new altitude assignment, dialed 28000 ft into the altitude alerter, pointed to it, and received acknowledgement from the PF that FL280 was the newly assigned altitude. I proceeded to look for traffic, and within seconds of setting the altitude alerter, it sounded, signaling passing through 27000 ft. The PF raised his finger to signify that we had 1000 ft left to climb to our assigned altitude. The PF began to reduce his rate of climb passing through 27500 ft and it appeared that a level off was in progress. I moved my attention to looking for the B737 and seconds later the altitude alerter went off, signaling that the aircraft was at 28300 ft. I looked at the altimeter as the PF pushed the aircraft back down to 28000 ft. The highest altitude that I noticed was 28380 ft. The B737 pilot complained to ZLA that they had received a TCASII alert and had initiated evasive action. ZLA asked us if the instruction to climb and maintain FL280 was acknowledged, I responded that it was. The B737 pilot continued to complain and asked how far off our altitude was, ZLA responded that our altitude was off by 400 ft. ZLA then asked us to call their number regarding a possible pilot violation. After we landed the PF called the center. Supplemental information from acn 313028: on a part 91 reposition flight, my copilot and I had just recently leveled off at FL280 and engaged the autoplt. Everything looked normal and operating correctly. Shortly after, an airliner reported a TCASII RA to climb and made an inquiry to ATC. ATC reported 'yeah, the lear busted his assigned altitude.' nothing more was discussed on frequency. Aircraft had previously had mode C problems, so I asked the next center for a verification of altitude, and this time ATC reported us 200 ft low. Mode C was written up on return to base.

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Original NASA ASRS Text

Title: AN AIR TAXI FREIGHT JET OVERSHOT CLRNC ALT. THE CAPT CITED AUTOPLT AND MODE C MALFUNCTIONS AS FACTORS.

Narrative: THE INCIDENT OCCURRED COMPLETING THE LAST LEG OF OUR SCK- DEN-LAS-SCK TRIP. BOTH PLTS WERE QUITE TIRED AS OUR SCK DEP WAS AT XO37 AM AND IT WAS NOW CLOSE TO XA00 AM. DEPARTING LAS ARPT ON THE OASIS 8 DEP/BEATTY TRANSITION, ZLA CLRED US TO FL350. THE ACFT WAS LIGHT AND WAS CLBING THROUGH APPROX FL260 AT 2000-3000 FPM WHEN ZLA INSTRUCTED US TO CLB AND MAINTAIN FL280 DUE TO TFC: A B737 WAS AT 12 O'CLOCK AT FL290. I ACKNOWLEDGED THE NEW ALT ASSIGNMENT, DIALED 28000 FT INTO THE ALT ALERTER, POINTED TO IT, AND RECEIVED ACKNOWLEDGEMENT FROM THE PF THAT FL280 WAS THE NEWLY ASSIGNED ALT. I PROCEEDED TO LOOK FOR TFC, AND WITHIN SECONDS OF SETTING THE ALT ALERTER, IT SOUNDED, SIGNALING PASSING THROUGH 27000 FT. THE PF RAISED HIS FINGER TO SIGNIFY THAT WE HAD 1000 FT LEFT TO CLB TO OUR ASSIGNED ALT. THE PF BEGAN TO REDUCE HIS RATE OF CLB PASSING THROUGH 27500 FT AND IT APPEARED THAT A LEVEL OFF WAS IN PROGRESS. I MOVED MY ATTN TO LOOKING FOR THE B737 AND SECONDS LATER THE ALT ALERTER WENT OFF, SIGNALING THAT THE ACFT WAS AT 28300 FT. I LOOKED AT THE ALTIMETER AS THE PF PUSHED THE ACFT BACK DOWN TO 28000 FT. THE HIGHEST ALT THAT I NOTICED WAS 28380 FT. THE B737 PLT COMPLAINED TO ZLA THAT THEY HAD RECEIVED A TCASII ALERT AND HAD INITIATED EVASIVE ACTION. ZLA ASKED US IF THE INSTRUCTION TO CLB AND MAINTAIN FL280 WAS ACKNOWLEDGED, I RESPONDED THAT IT WAS. THE B737 PLT CONTINUED TO COMPLAIN AND ASKED HOW FAR OFF OUR ALT WAS, ZLA RESPONDED THAT OUR ALT WAS OFF BY 400 FT. ZLA THEN ASKED US TO CALL THEIR NUMBER REGARDING A POSSIBLE PLT VIOLATION. AFTER WE LANDED THE PF CALLED THE CTR. SUPPLEMENTAL INFO FROM ACN 313028: ON A PART 91 REPOSITION FLT, MY COPLT AND I HAD JUST RECENTLY LEVELED OFF AT FL280 AND ENGAGED THE AUTOPLT. EVERYTHING LOOKED NORMAL AND OPERATING CORRECTLY. SHORTLY AFTER, AN AIRLINER RPTED A TCASII RA TO CLB AND MADE AN INQUIRY TO ATC. ATC RPTED 'YEAH, THE LEAR BUSTED HIS ASSIGNED ALT.' NOTHING MORE WAS DISCUSSED ON FREQ. ACFT HAD PREVIOUSLY HAD MODE C PROBS, SO I ASKED THE NEXT CTR FOR A VERIFICATION OF ALT, AND THIS TIME ATC RPTED US 200 FT LOW. MODE C WAS WRITTEN UP ON RETURN TO BASE.

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.