Narrative:

This occurred on a flight from psp to las in clear, high visibility WX a few mi southwest of tnp VOR. We had departed psp in a PA60 with 2 crew -- I was the pilot. We filed for and were cleared to climb to cruising altitude of 11000 ft. We were going through about 8000 ft climbing about 1000 FPM when I noticed that the cabin was not pressurizing. Then I observed the red warning light and thought we had a malfunction. The copilot and I temporarily directed our efforts to remedying that situation. Prior to this occurrence, some mins before, center advised us to stop our climb at 10000 ft because of traffic. I acknowledged and set the altitude alert for 10000 ft. While working on the cabin pressurization problem, the plane climbed through 10000 ft and kept going up. Suddenly I glanced at the altimeter and noticed we were at 11000 ft whereupon I stopped the climb and started a descent -- we were on autoplt. Simultaneously center asked our altitude and I replied 11000 ft and acknowledged we were cleared to 10000 ft and were starting back down. By this time we were at 10500 ft and descending and I asked 'which altitude should I hold -- 10 or 11?' I was told to standby, and after a min or two, hearing nothing more and realizing my last cleared altitude was 10000 ft, I continued the descent to that altitude. It's important to know that the altitude alert device did not 'beep' when we went through 10000 ft on the way up (more about this later). Finally another controller came on and advised us to maintain 10000 ft and in a min or so asked me to contact by phone when we got to las the los angeles area manager, which I promptly did upon arrival. I explained the situation, and was told not to worry. But was also told there was another aircraft within 5 mi, which the copilot had observed, and that was the problem. The rest of the flight proceeded without further incident. About the altitude alert device: I had the device removed and tested at an avionics shop about 2 months previously and reinstalled. It had been used extensively in march on a trip and I noticed that it seemed to perform erratically which was the original reason I had it tested. On the balance of the trip in question, it failed to beep several times, but otherwise performed in a normal fashion. It obviously needs repair even though the shop that tested it said that it tested ok.

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Original NASA ASRS Text

Title: A PA60 PLT OVERSHOT ASSIGNED ALT DURING CLB OUT WHILE TROUBLESHOOTING A PROB WITH THE PRESSURIZATION. THE CTLR HAD LIMITED THE ACFT AT AN ALT FOR TFC THAT WAS LESS THAN 5 NM AWAY.

Narrative: THIS OCCURRED ON A FLT FROM PSP TO LAS IN CLR, HIGH VISIBILITY WX A FEW MI SW OF TNP VOR. WE HAD DEPARTED PSP IN A PA60 WITH 2 CREW -- I WAS THE PLT. WE FILED FOR AND WERE CLRED TO CLB TO CRUISING ALT OF 11000 FT. WE WERE GOING THROUGH ABOUT 8000 FT CLBING ABOUT 1000 FPM WHEN I NOTICED THAT THE CABIN WAS NOT PRESSURIZING. THEN I OBSERVED THE RED WARNING LIGHT AND THOUGHT WE HAD A MALFUNCTION. THE COPLT AND I TEMPORARILY DIRECTED OUR EFFORTS TO REMEDYING THAT SIT. PRIOR TO THIS OCCURRENCE, SOME MINS BEFORE, CTR ADVISED US TO STOP OUR CLB AT 10000 FT BECAUSE OF TFC. I ACKNOWLEDGED AND SET THE ALT ALERT FOR 10000 FT. WHILE WORKING ON THE CABIN PRESSURIZATION PROB, THE PLANE CLBED THROUGH 10000 FT AND KEPT GOING UP. SUDDENLY I GLANCED AT THE ALTIMETER AND NOTICED WE WERE AT 11000 FT WHEREUPON I STOPPED THE CLB AND STARTED A DSCNT -- WE WERE ON AUTOPLT. SIMULTANEOUSLY CTR ASKED OUR ALT AND I REPLIED 11000 FT AND ACKNOWLEDGED WE WERE CLRED TO 10000 FT AND WERE STARTING BACK DOWN. BY THIS TIME WE WERE AT 10500 FT AND DSNDING AND I ASKED 'WHICH ALT SHOULD I HOLD -- 10 OR 11?' I WAS TOLD TO STANDBY, AND AFTER A MIN OR TWO, HEARING NOTHING MORE AND REALIZING MY LAST CLRED ALT WAS 10000 FT, I CONTINUED THE DSCNT TO THAT ALT. IT'S IMPORTANT TO KNOW THAT THE ALT ALERT DEVICE DID NOT 'BEEP' WHEN WE WENT THROUGH 10000 FT ON THE WAY UP (MORE ABOUT THIS LATER). FINALLY ANOTHER CTLR CAME ON AND ADVISED US TO MAINTAIN 10000 FT AND IN A MIN OR SO ASKED ME TO CONTACT BY PHONE WHEN WE GOT TO LAS THE LOS ANGELES AREA MGR, WHICH I PROMPTLY DID UPON ARR. I EXPLAINED THE SIT, AND WAS TOLD NOT TO WORRY. BUT WAS ALSO TOLD THERE WAS ANOTHER ACFT WITHIN 5 MI, WHICH THE COPLT HAD OBSERVED, AND THAT WAS THE PROB. THE REST OF THE FLT PROCEEDED WITHOUT FURTHER INCIDENT. ABOUT THE ALT ALERT DEVICE: I HAD THE DEVICE REMOVED AND TESTED AT AN AVIONICS SHOP ABOUT 2 MONTHS PREVIOUSLY AND REINSTALLED. IT HAD BEEN USED EXTENSIVELY IN MARCH ON A TRIP AND I NOTICED THAT IT SEEMED TO PERFORM ERRATICALLY WHICH WAS THE ORIGINAL REASON I HAD IT TESTED. ON THE BALANCE OF THE TRIP IN QUESTION, IT FAILED TO BEEP SEVERAL TIMES, BUT OTHERWISE PERFORMED IN A NORMAL FASHION. IT OBVIOUSLY NEEDS REPAIR EVEN THOUGH THE SHOP THAT TESTED IT SAID THAT IT TESTED OK.

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.