Narrative:

Problem arose when second officer got the ATIS and understood the altimeter setting as 2993 when actually it was 2933. He gave me the ATIS form and we set 2993 in our altimeters. Contributing factors: automatic pressurization was inoperative and the second officer had to give it a lot of attention continually. Confusion because ATC changed our clearance a number of times. We were vectored north for spacing then cleared direct to rains intersection (sebnd), descend to cross rains at 14000'. We don't usually go via rains (not in lt plan) so we had to take time to program rains into the INS. This is probably why we missed the altimeter given by ATC. ATC cleared us to make 2 360's over rains then direct to pirat intersection. As we were starting our second 360 we were cleared direct pirat descend to cross pirat at 8000' 250 KTS. Before we got to pirat we were reclred back to hold at rains at published climb to and maintain 14000'. We entered holding and I noticed on the TCAS there were 2 aircraft holding one at 1600' above us and the other 2600' above us. This was my first clue that we were 600' low. I asked ATC for an altimeter setting and they said 2933. We had been holding 600' lower than assigned. It was fortunate there was no aircraft holding below us. Suggestions: pilots should listen carefully when ATC clears you below 18000' and gives the altimeter setting and compare it with the ATIS setting. Anytime controller notices aircraft off assigned altitude pilot should be advised. The TCAS was designed for collision avoidance, however, this time it was used to determine we were at the wrong altitude.

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Original NASA ASRS Text

Title: ACR WDB ALT DEVIATION OVERSHOT DURING DESCENT DUE TO WRONG ALTIMETER SETTING. ERROR DETECTED WHEN FLT CREW NOTED TCAS II SHOWING OTHER TRAFFIC IN HOLDING PATTERN 1600' AND 2600' ABOVE THEM WHEN THEY SHOULD HAVE BEEN 1000' AND 2000' ABOVE.

Narrative: PROB AROSE WHEN S/O GOT THE ATIS AND UNDERSTOOD THE ALTIMETER SETTING AS 2993 WHEN ACTUALLY IT WAS 2933. HE GAVE ME THE ATIS FORM AND WE SET 2993 IN OUR ALTIMETERS. CONTRIBUTING FACTORS: AUTO PRESSURIZATION WAS INOPERATIVE AND THE S/O HAD TO GIVE IT A LOT OF ATTN CONTINUALLY. CONFUSION BECAUSE ATC CHANGED OUR CLRNC A NUMBER OF TIMES. WE WERE VECTORED N FOR SPACING THEN CLRED DIRECT TO RAINS INTXN (SEBND), DSND TO CROSS RAINS AT 14000'. WE DON'T USUALLY GO VIA RAINS (NOT IN LT PLAN) SO WE HAD TO TAKE TIME TO PROGRAM RAINS INTO THE INS. THIS IS PROBABLY WHY WE MISSED THE ALTIMETER GIVEN BY ATC. ATC CLRED US TO MAKE 2 360'S OVER RAINS THEN DIRECT TO PIRAT INTXN. AS WE WERE STARTING OUR SEC 360 WE WERE CLRED DIRECT PIRAT DSND TO CROSS PIRAT AT 8000' 250 KTS. BEFORE WE GOT TO PIRAT WE WERE RECLRED BACK TO HOLD AT RAINS AT PUBLISHED CLB TO AND MAINTAIN 14000'. WE ENTERED HOLDING AND I NOTICED ON THE TCAS THERE WERE 2 ACFT HOLDING ONE AT 1600' ABOVE US AND THE OTHER 2600' ABOVE US. THIS WAS MY FIRST CLUE THAT WE WERE 600' LOW. I ASKED ATC FOR AN ALTIMETER SETTING AND THEY SAID 2933. WE HAD BEEN HOLDING 600' LOWER THAN ASSIGNED. IT WAS FORTUNATE THERE WAS NO ACFT HOLDING BELOW US. SUGGESTIONS: PLTS SHOULD LISTEN CAREFULLY WHEN ATC CLRS YOU BELOW 18000' AND GIVES THE ALTIMETER SETTING AND COMPARE IT WITH THE ATIS SETTING. ANYTIME CTLR NOTICES ACFT OFF ASSIGNED ALT PLT SHOULD BE ADVISED. THE TCAS WAS DESIGNED FOR COLLISION AVOIDANCE, HOWEVER, THIS TIME IT WAS USED TO DETERMINE WE WERE AT THE WRONG 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.