Narrative:

At FL350 just prior to descent, PNF notified PF that he was going to get the pdx ATIS information while PF would monitor ATC communications. PNF understood the ATIS recording to state the altimeter setting to be 29.99 when actually the setting was 29.29. ATC gave the altimeter setting several mins before the required actual setting at FL180. At FL180 crew accomplished approach check and referred to company ATIS form for the altimeter setting of 29.99 instead of the actual 29.29. Aircraft descended to 9000 ft MSL on altimeter. Approach control questioned crew for altitude stating his equipment indicated an altitude of 8300 ft MSL. A second transponder was selected with same altitude reading. Approach control then stated altimeter setting, at which time crew realized the discrepancy, reset the altimeter and corrected to the proper altitude of 9000 ft MSL. Approach control stated there was no conflict. Remainder of approach and landing was normal. ATC approach control was contacted to explain the situation. Supervisor stated there was no problem nor any conflict. Contributing factors: 1) ATIS information with like sounding numbers 29.29 versus 29.99. 2) 2 crewmember aircraft monitoring 2 separate radios while performing flying duties which inhibited verification of information by both crewmembers. Possible solutions: 1) notify ATC you will be off his radio for 1 min while getting ATIS information. 2) slower, more pronounced ATIS recordings. 3) pilot initiated altimeter verification with ATC passing FL180 thus giving or verifying information in a more timely manner for the pilot.

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Original NASA ASRS Text

Title: ALTDEV ON DSCNT.

Narrative: AT FL350 JUST PRIOR TO DSCNT, PNF NOTIFIED PF THAT HE WAS GOING TO GET THE PDX ATIS INFO WHILE PF WOULD MONITOR ATC COMS. PNF UNDERSTOOD THE ATIS RECORDING TO STATE THE ALTIMETER SETTING TO BE 29.99 WHEN ACTUALLY THE SETTING WAS 29.29. ATC GAVE THE ALTIMETER SETTING SEVERAL MINS BEFORE THE REQUIRED ACTUAL SETTING AT FL180. AT FL180 CREW ACCOMPLISHED APCH CHK AND REFERRED TO COMPANY ATIS FORM FOR THE ALTIMETER SETTING OF 29.99 INSTEAD OF THE ACTUAL 29.29. ACFT DSNDED TO 9000 FT MSL ON ALTIMETER. APCH CTL QUESTIONED CREW FOR ALT STATING HIS EQUIP INDICATED AN ALT OF 8300 FT MSL. A SECOND XPONDER WAS SELECTED WITH SAME ALT READING. APCH CTL THEN STATED ALTIMETER SETTING, AT WHICH TIME CREW REALIZED THE DISCREPANCY, RESET THE ALTIMETER AND CORRECTED TO THE PROPER ALT OF 9000 FT MSL. APCH CTL STATED THERE WAS NO CONFLICT. REMAINDER OF APCH AND LNDG WAS NORMAL. ATC APCH CTL WAS CONTACTED TO EXPLAIN THE SIT. SUPVR STATED THERE WAS NO PROB NOR ANY CONFLICT. CONTRIBUTING FACTORS: 1) ATIS INFO WITH LIKE SOUNDING NUMBERS 29.29 VERSUS 29.99. 2) 2 CREWMEMBER ACFT MONITORING 2 SEPARATE RADIOS WHILE PERFORMING FLYING DUTIES WHICH INHIBITED VERIFICATION OF INFO BY BOTH CREWMEMBERS. POSSIBLE SOLUTIONS: 1) NOTIFY ATC YOU WILL BE OFF HIS RADIO FOR 1 MIN WHILE GETTING ATIS INFO. 2) SLOWER, MORE PRONOUNCED ATIS RECORDINGS. 3) PLT INITIATED ALTIMETER VERIFICATION WITH ATC PASSING FL180 THUS GIVING OR VERIFYING INFO IN A MORE TIMELY MANNER FOR THE PLT.

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.