Narrative:

We were en route to lga following the milton 2 STAR in the solberg VOR area. We were level at 13000'. ATC requested our altitude and we confirmed 13000'. They pointed out that we were squawking 1000' lower. I checked altimeter settings to see that we were not still at 29.92. We were set at 30.24. They then cleared us to 11000'. As we were leveling, ATC pointed out again that we were squawking 1000' low. I switched xponders, but the squawked altitude was still off 1000'. I then shut off the altitude squawk, figuring a mechanical malfunction. At no time was there any C/a. We were switched to approach control and they gave us an altimeter setting of 29.19. I immediately realized the problem and got to my correct altitude and altimeter setting. I discussed what happened with the first officer; we had let down from flight levels to 13000', necessitating an altimeter change from 29.92. The first officer was in the habit of repeating back only the last 2 digits of the altimeter setting (ie, .24). I didn't catch the mistake as he dialed in the wrong altimeter setting of 30.24 instead of 29.24 in the altitude alerting system. This is what I then used to dial my altimeter as I descended below FL180. The first officer promised that he would, from now on, repeat back all 4 digits of the altimeter setting to guard against further mishaps. Supplemental information from acn 129263: no time during the discussion was the altimeter setting questioned. Approximately 1 min later, another aircraft checked on the frequency. When the controller gave the altimeter setting of 29.24, the captain and I realized we had the wrong setting.

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Original NASA ASRS Text

Title: ACR MLG ALT DEVIATION OVERSHOT DUE ERROR IN ALTIMETER SETTING.

Narrative: WE WERE ENRTE TO LGA FOLLOWING THE MILTON 2 STAR IN THE SOLBERG VOR AREA. WE WERE LEVEL AT 13000'. ATC REQUESTED OUR ALT AND WE CONFIRMED 13000'. THEY POINTED OUT THAT WE WERE SQUAWKING 1000' LOWER. I CHKED ALTIMETER SETTINGS TO SEE THAT WE WERE NOT STILL AT 29.92. WE WERE SET AT 30.24. THEY THEN CLRED US TO 11000'. AS WE WERE LEVELING, ATC POINTED OUT AGAIN THAT WE WERE SQUAWKING 1000' LOW. I SWITCHED XPONDERS, BUT THE SQUAWKED ALT WAS STILL OFF 1000'. I THEN SHUT OFF THE ALT SQUAWK, FIGURING A MECHANICAL MALFUNCTION. AT NO TIME WAS THERE ANY C/A. WE WERE SWITCHED TO APCH CTL AND THEY GAVE US AN ALTIMETER SETTING OF 29.19. I IMMEDIATELY REALIZED THE PROB AND GOT TO MY CORRECT ALT AND ALTIMETER SETTING. I DISCUSSED WHAT HAPPENED WITH THE F/O; WE HAD LET DOWN FROM FLT LEVELS TO 13000', NECESSITATING AN ALTIMETER CHANGE FROM 29.92. THE F/O WAS IN THE HABIT OF REPEATING BACK ONLY THE LAST 2 DIGITS OF THE ALTIMETER SETTING (IE, .24). I DIDN'T CATCH THE MISTAKE AS HE DIALED IN THE WRONG ALTIMETER SETTING OF 30.24 INSTEAD OF 29.24 IN THE ALT ALERTING SYS. THIS IS WHAT I THEN USED TO DIAL MY ALTIMETER AS I DSNDED BELOW FL180. THE F/O PROMISED THAT HE WOULD, FROM NOW ON, REPEAT BACK ALL 4 DIGITS OF THE ALTIMETER SETTING TO GUARD AGAINST FURTHER MISHAPS. SUPPLEMENTAL INFO FROM ACN 129263: NO TIME DURING THE DISCUSSION WAS THE ALTIMETER SETTING QUESTIONED. APPROX 1 MIN LATER, ANOTHER ACFT CHKED ON THE FREQ. WHEN THE CTLR GAVE THE ALTIMETER SETTING OF 29.24, THE CAPT AND I REALIZED WE HAD THE WRONG SETTING.

Data retrieved from NASA's ASRS site as of August 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.