Altitude deviation.

Attributes
ACN	295620
Time
Date	199502
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : clt
State Reference	NC
Altitude	msl bound lower : 11000 msl bound upper : 12000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other descent other
Route In Use	arrival star : star enroute airway : ztl
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 17000 flight time type : 1500
ASRS Report	295620
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 250 flight time total : 15000 flight time type : 4000
ASRS Report	295629
Events
Anomaly	altitude deviation : undershoot altitude deviation : crossing restriction not met non adherence : clearance other anomaly other
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	flight crew : overcame equipment problem flight crew : became reoriented
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

This altitude deviation occurred on a flight from gso-clt in a 737-300 aircraft. After leveling at 11000 ft outside of magic intersection on the magic STAR arrival to clt, ZTL said to descend and maintain 11000 ft. We replied that we were level at 11000 ft. ZTL did not say anything further to us for about a min then again said to descend and maintain 11000 ft. We again looked at both altimeters and the altitude alerter window and replied that we were level 11000 ft. They said they showed us level at 12000 ft and pointed out traffic at 13000 ft at a range and direction I don't remember and then went on to communication with other aircraft. I thought there might be a malfunction with the transponder or the encoding altimeter. About that time, we discovered that the altimeters were set to 28.88 instead of the proper setting of 29.88. We quickly descended to 11000 ft and told ZTL that we were level at 11000 ft and had switched xponders, which we had. They verified that they showed us level at 11000 ft and no further comments about the altitude discrepancy were made. The aircraft we were flying had been in maintenance the night before and for what reason I don't know, the maintenance personnel had dialed the altimeters on both sides of the aircraft back to a sea level setting when the field elevation at gso is approximately 1000 ft MSL. We accomplished all checklists on the preflight but failed to notice that the second digit of the altimeter had been set to an 8 instead of a 9. This is something that is easy to miss, as I have never seen a 28 anything altimeter setting. I think it would not be a bad idea to have the second digit 8 and the 1 colored a different color to preclude this type of mistake happening again. When airborne we still had a hard time picking out the error because the 28 and 29 altimeter setting look so close and you never see a setting in the 28 range. Supplemental information from acn 285629: approach control advised us to descend to 11000 ft indicated 11000 ft. Approach responded we needed to descend to 11000 ft they showed us at 12000 and gave us altimeter setting 29.98. Checked ours, was set at 28.88.

Original NASA ASRS Text

Title: ALTDEV.

Narrative: THIS ALTDEV OCCURRED ON A FLT FROM GSO-CLT IN A 737-300 ACFT. AFTER LEVELING AT 11000 FT OUTSIDE OF MAGIC INTXN ON THE MAGIC STAR ARR TO CLT, ZTL SAID TO DSND AND MAINTAIN 11000 FT. WE REPLIED THAT WE WERE LEVEL AT 11000 FT. ZTL DID NOT SAY ANYTHING FURTHER TO US FOR ABOUT A MIN THEN AGAIN SAID TO DSND AND MAINTAIN 11000 FT. WE AGAIN LOOKED AT BOTH ALTIMETERS AND THE ALT ALERTER WINDOW AND REPLIED THAT WE WERE LEVEL 11000 FT. THEY SAID THEY SHOWED US LEVEL AT 12000 FT AND POINTED OUT TFC AT 13000 FT AT A RANGE AND DIRECTION I DON'T REMEMBER AND THEN WENT ON TO COM WITH OTHER ACFT. I THOUGHT THERE MIGHT BE A MALFUNCTION WITH THE XPONDER OR THE ENCODING ALTIMETER. ABOUT THAT TIME, WE DISCOVERED THAT THE ALTIMETERS WERE SET TO 28.88 INSTEAD OF THE PROPER SETTING OF 29.88. WE QUICKLY DSNDED TO 11000 FT AND TOLD ZTL THAT WE WERE LEVEL AT 11000 FT AND HAD SWITCHED XPONDERS, WHICH WE HAD. THEY VERIFIED THAT THEY SHOWED US LEVEL AT 11000 FT AND NO FURTHER COMMENTS ABOUT THE ALT DISCREPANCY WERE MADE. THE ACFT WE WERE FLYING HAD BEEN IN MAINT THE NIGHT BEFORE AND FOR WHAT REASON I DON'T KNOW, THE MAINT PERSONNEL HAD DIALED THE ALTIMETERS ON BOTH SIDES OF THE ACFT BACK TO A SEA LEVEL SETTING WHEN THE FIELD ELEVATION AT GSO IS APPROX 1000 FT MSL. WE ACCOMPLISHED ALL CHKLISTS ON THE PREFLT BUT FAILED TO NOTICE THAT THE SECOND DIGIT OF THE ALTIMETER HAD BEEN SET TO AN 8 INSTEAD OF A 9. THIS IS SOMETHING THAT IS EASY TO MISS, AS I HAVE NEVER SEEN A 28 ANYTHING ALTIMETER SETTING. I THINK IT WOULD NOT BE A BAD IDEA TO HAVE THE SECOND DIGIT 8 AND THE 1 COLORED A DIFFERENT COLOR TO PRECLUDE THIS TYPE OF MISTAKE HAPPENING AGAIN. WHEN AIRBORNE WE STILL HAD A HARD TIME PICKING OUT THE ERROR BECAUSE THE 28 AND 29 ALTIMETER SETTING LOOK SO CLOSE AND YOU NEVER SEE A SETTING IN THE 28 RANGE. SUPPLEMENTAL INFO FROM ACN 285629: APCH CTL ADVISED US TO DSND TO 11000 FT INDICATED 11000 FT. APCH RESPONDED WE NEEDED TO DSND TO 11000 FT THEY SHOWED US AT 12000 AND GAVE US ALTIMETER SETTING 29.98. CHKED OURS, WAS SET AT 28.88.

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.