A DC9-30 overshoots its assigned altitude when the PF, a company check captain, has a problem with the altimeter on his (the first officer's) side. C90, il.

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Attributes
ACN	472290
Time
Date	200005
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : ord.airport
State Reference	IL
Altitude	msl bound lower : 8800 msl bound upper : 9000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : c90.tracon
Operator	common carrier : air carrier
Make Model Name	DC-9 30
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude
Route In Use	arrival : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer observation : company check pilot oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 10000 flight time type : 5000
ASRS Report	472290
Person 2
Affiliation	company : air carrier
Function	flight crew : captain
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance
Consequence	other
Supplementary
Problem Areas	Flight Crew Human Performance Environmental Factor Aircraft
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

On radar vectors and descent to ord, approach control cleared us to 9000 ft. It was my leg as PF with a new captain on his first leg of operating experience. We had just received word that we were going to change approachs. The captain was looking for the new chart while I continued the descent. I was descending to what my altimeter indicated was nearing 9000 ft. I looked at the captain's altimeter for the actual leveloff (company procedure) and observed it was already indicating 8800 ft. Just as I was about to climb back up to 9000 ft using his altimeter, approach control cleared us to 7000 ft. I don't know if he saw us descending below 9000 ft and cleared us lower, or if his timing was just what we needed. Nothing further was said by approach control. Subsequent inspection showed the first officer's altimeter was 'sticking/slowing' at the 100 ft mark and was out of limits on descent, but would fall within limits after a short while when level. Maintenance replaced the altimeter.

Original NASA ASRS Text

Title: A DC9-30 OVERSHOOTS ITS ASSIGNED ALT WHEN THE PF, A COMPANY CHK CAPT, HAS A PROB WITH THE ALTIMETER ON HIS (THE FO'S) SIDE. C90, IL.

Narrative: ON RADAR VECTORS AND DSCNT TO ORD, APCH CTL CLRED US TO 9000 FT. IT WAS MY LEG AS PF WITH A NEW CAPT ON HIS FIRST LEG OF OPERATING EXPERIENCE. WE HAD JUST RECEIVED WORD THAT WE WERE GOING TO CHANGE APCHS. THE CAPT WAS LOOKING FOR THE NEW CHART WHILE I CONTINUED THE DSCNT. I WAS DSNDING TO WHAT MY ALTIMETER INDICATED WAS NEARING 9000 FT. I LOOKED AT THE CAPT'S ALTIMETER FOR THE ACTUAL LEVELOFF (COMPANY PROC) AND OBSERVED IT WAS ALREADY INDICATING 8800 FT. JUST AS I WAS ABOUT TO CLB BACK UP TO 9000 FT USING HIS ALTIMETER, APCH CTL CLRED US TO 7000 FT. I DON'T KNOW IF HE SAW US DSNDING BELOW 9000 FT AND CLRED US LOWER, OR IF HIS TIMING WAS JUST WHAT WE NEEDED. NOTHING FURTHER WAS SAID BY APCH CTL. SUBSEQUENT INSPECTION SHOWED THE FO'S ALTIMETER WAS 'STICKING/SLOWING' AT THE 100 FT MARK AND WAS OUT OF LIMITS ON DSCNT, BUT WOULD FALL WITHIN LIMITS AFTER A SHORT WHILE WHEN LEVEL. MAINT REPLACED THE ALTIMETER.

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.