Minor altitude overshoot arriving at iad, va. Altimetry was part of the problem.

Attributes
ACN	490810
Time
Date	200011
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : iad.tracon
State Reference	VA
Altitude	msl bound lower : 5800 msl bound upper : 6000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : iad.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 star : ns
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : cfi pilot : atp
Experience	flight time last 90 days : 190 flight time total : 14000 flight time type : 1700
ASRS Report	490180
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : overshoot non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	controller : issued advisory flight crew : returned to original clearance flight crew : returned to assigned altitude
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Copilot was flying and we were in a descent to 6000 ft MSL. As we approached 6000 ft I called 'there's our altitude' and noticed the copilot's altimeters was reading 100 ft higher than mine (130 ft is allowable according to the DC9 limitations). The copilot leveled the airplane using the autoplt and overshot (on my altimeter) 6000 ft by 200 ft, then he promptly began to climb back to 6000 ft on my altimeter. While he was climbing, approach control asked us if we were level at 6000 ft and stated the current altimeter setting. I replied that we were level at 6000 ft. No conflict with other traffic occurred.

Original NASA ASRS Text

Title: MINOR ALT OVERSHOOT ARRIVING AT IAD, VA. ALTIMETRY WAS PART OF THE PROB.

Narrative: COPLT WAS FLYING AND WE WERE IN A DSCNT TO 6000 FT MSL. AS WE APCHED 6000 FT I CALLED 'THERE'S OUR ALT' AND NOTICED THE COPLT'S ALTIMETERS WAS READING 100 FT HIGHER THAN MINE (130 FT IS ALLOWABLE ACCORDING TO THE DC9 LIMITATIONS). THE COPLT LEVELED THE AIRPLANE USING THE AUTOPLT AND OVERSHOT (ON MY ALTIMETER) 6000 FT BY 200 FT, THEN HE PROMPTLY BEGAN TO CLB BACK TO 6000 FT ON MY ALTIMETER. WHILE HE WAS CLBING, APCH CTL ASKED US IF WE WERE LEVEL AT 6000 FT AND STATED THE CURRENT ALTIMETER SETTING. I REPLIED THAT WE WERE LEVEL AT 6000 FT. NO CONFLICT WITH OTHER TFC OCCURRED.

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.