Deviation from assigned altitude. Altimeter setting.

Attributes
ACN	192244
Time
Date	199110
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : mdt
State Reference	PA
Altitude	msl bound lower : 6000 msl bound upper : 6500
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : bwi
Operator	general aviation : personal
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Retractable Gear
Flight Phase	cruise other
Route In Use	enroute airway : v12
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : commercial pilot : cfi pilot : instrument
Experience	flight time last 90 days : 35 flight time total : 1400 flight time type : 150
ASRS Report	192244
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	altitude deviation : excursion from assigned altitude
Independent Detector	other other : unspecified cockpit
Resolutory Action	none taken : anomaly accepted other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

While wbound on V12 I was told by the controller to reset the altimeter to the harrisburg setting. I had just come from the east and was set to the philadelphia setting of 29.89. The new setting (30.05) was substantially higher. When I crossed the pressure ridge, the altimeter changed suddenly to about 6250 ft instead of the assigned 6000 ft. The controller called and informed me that my mode C readout was 6500 ft. I immediately descended to 6000 ft. I believe no conflict occurred, but am not sure as I was in IMC. I believe the disparity between my altimeter reading and the mode C was caused by the sudden change as I crossed the pressure ridge. Shortly thereafter I 'broke out' and the flight was completed normally.

Original NASA ASRS Text

Title: DEV FROM ASSIGNED ALT. ALTIMETER SETTING.

Narrative: WHILE WBOUND ON V12 I WAS TOLD BY THE CTLR TO RESET THE ALTIMETER TO THE HARRISBURG SETTING. I HAD JUST COME FROM THE E AND WAS SET TO THE PHILADELPHIA SETTING OF 29.89. THE NEW SETTING (30.05) WAS SUBSTANTIALLY HIGHER. WHEN I CROSSED THE PRESSURE RIDGE, THE ALTIMETER CHANGED SUDDENLY TO ABOUT 6250 FT INSTEAD OF THE ASSIGNED 6000 FT. THE CTLR CALLED AND INFORMED ME THAT MY MODE C READOUT WAS 6500 FT. I IMMEDIATELY DSNDED TO 6000 FT. I BELIEVE NO CONFLICT OCCURRED, BUT AM NOT SURE AS I WAS IN IMC. I BELIEVE THE DISPARITY BTWN MY ALTIMETER READING AND THE MODE C WAS CAUSED BY THE SUDDEN CHANGE AS I CROSSED THE PRESSURE RIDGE. SHORTLY THEREAFTER I 'BROKE OUT' AND THE FLT WAS COMPLETED NORMALLY.

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.