Reporter alleges many mode C problems since the 30 NM veil went into effect.

Attributes
ACN	124087
Time
Date	198908
Place
Locale Reference	atc facility : dtw
State Reference	MI
Altitude	msl bound lower : 3000 msl bound upper : 11000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : dtw tracon : ont
Operator	general aviation : instructional
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Fixed Gear
Flight Phase	climbout : takeoff cruise other descent : approach
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : commercial pilot : cfi pilot : instrument
Experience	flight time total : 5200
ASRS Report	124087
Person 2
Affiliation	government : faa
Function	controller : departure
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude
Independent Detector	other controllera other flight crewa
Resolutory Action	none taken : anomaly accepted
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

My first 2 months operating experience and problems with current mode C equipment. Since the inception of mode C requirements within 30 NM of dtw, I have given instrument dual instruction or have flown several different aircraft that were reporting the wrong altitude to ATC. In some cases we were informed that we were 300' off even though we had the correct altimeter setting and our altimeter had checked out ok on the ground before and after the flight. Some of the equipment had recently been installed, and all equipment had recently been calibrated and certified per far 91. The calibrations and installations were not done all at the same shop. From this experience I must conclude that the current mode C equipment is not capable of remaining within tolerances for very long, or the calibrating equipment isn't very accurate. There should be some means besides calling ATC for the pilot to determine whether the transponder is reporting correct information.

Original NASA ASRS Text

Title: REPORTER ALLEGES MANY MODE C PROBLEMS SINCE THE 30 NM VEIL WENT INTO EFFECT.

Narrative: MY FIRST 2 MONTHS OPERATING EXPERIENCE AND PROBLEMS WITH CURRENT MODE C EQUIPMENT. SINCE THE INCEPTION OF MODE C REQUIREMENTS WITHIN 30 NM OF DTW, I HAVE GIVEN INSTRUMENT DUAL INSTRUCTION OR HAVE FLOWN SEVERAL DIFFERENT ACFT THAT WERE REPORTING THE WRONG ALT TO ATC. IN SOME CASES WE WERE INFORMED THAT WE WERE 300' OFF EVEN THOUGH WE HAD THE CORRECT ALTIMETER SETTING AND OUR ALTIMETER HAD CHECKED OUT OK ON THE GND BEFORE AND AFTER THE FLT. SOME OF THE EQUIPMENT HAD RECENTLY BEEN INSTALLED, AND ALL EQUIPMENT HAD RECENTLY BEEN CALIBRATED AND CERTIFIED PER FAR 91. THE CALIBRATIONS AND INSTALLATIONS WERE NOT DONE ALL AT THE SAME SHOP. FROM THIS EXPERIENCE I MUST CONCLUDE THAT THE CURRENT MODE C EQUIPMENT IS NOT CAPABLE OF REMAINING WITHIN TOLERANCES FOR VERY LONG, OR THE CALIBRATING EQUIPMENT ISN'T VERY ACCURATE. THERE SHOULD BE SOME MEANS BESIDES CALLING ATC FOR THE PLT TO DETERMINE WHETHER THE TRANSPONDER IS REPORTING CORRECT INFO.

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.