BH206 had an erroneous ATC radar altitude readout.

Attributes
ACN	488650
Time
Date	200010
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : msy.airport
State Reference	LA
Altitude	msl bound lower : 800 msl bound upper : 1500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : msy.tower
Operator	common carrier : air carrier
Make Model Name	Jet Ranger/Kiowa/206
Operating Under FAR Part	Part 135
Navigation In Use	other
Flight Phase	cruise : level descent : approach
Route In Use	approach : visual
Flight Plan	VFR
Person 1
Affiliation	company : air carrier
Function	flight crew : single pilot
Qualification	pilot : multi engine pilot : cfi pilot : atp pilot : instrument pilot : commercial
Experience	flight time last 90 days : 20 flight time total : 4000 flight time type : 50
ASRS Report	488650
Person 2
Affiliation	government : faa
Function	controller : local
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : less severe other anomaly other
Independent Detector	atc equipment other atc equipment : radar other controllera
Resolutory Action	controller : issued advisory controller : issued new clearance
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

I was flying under the floor of the class B airspace using one of our company's discrete transponder codes and operating with mode C. After landing and then departing from a nearby heliport, I contacted ATC to inform them of my intentions to land at the primary airport within class B airspace. ATC gave me a new squawk code, granted me a clearance to enter the class B airspace and noted a discrepancy between my actual altitude and what my encoder was indicating (the encoder was indicating approximately 600-700 ft higher than my actual altitude). ATC instructed me to 'stop altitude squawk' which I did. They did not seem to be overly troubled/upset with my erroneous encoder but I worry that it may have caused some concern regarding apparent airspace violations and for some overflying aircraft prior to it being noticed by ATC. Having some type of cockpit display of encoder altitude or by having ATC do an 'encoder check' on a periodic basis (ie, more often than the 24 month far 91.411 and 91.413 checks) may have helped in discovering the encoder error prior to me getting near the class B airspace.

Original NASA ASRS Text

Title: BH206 HAD AN ERRONEOUS ATC RADAR ALT READOUT.

Narrative: I WAS FLYING UNDER THE FLOOR OF THE CLASS B AIRSPACE USING ONE OF OUR COMPANY'S DISCRETE XPONDER CODES AND OPERATING WITH MODE C. AFTER LNDG AND THEN DEPARTING FROM A NEARBY HELIPORT, I CONTACTED ATC TO INFORM THEM OF MY INTENTIONS TO LAND AT THE PRIMARY ARPT WITHIN CLASS B AIRSPACE. ATC GAVE ME A NEW SQUAWK CODE, GRANTED ME A CLRNC TO ENTER THE CLASS B AIRSPACE AND NOTED A DISCREPANCY BTWN MY ACTUAL ALT AND WHAT MY ENCODER WAS INDICATING (THE ENCODER WAS INDICATING APPROX 600-700 FT HIGHER THAN MY ACTUAL ALT). ATC INSTRUCTED ME TO 'STOP ALT SQUAWK' WHICH I DID. THEY DID NOT SEEM TO BE OVERLY TROUBLED/UPSET WITH MY ERRONEOUS ENCODER BUT I WORRY THAT IT MAY HAVE CAUSED SOME CONCERN REGARDING APPARENT AIRSPACE VIOLATIONS AND FOR SOME OVERFLYING ACFT PRIOR TO IT BEING NOTICED BY ATC. HAVING SOME TYPE OF COCKPIT DISPLAY OF ENCODER ALT OR BY HAVING ATC DO AN 'ENCODER CHK' ON A PERIODIC BASIS (IE, MORE OFTEN THAN THE 24 MONTH FAR 91.411 AND 91.413 CHKS) MAY HAVE HELPED IN DISCOVERING THE ENCODER ERROR PRIOR TO ME GETTING NEAR THE CLASS B AIRSPACE.

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.