<< >> NASA ASRS Report 525309, September 2001

A GA aircraft from a flying club has a mode C altitude readout problem with several ATC facilities while using a handheld GPS near cgt, il.

Attributes
ACN	525309
Time
Date	200109
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : cgt.vortac
State Reference	IL
Altitude	msl bound lower : 5000 msl bound upper : 6500
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : c90.tracon
Operator	general aviation : personal
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Fixed Gear
Operating Under FAR Part	Part 91
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : instrument
Experience	flight time last 90 days : 22.3 flight time total : 2989 flight time type : 45.5
ASRS Report	525309
Person 2
Affiliation	government : faa
Function	controller : departure
Events
Anomaly	aircraft equipment problem : less severe non adherence : far non adherence : published procedure other anomaly other
Independent Detector	atc equipment other atc equipment : radar other controllera
Resolutory Action	controller : issued advisory flight crew : overcame equipment problem other
Consequence	faa : reviewed incident with flight crew other other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

On the evening of sep/fri/01, grissom approach reported mode C was reading 400 ft low (while level at 4000 ft mode C showed 3600 ft). This occurred just mins after turning on the heater for the first time this season. Route of flight was mao-mie-cgt-mdw. On the evening of sep/sat/01, we departed mdw assuming that mode C would be accurate if we left the heater off. This was after review of the club squawk book and seems no prior mode C errors. Ord departure reported mode C indicated 6500 ft, while I was level at 5000 ft. They asked if I had prior mode C problems. I replied yes, but thought the problem was resolved. Cycling power did not help. Flight continued without mode C. Near sbu VOR, I turned off a handheld GPS I was using to back up the vors and asked ind approach to verify mode C. While level at 5050 ft they indicated 5100 ft. The mode C error appears to be caused by the GPS. Steps to prevent future mode C errors: 1) alerted the next member to use the plane what happened. 2) alerted club planning officer. He said the avionics shop will take a look. 3) logged error in the club squawk book. Flight continued on to hao without further mode C errors while leaving GPS off. Also note on sep/fri/01 cvg and day approach did not indicate any errors.

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Original NASA ASRS Text

Title: A GA ACFT FROM A FLYING CLUB HAS A MODE C ALT READOUT PROB WITH SEVERAL ATC FACILITIES WHILE USING A HANDHELD GPS NEAR CGT, IL.

Narrative: ON THE EVENING OF SEP/FRI/01, GRISSOM APCH RPTED MODE C WAS READING 400 FT LOW (WHILE LEVEL AT 4000 FT MODE C SHOWED 3600 FT). THIS OCCURRED JUST MINS AFTER TURNING ON THE HEATER FOR THE FIRST TIME THIS SEASON. RTE OF FLT WAS MAO-MIE-CGT-MDW. ON THE EVENING OF SEP/SAT/01, WE DEPARTED MDW ASSUMING THAT MODE C WOULD BE ACCURATE IF WE LEFT THE HEATER OFF. THIS WAS AFTER REVIEW OF THE CLUB SQUAWK BOOK AND SEEMS NO PRIOR MODE C ERRORS. ORD DEP RPTED MODE C INDICATED 6500 FT, WHILE I WAS LEVEL AT 5000 FT. THEY ASKED IF I HAD PRIOR MODE C PROBS. I REPLIED YES, BUT THOUGHT THE PROB WAS RESOLVED. CYCLING PWR DID NOT HELP. FLT CONTINUED WITHOUT MODE C. NEAR SBU VOR, I TURNED OFF A HANDHELD GPS I WAS USING TO BACK UP THE VORS AND ASKED IND APCH TO VERIFY MODE C. WHILE LEVEL AT 5050 FT THEY INDICATED 5100 FT. THE MODE C ERROR APPEARS TO BE CAUSED BY THE GPS. STEPS TO PREVENT FUTURE MODE C ERRORS: 1) ALERTED THE NEXT MEMBER TO USE THE PLANE WHAT HAPPENED. 2) ALERTED CLUB PLANNING OFFICER. HE SAID THE AVIONICS SHOP WILL TAKE A LOOK. 3) LOGGED ERROR IN THE CLUB SQUAWK BOOK. FLT CONTINUED ON TO HAO WITHOUT FURTHER MODE C ERRORS WHILE LEAVING GPS OFF. ALSO NOTE ON SEP/FRI/01 CVG AND DAY APCH DID NOT INDICATE ANY ERRORS.

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.