Disparity between aircraft altimeter reading and TRACON's altitude readout caused pilot to discover that barometric gears had apparently failed in his altimeter.

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Attributes
ACN	117534
Time
Date	198907
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : fmy
State Reference	FL
Altitude	msl bound lower : 8500 msl bound upper : 8500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : fmy
Operator	general aviation : personal
Make Model Name	Small Aircraft, Low Wing, 2 Eng, Retractable Gear
Flight Phase	cruise other
Flight Plan	VFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : commercial
Experience	flight time last 90 days : 25 flight time total : 2100 flight time type : 150
ASRS Report	117534
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

En route from kissimmee, fl to key west, fl on VFR flight plan. North of ft myers indicating 8500' contacted ft myers approach for flight through their area. Noted that their 'calls' of my altitude differed from my indicated altitude. Monitored ATIS to confirm altimeter setting. When checking the barometric setting on altimeter I noticed the barometer window would move without any change of indicated altitude. By pushing in on the set knob I could make both the hands and barometer window work properly. I adjusted my cruise altitude up by the difference noted and then reset altimeter hands to the altitude called by approach. No incident resulted but situation could have been much worse if the altimeter had been used in an approach or IFR situation. In july of 1989 the altimeter was checked and did not fall under a malfunction or defect report. FAA form (8010-4) has been filed on this altimeter.

Original NASA ASRS Text

Title: DISPARITY BETWEEN ACFT ALTIMETER READING AND TRACON'S ALT READOUT CAUSED PLT TO DISCOVER THAT BAROMETRIC GEARS HAD APPARENTLY FAILED IN HIS ALTIMETER.

Narrative: ENRTE FROM KISSIMMEE, FL TO KEY WEST, FL ON VFR FLT PLAN. NORTH OF FT MYERS INDICATING 8500' CONTACTED FT MYERS APCH FOR FLT THROUGH THEIR AREA. NOTED THAT THEIR 'CALLS' OF MY ALT DIFFERED FROM MY INDICATED ALT. MONITORED ATIS TO CONFIRM ALTIMETER SETTING. WHEN CHECKING THE BAROMETRIC SETTING ON ALTIMETER I NOTICED THE BAROMETER WINDOW WOULD MOVE WITHOUT ANY CHANGE OF INDICATED ALT. BY PUSHING IN ON THE SET KNOB I COULD MAKE BOTH THE HANDS AND BAROMETER WINDOW WORK PROPERLY. I ADJUSTED MY CRUISE ALT UP BY THE DIFFERENCE NOTED AND THEN RESET ALTIMETER HANDS TO THE ALT CALLED BY APCH. NO INCIDENT RESULTED BUT SITUATION COULD HAVE BEEN MUCH WORSE IF THE ALTIMETER HAD BEEN USED IN AN APCH OR IFR SITUATION. IN JULY OF 1989 THE ALTIMETER WAS CHECKED AND DID NOT FALL UNDER A MALFUNCTION OR DEFECT REPORT. FAA FORM (8010-4) HAS BEEN FILED ON THIS ALTIMETER.

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.