ARTCC shows lear jet assigned FL350 to be 800 ft low at 34200 ft.

Attributes
ACN	300161
Time
Date	199503
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : irk
State Reference	MO
Altitude	msl bound lower : 34200 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zkc
Operator	common carrier : air taxi
Make Model Name	Learjet 24
Operating Under FAR Part	Part 91
Flight Phase	climbout : intermediate altitude cruise other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise other cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air taxi
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 7500 flight time type : 3300
ASRS Report	300161
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 2200 flight time type : 900
ASRS Report	300277
Events
Anomaly	aircraft equipment problem : less severe other anomaly other
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	none taken : unable
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

While flying lear jet as captain and my copilot was manipulating the flight controls, we were cleared to descend to FL350 from ZKC. We leveled off at FL350 and center said the altitude encoder read 34200 ft. We verified FL350 and then the readout was 34900 ft. Earlier that day, on several occasions, ATC said we indicated 300 ft lower than our actual altitude was. On this occasion however I watched as an md-80 who was level at FL330 turn to the east from his northeast heading. He must have had a RA and took action, due to our lower readout than our actual altitude. Callback conversation with reporter revealed the following information: the reporter stated the lear was a model 24D. The encoding altitude had been telling the ATC the lear was low on previous occasions. This lear had 2 xponders and both said the same that the lear was low. Checking with avionics experts, the lear may have 2 xponders but only 1 encoding altimeter. The encoding altimeter was probably faulty.

Original NASA ASRS Text

Title: ARTCC SHOWS LEAR JET ASSIGNED FL350 TO BE 800 FT LOW AT 34200 FT.

Narrative: WHILE FLYING LEAR JET AS CAPT AND MY COPLT WAS MANIPULATING THE FLT CTLS, WE WERE CLRED TO DSND TO FL350 FROM ZKC. WE LEVELED OFF AT FL350 AND CTR SAID THE ALT ENCODER READ 34200 FT. WE VERIFIED FL350 AND THEN THE READOUT WAS 34900 FT. EARLIER THAT DAY, ON SEVERAL OCCASIONS, ATC SAID WE INDICATED 300 FT LOWER THAN OUR ACTUAL ALT WAS. ON THIS OCCASION HOWEVER I WATCHED AS AN MD-80 WHO WAS LEVEL AT FL330 TURN TO THE E FROM HIS NE HDG. HE MUST HAVE HAD A RA AND TOOK ACTION, DUE TO OUR LOWER READOUT THAN OUR ACTUAL ALT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE LEAR WAS A MODEL 24D. THE ENCODING ALT HAD BEEN TELLING THE ATC THE LEAR WAS LOW ON PREVIOUS OCCASIONS. THIS LEAR HAD 2 XPONDERS AND BOTH SAID THE SAME THAT THE LEAR WAS LOW. CHKING WITH AVIONICS EXPERTS, THE LEAR MAY HAVE 2 XPONDERS BUT ONLY 1 ENCODING ALTIMETER. THE ENCODING ALTIMETER WAS PROBABLY FAULTY.

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.