An IFR air carrier jet thought that a VFR propeller aircraft was off of his VFR altitude.

Attributes
ACN	242456
Time
Date	199305
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : baf
State Reference	MA
Altitude	msl bound lower : 10000 msl bound upper : 10400
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zbw
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Flight Plan	VFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
ASRS Report	242456
Person 2
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude conflict : airborne less severe other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

VFR traffic (propeller) swbound previously reported level VFR 10500 ft with IFR jet traffic northbound at 10000 ft. Jet traffic and propeller traffic were issued TA's. Propeller traffic reported jet in sight, then jet traffic questioned mode C altitude of propeller. Propeller reported at 10400 ft, then the jet traffic reported that TCASII showed the VFR traffic at 10000 ft and visually he had appeared to be at 10000 ft.

Original NASA ASRS Text

Title: AN IFR ACR JET THOUGHT THAT A VFR PROP ACFT WAS OFF OF HIS VFR ALT.

Narrative: VFR TFC (PROP) SWBOUND PREVIOUSLY RPTED LEVEL VFR 10500 FT WITH IFR JET TFC NBOUND AT 10000 FT. JET TFC AND PROP TFC WERE ISSUED TA'S. PROP TFC RPTED JET IN SIGHT, THEN JET TFC QUESTIONED MODE C ALT OF PROP. PROP RPTED AT 10400 FT, THEN THE JET TFC RPTED THAT TCASII SHOWED THE VFR TFC AT 10000 FT AND VISUALLY HE HAD APPEARED TO BE AT 10000 FT.

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.