Less than standard separation between GA twin and another IFR aircraft.

Attributes
ACN	100329
Time
Date	198812
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : grv
State Reference	MD
Altitude	msl bound lower : 18500 msl bound upper : 19000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc tower : ord
Make Model Name	Small Transport, Low Wing, 2 Turboprop Eng
Flight Phase	climbout : intermediate altitude cruise other
Route In Use	enroute airway : zdc
Flight Plan	IFR
Aircraft 2
Operator	general aviation : corporate
Make Model Name	Small Transport, Low Wing, 2 Recip Eng
Flight Phase	climbout : intermediate altitude cruise other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 18
ASRS Report	100329
Person 2
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : required legal separation
Independent Detector	other other : unspecified atc
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	faa : investigated
Miss Distance	horizontal : 28800 vertical : 500
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	Pilot Deviation other

Narrative:

GA aircraft X was assigned FL180. Traffic aircraft Y was called at FL190. Shortly thereafter, altitude readout on X showed FL184. I asked aircraft X to verify at FL180. He said he was climbing to FL190. I told him he did not receive a clearance to climb and to return to his assigned altitude. Pilot clearly deviated from his assigned altitude.

Original NASA ASRS Text

Title: LESS THAN STANDARD SEPARATION BETWEEN GA TWIN AND ANOTHER IFR ACFT.

Narrative: GA ACFT X WAS ASSIGNED FL180. TFC ACFT Y WAS CALLED AT FL190. SHORTLY THEREAFTER, ALT READOUT ON X SHOWED FL184. I ASKED ACFT X TO VERIFY AT FL180. HE SAID HE WAS CLIMBING TO FL190. I TOLD HIM HE DID NOT RECEIVE A CLRNC TO CLIMB AND TO RETURN TO HIS ASSIGNED ALT. PLT CLEARLY DEVIATED FROM HIS ASSIGNED ALT.

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.