Air carrier medium large transport has near midair collision with unk turboprop aircraft.

Attributes
ACN	88420
Time
Date	198806
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : cew
State Reference	FL
Altitude	msl bound lower : 24000 msl bound upper : 24000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute airway : j2
Flight Plan	IFR
Aircraft 2
Operator	other
Make Model Name	Experimental
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 7000 flight time type : 250
ASRS Report	88420
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	conflict : nmac non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	none taken : unable
Consequence	faa : investigated
Miss Distance	horizontal : 0 vertical : 50
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

First officer and myself experienced what we believe was a near miss with an unk aircraft while level at an assigned cruise altitude of FL240. When this incident occurred we were established on J2 approximately 75 NM east of the crestview VOR, after having just descended from FL260. At the moment of occurrence, the first officer and myself heard the unmistakable noise of a passing turboprop aircraft at an extreme close proximity to our aircraft. The first officer at that instant saw a shadow passing from left to right immediately above us. The actual aircraft was not sighted. However, we were both convinced that what passed over us was another aircraft at nearly our altitude. With this in mind we filed a near collision report with the pensacola FAA. The only ATC known aircraft in our vicinity was a military spc, assigned an altitude of 27000'. The FAA is investigating the incident.

Original NASA ASRS Text

Title: ACR MLG HAS NMAC WITH UNK TURBOPROP ACFT.

Narrative: F/O AND MYSELF EXPERIENCED WHAT WE BELIEVE WAS A NEAR MISS WITH AN UNK ACFT WHILE LEVEL AT AN ASSIGNED CRUISE ALT OF FL240. WHEN THIS INCIDENT OCCURRED WE WERE ESTABLISHED ON J2 APPROX 75 NM E OF THE CRESTVIEW VOR, AFTER HAVING JUST DSNDED FROM FL260. AT THE MOMENT OF OCCURRENCE, THE F/O AND MYSELF HEARD THE UNMISTAKABLE NOISE OF A PASSING TURBOPROP ACFT AT AN EXTREME CLOSE PROX TO OUR ACFT. THE F/O AT THAT INSTANT SAW A SHADOW PASSING FROM LEFT TO RIGHT IMMEDIATELY ABOVE US. THE ACTUAL ACFT WAS NOT SIGHTED. HOWEVER, WE WERE BOTH CONVINCED THAT WHAT PASSED OVER US WAS ANOTHER ACFT AT NEARLY OUR ALT. WITH THIS IN MIND WE FILED A NEAR COLLISION RPT WITH THE PENSACOLA FAA. THE ONLY ATC KNOWN ACFT IN OUR VICINITY WAS A MIL SPC, ASSIGNED AN ALT OF 27000'. THE FAA IS INVESTIGATING THE INCIDENT.

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.