MD80 and a bizjet had less than comfortable separation in phl class east airspace.

Attributes
ACN	552480
Time
Date	200207
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : phl.tracon
State Reference	PA
Altitude	msl single value : 15000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : phl.tracon artcc : zdv.artcc
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : approach
Route In Use	arrival star : dupont
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : phl.tracon
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	552480
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	conflict : airborne critical other anomaly other
Independent Detector	aircraft equipment : tcas other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance flight crew : took evasive action none taken : detected after the fact other
Consequence	other
Miss Distance	horizontal : 0 vertical : 500
Supplementary
Problem Areas	Flight Crew Human Performance FAA Airspace Structure ATC Human Performance
Primary Problem	Ambiguous

Narrative:

TCASII RA. We were on the dupont arrival to phl at 15000 ft when TCASII traffic alert popped up at our 12 O'clock position at 10 mi. It was at our altitude. At 5 mi, we had an RA to descend. It passed overhead at approximately 1000 ft. ATC issued a descent clearance to 10000 ft about the same time that we started our descent, so I don't believe that an altitude deviation was a problem. We told ATC of the RA, but I did not use the terminology of an near midair collision. He stated that he had previous traffic in that area that popped up intermittently at 15500 ft and that now it showed behind us a that altitude. We believed that the aircraft was a small bizjet at 15000 ft and that we would have had a collision with it had we not responded to the RA. The first officer saw the aircraft out of his eyebrow window. He was also PF and responded immediately to the RA.

Original NASA ASRS Text

Title: MD80 AND A BIZJET HAD LESS THAN COMFORTABLE SEPARATION IN PHL CLASS E AIRSPACE.

Narrative: TCASII RA. WE WERE ON THE DUPONT ARR TO PHL AT 15000 FT WHEN TCASII TFC ALERT POPPED UP AT OUR 12 O'CLOCK POS AT 10 MI. IT WAS AT OUR ALT. AT 5 MI, WE HAD AN RA TO DSND. IT PASSED OVERHEAD AT APPROX 1000 FT. ATC ISSUED A DSCNT CLRNC TO 10000 FT ABOUT THE SAME TIME THAT WE STARTED OUR DSCNT, SO I DON'T BELIEVE THAT AN ALTDEV WAS A PROB. WE TOLD ATC OF THE RA, BUT I DID NOT USE THE TERMINOLOGY OF AN NMAC. HE STATED THAT HE HAD PREVIOUS TFC IN THAT AREA THAT POPPED UP INTERMITTENTLY AT 15500 FT AND THAT NOW IT SHOWED BEHIND US A THAT ALT. WE BELIEVED THAT THE ACFT WAS A SMALL BIZJET AT 15000 FT AND THAT WE WOULD HAVE HAD A COLLISION WITH IT HAD WE NOT RESPONDED TO THE RA. THE FO SAW THE ACFT OUT OF HIS EYEBROW WINDOW. HE WAS ALSO PF AND RESPONDED IMMEDIATELY TO THE RA.

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.