Air carrier has traffic in sight but follows TCASII RA to climb.

Attributes
ACN	249943
Time
Date	199308
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : phl
State Reference	PA
Altitude	msl bound lower : 5500 msl bound upper : 6300
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : phl tracon : grr
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	descent other
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	descent other
Flight Plan	VFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 100 flight time total : 19800 flight time type : 95
ASRS Report	249943
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 6000 vertical : 600
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were in phl approach control airspace in descent from 6000 ft. We had visual contact with VFR traffic which was also descending. The TCASII recognized the traffic, then issued a TA, then an RA. We followed TCASII in a 'climb' and stopped climb at 6300 ft. After advising ATC of RA, they questioned 'why.' we responded that we followed RA because of traffic. Apparently, traffic changed rate of descent. Visually, it had appeared that there would be no conflict.

Original NASA ASRS Text

Title: ACR HAS TFC IN SIGHT BUT FOLLOWS TCASII RA TO CLB.

Narrative: WE WERE IN PHL APCH CTL AIRSPACE IN DSCNT FROM 6000 FT. WE HAD VISUAL CONTACT WITH VFR TFC WHICH WAS ALSO DSNDING. THE TCASII RECOGNIZED THE TFC, THEN ISSUED A TA, THEN AN RA. WE FOLLOWED TCASII IN A 'CLB' AND STOPPED CLB AT 6300 FT. AFTER ADVISING ATC OF RA, THEY QUESTIONED 'WHY.' WE RESPONDED THAT WE FOLLOWED RA BECAUSE OF TFC. APPARENTLY, TFC CHANGED RATE OF DSCNT. VISUALLY, IT HAD APPEARED THAT THERE WOULD BE NO CONFLICT.

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.