Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Conflict Airborne Conflict; Deviation - Track / Heading All Types
Flight Crew Took Evasive Action
Human Factors
Descending to 9;000 feet on the BUNTS3 Arrival into PHL a target appeared on our MFD with no corresponding altitude. We began to look for the traffic and then received a TA alert from the TCAS and then spotted the target at our 12'oclock position within 3 miles. I then turned off the autopilot and turned at about 30-35 degrees bank to avoid colliding with the aircraft. The Captain called ATC and advised them we were maneuvering to avoid colliding with the traffic. After we were clear of the traffic we requested to direct BUNTS to return to the arrival. After we returned to course we asked ATC about the traffic and they said they didn't have a Mode C transponder and didn't think they were above 3;000 feet.Always be vigilant for traffic regardless if ATC advises you of them or not. Be especially vigilant if the traffic target does not have an altitude shown.
We were in VMC conditions and descending to cross BUNTS at 8;000. The TCAS showed a primary target a few miles ahead of us. We heard the 'traffic' call by the TCAS. We both started scanning even more in the 10-1 o'clock position that TCAS showed the traffic. I didn't have time to ask ATC; when I spotted the traffic at 12 o'clock and less than 3 miles; we were closing in fast (IAS was 250 knots). I called out 'traffic 12 o'clock' to the First Officer who was flying. He confirmed he saw it and immediately turned off Autopilot and made a sharp bank right to avoid the plane. As we turned right to overtake the plane; we passed about less than a 1/2 mile and passed through the same altitude (I could make out that it was a Piper Cherokee type plane with fixed gear). In the turn we notified ATC that we were deviating off course to avoid traffic at 9;500 ft traveling in a NE direction. ATC stated that he wasn't aware of any traffic in that area above 3;000 ft. We were cleared direct BUNTS by ATC after a lateral deviation of a few miles and continued to PHL uneventfully after avoiding and passing the traffic.
CL65 flight crew reported taking evasive action to avoid a collision with a light aircraft on arrival into PHL. Reporter stated the conflict aircraft had no altitude readout on the TCAS.