Gv first officer experienced a near midair collision with a high wing piper during a turn to final. ...

Narrative:

During a VFR; visual approach to ZZZ airport; we experienced a near mid-air collision with an aircraft that did not show up on our TCAS. After crossing the field at 3000 feet MSL; we entered a left downwind for runway 18 and saw 4 aircraft on TCAS in the area. We stayed at 3000 due to the fact that 1 aircraft was at 2500 feet MSL to the north of the field and another aircraft was at 2000 feet MSL to the east that announced he would be entering a left downwind. After passing the aircraft that was at 2000; we began a descent to 2000. Approximately 6 miles from the airport on a left downwind; I initiated a left turn to base that continued into a left turn to final. While level at 2000 and in a left turn; I looked out of the left cockpit window and saw an aircraft between our wing and fuselage and only slightly below us. The aircraft appeared to be a single engine; cloth covered piper; such as a tri-pacer or cub; that was white with a large blue stripe towards the bottom. I believe that the aircraft was 50 feet below our wing but quite possibly could have been much closer. At no point before or after seeing this aircraft did it ever show up on our TCAS; although several other aircraft were still being displayed at this time. I assume that this aircraft did not have an active transponder. We continued the approach and landed without incident. I spoke with the flight attendant who had been sitting on the left side of the aircraft and she saw the aircraft as well. She said she didn't see the aircraft until it was right next to us and thought we were going to collide.

Original NASA ASRS Text

Title: GV First Officer experienced a NMAC with a high wing Piper during a turn to final. The Piper was not detected in time to take any evasive action and may have passed within 50 feet; both vertically and horizontally.

Narrative: During a VFR; visual approach to ZZZ airport; we experienced a near mid-air collision with an aircraft that did not show up on our TCAS. After crossing the field at 3000 feet MSL; we entered a left downwind for runway 18 and saw 4 aircraft on TCAS in the area. We stayed at 3000 due to the fact that 1 aircraft was at 2500 feet MSL to the north of the field and another aircraft was at 2000 feet MSL to the east that announced he would be entering a left downwind. After passing the aircraft that was at 2000; we began a descent to 2000. Approximately 6 miles from the airport on a left downwind; I initiated a left turn to base that continued into a left turn to final. While level at 2000 and in a left turn; I looked out of the left cockpit window and saw an aircraft between our wing and fuselage and only slightly below us. The aircraft appeared to be a single engine; cloth covered piper; such as a Tri-Pacer or Cub; that was white with a large blue stripe towards the bottom. I believe that the aircraft was 50 feet below our wing but quite possibly could have been much closer. At no point before or after seeing this aircraft did it ever show up on our TCAS; although several other aircraft were still being displayed at this time. I assume that this aircraft did not have an active transponder. We continued the approach and landed without incident. I spoke with the flight attendant who had been sitting on the left side of the aircraft and she saw the aircraft as well. She said she didn't see the aircraft until it was right next to us and thought we were going to collide.

Data retrieved from NASA's ASRS site 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.

Attributes
ACN	1397487
Time
Date	201610
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Gulfstream V / G500 / G550
Operating Under FAR Part	Part 91
Flight Phase	Final Approach
Route In Use	Visual Approach
Flight Plan	IFR
Aircraft 2
Make Model Name	Piper Single Undifferentiated or Other Model
Operating Under FAR Part	Part 91
Person 1
Function	First Officer Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine Flight Crew Instrument
Experience	Flight Crew Last 90 Days 100 Flight Crew Total 5800 Flight Crew Type 600
Events
Anomaly	Conflict NMAC
Miss Distance	Vertical 50

Gv first officer experienced a near midair collision with a high wing piper during a turn to final. The piper was not detected in time to take any evasive action and may have passed within 50 feet; both vertically and horizontally.