Narrative:

When cleared for the visual approach to [runway] 4R in ewr at 3;000 ft on the way to intercept final; multiple targets started to paint on our TCAS between our 9 to 12 o'clock 500 ft to 1;000 ft below our altitude. Since the captain was flying and I was monitoring I started to look for those aircraft (usually low altitude helicopters). At first I spotted a drone; small in size dark gray and very shiny flying south southwest opposite to our direction of flight; and it coincided with the direction and altitude of one of the targets on the TCAS. Shortly after I spotted two more of these drones around the same altitude flying also south southwest and they were no factor but I still pointed them out to the captain. I felt the need to report it to tower; like I would if I saw a flock of birds; so the aircraft approaching behind [could] exercise caution while during their approach. Once upon landing I was given a phone number to explain the shift ATC supervisor what I saw. The question was raised by several people about why a device like a drone would paint on the TCAS as they would also have to have a transponder. I fully understand the operation and capabilities of the TCAS-transponder relationship; so my only conclusion is that those drones had an operating transponder onboard. After landing during the debrief with my captain; he says he only saw a 'balloon' and he would leave the phone call to ATC to me. The aircraft was never compromised; we didn't have to take evasive action and there was never an undesired aircraft state.

Related reports:

Google
 

Original NASA ASRS Text

Title: An air carrier First Officer on approach to EWR Runway 4R at 3;000 FT reported what appeared to be drones 500 FT to 1;000 FT below his aircraft's altitude at locations which coincided with TCAS targets.

Narrative: When cleared for the visual approach to [Runway] 4R in EWR at 3;000 FT on the way to intercept final; multiple targets started to paint on our TCAS between our 9 to 12 o'clock 500 FT to 1;000 FT below our altitude. Since the Captain was flying and I was monitoring I started to look for those aircraft (usually low altitude helicopters). At first I spotted a drone; small in size dark gray and very shiny flying south southwest opposite to our direction of flight; and it coincided with the direction and altitude of one of the targets on the TCAS. Shortly after I spotted two more of these drones around the same altitude flying also south southwest and they were no factor but I still pointed them out to the Captain. I felt the need to report it to Tower; like I would if I saw a flock of birds; so the aircraft approaching behind [could] exercise caution while during their approach. Once upon landing I was given a phone number to explain the shift ATC supervisor what I saw. The question was raised by several people about why a device like a drone would paint on the TCAS as they would also have to have a transponder. I fully understand the operation and capabilities of the TCAS-transponder relationship; so my only conclusion is that those drones had an operating transponder onboard. After landing during the debrief with my Captain; he says he only saw a 'balloon' and he would leave the phone call to ATC to me. The aircraft was never compromised; we didn't have to take evasive action and there was never an undesired aircraft state.

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.