Gulfstream IV / G350 / G450
Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Total 2200; Flight Crew Type 600
Situational Awareness
Conflict NMAC
Flight Crew Took Evasive Action
Aircraft
During our ILS approach to Runway 19 at TEB we had an immediate RA. There was never any TA prior to the RA. We were instructed to proceed direct UNVIL and to maintain 2000 ft until established on the LOC; and we were cleared for the ILS 19 into TEB. We were at 2000 ft; established on green needles; waiting for the glideslope to come in. All of a sudden; the RA announced descend; descend now and commanded a descent on the PFD (Primary Flight Display). I immediately turned the autopilot off and followed the RA. We descended approximately 300 ft and stayed there until clear of conflict announced. By then; the glideslope was coming alive and we continued on the approach. We notified Tower; and they asked a few questions both in the air and on the ground. They informed us that the traffic on their radar was showing 2500 ft. When the RA went off; it showed them at 200 ft above us. In the end; everyone was safe and no further action transpired. There was never a TA advising 'Traffic; Traffic' before the RA commanded a descent. This is a prime example of how even in VFR conditions; it is imperative to keep a sharp lookout.
GIV First Officer reported not receiving a TA but an RA and descending to clear the RA.