Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 163
Confusion; Distraction; Situational Awareness
Inflight Event / Encounter CFTT / CFIT
General None Reported / Taken
Airspace Structure; Chart Or Publication; Environment - Non Weather Related; Procedure
We were cleared direct to RIZER (the final approach fix for the ILS 24 at ISP) and then cleared for the visual approach.  We descended to 1;400 feet MSL (the glideslope intercept altitude for the ILS).  As we approached RIZER from the southeast (heading about 330 degrees); we began a slight descent to intercept RIZER at the glideslope crossing altitude of 1;271 feet.  As we started the descent; we saw towers that looked to be right under RIZER.  At about that time we got a 'Caution - Obstacle' alert. The Pilot Flying (First Officer) disengaged the autopilot and adjusted the pitch slightly.  At that point we were right over the towers and; if I remember correctly; about on glideslope.  After passing the towers; it dawned on me that it was dark and that alert should have triggered a go-around. For this particular approach; the glideslope altitude over RIZER is only 625 feet above the towers.  These towers are not the highest terrain on the chart and are kind of hidden behind the Localizer feather.  As you pitch down to capture the glideslope; it apparently takes very little pitch change to activate the alert.  Our first error was missing the towers on the chart.  An obstacle only 625 feet under the final approach fix is something you shouldn't miss.  Our second error was not going around.  By the time it dawned on me that it was night time and that the alert required a go-around; we were already past it. The final approach fix should be moved so it is not right on top of towers.  If it were a mile or two farther out; you would be better established on the glideslope before crossing the towers.
An air carrier Captain reported an EGPWS CAUTION OBSTACLE alert from towers 625 feet below RIZER intersection which is the ISP Runway 24 ILS glideslope intercept point.