Regional Jet 700 ER/LR (CRJ700)
Flight Crew Multiengine; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Flight Crew Last 90 Days 60; Flight Crew Total 6200; Flight Crew Type 2800
Distraction; Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Unstabilized Approach
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Executed Go Around / Missed Approach
Human Factors; Procedure; Aircraft
We were being vectored for the ILS 11 into Portland. The Captain was flying; I was the Non-Flying pilot. Portland Approach already had us descended to 2;000 feet and had given us a heading to intercept the Localizer. We started to configure the aircraft and had the flaps set to 20 degrees. Shortly after that; we received additional instructions from Portland Approach; descend and maintain to 1800 until established on the ILS; cleared the ILS 11; contact Portland Tower 120.9. We were real close to MAINA; the glideslope intercept altitude is 1;800 [feet]. The Captain set the altitude; armed the approach; and started the descent to 1;800 [feet]. I changed the radio to 120.9; armed the reversers; [and] set my nav source to display the ILS. After I did this; I noticed that our flight directors were not matched so I informed the Captain of this anomaly. Just as I was about to check in with Portland Tower; we got a landing gear horn. It startled me because it shouldn't have come on at that time. I vocalized it by saying; 'That's not right'. The criteria was there; low power setting; flaps out of zero; descending and the gear up but I thought that we were at an altitude that should have inhibited the warning. Then we got an oral warning; 'Too Low Gear'. We started to execute a missed approach. Just after we started the missed approach the Tower transmitted for us to go around. I then glanced at the altimeter and noticed that we had descended to 900 feet. I do not know why the autopilot did not capture the glideslope and we had descended below the glideslope or even how the Captain had missed it. I had looked away for about a minute to perform some of my before landing flows then I was startled and distract by what I thought was erroneous warnings. We circled around and had an uneventful landing. I think a contributing factor was Portland Approach giving us instructions to descend [to] 2;000 feet so close to MAINA. I do not know why the autopilot did not capture the altitude. I think that because we were set up to cross MAINA at 1;800 feet and that is the glideslope intercept altitude maybe as the autopilot was transiting to capture the glideslope maybe the autopilot went to pitch mode and kept descending. Probably a better technique would have been to stay at 2;000 feet and capture the glideslope outside of MAINA and follow it down.
CRJ-700 First Officer reported executing a go-around after descending below the glideslope and receiving a 'Too low gear' warning as well as an alert from the Tower.