Medium Transport; Low Wing; 2 Turbojet Eng
Flight Crew Air Transport Pilot (ATP)
Flight Crew Total 20000
Communication Breakdown; Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented
Human Factors
On vector approach to 8R IAH outside of EELPO at 5000 [ft] control cleared us for ILS to maintain 3000 [ft] until established. I did not realize First Officer had reset altitude window to 2000 [ft]. Descended to 2000 [ft] outside EELPO on autopilot. We failed to [verbalize] new altitude.
The captain and I were flying the last leg of a four day trip together. We were inbound on the GUSHR 2 RNAV arrival and upon initial contact with Houston Approach we were told to expect RWY 8L. We were subsequently told to expect RWY 8R and were assigned a heading and a clearance to descend to 6000 feet. With the aircraft set up for 8R ATC issued a heading to join the localizer for 8R; maintain 5000 feet until established; 190 knots to JELLI and 170 knots to EELPO; cleared for the ILS 8R. The vector placed us on the final near JELLI and at the same time we were approaching 5000 feet. As we joined and began to slow to our 170 knot speed I prematurely dialed the MCP altitude selector down to 2000 feet in reference to MATON. I did not initially verbalize this due to a number of other things going on at the time. The captain later acknowledged that he saw 2000 was set in the MCP altitude window. At this point we were slightly below the glideslope but as the approach progressed the aircraft continued to diverge further below the glideslope. I believe neither the captain nor I took action due to the false sense of security brought on by our now visual surroundings. ATC queried us regarding our status prior to our reaching MATON. At MATON we intercepted the glideslope and continued the approach to landing.
Air Carrier flight crew reports being cleared for the ILS to maintain 3;000 feet until established; but the First Officer elects to set the FAF altitude of 2;000 feet in the MCP window. His action resulted in a descent below 3;000 feet prior to glideslope intercept and received a query from ATC.