Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Distraction
Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Undershoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Became Reoriented
Human Factors
While descending on the DRLLR5 into IAH; I asked the Captain a question regarding the flight and we began to converse about the topic. I continued to monitor the descent and we were on speed and on altitude all the way through MPORT. The Captain had the bottom altitude of MPORT (16;000 ft.) in the altitude selector and once past MPORT it was not changed to the bottom altitude of DRLLR (13;000 ft.). Since the altitude selector was still at 16;000 ft.; it looked as if we would be fine with the restriction at DRLLR according to the vertical guidance. 5 miles from DRLLR I noticed we were actually high and told the Captain we needed to increase the vertical descent. He increased the vertical descent while maintaining the speed restriction but we passed DRLLR 400-500 feet above the restriction. The flight continued normally and we continued on the arrival into the visual on 26R. This event was caused by a discussion about the flight leading to a monitoring breakdown. As Pilot Monitoring; I lost focus of the descent path and did not realize the bottom altitude of DRLLR was not set. By the time I realized and queried the Captain to increase the descent rate it was too late. I should have waited to ask a question until we were on the ground considering we were already on the arrival. This would have allowed me to monitor the descent rate more accurately and avoid being high at DRLLR. I also probably would have caught the altitude still being set to MPORT.
First Officer reported missing a crossing altitude on the DRLLR FIVE Arrival into IAH.