Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Flight Crew Became Reoriented; Flight Crew Took Evasive Action
Human Factors
Cleared for the visual to runway 5R into TYS at 4000 feet on a right downwind. The First Officer stated he would begin the descent as we slowed down and dialed in 2000 feet. We had previously discussed using 2500 for the missed approach altitude if necessary; but I had looked at the MFD and determined that he would be on final by the time we hit 2000 feet so chose not to say anything about it. This was my fault; because at that point I usually have the MFD zoomed in to the 2.5/5 NM range; but still had it at the 5/10 range. We hit 2000 feet during the base leg and the First Officer called for flaps 8 and flaps 20. After the flaps were at 20; before making the final turn we got a 'Terrain; Terrain' warning. Followed shortly after that was the landing gear buzzer. I requested the First officer add some power and climb us up a few hundred feet until we make our turn to final and finish configuring. He disconnected the autopilot and complied. We finished configuring and landed without incident.My complacency on when I tune the MFD rings. After we got on final the First Officer had stated that he probably should have used 2500 instead of 2000; and I agreed with him and explained my reasoning for not mentioning it at the time. Simply put; we should always be using 1500 AGL when cleared for a visual approach; especially if being vectored towards the 5 mile final.
Air Carrier Captain; as the pilot monitoring; reports getting too low during a night visual approach to Runway 5R at TYS causing a terrain warning and correction by the First Officer.