If a plane icon is moving on the map, yes. That's ADS-B, the aircraft's own GPS position broadcast, updated every few seconds. No icon means the flight isn't airborne at the moment: either before pushback, already landed, or a day it doesn't operate.

Scheduled equipment is the 320. The live tracker shows the actual tail and registration when UA 2135 is airborne. Carriers swap aircraft often enough that you'll sometimes see a different airframe than the scheduled type.

Every day of the week. On days outside that pattern this page will show the schedule but no live aircraft.

Scheduled 4h 32m gate to gate from SEA to IAH. Actual air time varies with winds and ATC routing. Tailwinds can shave 15 to 20 minutes on long segments.

GPS-accurate via ADS-B. Typically within 30 meters horizontally, updated every 5 to 10 seconds. If the broadcast drops over oceans or mountainous terrain, the map holds the last-known position and the label changes to reflect the signal gap.

A projection from current position, groundspeed, and remaining distance. It doesn't account for descent procedures, holding, or ATC vectoring near the destination. Trust it within plus or minus 10 minutes once the flight is past the halfway mark.

United Airlines is a star_alliance member, so you may see this flight ticketed under a partner airline's code as well. The live aircraft is the same regardless of which code is on your ticket.