When using IRIS you can choose from a variety of flight modes that will allow your IRIS to behave in different ways and to perform all sorts of autonomous actions. Some of this flight modes require GPS lock prior to take off. 
–Stabilize mode: Stabilize mode allows you to fly your vehicle manually, but self-levels the roll and pitch axis. Click here for more information
–Altitude Hold Mode: In altitude hold mode, the copter maintains a consistent altitude while allowing roll, pitch, and yaw to be controlled normally. Click here for more information.
–Loiter Mode: Loiter automatically attempts to maintain the current location, heading and altitude. The pilot may fly the copter in Loiter mode as if it were in manual. Releasing the sticks will continue to hold position.
Good GPS position, low magnetic interference on the compass and low vibrations are all important in achieving good loiter performance. Click here for more information.
–RTL Mode: In return to launch (RTL) mode, the copter navigates from its current position to hover above the home position. The behavior of RTL mode can be controlled by several adjustable parameters. This page describes how to use and customize RTL mode. Click here for more information.
–Auto Mode: In Auto mode the copter will follow a pre-programmed mission script stored in the autopilot which is made up of navigation commands (i.e. waypoints) and “do” commands (i.e. commands that do not affect the location of the copter including triggering a camera shutter). Click here for more information.
For additional flight modes click here