The plot starts at a point in which the inertial flight path angle is zero and the velocity is nonzero. That is because space has been chosen as the frame of reference; that implies that Earth's rotation is taken into account. So the launch vehicle already has a horizontal space-fixed velocity of about 410 meters per second due East when it is sitting on the launch pad in Florida. When the launch vehicle is ascending, the vertical component of the velocity is increasing, and therefore the inertial flight path angle is increasing. But at the same time the launch vehicle is starting to pitch over to gradually maneuver into an orbit in which it is aligned along the local horizon (flight path angle is zero). So the flight path angle increases at lift-off, will reach a maximum at which the vertical component of the velocity will reach a maximum, and will then taper off to zero when an orbit has been obtained.

The four launch abort modes
Abort mode I
In this picture is also shown which abort procedures are available in time during the ascent. Four abort modes are distinguished, each corresponding to the three flight regimes: atmospheric, transitional or suborbital and space. In mode I, three submodes are distinguished, reflecting the three modes of operation of the Launch Escape System depending on the altitude and velocity of the launch vehicle.

Abort mode IV (insertion into a contingency orbit)
In the last minutes of the ascent, near orbit insertion, the abort mode decision process is somewhat complicated. If the actual trajectory is then deviating too much from the nominal trajectory, the decision whether to start a reentry or to attain a contingency orbit depends on rapidly changing abort cue conditions. In general, abort mode IV, the contingency orbit, is preferred. It provides the capability to meet some of the mission objectives and gives ground control and the flight crew time to select proper landing areas and make preparations for reentry.
In mode IV the Service Module main engine (SPS) would have been used to separate the CSM from the S-IVB stage and insert the CSM into a contingency orbit.

Abort mode III
Abort mode III, in contrast, is a rather hectic and most complicated procedure. Its objective is to have a landing in the Atlantic Ocean. But in this phase of the ascent the spacecraft has attained near-orbital altitude and near-orbital velocity, and it is approaching the African coast rapidly.
In contrast to the abort modes I and II, the spacecraft has to be actively guided and controlled to meet the proper reentry trajectory conditions. Without guidance the landing footprint is unacceptably large, and the spacecraft might follow a high G-load and high heat load reentry trajectory, which will endanger the crew.

If it is to land in the Atlantic Ocean to avoid a high-risk land landing on African soil, the reentry software of the Apollo Guidance Computer (AGC) needs flight data for proper descent trajectory control. These flight data basically contain data on the spacecraft's position, velocity, acceleration and the location of the selected landing area. The required flight data is acquired from the inertial navigation system, which is connected to the AGC. In the same short period of time, the flight crew has to initiate a propulsion maneuver with the Service Propulsion System to decrease the velocity, has to separate the command module from the service module and has to initiate the reentry procedure.

Controlling the lift vector by controlling the roll angle
The reentry trajectory control is left to the Apollo Guidance Computer (AGC) by controlling the roll angle of the spacecraft during its reentry. The Apollo command module has been deliberately designed to have a center of gravity which doesn't coincide with its geometric center. This will result in an imbalance of the aerodynamic forces acting on the heat shield, causing it to tilt slightly with respect to the direction of flight during the descent. This tilt will result in a lifting force perpendicular to the drag. By controlling the roll angle, the lifting vector could be pointed in all directions in a plane perpendicular to the direction of flight. So by controlling the roll angle, an upward, downward and sideward lift can be created.

This mechanism enables the software by employing the Reaction Control System (RCS) to control the descent trajectory to have a controlled landing in a pre-selected landing area.

Abort mode II
This ability to create upward and downward lift by controlling the spacecraft's roll angle is also used during a mode II abort. But in that phase of the ascent, the landing footprint and its location are not much of an issue, so attitude control is not used for trajectory control but just to minimize the G-load on the spacecraft during descent. Therefore, the spacecraft is fixed in a "maximum upward lift" attitude, because of which reentry software doesn't require flight data from ground-based stations like in abort mode III.

Contingency orbit insertion using the S-IVB stage
The S-IVB stage could also be used to bring the spacecraft into a contingency orbit. This option was designed for cases in which the S-II stage would fail during flight, endangering the crew. The option became available when threshold values for altitude and velocity were met.