Manual abort
An abort could be initiated by the Apollo crew by turning a lever (marked in red in the figure above).
There were basically two types of cues for aborts:

1. the cues for imminent danger which were provided by the displays reflecting the flight behavior and the technical status of the launch vehicle;
2. an abort request from Mission Control.

Automatic abort by EDS
However, during the two or three minutes of the ascent, an abort would have been triggered automatically by the Emergency Detection System (EDS):

1. in case of a structural failure between the command module and the instrument unit on top of the S-IVb stage;
2. if two or more S-IC engines drop below 90% of rated thrust;
3. and/or if pitch, yaw or roll redline rates would have been exceeded.

During one of the most critical phases of an Apollo mission, the launch, the flight was monitored meticulously. The three dark charts in the middle (3, 4 and 5) are plotboards. The actual flight trajectory was plotted in real-time on a template which contained predrawn expected nominal trajectories, limit lines and abort mode boundaries.
These displays enabled flight controllers to spot trajectory deviations and to make assessments and decisions on flight abort options.

The primary charts for the flight controllers
The three dark charts in the middle might look somewhat complicated at first glance. But these charts were designed to display the plots at three different scales for a compact and cohesive presentation of graphical information. The smaller the scale, the more details were displayed. (see figure 9)
The trajectory from S-II / S-IVB staging until orbit insertion was displayed on the smallest scale for a better view of the various abort options which were available near the moment of orbit insertion.

The left dark chart (no.3) in the photo is an Altitude - Range chart.
The middle one (no.4) is an Inertial Flightpath Angle - Inertial Velocity chart.
The right one (no.5) is also an Inertial Flightpath Angle - Inertial Velocity chart on three somewhat different scales. This chart was focused on the S-IVB-powered flight phase up to orbit insertion. The three predrawn somewhat triangular-shaped curves were representing the boundary lines of a particular abort option (mode IV) for different altitudes, which involved the use of the Service Propulsion System (SPS) of the Apollo spacecraft to achieve a contingency orbit.

The various abort options near the end of the launch phase
The smallest scale in the three charts was meant to monitor the last phase of the launch, which was the S-IVB-powered flight up to orbit insertion, more closely. In this phase, in which the launch vehicle would have been approaching the African coast rapidly, various abort options became available in rapid succession, for which a quick decision-making process was required. All these abort options were very dependent on rapidly changing flight parameters and were devised to avoid a high-risk landing on African soil.

All these options would have led to the following three situations:

• landing short: in the Atlantic Ocean a couple of hundred kilometres in front off the African coast;
  
• landing long: landing across the African continent in the Indian Ocean;
  
• insertion into a contingency orbit.

In the ascent or boost phase, three flight regimes have been distinguished: atmospheric, transitional or sub-orbital and space. For each regime an abort procedure has been designed.
In the picture shown above, four abort modes have been depicted. However, mode IV is not an abort procedure in the strict sense, because this mode will not result in a quick reentry. The objective of abort mode IV is to achieve a contingency orbit.

Abort mode I
Abort mode I is explained in figure 4.

In the abort modes II and III, the reentry trajectory could be controlled by controlling the roll angle of the command module during descent.

Abort mode II
In mode II the Service Module RCS engines or the SM main engine propel(s) the CSM away from the launch vehicle. When the CSM is at a safe distance, the CM is separated from the SM and manoeuvred into a reentry attitude.
In the mode II abort procedure, the CM's roll angle would have been set to obtain a full lift-up attitude. The blue dotted curve represents the last possible mode II trajectory, which began at the so-called mode switch-over point, at which so much velocity would have been gained that it would have become necessary to switch to mode III.

Abort mode III
In mode III the SPS has to be used, not only to separate from the booster as in mode II, but also for a retrograde burn in order to be able to land some 1000 km off the African coast, some 6000 km downrange. This specific landing area is called the Atlantic Discrete Recovery Area (ADRA).
Besides the retroburn, the descent trajectory needs to be actively controlled to land in the ADRA. In order to have a controlled burn for the required Δv and a controlled descent, flight data need to be acquired from the onboard inertial navigation system.
It is a rather complicated and hectic sequence:

• program initiation for the SPS retroburn;
• retroburn;
• SM-CM separation;
• program initiation for reentry control.

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 (see figure 7).

The "Fixed-Δv" abort mode: a beyond-Atlantic abort mode
The window of opportunity for mode III was closing when the booster (S-IVB stage) was about to cut-off and orbit insertion was almost achieved. When, nevertheless, an immediate return of the crew would suddenly have become necessary, a so-called "fixed-Δv" abort mode could be used, which would result in a landing in the Indian Ocean across the African continent. The selected landing area was called the Indian Ocean Recovery Area (IORA) (see figure 6).

For this abort mode to execute, it had to be determined first, based on the predicted initial velocity at abort, whether a retrograde burn (to reduce velocity) or a posigrade burn (to gain velocity) would be required to land at IORA.

IORA had the advantage that this landing area could be used for all launch azimuths. The choice for the geographical location of IORA was deliberate. The geographical central angle between the launch pad and IORA is 180°; IORA is therefore the location where all ground tracks of all various launch azimuths intersect.

In abort mode I the motor (L/E motor) of the launch escape tower (LET) would have been used to propel the CM away from the launch vehicle. A pitch control motor (P/C motor) at the top of the tower would have been used to provide the proper pitch angle for the evasive maneuver.

The hardware of the Earth Landing System (ELS) consisted of two drogue chutes, three main chutes with their three pilot chutes and five chute mortars to have the parachutes deployed. The ELS had to be armed to enable the parachute deployment sequence.

Abort mode I had been divided into the submodes IA, IB and IC mainly because of the rapidly decreasing atmospheric pressure during the ascent.
The only difference between mode IA and IB, however, was that in mode IA a propellant dump of the Reaction & Control System (RCS) would have been executed to prevent a possible fire source at landing. This procedure was omitted in mode IB.
In modes IA and IB, a canard system in the top of the LET would have been used to induce a pitch tumble to put the CM in a proper attitude, blunt end forward.

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.

Three types of recovery areas were distinguished:
1. ACRA: the Atlantic Continuous Recovery Area, stretching from the launch pad to 6000 km downrange;
2. ADRA: the Atlantic Discrete Recovery Area, a specific area 6000 km downrange;
3. IORA: the Indian Ocean Recovery Area, which is an area, some 19 000 km downrange, which the trajectories of various launch azimuths have in common.
   The so-called central angle between the launch pad and IORA is 180°.

Mode III
Mode III came into effect when the landing area, in case of a mode II abort, had approached ADRA. In order to land at ADRA, a retro maneuver with the SPS became necessary to reduce the velocity. And after SM-CM separation, the descent trajectory of the CM had to be controlled to create safe reentry conditions and to land at or near the ADRA.

The "Fixed-Δv" abort mode
If, however, at the moment of abort, the velocity would have become too high to make it to the ADRA, and an immediate return of the crew was required, then a retrograde burn maneuver or a posigrade burn maneuver needed to be planned to aim for a landing in IORA across Africa. These procedures were designed to avoid a high-risk landing on the African continent.

In order to execute mode III, or the "Fixed-Δv", abort mode procedure, flight data needed to be uploaded to the spacecraft's guidance computer for a precise burn and to enable the guidance computer to control the reentry trajectory by controlling the spacecraft's roll angle during the descent.

Mode IV
The mode IV abort, a Contingency Orbit Insertion (COI) maneuver using the SPS, was highly preferred above the very complicated and risky mode III procedure. In figure 8 is illustrated which trajectory conditions had to be met to achieve an orbit when using the mode IV abort procedure. Otherwise, mode III was left as the only option for a safe return of the crew.

This chart illustrates the complexity of the abort decision-making process near the moment of orbit insertion. The objective to avoid a high-risk landing on African soil as much as possible had a large impact on the abort mode management. In the last three minutes of the launch phase, the various abort options became available in rapid succession. Using mode III or "Fixed-Δv" mode was considered highly unlikely. The boost flight was considered the most risky part of the launch. But so close to orbit insertion and with the mode IV (SPS to orbit) capability available, only a fatal spacecraft system failure, which could have endangered the crew, would have made an immediate return necessary through a mode III or a "Fixed-Δv" abort. However, such an event was considered as highly unlikely.

The mode IV abort partly overlaps mode II but entirely overlaps mode III. Mode IV was preferred because it was a far less hectic procedure than mode III and could provide some options for an alternative mission in Earth orbit.

Shifting retroburn times in mode III
There was a range in which a retrograde SPS burn was not needed to land in ADRA. By controlling the descent trajectory, the initial velocity might vary within a certain range, as indicated with the blue area in the chart.
But beyond that range (into the light red area), a controlled retroburn was needed to obtain the proper -Δv. The required -Δv depends on the initial velocity (velocity at abort). The velocity was measured constantly by the onboard inertial platforms in the spacecraft and the Instrument Unit on top of the S-IVB stage and a nearby tracking station (Canary Island Tracking Station). These data were sent to Mission Control via the Manned Space Flight Network (MSFN) and enabled Mission Control to determine the required retroburn time to obtain the required -Δv.
In the case that a mode III abort had to be initiated, the calculated required retroburn time and other flight data had to be uploaded into the Apollo Guidance Computer for a controlled retroburn and for a controlled descent.

This chart has been redrawn from a photo (shown in figure 10) of an actual chart to be used during the launch phase of an Apollo mission. These kinds of charts were used by the Flight Dynamics Support Group in one of their plotters. This group was located in a room adjacent to the Mission Operations Control Room at the Johnson Space Center in Houston.
(For more information about these mission support groups.)

The graphical information is displayed at three different scales. That is because the monitoring requires an increasing rate of meticulousness. The last phase of the mission is depicted in red. In this phase of the launch between S-IVB stage ignition and orbit insertion, various abort options become available in rapid succession with the aim of avoiding a risky landing on African soil.

The chart contains curves of predrawn nominal trajectories, limit lines and abort mode boundaries. The actual trajectory was plotted in real time on this chart to spot deviations from the expected nominal trajectories. The chart is presenting the successive available abort modes along the ascent trajectory, which enables the flight controllers to make adequate decisions with regard to the abort options in case of emergencies.

In figure 9b comments have been added to the chart.
To retain some of the authenticity of the original chart, the same US customary measurement units have been used in the redrawn version.

Markings for modes I, II and III have been left out.
In the chart only two abort modes are represented: the S-IVB to contingency orbit insertion and the mode IV abort (SPS to contingency orbit insertion). Modes I, II and III have been left out.

S-IVB to COI capability
COI stands for Contingency Orbit Insertion. This option became available when the Saturn V stack had obtained a certain velocity and altitude. In case of a mid-flight failure of the S-II stage, the S-IVB stage could be used to take over the powered flight to bring the spacecraft into orbit. In such an occurrence the capability for a TransLunar Injection burn is, however, lost.

Personal note:
Maybe there was a maximum time (one minute?) by which an S-IVB ignition could be moved up for a COI burn before the amount of propellant had dropped below a threshold value at which the TLI burn capability would have been lost.

Mode IV: SPS to COI capability
The abort mode IV involved a COI by using the SPS. For inertial flight path angles above zero, this mode IV could be performed in two ways:

1. An SPS posigrade burn as soon as the mode IV option becomes available;
2. Suspend the SPS posigrade burn until the apogee was achieved. The burn at the apogee was called an apogee kick. This procedure was meant to optimize the efficiency of the burn to achieve an orbit with a perigee of 139 km (75 nautical miles).

Some additional limit lines in chart no.4 in figure 2
That chart shown in the group displays of the Mission Operations Control Room was a projection version of more or less the same chart.
But a perceptive eye might discover that on that version there are a predrawn mode II limit line, a predrawn short line marking the moment of LET jettison and a predrawn exit heating limit line (the small wiggling curve left, near the chart boundary).
The long limit line is an element of the part that is drawn on the smallest scale, which focuses on the near-orbit insertion trajectory and is marking the upper limit of mode II. The short horizontal line belongs to the medium-scale part of the chart and is marking the moment of LET jettison, the ending of mode IC and the beginning of mode II.
The small wiggling curve belongs to the medium-scale part too.
The three limits have been drawn in figure 9b (dotted black lines) for comparison.

Abort mode III has been left out.
In this projection version of the chart, the markings for abort mode III have been left out. For mode III, boundary markings would be helpful, if not essential, to make the proper decisions. However, mode III is overlapped by mode IV, the preferred abort mode. So there is no gap in the abort mode coverage. However, mode III would have been used if an immediate return of the crew, that close to orbit insertion, became urgently necessary. For example, it would have required life-threatening failures of the Service Module or the Command Module to trigger an abort mode III. The likelihood of such an occurrence was estimated to be very small.

The chart shown above has been used by flight controllers in charge of flight dynamics and flight safety during the launch phase of the Apollo 8 mission. This chart has been used at one of the plotters in the Flight Dynamics Staff Support Room.
A projected version of this chart was shown on one of the large group displays in the Mission Operations Control Room (MOCR).