What is A/P on Boeing 737? (Autopilot)

Autopilot, abbreviated as A/P, is a critical component of modern aircraft, including the Boeing 737. It is a sophisticated system that assists pilots in controlling the aircraft by automating several aspects of the flight. Autopilot is designed to relieve pilots of mundane and repetitive tasks, allowing them to focus on higher-level decision-making and ensuring a safe and efficient journey.

In this article, we will delve into the details of the autopilot system on the Boeing 737, its functionalities, and how it contributes to the overall flight operations. So, let’s buckle up and explore the world of autopilot on this iconic aircraft.

How Does the Autopilot Work?

The autopilot system on the Boeing 737 utilizes a series of sensors, computers, and actuators to maintain the desired course, altitude, speed, and attitude of the aircraft. It receives information from various sources, such as inertial navigation systems (INS), Global Positioning System (GPS), air data computers (ADC), and flight control computers (FCC).

These sensors continuously provide crucial data, such as the aircraft’s position, speed, altitude, heading, and vertical speed. The autopilot uses this information to calculate the necessary control inputs to achieve the desired parameters set by the pilots.

For example, let’s say the pilots want to climb to a specific altitude. They would input the desired altitude into the autopilot system. The autopilot would then adjust the aircraft’s pitch, throttle, and other control surfaces to achieve and maintain the desired climb rate and altitude. This process is performed continuously throughout the flight to ensure the aircraft remains on track.

The autopilot system also compensates for external factors, such as wind direction and speed, by automatically adjusting the aircraft’s flight control surfaces. This capability ensures the aircraft stays on course, even in the presence of external disturbances.

Autopilot Modes on Boeing 737

The autopilot system on the Boeing 737 offers various modes that cater to different phases of flight. Each mode serves a specific purpose and allows for precise control over the aircraft. Let’s take a closer look at some of these modes:

1. Attitude Hold (ATT)

The Attitude Hold mode, as the name suggests, holds the current attitude of the aircraft. This mode is typically engaged during manual flight or when the pilots want to maintain a specific pitch and bank angle. Attitude Hold mode is particularly useful during climb, descent, and level flight phases.

When engaged, the autopilot system will automatically adjust the aircraft’s control surfaces to maintain the desired attitude. This allows pilots to focus on other crucial tasks, such as communication with air traffic control and monitoring the aircraft’s systems.

2. Heading Select (HDG SEL)

The Heading Select mode enables the pilots to select a specific heading for the aircraft to follow. This mode is particularly valuable during the en-route phase, where the aircraft needs to navigate along a specific flight plan or airway.

Once engaged, the autopilot system will adjust the aircraft’s heading by automatically manipulating the control surfaces. It ensures that the aircraft stays on the desired path, relieving the pilots from continuously making manual adjustments.

3. Altitude Hold (ALT SEL)

The Altitude Hold mode allows pilots to select and maintain a specific altitude during climb, descent, or level flight. It is an essential mode during cruise phases, where the aircraft needs to maintain a steady altitude.

Once the desired altitude is selected, the autopilot system adjusts the aircraft’s pitch and throttle to maintain the selected altitude. It takes into account factors such as weight, speed, and external conditions to ensure precise altitude control.

These are just a few examples of the autopilot modes available on the Boeing 737. Each mode plays a crucial role in different phases of flight and contributes to the overall automation and safety of the aircraft.

Autopilot Limitations and Pilot Involvement

While the autopilot system is a remarkable technological advancement, it is important to note that it has its limitations. Autopilot cannot replace the need for skilled pilots who can make critical decisions and handle unexpected situations.

The autopilot system is designed to assist pilots, but it does not replace their judgment and expertise. Pilots are responsible for monitoring the autopilot’s performance, maintaining situational awareness, and taking control when necessary.

Furthermore, the autopilot system is not capable of handling all aspects of flight. It is primarily designed for cruise phases and straightforward flight conditions. During takeoff, landing, and critical phases of flight, pilots must take manual control of the aircraft.

The autopilot system is also unable to handle unforeseen circumstances, such as severe weather conditions or system failures. In such cases, pilots must be prepared to disengage the autopilot and take immediate manual control to ensure the safety of the aircraft and its occupants.

As technology continues to advance, autopilot systems are becoming increasingly sophisticated and capable. However, they remain a tool in the hands of skilled pilots who rely on their training and experience to safely operate the aircraft.


The autopilot system on the Boeing 737 is a vital component that enhances the aircraft’s safety and efficiency. It automates various flight control tasks, allowing pilots to focus on higher-level decision-making and reducing their workload.

By understanding how the autopilot system works and the different modes available, pilots can effectively utilize this technology to their advantage. However, it is crucial to remember that the autopilot system should never replace the skills and judgment of experienced pilots.

As we continue to witness advancements in aviation technology, the autopilot system will undoubtedly evolve, providing even greater capabilities and benefits for pilots and passengers alike.

For More: What is WXR on Boeing 737? (Weather Radar)