What is INBD on Boeing 737? (Inboard)

The Boeing 737 is one of the most popular commercial aircraft in the world. It has proven to be reliable and efficient, making it a favorite among airlines and passengers alike. But have you ever wondered what “inboard” means when referring to the Boeing 737? In this article, we will explore the concept of inboard on the Boeing 737 and its significance in the aircraft’s design and operation.

The Role of the INBD Label on the Boeing 737

When looking at the technical documentation or diagrams of the Boeing 737, you may come across the abbreviation “INBD.” This abbreviation stands for inboard, which refers to the positioning of certain components or systems within the aircraft.

In aviation, “inboard” generally indicates that a specific component or system is located closer to the aircraft’s centerline. The inboard region is towards the inner part of the aircraft, while the outboard region is towards the outer part. Understanding the inboard and outboard regions is crucial for maintenance crews and engineers as it helps them identify the positioning of various components and systems for troubleshooting, repairs, and upgrades.

For example, when referring to the inboard flaps, it means that these flaps are closer to the centerline of the aircraft, while the outboard flaps are positioned towards the wingtips. The inboard flaps play a vital role in controlling the aircraft’s lift, drag, and stability during takeoff and landing. They extend and retract based on the flight phase, allowing the pilot to optimize the aircraft’s performance in different conditions.

Moreover, the INBD label can also be associated with engine components. The inboard engine refers to the engine that is mounted closer to the fuselage, while the outboard engine is mounted towards the wingtip. This distinction is important for engine maintenance and operation as it determines the accessibility and servicing procedures for the engines.

Understanding the inboard and outboard regions of the Boeing 737 is essential for aviation professionals to ensure proper maintenance, system integration, and troubleshooting. It allows for efficient inspections and repairs by identifying component locations and contributing to the aircraft’s overall safety and performance.

Inboard Systems of the Boeing 737

Several critical systems and components are categorized as inboard on the Boeing 737. Let’s take a closer look at some of these inboard systems and their functions:

1. Inboard Wing Slats and Flaps

The wing slats and flaps are essential for generating lift and controlling the aircraft’s speed and stability during takeoff and landing. The inboard wing slats and flaps are located closer to the fuselage or centerline of the aircraft. These high-lift devices extend and increase the wing surface area, allowing the aircraft to achieve lower speeds without stalling and to maintain control at lower altitudes.

The inboard wing slats and flaps of the Boeing 737 have multiple positions, each serving a specific purpose. During takeoff, they are typically extended to increase lift and improve the aircraft’s climb performance. On approach and landing, they are deployed further to enhance lift, slow down the aircraft, and improve its maneuverability.

2. Inboard Fuel Tanks

Fuel is a critical component of any aircraft, and the Boeing 737 is no exception. The inboard fuel tanks are located toward the centerline of the aircraft, closer to the fuselage. These tanks are responsible for storing and supplying fuel to the engines throughout the flight.

The Boeing 737 typically has multiple fuel tanks: the inboard tanks, outboard tanks, and center tanks. The inboard fuel tanks have specific capacity and distribution systems designed to maintain the aircraft’s balance and stability during flight. They are connected to the fuel management system, which ensures a constant supply of fuel to the engines and monitors fuel levels for operational efficiency.

3. Inboard Avionics and Electrical Systems

The avionics and electrical systems play a crucial role in the overall operation and safety of the aircraft. The inboard avionics and electrical systems of the Boeing 737 are located closer to the centerline, typically integrated within the fuselage structure. These systems include various components such as flight control computers, communication systems, navigation equipment, and electrical power distribution units.

By positioning the avionics and electrical systems inboard, the Boeing 737 ensures a more balanced distribution of weight, improves accessibility for maintenance and repairs, and minimizes the risks of damage from external factors like turbulence or bird strikes.

The inboard avionics and electrical systems are interconnected through wiring harnesses, providing seamless communication and power distribution throughout the aircraft. They are also integrated with displays and control interfaces in the cockpit, allowing pilots to monitor and manage various flight parameters and system statuses.


The inboard region of the Boeing 737 plays a crucial role in the aircraft’s design, performance, and maintenance. Components and systems located inboard, such as the flaps, fuel tanks, and avionics, are strategically positioned for optimal functionality, weight distribution, and accessibility. Understanding the inboard concept helps aviation professionals troubleshoot, maintain, and operate the aircraft more efficiently.

Next time you come across the abbreviation “INBD” in relation to the Boeing 737, you will have a better understanding of its significance and the positioning of components within the aircraft.

For More: What is POS on Boeing 737? (Position)