Flight Redemptions

What is AGB in Aviation? (Accessory Gear Box)

Updated: February 16, 2024

What is an Accessory Gear Box (AGB)?

An Accessory Gear Box (AGB), also known as an Accessory Drive Gearbox, is a vital component in aircraft engines. It is responsible for transmitting power from the engine to various aircraft systems and accessories. The AGB is typically located at the front of the engine and is driven directly by the engine's main drive shaft. It plays a crucial role in the overall performance and functionality of the aircraft.

The Accessory Gear Box is designed to drive the engine's accessory systems, such as the generator, hydraulic pumps, fuel pumps, and air conditioning compressors. It transfers power through a series of gears and shafts, ensuring that the accessories receive the necessary mechanical energy to function properly. The AGB also provides a means of controlling the speed and power output of these systems, allowing pilots to adjust and regulate their operation as required.

AGBs are commonly used in gas turbine engines, which are widely used in commercial and military aircraft. These engines require a reliable and efficient means of driving the various accessories and subsystems to ensure optimal performance and safety. The AGB is specifically designed to meet these requirements, providing a robust and durable solution for transmitting power throughout the aircraft.

Importance of the Accessory Gear Box

The Accessory Gear Box plays a crucial role in the overall operation of an aircraft. It ensures that the engine's accessories and subsystems receive the necessary power and operate at the correct speeds. Here are some key reasons why the AGB is of utmost importance:

Power Transmission

The primary function of the Accessory Gear Box is to transmit power from the engine to the various accessories and subsystems. It accomplishes this by transferring rotational motion from the engine's main drive shaft to the accessory drive shaft. This power transfer ensures that the accessories receive the required mechanical energy to perform their intended functions.

For example, the generator in an aircraft relies on the AGB to drive its rotor, which generates electricity to power the aircraft's electrical systems. Similarly, the hydraulic pumps require the AGB's power transmission to provide hydraulic pressure for operating various flight control surfaces and landing gear.

By effectively transferring power, the Accessory Gear Box enables the proper functioning of these critical systems, ensuring the aircraft operates safely and efficiently.

Speed Control

The AGB also plays a vital role in controlling the speed of the engine's accessories and subsystems. It allows pilots to adjust and regulate the rotational speed of these systems, depending on the aircraft's requirements and operating conditions.

For instance, during takeoff or climb, the engine may need to provide maximum power to meet the aircraft's performance demands. In such cases, the AGB allows the accessories to operate at higher speeds, supplying the necessary power output. Conversely, during cruise or idle conditions, the AGB allows for lower accessory speeds, conserving fuel and reducing wear and tear on the components.

This speed control capability provided by the Accessory Gear Box ensures that the aircraft's systems operate optimally, balancing power requirements with fuel efficiency and component longevity.

Common Challenges and Maintenance of Accessory Gear Boxes

While Accessory Gear Boxes are designed to be robust and reliable, they can still face certain challenges and require regular maintenance to ensure their continued performance. Here are some common issues associated with AGBs:


Accessory Gear Boxes can generate significant heat during operation, especially due to the high rotational speeds and power transmission involved. Overheating can lead to a loss of lubrication, increased friction, and potential damage to the gears and other components.

To mitigate this issue, AGBs are typically equipped with cooling systems, such as oil coolers or air ducts, to dissipate heat and maintain optimal operating temperatures. Regular inspection and maintenance of these cooling systems are crucial to prevent overheating and ensure the AGB operates within its designed temperature range.

Lubrication and Contamination

Proper lubrication is essential for the smooth operation and longevity of the Accessory Gear Box. Lubricating oil is used to reduce friction between the gears and other moving parts, minimizing wear and ensuring efficient power transmission.

However, over time, lubricating oil can become contaminated with debris, particles, and moisture, compromising its effectiveness. Contaminated oil can lead to increased friction, accelerated wear, and potential damage to the AGB components.

Regular oil analysis and scheduled oil changes are necessary to maintain proper lubrication and prevent contamination-related issues. Additionally, frequent inspection of oil filters and seals is important to ensure they are functioning correctly and preventing contaminants from entering the AGB.

It is important to note that each aircraft and engine manufacturer may have specific maintenance requirements and intervals for AGBs. Following these guidelines and conducting regular inspections and maintenance tasks can help identify and address potential issues before they escalate.


The Accessory Gear Box (AGB) is a critical component in aircraft engines, responsible for transmitting power from the engine to various accessories and subsystems. It plays a vital role in power transmission and speed control, ensuring the proper functioning of the engine's accessories. Regular maintenance and adherence to manufacturer guidelines are essential to address common challenges associated with AGBs and ensure their optimal performance. By understanding the importance of the Accessory Gear Box and taking appropriate measures, aircraft operators can ensure the safe and efficient operation of their aircraft.

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