Understanding Honeywell Auxiliary Power Units (APUs)

What is a Honeywell Auxiliary Power Unit (APU)?

A Honeywell Auxiliary Power Unit (APU) is a small gas turbine engine manufactured by Honeywell Aerospace, typically located in an aircraft’s tail. Since their introduction in the early 1950s, Apus have become essential systems, enabling aircraft self-sufficiency on the ground and providing vital backup power in flight.

When an aircraft is parked, the APU generates electrical power for onboard systems like air conditioning and cockpit displays, making it unnecessary to run the main engines or connect to external ground power. It also supplies the pneumatic power (bleed air) needed to start the main engines, enabling an independent departure.

A functioning APU is crucial. In flight, it serves as a vital backup power source, enhancing operational safety. On the ground, a failure can derail an entire flight schedule, leading to costly delays, cancellations, and even significant fines. Consequently, the reliability and performance of the APU are essential for modern aviation operations.

Key Features of Honeywell Apus

Every Honeywell APU is built around a sophisticated gas turbine, such as the advanced HGT1700, which provides reliable electrical and pneumatic power. This integrated design ensures both aircraft independence on the ground and backup power in the air.

Its key components include a highly efficient two-stage axial turbine and an innovative dual-purpose starter/generator. This starter/generator first brings the APU to life and then switches to generating the aircraft’s electrical power. The integrated design not only reduces weight and complexity but also enhances reliability.

Modern Honeywell Apus also feature high-efficiency modes, which use advanced hardware and autonomous software to control airflow and improve fuel consumption by 1-2%.

331 Series – Powering Wide-Body Giants

Designed for wide-body aircraft with greater power demands, the Honeywell 331 Series delivers the high electrical and pneumatic output needed for extensive systems on long-haul airliners and heavy-lift military aircraft. The series provides ample power for everything from environmental controls to starting main engines, all while incorporating key improvements in efficiency, emissions, and durability.

131 Series – Best-Selling APU for Commercial Aircraft

The Honeywell 131 Series, especially the 131-9 model, is the industry’s best-selling APU for single-aisle commercial aircraft like the Airbus A320 and Boeing 737. Its design, featuring a two-stage axial turbine and a single starter/generator, reliably delivers both electrical and pneumatic power. Advanced hardware and software controls further improve fuel efficiency, reduce emissions, and extend engine life, making it a top choice for airlines seeking dependability and economy.

Honeywell APU Market Position and Competitors

Honeywell is a dominant force in the APU market, a position largely driven by the success of its 131 Series. The widespread adoption of this series on best-selling single-aisle aircraft, including the Airbus A320 and Boeing 737 families, has solidified its leadership position.

The APU market is competitive, with major players like Pratt & Whitney and Saran also competing for market share. North America is a key market, accounting for over 32% of global share in 2024, where Honeywell is a leading supplier that responds effectively to technological advancements and evolving airline fleet requirements.

The APU sector is growing, driven by the aviation industry’s focus on greater fuel efficiency and lower emissions. Honeywell addresses this demand through continuous innovation. By introducing features like high-efficiency modes, the company provides Apus that save fuel and reduce their environmental footprint, maintaining its position as an industry leader.

Maintenance and Support for Honeywell Apus

Beyond initial performance, consistent APU reliability is critical, as any failure can trigger costly operational disruptions. To mitigate this risk, Honeywell offers a comprehensive maintenance and support framework designed to maximize uptime and extend the life of its units.

Central to this framework is the comprehensive Maintenance Service Plan (MSP). This plan shifts the focus from reactive repairs to proactive maintenance, aiming to prevent issues before they arise and keep the APU in optimal condition through:

• Scheduled inspections

• Necessary repairs

• Parts replacement

Backing this plan is Honeywell’s global customer support network, which offers operators worldwide access to technical assistance and ensures a rapid response to any operational issues. Whether an aircraft is at its home base or a remote location, this global reach provides peace of mind and minimizes ground time.

Future of Honeywell Apus

With the aviation industry shifting toward greater sustainability and efficiency, Honeywell is evolving its APU technology to reduce environmental impact and lower operational costs. This focus ensures its Apus will remain integral to the next generation of aircraft.

Compatibility with Sustainable Aviation Fuel (SAF) is a top development priority. Integrating SAF capabilities is essential for aligning with stricter global regulations and supporting the industry’s move toward greener aviation. This commitment to sustainability, combined with continuous improvements in performance and reliability, positions Honeywell to lead the development of Apus for future commercial and military aircraft.