9912484-1 – Textron Aviation OEM Auxiliary Power Unit (APU)
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Overview
The Textron Aviation 9912484-1 is a complete, certified Auxiliary Power Unit (APU) assembly, a critical gas turbine engine manufactured by Honeywell. This unit, specifically the Honeywell RE100 series, is designed to provide pneumatic and electrical power to the aircraft on the ground, independent of the main engines. It supplies bleed air for the environmental control system (ECS) to heat or cool the cabin and provides shaft power to a starter/generator to produce electrical power for ground operations and to assist with main engine starting. The APU is a compact, self-contained turbine engine mounted in the aft fuselage, enabling the aircraft to operate in remote locations without ground support equipment, significantly improving operational flexibility and efficiency.
The 9912484-1 is an OEM-specified component, ensuring seamless integration and performance with the aircraft's control systems. Its role is fundamental to the aircraft's pre-flight preparation and ground functionality, providing a reliable power source that reduces main engine fuel burn and wear during ground stops.
Key Features
High-Performance, Self-Contained Gas Turbine Engine
Dual-Function: Provides both Pneumatic and Electrical Power
Integrated Failsafe and Monitoring Systems
Digital Electronic Control Unit (ECU) for Automated Operation
Designed for On-Ground and In-Flight Operation (Emergency Backup)
Technical Specifications
Part Number: 9912484-1
Component Type: Auxiliary Power Unit (APU)
OEM Manufacturer: Honeywell International Inc. (cataloged by Textron Aviation)
Engine Model: Honeywell RE100 series (RE100[XL] or similar variant)
Function: Provides pneumatic (bleed air) and electrical power (via an integrated starter/generator)
Ratings: Governed speed is maintained at 100% RPM. EGT (Exhaust Gas Temperature) is limited to 690°C.
Material: The APU is constructed from a combination of high-strength, lightweight alloys, including A-286 CRES (Corrosion-Resistant Steel) and Inconel for the hot section (turbine rotor, combustor), and aluminum or titanium alloys for the cold section (compressor). Specific material compositions are proprietary.
Governing Specifications: Certified under FAA TSO (Technical Standard Order) and other relevant civil aviation authority standards.
Aircraft Compatibility
Cessna Citation Excel (Model 560XL)
Cessna Citation XLS (Model 560XL)
Cessna Citation XLS+ (Model 560XL)
Note: The APU was optional on early Citation Excel models but became a standard feature on the XLS and XLS+ variants. The aircraft's Illustrated Parts Catalog (IPC) must be consulted for final part number verification and applicability to a specific airframe and serial number.
Applications
Ground Operations: Powers cabin heating/cooling, lighting, and avionics without the need for main engine operation or an external ground power unit (GPU).
Engine Starting: Provides bleed air to start the main Pratt & Whitney Canada PW545 series turbofan engines.
In-Flight Backup: Can be started and operated in flight to provide an emergency backup source of electrical power and bleed air.
Why Choose 9912484-1?
The 9912484-1 is a complex, life-limited, and safety-critical component. As a complete OEM-certified unit, it provides the highest level of reliability and performance assurance. The APU's digital electronic control unit (ECU) is specifically programmed to manage the power output, monitor system health, and perform automatic shutdowns in the event of an overspeed, high EGT, low oil pressure, or fire, among other conditions. Using a non-certified or incorrectly repaired unit can introduce significant airworthiness risks, including fire, uncommanded shutdown, or damage to other aircraft systems. Purchasing a new or serviceable APU with complete trace documentation is essential to maintain compliance with regulatory standards and ensure the safety of the aircraft and its occupants.
The Honeywell RE100 APU operates on the fundamental principles of a gas turbine engine, utilizing a Brayton cycle. Air is drawn into the engine and compressed by a single-stage centrifugal compressor. This high-pressure air is then directed into an annular combustor, where fuel is introduced and ignited. The hot, expanding gas flows through a single-stage axial turbine, which is mechanically coupled to the compressor and the accessory gearbox. The turbine extracts energy from the high-temperature gas to drive the compressor and a starter/generator. A portion of the high-pressure bleed air from the compressor section is tapped for the aircraft's pneumatic systems. The design incorporates advanced materials such as nickel-based superalloys (Inconel 718) in the turbine section, providing exceptional creep strength and oxidation resistance at elevated temperatures, critical for life-limited components. A robust, fully-integrated digital control system manages fuel flow, speed governing, and temperature regulation, ensuring the engine operates within its designed envelope for maximum efficiency and component life.
Note: The APU is a serialized, life-limited component and is subject to mandatory inspection intervals and potential replacement of critical life-limited parts (LLPs) such as the turbine rotor and compressor impeller. Installation and all maintenance procedures must be performed by an appropriately rated facility and certified A&P mechanics in accordance with the APU's Component Maintenance Manual (CMM) and the aircraft's maintenance program.
