Honeywell auxiliary power unit

Honeywell auxiliary power units are a series of gas turbine auxiliary power units (APU) made by Honeywell Aerospace. Honeywell started manufacturing APUs in the early 1950s and since then they can be found on many aircraft.^[1] Over the years Honeywell have produced more than 95,000 APUs and more than 36,000 are still in service.^[2]

In 2018 Honeywell had a 65% share of the airliner APU market and is the sole supplier for the Airbus A350, the Boeing 777 and single-aisle airliners: the Boeing 737 MAX, Airbus A220 (formerly Bombardier CSeries), Comac C919, Irkut MC-21 and Airbus A320neo after Airbus removed the Hamilton Sundstrand APS3200 option. Pratt & Whitney Canada (P&WC) claims the remaining 35% of the APU market with the Airbus A380, Boeing 787 and Boeing 747-8.^[3]

The 131-9D initially was designed for the McDonnell Douglas MD-90 series; the 131-9B became standard equipment on Boeing 737NG; the 131-9A on the Airbus A320 family.^[4] The 131-9C has entered service aboard the Airbus A220 (formerly Bombardier C-Series). The 131 Series uses a two-stage axial turbine and a single generator which starts the APU.^[5]

The 331 series are found on many wide-body Boeing and Airbus aircraft and the Honeywell 331-200 introduced several new technologies such as digital electronic control and the eductor for oil cooling, which eliminated the need for cooling fans. The development of a turboprop derivative from the Honeywell TPE331 also reduced development time and production costs.^[6][7] Its applications include Airbus A220 -100 and -300 series, A300, A330, A340, Boeing 767 and 777, Bombardier CRJ700/900/100, Comac C919 and Irkut MC-21.

• Auxiliary power unit
• Pratt & Whitney Canada

• Passenger aircraft and their APUs (pg. 7)
• Pratt & Whitney Canada APUs