The Bombardier Learjet 45 jets have two different engine choices. Initially, Bombardier Learjet selected the AlliedSignal TFE731-20R engine to be the Learjet 45 engine. AlliedSignal acquired/merged with Honeywell in 1999 and Honeywell was selected as the new company name for the combined firm. Because of the merger, the engine is now the Honeywell TFE731-20R. An improved version of the -20R engine was introduced after aircraft serial number 45-052 and is referred to as the Honeywell TFE731-20AR. Most Learjet 45s built before 2004 have the Honeywell TFE731-20AR engines.

The New Learjet 45 Engine

In 2004, Learjet announced the arrival of the new Learjet 45 XR, a Learjet 45 with a new version of the TFE731-20 series engine. As part of the revamp of the aircraft, the Learjet 45 engine was upgraded to the Honeywell TFE731-20BR engine. The Honeywell TFE731-20BR engine allowed the Learjet 45 to have a reduced balanced field length, better performance in hot and high conditions, and enhanced payload to range numbers. The only difference between the TFE731-20BR and the TFE731-20AR is that the TFE731-20BR operates at higher Interstage Turbine Temperature (ITT) ratings, according to the type certificate for the TFE731 series engines.

The Honeywell TFE731-20BR engine is available as an upgrade to older Learjet 45s. The older Learjet 45s TFE731-20AR can be upgraded to the TFE731-20BR without installing a new engine. Learjet Service Bulletin 45-72-1 outlines the process of upgrading the Learjet 45 engine and gives information on the other service bulletins needed to perform the changes.

The Bombardier Learjet 45 and 45 XR Engine The Honeywell TFE731-20

Above photo of the Bombardier Learjet 45 Engine or the Learjet 45 XR engine by Honeywell. Photo used under the fair-use provision.

Below are the specifications for the engine. The information for the engines is from the FAA type certificate for the engine and data published by Bombardier.

Learjet 45 Engine Specifications - TFE731-20 Specifications

Honeywell TFE731-20 Series (-20AR ,-20BR, and -20R)
Thrust: 3,500 Pounds (lbs) (15.56 kN) Takeoff at Sea Level Thrust: 3650 lbs
Flat rated to: ISA + 25°C (104°F) (BR Version)
Weight (Dry): 895 lbs
Fuel: Jet A, Jet A-1, JP-8 conforming to Honeywell specifications
Aviation Gasoline or Avgas ASTM D 910 Grades 80 or 100LL no more than 500 gallons every 100 hours of operation may be used for emergencies.
Oil: Conforming to Honeywell specification EMS53110.
TFE731-20R Applied for certification on 1/19/1993 and issued or amended on 4/4/1997

RPM Limitations (Revolutions per minute)

Takeoff/Maximum Continuous: Low Pressure Rotor (N1): 21,000 RPM High Pressure Rotor (N2): 31,485 RPM
Maximum Transient (control overshoot): Low Pressure Rotor (N1): 21,105 RPM High Pressure Rotor (N2): 31,957 RPM

Temperature Limits

Max Interstage Turbine Temperature (ITT) Limits
F = Fahrenheit C = Celsius

TFE731-20AR Max Continuous: 1,726 F (941 C) Takeoff: 1,766 F (963 C) Starting Air/Ground: 1,726 F (941 C)
TFE731-20BR Max Continuous: 1,816 F (991 C) Takeoff: 1,871 F (1022 C) Starting Air/Ground: 1,822 F (994 C)
TFE731-20R Max Continuous: 1,726 F (941 C) Takeoff: 1,766 F (963 C) Starting Air/Ground: 1,726 F (941 C)

Note: The normal 5-minute takeoff time limit may be extended to 10 minutes for engine out contingency.

Maximum Oil Inlet Temperature Range:

Fan Gearbox Inlet Maximum: Sea Level to 30,000 feet: 260 F (127 C) Above 30,000 feet: 284 F (140 C)
Accessory Gearbox Inlet Maximum: Sea Level to 30,000 feet: 300 F (149 C) Above 30,000 feet: 315 F (157 C)
Fan gearbox oil inlet temperature transient of 300 F (149 C) for a maximum of 2 minutes.

Fuel and Oil Pressure Limits

Fuel pump inlet pressure
Minimum: 5 pounds per square inch (psi) above true vapor pressure
Maximum: 50 psig

Oil pressure

Minimum: 50 psig
Normal operating range: 65 to 80 psig

The engine is a turbofan that has the following features: One stage geared fan, four stage axial flow low pressure compressor, one stage centrifugal high pressure compressor, annular combustor, one stage
high pressure turbine, and three stage low pressure turbine.

Engine Differences

TFE731-20 Same as the TFE731-60 basic model except one-stage geared fan (midspan
dampered rotor blade), modification to the tangential onboard inducer
(TOBI), DS material for first-stage LP turbine blade, different HP
turbine nozzle area, different combustor and fuel atomizer shroud
cooling scheme, different external assembly (plumbing, electrical, etc.).

TFE731-20R Same as TFE731-20 except the -20R incorporates the APR and/or MPR

TFE731-20AR Same as TFE731-40R except different external assembly (plumbing,
electrical, etc.).

TFE731-20BR Same as TFE731-20AR except operates at the higher ITT ratings of the
-40R engine.

Also note that the Honeywell TFE731-20 series engines also have the -1B designation at the end: TFE731-20R-1B, TFE731-20AR-1B and TFE731-20BR-1B. Also the Bombardier Learjet 45 Engine is known as the LJ45 Engine.