The Allison Model 250 is the world's most successful small gas turbine small engine. Designed for 250 hp and first flown in 1961, most manufacturers at the time expected piston engines to fill this market. The U.S. military designation for this engine is the T63.
Now built by Rolls-Royce, over 28,000 T63/250s have been produced.
 

models

• 250-B17C: 420 hp (313 kW)
• 250-C20B: 420 hp (313 kW)

specifications

• Turboprop/Turboshaft
• Compressor: 6-stage axial + 1 centrifugal
• Turbine: 2-stage gas-generator/
• 2-stage power
• Mass flow: 3.1 lbs/sec
• Pressure ratio: 6.3

used by

• Bell 206 JetRanger
• G.A.F. Nomad
• Hughes OH-6 Cayuse