The engine that made the jumbo possible

The JT9D made the Boeing 747 possible. When RA001 first flew on 9 February 1969 it ran on four JT9Ds rated at 43,500 lbf (193 kN) each - the first high-bypass turbofans ever to fly on an airliner, and far quieter and more economical than the turbojets the 747 was meant to replace.

Key facts
Applications	747-100, -100B, -200, -200B, -200F, 747SP, -300 (never -400 or -8)
Thrust classes	JT9D-3/-3A 43,500 lbf; -7A 46,150 lbf; -7F 48,650 lbf; -7J 50,000 lbf; -7R4G2 54,750 lbf
Bypass / fan	4.8:1 ratio; 92.3 in fan (-3A), 93.4 in (-7 series)
Launch customer	Pan Am - first revenue JT9D 747 flight 22 January 1970, JFK - LHR

The JT9D entered airline service on Pan Am 747-100s in January 1970 and was the only engine offered on the 747-100. Early reliability was poor: compressor stalls, fatigue cracks and a distinctive casing distortion nicknamed "ovalization" caused serious delays in 1970 - 71. A catastrophic engine-and-wing fire on a Pan Am 747 at JFK in July 1970 forced FAA inspections across the fleet.

Pratt & Whitney redesigned the titanium thrust frame that carried the engine, curing the ovalization problem, and later JT9D variants grew steadily in thrust. The JT9D-7R4G2 at 54,750 lbf took the engine onto the 747-300, while the 747SP was powered by JT9D-7 variants up to 50,000 lbf - the NASA/DLR observatory SOFIA, a 747SP, still flies on four JT9D-7Js.

The JT9D family ultimately logged more than 169 million flight hours across all applications, proving the high-bypass concept the whole industry now uses.

The engine that made the jumbo possible

The JT9D is inseparable from the 747 because for the first three years it was the only engine on the type. When RA001 first flew in February 1969 it ran on four JT9Ds, and for a 747-100 there was no alternative - which gave Pratt & Whitney extraordinary leverage in the type's early commercial life, with Pan Am as launch customer.

The early engine was also a difficult one. The first years of 747 operation were marred by compressor stalls, fatigue cracking and casing distortion - the "ovalization" that came to characterise early JT9D-powered 747s - producing serious delays in 1970 and 1971. A catastrophic engine-and-wing fire on a Pan Am 747 at JFK in July 1970 grounded the fleet and forced inspections across the type. Pratt's redesign of the titanium thrust frame that carried the engine cured the structural distortion that had been behind much of the trouble.

Long life and long reach

What makes the JT9D remarkable is how long it kept mattering. Variants grew in thrust through the -200, the -200B, the -200F, the 747SP and the -300, the -7R4G2 variant taking the engine to 54,750 lb on the -300. The NASA/DLR SOFIA observatory, a converted 747SP, still flies on four JT9D-7Js. The family ultimately logged more than 169 million flight hours, and it proved the high-bypass turbofan concept that the entire industry now builds on. By the time the 747-400 arrived, the CF6, RB211 and PW4000 had ended the JT9D's exclusivity, but the engine had already defined the type.

Related

• Fuel system
• Hydraulic systems
• Electrical system
• 747-8 systems differences