This explains how the Fan up front is well worth the MOD..

Pratt & Whitney’s new PurePower Geared Turbofan aircraft engines are impressive beasts. Scheduled to enter commercial service before the end of the year, they burn 16 percent less fuel than today’s best jet engines, Pratt says. They pollute less. They have fewer parts, which increases reliability. And they create up to 75 percent less noise on the ground, enabling carriers to pay lower noise fees and travel over some residential areas that are no-fly zones for regular planes. Airbus, Bombardier, Embraer, Irkut, and Mitsubishi have certified the engines for use on their narrowbody craft. JetBlue, Lufthansa, Air New Zealand, Malaysia’s Flymojo, and Japan Airlines are among the engine’s 70 buyers in more than 30 countries.
To people outside the aircraft business, what may be most remarkable about the engines is that they took almost 30 years to develop. That’s about 15 times as long as the gestation period of an elephant and unimaginably longer than it takes to pop out a smartphone app. Could Pratt have gotten the hardware out faster? Probably. But industrial innovation on the scale of a commercial jet engine is inevitably and invariably a slog—one part inspiration to 99 parts perspiration.
In Pratt’s case, it required the cooperation of hundreds of engineers across the company, a $10 billion investment commitment from management, and, above all, the buy-in of aircraft makers and airlines, which had to be convinced that the engine would be both safe and durable. “It’s the antithesis of a Silicon Valley innovation,” says Alan Epstein, a retired MIT professor who is the company’s vice president for technology and the environment. “The Silicon Valley guys seem to have the attention span of 3-year-olds.”