Aircraft engines have never been safer and more reliable than they are today. Engines of all stripes have made great strides when it comes to this all-important measure.
In the debate over the alternate engine for the F-35 Joint Strike Fighter, however, there’s an edge when it comes to reliability and safety. And the Pratt & Whitney F135 holds that edge.
An engine’s performance is tied to pedigree. Fighter engines that mature as part of a twin-engine platform end up safer and more reliable than those that are developed solely for a single-engine aircraft.
We know that the F135 engine was borne of the F119 engine that is currently powering the F-22 Raptor twin-engine fighter. In fact, the F135 uses the same core as the F119, which itself has benefited from more than 22 million hours of F100 operational flight time world wide, leading directly to better reliability.
The Pratt & Whitney F100 family of engines powering the F-16 has a much lower U.S. Air Force mishap rate than the competing F110 engines on the same platform (the second engine of the Great Engine War; see previous blog entry). The F100 matured in the twin-engine F-15, while the F110 was developed on just the single-engine F-16. The cumulative mishap rate for the F100 is at least 15 percent less than its F110 competitor. In fact the latest generation F100 engine has a mishap rate of zero.
The reasons for this gap in reliability are two-fold. First, an engine matured in a twin engine application can experience a more robust operating environment based on the different missions accomplished by the different aircraft. Twin engine aircraft can perform more challenging maneuvers with less risk of aircraft loss because of the second engine. Second, the maturity time increases at a greater rate for twin-engine jets because hours and learning are logged at twice the rate.
An engine brought in late in the game for a single-engine aircraft still must go through the same trial-and-error process, but without that crucial backup of a second engine.
An alternate engine actually reduces the rate of maturity of the fleet-wide propulsion system because two different engines reduce the accumulated time for maturing either one.
Furthermore, the idea that an alternate engine would prevent fleet-wide groundings ignores the fact that such groundings due to propulsion issues are virtually unheard of these days.
Advances in safety risk management and mitigation practices have all-but-eliminated the need to ground entire classes of aircraft when issues arise. If an engine issue were to arise, specific bases would likely call for a local safety stand-down to take a corrective action while letting the fleet to continue to fly safely.
Even if fleet-wide grounding were a legitimate concern, an unneeded second engine would not be an effective safeguard. The fact that the alternative engine doubles the number of vendors, parts and procedures makes it mathematically more likely that some portion of the fleet might be grounded due to an adverse incident. This is an issue that was highlighted by Senator Tom Harkin back in 2007. Senator Harkin, a Navy pilot in the 1960s, said: "We had problems all the time . . . and there was a series of supply problems and mix-up problems with parts and everything” (Inside the Air Force, 12/14/07). So the alternate engine actually makes the F-35 less safe and reliable.
With all of this, we can now add safety and reliability to the long list of reasons that the alternate engine for the F-35 is a bad idea.