The news that an F135 engine experienced an incident that caused damage during testing recently has prompted some questions about exactly what it means to the program.
The good news is that initial information suggests it will not negatively affect engine tests or current flight test schedules.
The first point to make is that Pratt & Whitney is conducting a thorough investigation into the incident, working closely with the Joint Program Office to figure out exactly what caused the incident.
It is also important to note that this is exactly the type of thing you expect and want to find during the advanced stage of testing that the F135 engine is undergoing at this point so it does not become an operational concern. Because the program is so mature – more than 12,500 hours of ground and flight testing – the engine is being put through extremely rigorous testing, pushing the engine much harder than during earlier testing phases. The engine which experienced the incident had the equivalent of eight years of use on it, and the test being performed was in conditions simulating extended supersonic flight at high altitude.
As we have mentioned before, the F135 engine is based on the F119, which is powering the F-22 aircraft, and has more than 100,000 successful operational flight hours. Because the F135 is derived from such a proven engine, we have been able to retire more than 90 percent of the risk associated with the engine. In contrast, an entirely new design, such as the alternate engine, is likely to have a high rate of incidents; much higher than the F135 program has seen. Defense Secretary Robert Gates himself expressed this opinion in relation to the alternate engine. In fact, when you look at the F135 program as a whole, there have been relatively few problems over the more than eight years of development and testing of the engine.
One reason we can say the recent incident is not likely to affect the program schedule or overall flying operations is because the testing was on the second generation of the engine rather than the first. Again, this is a benefit of the maturity of the F135 program. The hardware on the first generation of the engine has already been fully tested and qualified, and is right now safely meeting program schedule requirements. These are the engines being used on the current flight test program.
There’s an important technical point to make about the incident. It was contained in the fan and high compressor sections of the engine and did not affect the turbine section, which had been redesigned after previous testing revealed an issue.
Testing is done for a reason – to find issues before the engine is put into production and ensure the highest possible operational reliability. No rational person would argue that it should be any different.
So how does this affect the alternate engine debate? It has been reported that the F136 has suffered three test failures, and has fewer than 50 hours of SDD test time, since commencing SDD testing in January.
By comparison, P&W’s F135 had four engines running, both CTOL and STOVL configurations, and had accumulated 695 hours nine months into SDD testing. It should also be noted that GE claims they have already spent 70% of the $2.4B allocated to develop their engine, yet they have only accumulated 50 hours of test with no engines currently running. In comparison the F135 Program had more than 6,500 hours and 9 engines in the test program at the same funding point.
This isn’t to say that the competition makes bad engines. To the contrary, they make excellent products. The fact is, as even GE freely admits on the record, that all high performance jet engines will experience issues in the development phase. The F135, however, since it was derived from the proven F119, would be expected to have fewer problems in development and history has proved that. That is one of the reasons it was chosen initially. And, that has proven to have been what has happened. Having an alternate engine doesn’t provide insurance against these issues, it just means the there will be additional risks and issues associated with that second engine. And, that drives up costs and puts the schedule at risk – risks we can’t afford now.