Despite challenges sustaining the engine for the Defense Department’s F-35 fighter, Raytheon Technologies [RTX] CEO Greg Hayes said on Tuesday that he doesn’t expect the military services to fund an effort to bring on General Electric [GE] as a second supplier of engines to compete with his company’s F135 engine on the program.

“I will tell you that is a multi-billion-dollar, multi-year effort to bring that engine back in line and given the cost challenges on the program, it seems unlikely that any of the services are going to spend that kind of money for an extra engine when in fact our engine is actually performing quite well in service,” Hayes said on Raytheon Technologies’ first quarter earnings call in reply to a question from Ron Epstein, an aerospace and defense analyst with Bank of America Merrill Lynch. “We’re meeting the reliability targets. We’re meeting the fuel burn targets.”

The F135 engine, built by Raytheon Technologies’ Pratt & Whitney segment, was discussed at length last Thursday during a hearing hosted by the House Armed Services Committee to review the F-35 program.

Epstein, in his question to Hayes, said that GE has been “raising their rhetoric…at least with the investment community” on the potential of a second engine source for the F-35 given the sustainment challenges with the F135.

Lawmakers at the hearing heard from the Air Force general in charge of the F-15 integration office, who said 21 of the Air Force’s F-35s are grounded because they lack a serviceable engine, that that engines are having to be removed and repaired from aircraft faster than the depot production can keep up. The Government Accountability Office also reported that sustaining the F135s “may pose its greatest sustainment risk” to the aircraft program “over the next 10 years.”

Hayes said that Pratt & Whitney has “done a good job” of producing F135 engines, adding about 50 are “sitting at the final assembly line” to be installed on F35s. However, he said, the company “didn’t do a great job at the sustainment center” because it underestimated the amount of test equipment and personnel due to the volume of work.

Raytheon Technologies has “committed” to working with the F-35 Joint Program Office “to put the equipment in place necessary to service the engines so get back on…contract performance levels by the end of this year,” Hayes said. “A lot of work to do, but again, we were caught by surprise in terms of the amount of hours that were being flown. We were surprised at the scope of the work that was required on some of these but we will catch up.”

The Pentagon decided more than a decade ago to go with a single engine supplier for the F-35, with Pratt & Whitney’s F135 being the winner. The GE-Rolls Royce partnership developing an alternative F136 engine for the F-35 abandoned the effort in 2011 after the Pentagon and lawmakers on Capitol Hill stopped their support for the program as unneeded and too expensive.