Цитата Сообщение от Maximus_G
Ну в статье довольно точно указано:

The specific area of concern is the "rotor inlet temperature margin," William J. Gostic, vice president of F135 programs, told AW&ST. The immediate fix involves adjusting the engine's bypass ratio to optimize air flow through the engine's core where the most extreme temperatures are experienced. JSF engine manufacturers have the unique problem of designing a Stovl propulsion system with a variable bypass ratio that supports conventional engine operations in addition to periodically supplying thrust for the wing-mounted roll posts and the tail-mounted three-bearing swivel module.

"Currently, we do not have the level of [rotor inlet temperature] margin we desire to have at the end of the [demonstration and] development program," which is still about two years away, Gostic says. He also points out that there is no military requirement for the margin and that the Stovl engine has already demonstrated the 40,550-lb. specification level of thrust.

Some propulsion analysts suggest that the engine's combustor--where fuel and air are mixed and ignited--is too small because, to save money, it was derived from the F-22 engine. As a result, it doesn't have the necessary airflow without additional bypass air. Increasing bypass air can rob an engine of efficiency.
Теперь понятно.
Похоже, что перегреваются детали ротора двигателя.
Нехорошо это, чревато прочностными проблемами, повышенным износом.