Первым недостатком является его ненадежный и плохо спроектированный двигатель – "самый большой, горячий и тяжелый двигатель, который когда–либо устанавливался на истребитель". Он тяжелее своего предшественника из–за необходимости приводить в действие турбовентилятор модификации с вертикальной посадкой F–35B и, как следствие, тяжелее двигателей других боевых реактивных самолетов с сопоставимой тягой.В 2012 году конструкторы признали ограничения, имеющиеся в двигателе, и снизили характеристики производительности основной модификации F–35A: допустимая перегрузка при повороте была снижена с 9 до 4,6g, а набор скорости с 0,8 Маха до 1,2 Маха увеличен на 8 секунд. В соответствии с отчетом, представленным в 2014 году, среднее время полета между сбоями выше ожидавшегося
The F–35's engine is failing at too high a rate, and its reliability is not improving fast enough to be approved for operational use. The F–35 has a poorly designed, unreliable engine – the largest, hottest, and heaviest engine ever put in a fighter plane. It is a highly stressed derivative of the F119 engine, which powers the F–22. Because of the need to drive the F–35B lift fan, it is about 2,000 lbs heavier than other combat jet engines of comparable thrust. The project recognized the engine's limitations in 2012 by announcing an intention to change performance specifications for the F–35A, reducing sustained turn performance from 9.0g to 4.6g and extending the time for acceleration from 0.8 Mach to 1.2 Mach by 8 seconds. As in September 2014, the Government Accountability Office reported that "[d]ata provided by Pratt & Whitney indicate that the mean flight hours between failure for the F–35A engine is about 21 percent of where the engine was expected to be at this point in the program." But engine reliability is not improving; it has flatlined.
The F–35 requires a runway at least 8,000 feet long to operate from. By comparison, the F–16's minimum runway length requirement is 3,000 feet.
The F–35's operating cost of $50,000 per hour means that we won't be able to afford to give its pilots enough flying time to be fully proficient. The same problem afflicts the F–22 with its $70,000–per–hour operating cost. Raptor pilots get 10 to 12 hours per month in the cockpit when 20 hours are needed to be able to make split–second decisions in combat.
Being designed as a light bomber, the F–35 is less maneuverable than fighter designs up to 50 years old and will be shot out of the sky by modern fighter aircraft. Thus, it wasn't a surprise when an F–16 outflew an F–35 in mock combat in early 2015, a result entirely predictable from simulation. What is telling is that the F–35 is not being flown against other aircraft types on an at least monthly basis. The latest derivative of the Su–27 Flanker, the Su–35, is expected to be able to shoot down 2.4 F–35s for every Su–35 lost. China is in the process of acquiring 24 Su–35s. In combat, those 24 Chinese Su–35s will shoot down 58 F–35s before all being shot down themselves. The Russians have followed the Su–35 with the T–50, which will be close to the F–22 in combat effectiveness but without the cost of maintaining the radar–absorbant material (RAM) coating
The F–35 uses its fuel for cooling its electronics. The aircraft won't start if its fuel is too warm, making deployment in warmer regions problematic. At the Yuma and Luke U.S. Air Force bases in Arizona, fuel trucks for the F–35 are painted white, parked in covered bays, and chilled with water mist systems because the jet won't even start if the fuel is already too warm to cool the electronics.
The F–35 has a logistics system (ALIS) that requires an internet connection to a centralized maintenance system in the United States. ALIS is kept permanently informed of each aircraft's technical status and maintenance requirements. ALIS can, and has, prevented aircraft taking off because of an incomplete data file. If the internet link is down, the aircraft can't fly even if there is nothing wrong with it. This is one of the more bizarre problems. It could lead to a situation in which enemy aircraft are inbound and the F–35s are refueled and ready to go but can't take off to meet the threat.
Первый тестовый полёт F-35B с десантного корабля USS Wasp