Reports continue to surface about various problems with F-35 fighter jets after decades of development and over a trillion of dollars invested, including multiple extensions of the programme's budget.

US Senator Chuck Grassley has questioned the effectiveness of the Pentagon's handling of its F-35 Joint Strike Fighter programme in a letter to Defence Secretary Mark Esper. The senator argued that the programme's mismanagement has led to "delays to the mission readiness" and to jets being unsafe for the pilots flying them.

"Since its inception, the F-35 Joint Strike Fighter has been plagued by technical issues, delays and exorbitant costs", Grassley wrote.

Grassley pointed out, citing March and June reports by the Pentagon’s inspector general, that the DoD's failure to keep track of the programme's actual costs has led to "financial waste". The March probe showed that the US Department of Defence “does not know the actual value” of the jets its buying because it left the task of keeping records to the Lockheed Martin Corp, responsible for their production.

The lawmaker further recalled an incident when the flying time of “mission-ready” planes was inflated. The DoD has been installing some of the F-35's parts, even though they were not ready for it because they lacked electronic records to boost the operational time of the "mission-ready" jets. This led to increases in incentive fees, paid by the Pentagon to Lockheed Martin.

"These reports indicate significant mismanagement and poor oversight of the F-35 program on the part of DOD. So long as these issues remain, DOD will continue hemorrhaging money on the F-35 program", Grassley wrote.

Despite spending decades on development and over $1.5 trillion, the costly F-35 jets reportedly continue to struggle with technical issues. Documents recently obtained by Defence News revealed that in 2018 the fighter jet had 13 issues that could cause death, severe injury or illness, loss or damage to the aircraft.

Namely, the F-35 cabin sometimes experience pressure spikes giving pilots ear and sinus pain, the jet's structure suffers structural damage at speeds over Mach 1.2 and its batteries may prompt errors during cold weather at or near minus 30 degrees.