Lockheed Martin to convert three F-35s as flight test aircraft
April 23, 2025
The F-35 Joint Program Office (JPO) has wanted to expand its test fleet for some years, since existing test aircraft are becoming increasingly unrepresentative of today’s Technology Refresh 3 standard, and tomorrow’s Block 4 configuration. Some aircraft in the test fleet may also be suffering from reduced availability due to obsolescence and age, or even becoming structurally fatigued.
A shortage of test aircraft was held to be partially to blame for delays in testing TR-3, and the JPO has said that the scope of the Block 4 upgrade will require a higher test tempo than has been achieved in recent years if an operational capability is to be fielded in a timely manner. Up to now, the test team has been supplementing its force with production aircraft, but these are not the optimal solution for flight sciences testing. New dedicated test aircraft will therefore be required In order to maintain a high tempo of testing and to avoid any increase in what is an emerging test capability gap.
In January 2023, Lockheed Martin was issued with a similar US $320 million contract modification to provide non-recurring engineering services to support the production of six new F-35 flight science test aircraft. The more recent contract modification is understood to provide for the conversion of three further test aircraft, and was emabled by an amendment to the fiscal 2025 Air Force budget sponsored by Rep. Rob Wittman (R-Va.).
The conversion of production aircraft to flight sciences test aircraft is likely to involve the installation of load-sensing and measuring instrumentation, telemetry equipment, cameras and recorders, and might see the removal of some hardware not required for the test mission.
The Navy made the contract modification to the US $1 billion contract originally awarded to Lockheed Martin in December 2022. This covered the supply of 118 Lot 18 F-35 aircraft for the US armed forces and a number of allies. The Government Accountability Office has warned that sourcing the new test aircraft from Lot 18 production means that they are unlikely to be delivered before 2029.
On 21 April 2025, the US Department of Defense announced that Naval Air Systems Command would obligate funds for the contract modification using fiscal 2025 research, development, test and evaluation funds from the Air Force and the Navy and non-US DoD programme partner funds. Work will be undertaken in Texas, California, Florida, Maryland, New Hampshire, Denmark and the UK.
The Pentagon has said that the converted test aircraft will “allow for future, holistic flight science testing of Block 4 capabilities for the Air Force, Marine Corps, Navy, non-US Department of Defense programme partners, and Foreign Military Sales (FMS) customers.” The work is due to be completed by December 2028.
There has been some speculation that some or all of the three additional test aircraft could be intended to replace the three instrumented test aircraft used by the UK’s No.17 Test and Evaluation Squadron at Edwards AFB. These aircraft (BK-01/ZM135, BK-02/ZM136 and BK-04/ZM138) were all LRIP (Limited Rate Initial Production) F-35Bs from Lots 3 and 7, and are scheduled to be de-modified and replaced. One later Lot 14 aircraft (BK-31/ZM165) was delivered to No.17 Squadron at Edwards AFB on 21 June 2023, but it is not clear whether this has been modified with flight test instrumentation.
