Today, news outlets are reporting on what seems like a new F-35 development revelation: that the jet’s radar system is not reliable and has to be restarted regularly. But this isn’t a newsworthy issue—it’s just one tiny bullet point in a long list of F-35 deficiencies that were brought on by the flawed Joint Strike Fighter concept to begin with, and the even more flawed development and procurement plan that followed.

The sudden high-profile nature of the F-35's radar stability problem is puzzling, as the report that detailed it and many other issues has been out for some time. Few outlets actually quote the report itself, so I’ll do it here:



“Results from 3iR6 flight testing demonstrated partial fixes to the five “must fix for Air Force IOC” deficiencies, showing some improved performance. Poor stability in the radar, however, required multiple ground and flight restarts, a condition that will reduce operational effectiveness in combat.

Instabilities discovered in the Block 3i configuration slowed progress in testing and forced development of additional software versions to improve performance. Two additional versions of the 3iR5 software were created in an attempt to address stability in start-up of the mission systems and inflight stability of the radar. Overall, radar performance has been less stable in the Block 3i configuration than in Block 2B. The test centers developed a separate “radar stability” series of tests—including both ground startup and inflight testing—to characterize the stability problems. Radar stability is measured in terms of the number of times per flight hour that either of these events occurred: a failure event requiring action by the pilot to reset the system; or, a stability event where the system developed a fault, which affected performance, but self-corrected without pilot intervention. For the last version of Block 2B software—2BS5.2—the test team measured a mean time between stability or failure event of 32.5 hours over nearly 200 hours of flight testing. For 3iR6, the time interval between events was 4.3 hours over 215 hours of flight testing. This poor radar stability will degrade operational mission effectiveness in nearly all mission areas.”

So there it is: the radar software currently flying on the non-test F-35s, including those supposedly “operational” F-35Bs owned by the Marine Corps, had a meantime between failure of 32.5 hours. This is not a horrible statistic considering that—regardless of what the Pentagon will tell you—the F-35 is still a weapon system deep in development. Now the new software being tested is a different story, with just an average of 4.3 hours between major failures.

Obviously, there are major bugs in this newer package of code, but that also is nothing new. The F-35's software remains mired in developmental issues and remains behind schedule. We know that and have known that for years. And when it comes to radar reliability, in defense of the program in this particular instance, fighter aircraft radars are not historically known for their rock-solid reliability. Quite the contrary, in fact.

Before the advent of Active Electronically Scanned Array (AESA) radars (here is a good primer on those), mechanically-scanned radar systems installed in fighter and attack aircraft were notoriously finicky.



You can imagine why: moving a radar array around rapidly under as much as nine times the force of gravity, while being buffeted and vibrated, as well as dealing with the jolt of landing over and over, would take its toll on any electro-mechanical system. There’s also the harsh environments that these airborne radar sets could find themselves in, with extreme heat, cold and high humidity all being factors.

The AESA radar does away with the mechanical steering components of mechanically scanned array radars and they also usually include a total digitalized upgrade the radar’s back-end. In the end they represent significant leaps in capability and reliability.

Take the F-15 that was introduced in the 1970s, for instance. Its APG-63 radar evolved into one of the most capable in the world, but even as the system matured, it was not very reliable. The average time between failures was around 10-15 hours.

The new APG-63V3 AESA radar, which is finding its way onto the F-15C/D fleet, has a targeted increased time between failure by a factor of as much as 10 to 30, depending on the source.

With this in mind, yes, the F-35's radar woes are an issue, but they appear to be mainly software related. The F-35's APG-81 AESA has been in development for many years, and has flown on BAC-111 and CATbird test aircraft long before on the F-35 itself.


Additionally, it features proven components found on operational AESA arrays today, including its cousin, the F-22 Raptor APG-77. As such, the issue is just one of a long list of other issues, and many of those are far more eyebrow raising than this one.

It’s strange that the media would jump on this seemingly obscure developmental issue today, and without proper explanation these stories seem as if the F-35's radar is completely useless, even though the only supposedly operational aircraft that are flying today are using an older version of the software that features a far higher reliability when radar usage is concerned.


One could take any of the F-35's many smaller issues and make a headline out of them for the day, even the unglamorous ones. For instance, the aircraft’s weapons bays:

“Testing to characterize the vibrational and acoustic environment of the weapons bays demonstrated that stresses induced by the environment were out of the flight qualification parameters for both the AIM-120 missile and the flight termination system (telemetry unit attached to the missile body required to satisfy range safety requirements for terminating a live missile in a flight test).

This resulted in reduced service life of the missile and potential failure of the telemetered missile termination system required for range safety.”

And even more issues with the F-35's weapons bays:


“Testing to characterize the thermal environment of the weapons bays demonstrated that temperatures become excessive during ground operations in high ambient temperature conditions and in-flight under conditions of high speed and at altitudes below 25,000 feet. As a result, during ground operations, fleet pilots are restricted from keeping the weapons bay doors closed for more than 10 cumulative minutes prior to take-off when internal stores are loaded and the outside air temperature is above 90 degrees Fahrenheit.

In flight, the 10-minute restriction also applies when flying at airspeeds equal to or greater than 500 knots at altitudes below 5,000 feet; 550 knots at altitudes between 5,000 and 15,000 feet; and 600 knots at altitudes between 15,000 and 25,000 feet. Above 25,000 feet, there are no restrictions associated with the weapons bay doors being closed, regardless of temperature. The time limits can be reset by flying 10 minutes outside of the restricted conditions (i.e., slower or at higher altitudes). This will require pilots to develop tactics to work around the restricted envelope; however, threat and/ or weather conditions may make completing the mission difficult or impossible using the work around.”

When you look at how troubled the F-35's development continues to be, even after the Marine Coprs has declared the jet operational largely under phony circumstances, and the Air Force looks to do the same soon, the F-35's radar software glitch is just a bug—and really the least of program’s worries.

Contact the author at