EDWARDS AIR FORCE BASE, Calif. — As debate rages in Washington over replacing the A-10 attack plane with the fifth-generation joint strike fighter, test pilots at Edwards Air Force Base, California, are getting a firsthand look at the F-35's capabilities.

So which platform is better for protecting soldiers in a firefight: the A-10 or the F-35? Lt. Col. Raja Chari, who started out flying F-15 Strike Eagles and is now director of the F-35 integrated test force and commander of the 461st flight test squadron, weighed in during an interview here with Defense News.

"You need to really define: What exactly are you talking about when you say [close-air support]? The way you define the question will dramatically affect the answer that you come up with," Chari said Tuesday, fresh off his latest F-35 test flight. "Are you talking about CAS in a low-threat environment, or CAS in a high-threat environment? Basically, contested or uncontested?"

If US forces are fighting in a high-threat environment, the A-10 "isn't really in the conversation," Chari said. While the Warthog performs well in Iraq and Afghanistan, where the skies are uncontested, it is not suited for operating against more sophisticated air defenses.

Commanders can send an A-10 into a high-threat battlefield, "but you can only do it once," Chari said.

Critics of the Air Force's plan to retire the A-10 and replace it with the F-35 often claim that the Warthog can loiter over the target for 90 minutes, while the F-35A can only stay on station for 20 to 30 minutes. But Chari said in an uncontested environment, where tankers would be available, the F-35 can easily loiter above the battlefield for an hour and a half.

A pilot from the 61st Fighter Squadron at Luke Air Force Base prepares for take off July 28, 2015. Since 2010, the F-35 Lightning ll has flown more than 30,000 hours. (U.S. Air Force photo by Staff Sgt. Staci Miller)

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A pilot from the 61st Fighter Squadron at Luke Air Force Base, Ariz., prepares for take off July 28, 2015.

Photo Credit: Staff Sgt. Staci Miller/US Air Force

"If you are talking a non-contested environment, which would be the only place you could make that comparison with the A-10, you are going to have tankers, so it's kind of moot," Chari said. "You could easily get to 90 minutes if you are 15 minutes from where you are going to loiter."

In current operations against the Islamic State group in Iraq and Syria, commanders use a variety of platforms to perform CAS: the A-10, the F-15, the B-1 bomber and unmanned MQ-9 Reapers. The F-35 will have the same advantages of the F-15 — that it can get to a target faster than the A-10, Chari said, also noting that the F-35 has a bigger gun than the F-15.