At EAA AirVenture 2026 in Oshkosh, Wisconsin, Mid-Continent Instruments and Avionics and True Blue Power president Matthew Harrah stood in front of an  SIAI-Marchetti S.211 jet trainer, one of only about a dozen flying in U.S. civilian hands. It doubled as both a showpiece and working test bed.

As chief test pilot for the company, Harrah uses the airplane to push the company’s instruments and batteries through real flight-test conditions. 

Jonathan Welsh, lead editor of The Aviation Consumer, visited the display to walk through what’s changed under the cowling.

The S.211 itself is a rarity on the American ramp.

Originally SIAI-Marchetti’s jet trainer for the Singapore and Philippine air forces in the 1980s, only about a dozen of the roughly 60 built have found their way into U.S. civilian hands, brokered largely out of surplus military inventories. Harrah’s airplane turns heads at any airshow, but it’s more than a showpiece. 

“The main reason we ended up with this airplane really was for flight tests,” Harrah said. “We do a lot of things that require a high angle of attack, because we do attitude indicators and all kinds of other instruments — all solid state these days. Plus, we still take care of some mechanicals. The simple reality is that we need something that gives us a little bit more safety margin.”

That safety margin, according to Harrah, is the whole point of a flight-test program. 

“Everything you do in a flight test is about risk management,” he said. “We really focused on trying to say, ‘Let’s find the right airplane that’s reliable, that’s efficient, that allows us to do the kind of testing that we do without having any kind of an issue.’”

The centerpiece under the S.211’s cowling is True Blue Power’s Gen5 TB50, a 50 amp-hour lithium-ion, main-ship battery built as a same-size replacement for the lead-acid units that have powered piston and turbine starts for decades. 

Harrah leaned on the company’s long-running tagline to walk through why it matters. 

“We always say, ‘Start lighter, start faster, start smarter,’” Harrah said. “We took 45 pounds out of the airplane just in going to our TB50 lithium battery compared to the lead acid. We’ve got a very narrow center of gravity, so it got us back midrange, right in the middle of the center of gravity envelope, which was fantastic for being able to load up the aircraft.”

The “faster” claim is where the demonstration got specific.

“For us, that’s 10 percent of the high-speed compressor,” Harrah said, describing the moment fuel is introduced on a jet start. “It was taking 12 seconds on the lead acid. We’re now doing it in about four seconds. You basically hit the starter switch and move your hand to the throttle. You’re at 10 percent, and you’re already bringing fuel in.” 

The payoff isn’t just a quicker start, according to Harrah. It’s a cooler, gentler one.

“From there, it means we’re running between 90 and 100 degrees [Celsius] cooler on the start,” he said. “Anybody who flies a large aircraft would recognize it’s a lot less wear and tear on the starter.” 

Brush-type starter-generators are particularly relevant.

“The biggest problem isn’t the energy coming into the starter initially,” Harrah said. “It’s the friction of the brushes on a lot of these brushed starter-generator motors that start to wear and get hot, and that’s the main wear factor. Also, the cooler temps are just a lot easier on the burner section of the engine.”

The “smarter” part is a digital data bus built into the battery itself. 

“We’ve got a data connector on the bottom of the battery, and we’re able to sit there and tell you exactly what the state of charge is and what the health of the battery is,” Harrah said. “So you don’t run into issues with getting into a hot start, because we’re going to tell you you’ve only got a certain percent state of charge left. You’re not trying to force something just off voltage.” 

He noted the voltage difference is dramatic on its own: “Normally on a lead acid, you’d be down to 13 volts at start. We actually stay about 20, 21 [volts].”

Walsh and Harrah turned to Doc, the restored Wichita-based B-29 Superfortress that, coincidentally, flew over the interview mid-taping.

“If you got a big radial engine, like in Doc that we just saw fly over—they’ve got three of our TB40 batteries inside that airplane,” Harrah said. “The difference is just so remarkable…in the way they’re able to turn the prop blades. Normally, for a big radial, you have to count 12 blades. It is amazing how much better they’re now able to motor that thing to get past the hydraulic lock. It’s been really impressive to see, and we’ve been excited to be able to support their efforts.”

Harrah said that same benefit scales down to the S.211’s turbine and up to the biggest warbird piston engines flying today.

“The partnership we’ve had with Doc has been great, and that’s generated quite a bit more of the interest,” he said. “We’re working with everything, T-28s, you get into the big Merlins, the Packard Merlins, 1650s. You pick your motor, and they’re all going to absolutely benefit from it at the end of the day.”

One habit Harrah said has quietly disappeared from his own preflight routine is disconnecting the battery. 

“I am yet to unplug the battery from the airplane,” he said. “A lot of people who fly jets would say if it’s in your lane, you disconnect the battery. If you’ve ever flown a CJ or something like that, that was the first step—you always unplug the battery. We never unplug the battery because of the way the battery management system works. We’re not dealing with this kind of constant draw.”

He offered a real-world number from filming the company’s own testing.

“You can go all the way down to 30 percent state of charge and still get the exact same kind of power out when you start,” Harrah said. 

Recovery was just as quick in testing.

“I was down to 70 percent state of charge,” he said. “Within five minutes I was back north of 90 [percent].” 

Any pilot who flies under 91.187’s 30-minute IFR reserve-power requirement knows that recharge speed is more than a convenience. 

“Now when you take off, that emergency power that you want to have—that 30 minutes of emergency power—it’s pretty much guaranteed you’re going to have it,” Harrah said. “And that’s one of the real safety features that you get behind the battery.”

Longevity is nearly as important, and Harrah said the Gen5 TB50 will be in the test airplane for eight to ten more years.

“They can take 10,000 cycles,” he said. “When you think about what you see out of a lead-acid battery, there’s no way—you’re always going to be less than a thousand cycles.” 

Storage tolerance matters too, particularly for owners who fly seasonally. 

“Easily, you’re going three months without having to put a battery tender on it without any issue,” Harrah said. “The beauty of a lithium-ion battery is they really love to be used…but when it does sit, it doesn’t lose a lot of energy.”

True Blue Power’s lineup now spans a 28 amp-hour, 12-volt battery aimed at the homebuilt and light GA market through 60 amp-hour packs, plus emergency standby batteries used across much of the business jet fleet. 

Harrah singled out one feature built for owners in colder climates. 

“We always think about people up in Canada who are breaking their backs every time they get a cold night,” he said. “If you have to haul a 90-pound battery around, that’s pretty painful. Now you’ve got a 45-pound battery, but you can also just leave it in the airplane because we’ve got the built-in heaters. You just hit a button and it warms itself up. Have a cup of coffee, and then you’re ready to go launch.”

The S.211’s panel doubles as a showcase for the rest of Mid-Continent’s catalog—an MD23 Flex-family standby attitude indicator, altimeter, and the company’s battery status indicator that displays the state of charge right on the instrument, a clock with USB charging ports, and an AC inverter the company has been flight testing in the airplane’s notoriously hot, breezeless nose section to support Starlink connectivity retrofits.

All of it traces back to a simple frustration that Harrah thinks the industry has tolerated for too long. 

“We get used to it—that’s kind of the bad thing in aviation,” he said. “We get used to living with pain, and we shouldn’t have to. So that’s part of our thing when we think about products that we build: How can we make the life of the average pilot, aircraft operator, and owner a lot better.”

Click here to learn more about Mid-Continent Instruments and Avionics and True Blue Power.