Petrov and Bunin exchanged triumphant glances. While Russia’s stealth bomber was primarily intended as a strategic strike platform to hit high-value fixed sites—enemy command centers and air bases, for example—they’d just demonstrated an additional capability to conduct attacks on well-camouflaged tactical targets. That made the PAK-DA a match for America’s B-2s, which had been used for years against terrorists in Afghanistan, Libya, and Syria.

“Understood, Chkalov,” Petrov said. He glanced across the cockpit at his copilot. “What’s left on our checklist, Oleg?”

“Just one more computer test,” Bunin told him, reading a menu of action items from one of his displays. “We need to verify the handoff between our primary and secondary computers in case of trouble.”

Petrov considered that. Because the bomber prototype relied so heavily on computers to manage its advanced fly-by-wire flight controls, weapons, defenses, and sensors, it was equipped with redundant backup computer systems. If its crew lost their main computer, either because of battle damage or some other malfunction, secondary systems were supposed to take over automatically. They’d successfully demonstrated this switching capability several times on the ground. Now it was time to make sure it worked when it counted, in the air.

“We’ll head back to the barn,” he decided. “And conduct that last test on our way.”

He rolled the PAK-DA into another turn, this time back around to the northwest. A new steering cue appeared. They were roughly one hundred kilometers from the test center’s Akhtubinsk military airfield, approximately eleven minutes’ flying time at their present speed.

“Standing by to shut down the primary computer,” Bunin said. His fingers were poised over a menu on his largest MFD.

“Permission granted,” Petrov replied.

Bunin tapped one of the icons on his screen and then used the virtual keyboard that appeared in response to enter a code confirming his instruction. Tupolev’s software engineers wanted to make sure no one could shut down the aircraft’s computer systems with a simple accidental finger swipe.

Immediately, every multifunction display in the cockpit went dark.

And stayed dark. So did Petrov’s HUD.

“Der’mo,” he snarled. “Shit.” When they’d tried this out on the ground, the secondary computer had taken over so fast that all they’d noticed was a slight flicker on the screens. “Bring the secondary computer up manually.”

“Yes, Colonel,” Bunin said. He flipped open a panel on the console set between them and pushed a system reset button. Nothing happened. He tried again, but all the screens stayed blank.

“Go back to the primary computer,” Petrov ordered.

Bunin nodded and punched the main computer’s manual reset button. Again, there was no response.

Turbulence buffeted the bomber. Caught by a sudden gust, it banked slightly to the right. Instinctively, Petrov tried to level out again. The stick felt dull and mushy in his hand. Like all flying wings and many other advanced military aircraft, the PAK-DA prototype was inherently unstable. It relied heavily on computerized fly-by-wire systems to make the adjustments to its elevons and rudders that were necessary to maintain controlled flight.