Nobody had seen it before because nobody had looked at both engines at the same time. Every diagnostic protocol in the book isolates each engine as an independent system: you check the left, then you check the right, separately, always.
But the CA-90 has a crossfeed system: a butterfly valve that allows fuel to balance between the left and right wing tanks during flight. It's a safety feature. It's also the only system that physically connects both engines' fuel supply.
"Your crossfeed valve is cycling," Faith said. "Every 8 seconds it opens when it shouldn't. It pulls fuel from the left engine feed line for 3/10 of a second. That's enough to starve the left engine just slightly. Not enough to trigger an alarm, but enough to destabilize combustion over time. Run it for 90 seconds, and the instability cascades. Both engines read it as a flameout condition and shut down."
The room was silent. Neil was staring at the overlaid data like he was seeing it for the first time—because he was.
Todd Whitmore spoke from the back wall: "That's a coincidence, not a diagnosis. A 3/10 of a second fuel dip doesn't ground an aircraft."
Faith didn't look at him. "Fifty of them in 90 seconds does."
Dr. Sutter wrote something in her notebook; she didn't look up.
Revelation two: the smell.
Faith asked Neil to restart both engines. When they spooled up, she did something nobody expected: she walked away from the diagnostic console, away from the engine nacelle. She walked downwind, about 20 feet behind the left engine's exhaust port, and she stood there, breathing slowly through her nose.
Todd laughed. "What's she doing now, yoga?"