One of them held up a hand. Sir, we're in pre-departure sequence. You need to get Derek Vaughn. Caleb kept walking right now. Get him now.
He walked past the ground crew, past the fuel truck, and stopped at the base of the aircraft stairs. The engines were building toward full pressure. The noise was immense. He pressed one hand against the fuselage skin. There, faint, but present, a vibration that was separate from the engine harmonics, lower frequency originating somewhere in the midfuselage section.
Derek appeared at the top of the stairs. Hart, what the? Shut the engines down, Caleb said. We're in the middle of a power test. Shut them down, Derek.
Derek looked at the diagnostic screen in his hand. Everything is green. Every system is I can feel something in the fuselage skin that shouldn't be there during a power test. The sensor housing issue corrupted the diagnostic data network before I repaired it. The green readings you're looking at might not be.
Our systems are showing clean across the board. Then shut them down and show me I'm wrong. Caleb looked up at him without raising his voice. What does it cost you to be wrong for 5 minutes? What does it cost her if I'm right?
Derek stared at him from the top of the stairs. Vanessa Sterling appeared beside him. She was looking down at Caleb, one hand on the railing of the aircraft stairs, and her expression was entirely different from the one she'd worn when she handed him the money. Something was moving behind her eyes. She was actually looking at him, not at the mechanic, not at the man in the faded jacket, but at whatever was behind his face.
He wasn't angry. He wasn't trying to create a scene or assert himself or reclaim something she had taken from him. He was scared, not for himself, for whatever was happening inside that fuselage. She looked at Derek. "Shut them down," she said.
The engines wound down in stages, not all at once. But in that particular descending sequence that Caleb had heard hundreds of times, the turbines releasing pressure like a held breath slowly let go. The ground crew stood watching with the specific uncertainty of people whose schedule had just been rearranged by someone they had no framework for understanding. Derek Vaughn came down the aircraft stairs with the expression of a man who had agreed to something he was already preparing to regret. Vanessa followed him down.
She had changed nothing about her posture or her face, but something had shifted in her attention. She was focused in a way she hadn't been 20 minutes ago when she handed Caleb the $100 bill and walked away from him like he was a receipt she'd already forgotten. "You have 10 minutes," Derek said. Caleb didn't bother responding to the timeline. He went to the starboard side of the fuselage and pressed both palms flat against the skin just aft of the wingroot.
He closed his eyes. This was not theatrical. Was the same thing he did with his truck when it started making a sound. He didn't recognize removed the noise. removed the information and just listened to the physical thing telling him what was wrong with it. Nothing's showing on the diagnostics, Derek said from behind him.
He was holding his tablet like a shield. I know. Both primary and secondary systems are reading clean. We ran the automated cycle twice before you arrived this morning. Now that too.
So what exactly are you, Derek? Vanessa's voice. Quiet. Final. Derek stopped talking.
Caleb moved forward along the fuselage, keeping contact with the skin as he walked. He was not entirely sure what he was looking for. That was the honest truth of it. He had heard something during the power up sequence, felt it more accurately in the way that sound at a certain frequency becomes less a thing you hear and more a thing you register in your sternum. And he had learned across many years of working on aircraft that the difference between a problem and a catastrophe was often the willingness to stop and look when something felt wrong, even when the screen said otherwise.
He stopped near a service access panel about 12 ft aft of the wing trailing edge. He crouched down. The panel was secured with the standard quarter turn fasteners, and he had his driver out before he'd consciously decided to open it. He popped the fasteners, lifted the panel, and leaned in with his flashlight. The wiring harness inside was routed correctly.
The structural components visible from this access point looked clean. The light slowly, then he found it. Not in the wiring, in the structure, in the environmental control system ducting that ran through this sections, a secondary conduit, the kind that managed bleed air routing between the engine and the cabin pressure systems. The conduit had a coupling joint in this section, and the coupling had a thermal sleeve around it. The sleeve was there to protect against heat differential expansion during flight.
The sleeve was cracked, not catastrophically, not in a way that would fail immediately on the ground, but it was cracked longitudinally along about 4 in of its length, and the crack had exposed the underlying coupling to direct heat contact. Under sustained flight conditions extended cruise altitude, the thermal cycling of pressurization and depressurization, the coupling would expand unevenly. The joint could begin to fail. bleed air could escape into the structural cavity. Caleb sat back on his heels and let out a slow breath. Behind him, he heard Vanessa move closer.
"What did you find?" she asked. He showed her with the flashlight. She crouched beside him without any hesitation about the condition of her slacks, which he noted without comment. The thermal sleeve on this bleed air coupling is cracked. He said, "You can see the longitudinal split right there.