In an OVBD COOL FAIL scenario, which valve failed to open after landing?

• A. Ground valve
• B. APU bleed valve
• C. Pack isolation valve
• D. Cabin pressure relief valve

Answer: (A)

When cooling of the outboard bleed (OVBD) circuit on the ground depends on an ambient-air path, a valve labeled to provide that ground cooling must open after landing. If that ground-facing valve doesn’t open, the OVBD cooling flow can’t purge and shed heat, so a COOL FAIL condition is reported even though the aircraft is on the ground. That’s why the ground valve is the correct choice here: it’s the component that directly enables the required cooling path once the airplane has landed.

The other valves serve different roles not directly tied to this post-landing OVBD cooling function. The APU bleed valve controls bleed air from the APU, which isn’t the essential cooling path for OVBD on the ground. The pack isolation valve governs flow to the environmental control packs, not the OVBD cooling loop’s ground cooling path. The cabin pressure relief valve is a safety device to prevent overpressure in the cabin and isn’t involved in the OVBD cooling scenario after landing.