A B747-400 Captain reported a collegial atmosphere between the flight crew and numerous ground support staffs when confronted with a mechanical issue that proved insurmountable and resulted in a flight cancelation.

Narrative

Upon arriving at the gate; we were notified there was a rupture in the bleed duct in the left wheel well. The duct is from the APU to the bleed manifold. The rupture was extensive and showed some charring around the area of the rupture. We had a conference call with Maintenance Control and Dispatch. This was a very serious problem concerning the APU bleed valve to protect the reverse flow from the engines back to the APU. The Maintenance Manager briefed us on the details required to certify the aircraft for flight. After two plus hours of completing a check of the system; it was determined that the aircraft could not be operated safely. The cause of the rupture was never determined and the location was of great concern due to the potential of an inflight fire because the check valve to prevent back flow was not in full operation. The entire team did a great job of working the issue and keeping the flight crew well informed; the flight was canceled and the flight and cabin crew were rescheduled.