The Accession of the Flame is a ceremony in Airyglyph in which a soldier becomes a fully-fleged Dragon Knight.
Many soldiers had taken the ceremony, but in Albel Nox's case, the dragon did not find him worthy and attempted to incinerate him. His father saved him by taking the brunt of the flame, killing him the process. Albel didn't escape uninjured though, as he lost his arm in the process.
A ceremony in the military superpower of Airyglyph that marks a covenant with the air dragons that are such a vitally important part of the Glyphian military. The ceremony is essentially a proposal from knight to dragon to join forces and fight together. Attempting a covenant with a powerful air dragon is an extremely dangerous act, and the success rate of such ceremonies is said to be less than 30%. Of course, the more powerful the partner, the more dangerous the fight needed to complete this ceremony. It is not uncommon for knights with the hubris of exaggerating their own prowess to pay with their lives.