14 CFR § 27.993

Each fuel line must be installed and supported to prevent excessive vibration and to withstand loads due to fuel pressure and accelerated flight conditions.

Each fuel line connected to components of the rotorcraft between which relative motion could exist must have provisions for flexibility.

Flexible hose must be approved.

Each flexible connection in fuel lines that may be under pressure or subjected to axial loading must use flexible hose assemblies.

No flexible hose that might be adversely affected by high temperatures may be used where excessive temperatures will exist during operation or after engine shutdown.