When is the resistance of the current return path through the aircraft considered negligible?

The resistance of the current return path through the aircraft is considered negligible when the structure is adequately bonded. Adequate bonding ensures that various parts of the aircraft's electrical systems are effectively connected to a common ground, which minimizes resistance in the return path for electrical currents. Proper bonding helps maintain a low-resistance path for the return current, which is essential for reliable operation of the avionics and electrical systems.

When the aircraft structure is bonded correctly, it also reduces the potential for electromagnetic interference and helps in dissipating static electricity. This is critical for maintaining the performance of sensitive electronic systems. The use of bonding is a standard practice in aviation to ensure that electrical circuits function correctly and safely.

While circuits being powered, the aircraft being on the ground, or all components being functional might influence operational conditions, they do not directly relate to the idea of resistance being negligible in the return path. Adequate bonding is the key factor that directly affects the resistance of the current return path.