AEM - Insulator Washing
Insulators are designed to isolate a live conductor from ground. The effectiveness of insulator strings degraded as mineral deposits built up on the plates, leading to leakage (which could be heard over the intercom as the aircraft passed the structure in question): then with lightning strikes, damage could lead to flashover, evidenced by burn marks on the porcelain plates. Seasonally, power authorities contract helicopter cleaning of the insulators to reduce leakage and reduce risk.
We used MD 500s equipped with a belly tank for demineralised water, a pump and a neutral forces mount for a 6 metre Kevlar boom tipped with a high pressure nozzle. A linesman operated the boom from the left rear seat. When operating correctly, the aircraft would approach the structure with the boom stowed pointing forward. As the distance closed, the operator would release the boom and swing it to point at the structure as the aircraft came to a hover. The pilot would lift and lower the helicopter to give the operator coverage of the string before moving to the next. The boom would be stowed as the aircraft began to move off and unlatched again for the next tower during deceleration.