Contractors hired by Hawaiian Electric Co. will use helicopters to replace outdated tranmission towers in the Koolau Mountains behind Manoa, St. Louis Heights and Palolo, the utility announced today.

The towers carry power lines between Honolulu and the Windward side of the island. Crews will replace six aluminum towers with upgraded steel structures, according to HECO.

Helicopters are being used because of the remote location of the work sites, the difficult terrain, and a desire to minimize the impact to surrounding vegetation, HECO said in a news release.

The work is scheduled to be conducted from 8 a.m.  to 3:30 p.m. Monday through Saturday. The project has already started and is expected to be completed by the end of October.