The Navy has completed plans for basing up to 24 tilt-rotor Osprey aircraft and 27 Cobra and Huey helicopters at the Kaneohe Bay Marine Corps base, but questions persist over how much noise the aircraft will create for area homes.

"We don’t know about the noise from (Ospreys), because there never was an opportunity to hear the aircraft," said state Rep. Cynthia Thielen, who represents Kailua and Kaneohe Bay.

The Department of the Navy approved the basing plan last week. The additional aircraft, expected to arrive through 2018, would bring 1,000 active-duty personnel with 1,106 dependents, and increase annual flights to 79,000 in the coming years from 53,000 in 2009, an environmental impact statement reports.

A Marine Corps aviation plan envisions the service in 2025 to be a "fast, lethal expeditionary force that is ready for the uncertainties of future combat operations, yet has the staying power of engagement in the most austere conditions imaginable," the EIS says.

To achieve that, the Marine Corps "must restructure and rebase its forces in the Pacific over the next 10 years," the report says.

The EIS says flight paths for Osprey touch-and-go practice would be similar to those of current P-3C Orion propeller aircraft that loop around Kaneohe Bay before landing.

"Noise-sensitive areas" would experience a 1- to 3-decibel increase using a 24-hour, day-night sound average. Areas with average noise levels of 65 decibels or greater would be limited to the Marine base, Coconut Island and the tip of Kealohi Point, the EIS says.

Thielen, in a letter to the Navy, criticized the day-night average as providing only a "general idea as to the cumulative noise level averaged over a 24-hour period."

"As a result, the (EIS) fails to provide citizens, especially those living closest to the flight patterns, with the critical information that they want the most: how loud will aircraft noise be in their specific neighborhood; what is the loudest aircraft sound that they can expect to hear; and what times of day will this be?"

A chart in the EIS shows the "maximum instantaneous sound level" in the vicinity of Kealohi Point at about 81 decibels for Ospreys, 88 decibels for the current CH-53E Super Stallion helicopters, 82 decibels for P-3C Orions and just over 90 decibels for Air Force C-17 cargo carriers.

By comparison, a power mower at 3 feet is 107 decibels.

Base spokeswoman Capt. Pam Marshall said, "We are constantly engaging the local community to address noise concerns."

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