A picture of the four locations where helicopter noise was measured. (BridgeNet)

A picture of the four locations where helicopter noise was measured. (BridgeNet)

The authors of a helicopter noise study explained their findings to a few Haines Borough Assembly members and residents at a Wednesday meeting. The study measures helicopter noise at a private heliport site near 26 Mile of the Haines Highway. It’s unclear whether the study will prompt borough government to draw up local noise regulations.


Last year, the assembly approved a conditional use permit allowing heliski company Southeast Alaska Backcountry Adventures, or SEABA, to operate a heliport off Chilkat Lake Road.

Some neighbors think the quiet area close to dozens of residences is not appropriate for helicopter operations. 26 Mile resident Jessica Plachta appealed the assembly’s decision in court. Even before that case, the borough expressed interest in conducting a noise study to gauge the impacts of helicopters in the area.

The study cost the borough $41,300. It was conducted by Mead and Hunt and BridgeNet International. Paul Dunholter is one of the authors. He said the study measured a few things: first, the noise helicopters make in comparison to the ambient, or background sound of the area. Helicopter sound at the helipad site reached 100 decibels. Dunholter said at the four sites where sound was measured, the ambient noise averaged between 20 and 35 decibels. He says, that’s really quiet, similar to what you would find in a national park.

“In the 20’s is a very low ambient,” Dunholter said. “Urban areas are much higher than that, they’ll be in the 50’s or so. And undeveloped areas will be maybe in the 30’s.”

He says the low ambient helps explain another factor the study measured – the duration of time you can hear the helicopter noise when it operates. For each of the flights, the average “time above ambient” was about six minutes. Some of the noise from the flights lasted as much as 12 minutes.

The maximum noise level for the site at the helipad was about 100 decibels. For the site furthest, it was about 65.

“So those are clearly audible events if you’ve got an ambient in the 20’s, even the lowest one, that’s a 40 [decibel] increase in noise.”

But it’s not the maximum noise levels that can be compared to current federal standards. The Federal Aviation Administration uses a cumulative metric called DNL that measures how loud helicopters are and how often the noise occurs, and averages it throughout the day. At the closest residential site where noise was measured, the average DNL was 51. The FAA maximum is 65 for residential land.

During the week in March that the firm recorded helicopter noise, there were nine flights. Study authors admit that that was probably low. So they calculated for 5, 10, 15 and 20 flights a day. For 10 flights per day, the DNL at the closest residential site 59. For 20, it’s 62, getting  close to the FAA maximum.

Taking an example of 10 flights per day, the study authors say there would be about an hour of time total where people at residences near the helipad would be able to hear helicopter noise. Dunholter said the FAA’s noise standards are not perfect.

“From a community standpoint, the federal DNL criteria is difficult to apply in a quiet setting like this for helicopters,” he said.

Plachta said the study’s use of a measurement called A-weighting is misleading. A-weighting mimics how the human ear hears sound, and it favors mid range-frequency noise. It discounts low frequency. Plachta said it’s not a valid means to measure helicopter noise.

“Why would you want to produce a report pretending that [low-frequency] noise isn’t there?” she asked.

Dunholter said that’s an argument that is ‘out there in the industry.’ He said if they had used  C-weighting, which measures for lower frequencies, there’s no criteria to compare it with. In his view, they used the best measurements available, even if they don’t give the whole picture. He says the problem with noise is there’s no perfect measurement. Everyone reacts differently to sound.

“The whole community noise thing, is a fluid, argumentative environment of people not agreeingm,” Dunholter said.

Right now, the area around 26 Mile is zoned for general use. If residents wanted the heliport off the table, they could petition to zone it residential. George Campbell was one of three borough assembly members at the meeting. He said since the data in the study is from one week in March, it’s not enough information to make a zoning change.

“They had a very short window of time they were there,” Campbell said. “We had a strange winter, we didn’t have the snowmobile activity we usually have at 26 Mile. In the summertime, you can sit there and hear ATVs running up and down the roads. So it’s interesting data, but it’s a very small snapshot.”

One criticism some people have leveled at the borough is why pay for a noise study when there are no local noise regulations to compare its results to? Borough Manager Dave Sosa has said the study could be used if the borough were to come up with local noise restrictions. But the assembly members at the meeting didn’t seem keen to make that sort of recommendation yet.

Sosa said there are two businesses that are planning to submit requests for heliport conditional use permits, including SEABA at 26 mile, since their permit has expired. Sosa urged the assembly not to put the study aside, but to use it to make decisions about what he calls a ‘long-standing issue.’

“What do we want to do to deal with an issue that is repeatedly coming before the assembly and the planning commission and which needs resolution?” Sosa asked.

The noise study will likely come up as a discussion topic before the full borough assembly at an upcoming meeting.

Full noise study here.

Powerpoint summarizing findings here.