Seaplane Safety Issues

Part 2- Seaplane Noise
 

I confess I have little patience with people who move into brand new houses near an airport that has been in existence for several decades and who then complain about the airplane noise. Washington Dulles is a case in point.

When it opened in the early 1960's about the only thing disturbed was an errant steer or two, then came the building boom, and all of a sudden community associations in Sterling and Herndon, VA began to complain about "those noisy airplanes."

Swank neighborhoods in McLean and Great Falls, VA voice the same complaints about National Airport (opened in the 1940's). In both cases approach and departure profiles for those airports were altered to expose neighborhoods to the smallest noise footprint possible. The people on the ground are happier (although some won't be happy unless both airports are closed), but the pilots are not because the profiles mean operating at reduced throttle settings or cutting power at critical moments in flight-not to mention the interesting turns to stay over the Potomac River when approaching National Airport to land on Runway 18.

Fifteen years ago when I was house-shopping, I considered buying near the airport where I had learned to fly. The realtor showed me a house just a block or two from the airport grounds, and I remarked from the house's back deck that I had a view of the airport and its airplanes.

"Oh, "she said, "don't worry. That noisy place will soon be closing down. The community association is seeing to that." Imagine her surprise when I indicated that having the airport close by was a positive factor in any purchase decision I would make. (That airport is still in operation, by the way.) Airports have their noise "problems, "real or imagined, and seaplane

operations seem to attract what many aficionados feel is undue attention. At the heart of many complaints about seaplanes is not the issue of safety, which, as we saw in part one of this series, we all need to work on. Some may use the catch-all "safety" to mask their real annoyance-noise.

Is It Really Noise?

Many times communities who don't like the noise of aircraft couch their complaints in safety terms. An airport and a community could have co-existed for dozens of years safely, but instead of coming out and saying they don't like the noise, people will write their legislators about the "safety problem. "One would think airplanes rained out of the sky into their backyards on a daily basis.

One example was Annapolis, MD several years ago. The Maryland State Legislature was about to ban seaplanes from the Severn River because they were "unsafe," so said the legislators. In this case, FAA safety officials went before the appropriate committee and testified that there was no safety problem. It turns out the problem was the owners of half-million dollar, waterfront homes thought they would be disturbed by the noise from the single seaplane that had been operating there. Of course, the noise from their power boats was okay; it was just the seaplane that was noisy.

This story had a happy ending; the Maryland legislature did not ban seaplanes from the Severn. Not all occurrences such as these have had happy endings, though. More and more across the country, state and local jurisdictions have excluded seaplanes from waterways, even those where there had been a long and safe precedent of operation.

As we have seen in Part 1 of this series, quite often safety is not really the issue, given the accident history: only three boat/seaplane accidents and virtually no non-seaplane property accidents over the 13-year period. What it comes down to is that, well, a small airplane with a two-bladed prop is noisy.

But that doesn't mean that aircraft and communities cannot come to a compromise that assures home owners of their serenity and pilots of their access. The Helicopter Association International (HAI) with their "Fly Neighborly" program has won over many a community that previously wanted helicopters banned from the airspace over its homes. There is no reason why the same can't be true of seaplanes.

FAA Noise Studies

FAA recommends that noise impact studies be developed at airports that have or expect adverse noise impacts with their neighboring communities. Grants may be issued to publicly owned airports for this purpose under the Airport Improvement Program, subject to the availability of funds and national priorities. Privately owned airports may be considered for funding when the airports are designated as "reliever" airports in major metropolitan areas with congested commercial airports. Most private airports and seaplane landing areas come no where close to that many operations, but FAA is available to assist and advise on privately financed studies. Occasionally, the seaplane base operator will pay for the noise impact study, but for most seaplane operators the cost is exorbitant. And a contractor's report is likely to favor the position of the entity paying the bills.

Unless the community is Lake Union in Seattle, WA or Lake Hood in Anchorage, AK, the exposure to seaplanes is likely to be single aircraft for infrequent operations. Still, the amount of noise tolerated by any jurisdiction across the country varies according to the community. The federal standard for aircraft noise in a residential area is DNL 65 decibels (dB). (DNL is a measure of noise exposure over 24 hours.) According to how noise exposure is calculated, a Cessna 185 that makes 52 takeoffs per year-one a week-won't cumulatively exceed DNL 65 dB for a listener more than 2,000 feet from the start of the takeoff roll and 250 feet from the takeoff centerline.

Seaplane Noise - Takeoff and Landing

During takeoff an airplane or seaplane uses the most propeller velocity to become airborne. With certain exceptions, takeoffs are accomplished at full power, and power is reduced once the aircraft is established in the climb.

Overflights at 500 feet at cruise power settings can expose people on the ground to far more noise than a landing seaplane. "Dragging" the area before landing is a common practice especially if you are unfamiliar with the water landing area or if you have reason to suspect debris or obstacles might be in the water.

Landings are generally made at greatly reduced power settings, and, consequently, the noise comparison between takeoffs and landings favors landings. According to a Seaplane Pilots Association study, "In fact, seaplane noise levels at low throttle settings may be generally below background noise levels and thus are not measurable."

Most of the noise generated by any airplane comes from the propeller tips. Many are under the misconception that it is engine or exhaust pipe noise that people complain about because we tend to think in terms of automobiles.

The propeller tip Mach number-the tip speed related to the speed of sound at the existing air temperature-and horsepower input to the propeller determine airplane noise output. The number of blades and the propeller's diameter also determine noise output to a lesser degree.

A rule of thumb is that doubling the horsepower at the same tip speed results in an increase in the sound level of five dB. To put it in everyday terms, a five percent increase in RPM will create an increase in the noise level of at least 1.5 dB. (It can increase 3-4 dB.) When tip speed is higher than .9 Mach, "noise levels increase dramatically, "according to SPA.

Table 1 shows eight typical seaplanes and their noise levels as measured from a standard distance of 1,000 feet in a river valley setting. In larger water areas, noise levels may actually be less.

Noise studies have shown that a person perceives different levels of noise from an airplane depending upon the person's position relative to the airplane. The sound is greatest at the prop tips at about 105¼ from the front of the aircraft or about 15¼ aft of the wing tips. As you move forward, the noise level drops by about seven dB up to 30¼ off the nose then drops

precipitously after that. When you move aft, noise decreases more rapidly, dropping up to 12 dB when 160¼ aft of the nose or about 70¼aft of the wing tip. What this means is that when you are directly in front of or behind a seaplane, you perceive considerably less noise than if you were beside it.

As we said, propellers are noisiest when the tip speed is around .9 to .95 Mach, but three-bladed props make less noise than two-bladed props. Three-bladed props develop more thrust for a given rpm than a two-bladed prop at the same rpm; thus, the tip speed is not as great, and the noise is less.

One seaplane FBO converted its Cessna 185's and 206's to three-bladed props and noted a five to six dB decrease for some model propellers.

Q-tip props are thought to be another route for noise reduction. The curled-up tips of the prop blades reduce the airflow off the end of the tip, much like winglets reduce wake vortex at wingtips. The manufacturer does not claim that the Q-tip prop reduces noise, but its diameter is two inches less than the props it replaces. At the same RPM as a non-Q-tip prop it produces more thrust at a less tip speed and thus less noise.

In addition to a person's relative position to the seaplane, noise decreases as the seaplane moves away from the person, generally three to seven dB decrease for each doubling of the distance. For example, if a seaplane's noise level is 87 dB at 1,000 feet, that level should decrease to around 82 dB at 2,000 feet. These figures are approximate, and factors such as temperature, obstacles in the vicinity, and strong winds can affect the noise level as perceived by a person. Vegetation such as thick, tall grass or trees can attenuate noise significantly, but a seaplane operating on open water will have very little help from the surrounding flora. A person's distance from the seaplane and the type of seaplane are the most significant factors in determining the impact of seaplane noise. By virtue of the seaplane's "ideal"operating locale-open water on whose shores may be houses with outdoor decks, docks, pools-noise impact from a seaplane may be attenuated very little.
 
 

What is Too Much Noise?

As we said earlier, the answer to this question depends. People who live on one of those airport residential areas are probably way more tolerant of airplane noise than residential areas where people have little or no experience with aviation. An airplane developing full power on takeoff is music to my ears and perhaps yours, but to some it is a dissonant cacophony. And these may be the very people who think nothing of subjecting their entire neighborhood to their riding lawn mowers or leaf blowers. Somehow, they believe that the seaplane-perhaps because it is bigger-is noisier, and many are surprised when comparative tables show common, neighborhood noises which are as loud or louder than seaplanes. However, people become inured to lawn mowers, dishwashers, etc., because they are in common usage. The seaplane showing up in the neighborhood may be a rare occurrence, and, as such, it attracts more attention than the newest yuppie toy, the lawn tractor.

Table 2 is a comparison of the sound levels of various seaplanes and common neighborhood noise. It is interesting to note that a quiet house at 0530 has a perceived sound level of 30 dB and that the next noisiest thing after a robin singing at 50 feet is a DC-10 overhead at 5,000 feet. 

Am I Compatible with the Neighborhood?

Out of courtesy and to save a lot of grief, every seaplane operator should ask him- or herself this question.

???????How does my seaplane noise compare to background noise in the neighborhood? If the neighborhood is sandwiched between an interstate highway and your seaplane operations, your noise could get lost in the background.

???????How does my seaplane noise compare with any power boats, motorcycles, trains, trucks, lawn mowers, etc., in the vicinity? A chain saw or motorcycle 25 to 50 feet away far exceeds seaplane noise at 1,000 feet.

???????What is the community's normal activities and what kind of noise does this produce? Obviously, if you want to operate near a retirement home or progressive assistance community, the normal noise levels may be fairly low, and your single takeoff would be highly disruptive.

???????What is the frequency of seaplane activity as compared to similar noise impacts? If the community has little objection to one neighbor who operates a motorcycle in the neighborhood on a daily basis, they may not notice seaplane noise. However, if you consistently operate at times of quiet in the neighborhood, your seaplane activity will stick out like a sore thumb.

One good thing: Outside of Alaska, very little seaplane activity occurs at night, so you're not likely to disrupt anyone's sleep. (Of course, if you operate near a neighborhood where the majority of people work a night shift and sleep during the day...)

???????What are the cumulative effects of seaplane noise when compared to peak noise levels in a community? If everyone in the community mows their lawns starting at 1000, your takeoff may go overlooked at the time.

What all these questions are trying to do is instill a sense of community in you, the seaplane pilot. You may only be transiting the area, but you want to leave people with a good impression of seaplanes and seaplane pilots. SPA publishes a water landing directory, and it also has field directors who are very familiar with their part of the country. A little homework on the community before you fly into it will go a long way in your having a good, safe operation. If you work it right, the next seaplane pilot who flies into the area you left will have an easier time of it. Education goes a long way as well.

As we said, many people assume that a seaplane is noisy because of its size and their lack of familiarity with it. Some communities may only be convinced after hiring someone to come in and measure noise levels at various times and for various noise-makers. And there will always be some who will never change their minds about seaplane noise no matter how many charts and graphs you show them.

A favorite vacation spot of mine is a lakeside cabin in the northeast. The neighbors there think nothing of the constant din from power boats and personal watercraft because it is a waterfront community; they expect boats to be noisy. But when I mentioned I wanted to land a seaplane there, you would have thought I had suggested devil worship. It turns out another aspect of aviation had ruined it there for seaplanes: The local national guard regularly flies its helicopters and its C-130's low and slow and noisily over the lake. And no amount of logical argument could dissuade them that the noise of a C-172 on floats would be lost among the skiboats and JetSki races. For the most part, if you work with a community, listen to its concerns, present them with convincing evidence, you may be able to turn their concerns.

When all else fails, offer people rides in a seaplane. Show them how safely you operate, how you take community issues in consideration during your operation. Always keep in mind that even though airplane noise is music to your ears, you may have been startled out of peaceful reverie by a blatting motorcycle or the whine of a chain saw. As HAI puts it, "Fly Neighborly!"

?AvStop Online Magazine                                                                                                      Contact Us              Return Home