NOISE-Bad Sounds!

My wife and I sit reading on our boat in a quiet inlet on Trinity Lake, all is warm and calm. We hear a personal watercraft and soon it is in our inlet with water flying everywhere and huge waves. The noise of the engine various from growling to shrieking as the vehicle zooms in and out of it?s own wake. The shore birds at first retreat and then fly off. I jump up to start the engine with the intent of running the damn thing down but reason takes over and we leave for nearby miles of unoccupied lake. As I settle down with the relatively quiet drone of the boat engine it occurs to me that the anger that I just experienced is the same anger that ground bound people feel when buzzed by aircraft. Our community at Trinity Center has homes all along and close to the west side of the runway that overlook the airport and the lake. Even on a busy day the sounds of an arriving and departing aircraft don?t seem obtrusive. Sometimes we even miss the small Citation?s that come and go. There have been occasions; however, when landing and takeoff noise became a problem. One of our past airport residents flew a classic Ercoupe, a small low powered 2-seater. One day I noticed that he did about 30 touch and goes in a row in a very tight pattern. It didn?t bother me at first but after I got a call from a non pilot indicating serious displeasure I went over to ask if in the future he could do some of the practice elsewhere or at least spread out the activity with less noise. The next day it was obvious that he did not heed a reasonable suggestion; he started again and I lost count after about 50 touch & goes. I walked over to wait for the final landing-soon thereafter the final landing occurred in the rocks off the end of the runway due to the fuel exhaustion. The plane was removed in pieces before nightfall probably to avoid reporting the accident. Since the pilot was not seriously injured it occurred to me then that for non-pilots it would be a fitting end to the noise. It certainly avoided a confrontation and potentially serious community relation?s problem.

I have pilot neighbors that live closer to our runway than I do; they invariably like airplane noise just like the crowd in the old days at the San Jose, Costa Rica, Juan Santamaria Airport. I will never forget my first landing at that international airport in the early 70?s. I taxied up to the main ramp and as I got out of my Bonanza I was astounded that the art deco looking multi-story terminal building with open observation decks on two levels was jammed with people looking out over the airport. I thought maybe some famous person was going to arrive or some event was about to take place. So I asked at the flight office what the crowd was all about. By that time I had noticed that there were also crowds of people at ground level behind the perimeter fence, which reinforced my suspicion that something big was about to happen. On the contrary I was informed, that was the usual crowd simply enjoying the afternoon comings and goings at the airport.

Based upon several observations I have a theory that minor single event noise events are ignored whereas protracted in your face sound can be worse than torture and is not forgotten. I once built an apartment one lot & a service road removed from a little used railroad track. In fact I never heard it because it came by only twice a day, both early in the morning and in early in the evening. One day I asked the tenant who had been there over a year about the railroad noise. At first he said ?what railroad noise? ?, then he recalled that he heard it the first week but not again. He speculated that he must have gotten used to it and even his visitors didn?t seem bothered by it.

So how do we as pilots avoid making offending aircraft noise? how do we minimize bad community PR due to noise? There are many effective ways although it would be easier if people were on the verge of needing a hearing aid like your writer. For those who can hear, we need to reduce the noise level at the source, the noise duration and the noise event frequency. Equally important, we must increase the distance between the aircraft noise source and the ground observer. External aircraft noise is mainly generated by the propeller tips going transonic (approaching the speed of sound) rather than the engine exhaust system or the airframe. There is a large increase in noise if the propeller tips are in or above the transonic speed range. The propeller tip speed is proportional to the propeller diameter and using a lower RPM can reduce it. This is particularly important when conditions permit the pilot to safely use lower power. My 1949 A-35 Bonanza had an 88-inch propeller that was very loud at takeoff at 2600 RPM particularly on days where I climbed out heavily loaded in instrument conditions. The noise monitors at Torrance Airport showed that a more acceptable noise level was at 2450 RPM. This usually turned out to be a good tradeoff because on most occasions I was still able to get to the same altitude over the homes near the noise monitor. My newer Bonanza had an 84-inch propeller that operated at 2650 RPM maximum and also violated the noise criteria. After a notice to appear at the Airport Noise Commission I found that lowering the takeoff RPM by 100 solved the problem (not wanting to adjust the power after takeoff I usually made the adjustment prior to lift off). Sometimes when I needed max power for safety I asked for a noise test, which was not an offense if the noise limits were violated. This avoided a noise citation, even though it did not reduce the noise, however I only did this when safety was a more important consideration. Since the noise level is proportional to the inverse of the square of the distance between the noise source and observer I varied my flight path to increase my distance from the noise monitors. Eventually, I found that the two bladed very efficient propeller was not qualified for use on the bigger replacement IO-550 engine-a new 3-bladed Hartzell Scimitar propeller solved the problem and with it?s shorter diameter it is significantly quieter. That?s new technology and smart practical politics! Landings are generally quieter than takeoffs; however, a massive increase of power to correct the glide path or to go around needs to be avoided by simply making a good approach using minor power adjustments.

At Trinity Center the airport traffic pattern is over the lake away from homes. When a pilot flies over town for whatever reason the noise is noticeable whereas it?s not noticeable if you fly the prescribed pattern. This is a good example of the importance of distance. The repetitive noise of touch and goes can be broken by doing a few at a neighboring airport, flying a extended pattern and or doing some air work to break the sequence. This is why airports with lots of training activity usually disallow touch & goes during non-business hours as a first step to reduce noise complaints. Reducing the takeoff RPM sometimes is easy particularly if you have a light load, have a cool temperature and are at a low altitude airport. If it is necessary to use the maximum power near sensitive noise areas try to reduce to climb RPM as soon as it is safe or perhaps after 500FT AGL. Varying your flight path at low altitudes to fly over less noise sensitive areas usually doesn?t add significantly to the flight time; flying high is best to minimize noise. One important point to always to keep in mind is that there are noise sensitive people on the ground in areas that are not obvious. For example, it was shown at Torrance that the ambient street noise from trucks was higher than the originally proposed aircraft noise limits. In rural areas the background noise can be near zero. As a result sometimes one lone secluded cabin occupant in a very quiet area can create more anti airport sentiment than a housing tract surrounding a busy airport, so whenever you are near the ground you?re closer to a noise sensitive situation and it is good PR to do everything possible to minimize your noise intrusion. I complained when a Citation flew down lake at 100FT AGL over lots of boaters, I can attest that there is an order of magnitude decrease in noise level with a normal climb-out. Being a good airport neighbor is certainly in the interest of every pilot in order to preserve and expand our airports. Won?t you be my (quiet) neighbor?

George Loegering
CPA VP Region I
Editor’s Note: Noise continues to be a major factor causing problems around the airport. Please do your part by flying friendlier