What's all the noise about?

Around the country, small general aviation airports are closing at a distressing rate - about one per week. The usual culprits behind these closures are well-organized homeowners or land-hungry developers. All too often, the impact of aircraft noise on the surrounding community is the glue that seals the airport's fate.

And even if they don't close an airport outright, many municipalities enact strict noise abatement programs. The enforcement is serious and fines can be steep. Which means that, on top of everything else that pilots must know, they have to learn about one more important subject: noise abatement, or "How I learned how to fly quietly and safely all at the same time."

Formal noise abatement programs are common at larger, busier airports, especially those with lots of jet traffic. The majority of general aviation airports do not have them, but the number is increasing. Even if your airport doesn't have one, you need to be familiar with noise abatement procedures and ways to fly quietly, because sooner or later your flying will take you to an airport where noise abatement is a way of life.

The legalities

One of the first steps in enforcing a noise abatement policy is to get some laws on the books. Typically, an airport sponsor (whether we're referring to a city or an independent airport authority) causes a local ordinance to be added to the city's municipal code. This ordinance usually provides for "due process" (to ensure equity and reasonableness), and it lays out the details of the entire noise-abatement plan. The ordinance also may set forth maximum daytime and nighttime noise levels, or prohibit or restrict certain aircraft operations - for example, no touch and goes on Sundays.

You're busted

Generally, pilots can be cited for exceeding noise limits and/or performing an operation that is prohibited or restricted. First-time violations ordinarily prompt a warning letter to the registered owner of the aircraft. The letter explains the airport's noise abatement policy and may request that the offending pilot call the noise abatement office. Further violations can result in fines and/or criminal charges; excessive violations may cause the aircraft and/or pilot to be banned from the airport. Keep in mind that unless the powers that be are really trying to close an airport, the primary goal of these noise abatement programs is compliance and a reduction in noise complaints from airport neighbors, rather than generation of revenue from fines.

How do they enforce these ordinances, you ask? In short, with a very sophisticated monitoring system. Microphones (or monitors, as they are called) are strategically placed in noise-sensitive neighborhoods around the airport. The microphones are connected to a multi-track tape recorder which records aircraft noise as well as conversations taking place on tower, ground, and approach control frequencies 24 hours a day. As you can imagine, these air traffic control transmissions are crucial in identifying a "noisy" aircraft. A computer analyzes the noise levels from the microphones, keeps track of noise events, tags noise violations, and stores noise data. Using a system like this, a noise control specialist can easily track down an aircraft - and eventually, its pilot.

The FAA's stance

The FAA, to avoid legal exposure, usually does not get involved with these local ordinances. The only FAA involvement that you may experience directly is with tower controllers, who will advise pilots that a certain operation would violate a local noise ordinance. At that point, it's up to the pilot whether he or she wants to perform the operation in question, since controllers will generally grant the clearance if it doesn't violate the federal aviation regulations.

Spreading the word

Since almost all noise violations are from transient aircraft, it's essential that noise abatement offices "advertise" their local noise abatement policy through as many avenues as possible. They publish procedures and information in commercially available "pilot guides," AOPA's Airport Directory, and the FAA Airport/Facility Directory (A/FD); the latter two list noise abatement policies under "airport remarks." Instrument students sometimes can find noise-abatement information on the back of Jeppesen instrument approach plates. In addition, the airport automated terminal information system broadcast often includes advisories that noise abatement procedures are in effect. Some airports, such as Santa Monica Municipal in Santa Monica, California, have placed their noise abatement information on the Internet. The procedures might also be posted on signs near the runway, perhaps near the run-up area, to give all pilots a last-minute reminder. If you plan to fly to an unfamiliar airport with a noise abatement program, it would be prudent to call the airport's noise abatement office before you go to find out the details, especially with regard to nighttime operations.

A noise primer

In order to fly quietly, we need to know a little about how sound and noise work. Noise is just bothersome or annoying sound. But because noise is sound, it obeys the laws of physics. And we can use those laws to help us fly quietly.

The basic unit for measuring the relative loudness of sound is the decibel (dB), named in honor of Alexander Graham Bell, the inventor of the wired telephone (remember those?). For reference, normal conversation is about 60 dB, while a rock group plays at about 110 dB. Because noise is measured on a logarithmic rather than linear scale, a small change in dBs is easily discerned. A 10-dB increase in sound level is not a 10 percent increase; 10 dB is a very large increase in loudness. We need to remember that when talking dBs, a 3-dB or 4-dB change in sound level is easily noticed, so every dB counts! Another term that you may hear when dealing with noise abatement is single event noise exposure level, or SENEL. This figure (also in dB) measures not only how noisy an aircraft is, but also how long the noise event lasts. SENEL could be described as an "annoyance index." Consider this: A sonic boom is a very loud event, perhaps 90 dB or more. However, it only lasts a second or two. Startling, but not that annoying. On the other hand, a roaring leaf blower outside your bedroom window at 6:30 a.m. is annoying. The leaf blower is certainly not as loud as the sonic boom, but its noise lasts longer and is certainly more irritating.

Sources of aircraft noise

Excluding jets, the main sources of airplane noise are the propeller and the engine. Of the two, propeller noise is dominant. The amount of noise that a propeller makes depends greatly upon how fast it's turning (its revolutions per minute, or rpm). A propeller becomes very noisy (and inefficient) when the speed of its blade tips approaches the speed of sound. With a fixed-pitch propeller, there is no way to reduce propeller rpm other than to reduce power. However, with constant-speed propellers, pilots can reduce manifold pressure and rpm after takeoff to reduce prop noise as long as it is done safely and in concurrence with the aircraft's pilot's operating handbook (POH). This technique is effective with high-performance singles, light twins, and cabin-class twins.

Noise abatement techniques

It's relatively easy to learn how to fly quietly. One of the key tactics is simply to put as much distance between your aircraft and the noise-sensitive areas (and the noise monitors) as possible. On departure, gaining altitude quickly within the airport's boundaries will minimize your noise footprint after leaving the airport area. To help accomplish this, at towered airports you can request the longest runway available and avoid intersection departures - even though they sometimes can save you a few minutes.

In most cases, best performance is obtained by applying maximum takeoff power prior to brake release. Use the takeoff technique recommended in the POH. Of course, you should know your published rotation speed and climb out at your best angle or best-rate-of-climb speed - reach pattern altitude quickly to keep your noise footprint as small as possible. If your aircraft's POH recommends flaps for takeoff, set them appropriately. After reaching a safe altitude, and preferably while still within the airport's boundaries, accelerate to cruise-climb airspeed and set cruise-climb power. Retract the flaps at a safe altitude and airspeed.

Don't forget to brief your passengers that you'll be making a noise-abatement departure. You don't want them to be worried about the steeper climb angle or think the engine is faltering when you reduce power. Pilots who fly (or plan to get checked out in) high-performance aircraft should be especially cautious with noise limits. High-powered engines and their constant-speed propellers have the potential to create much more noise than trainers do, especially on takeoff. Get a thorough checkout that includes noise abatement procedures.

Your next consideration should be your route. At any airport, you should plan your departure route to avoid noise-sensitive areas.

If you are performing touch and goes, plan your touchdown in the first third of the runway. Landing long puts you farther down the runway, and this results in less altitude over the monitors after you "go."

While en route, try to maintain at least 2,000 feet above ground level (agl) over populated or noise-sensitive areas. If your airplane has a fixed-pitch propeller, consider using 55 percent or 65 percent cruise power settings when transiting noise-sensitive areas. The lower power settings will greatly reduce your aircraft's noise. When on approach for landing, utilize low-energy (reduced power), high-profile (steep) descents. (Again, consult the POH.) Delay using flaps until needed to preclude "dragging" it in at low altitude and excessive power.

Finally, when utilizing any noise abatement technique, remember that you, the pilot in command, are the final authority for the safe operation of the aircraft. You should never compromise safety for noise abatement concerns.

Noise awareness

The future of many small airports can depend on the public's perception of them. If the nonflying public regards them as just a home for those noisy "little planes," their future is dimming fast. Noise abatement programs do help alleviate the public's concern over aircraft noise while striking an acceptable balance between the needs of airport users and the interests of local residents. We should strive to comply with them as best we can, and to be conscientious of noise-sensitive areas even where noise abatement programs do not exist. By using the simple noise-abatement techniques presented here and flying quietly over noise-sensitive areas, we can make a positive contribution to the quality of our environment, and quite possibly to the survival of general aviation itself.

Christopher L. Parker is a CFI and an aviation author, speaker, and FAA remedial training specialist. He is captain of a Canadair Challenger for a private operator based in Ontario, Canada.