By Breeze Geier
Remember when your GA airport was out in the boonies and you departed over forest or swamp? Look down these days and youre likely to be climbing out over neighborhoods and schools. And, although the folks down there chose to live next to an airport, they dont hanker much for them noisy flyin machines.
As population density near GA airports continues to grow, many municipalities are adopting anti-noise ordinances. Local governments have been regulating GA aircraft noise for over 30 years.
The City of Santa Monica, near Los Angeles (where 130,000 residents live within two miles of the airport), banned jet aircraft operations and imposed flight restrictions in the early 1970s. Subsequent litigation defined a municipalitys authority to regulate airport noise. The ban on jets was stricken but the city was allowed to impose reasonable, nondiscriminatory flight restrictions as long as they do not conflict with federal rules or statutes.
Currently, a first-time violator gets off with a warning. The fines for subsequent infractions climb like an F-16. The second offense will cost you $2,000, the third $5,000 and the fourth a whopping 10 grand. You read correctly: $10,000.
Another violation and your privileges will be suspended for six months. One more strike and youre out – banned from the airport until the devil issues ice skates.
To support suburbanite slumber, the airport is closed for takeoffs between 2300 and 0700 local time except in emergencies and only with the managers written blessing, and you cant crank the cylinders until 0800 on weekends. Although the airport is always open for landings, voluntary restrictions urge pilots to limit their landing operations to these same hours.
Theres a list of jet aircraft that are deemed unlikely to be able to meet the noise restrictions and they are banned from the airport after only one noise violation. If they return, a subsequent violation results in a misdemeanor charge. All that from a city where car alarms blare throughout the night like blitzkrieg air raid sirens. Go figure.
Its not easy for an airport to establish noise regulations. The FAA has promulgated 95 pages of detailed rules in tiny type that a local regulating authority must follow in order to establish anti-noise ordinances. These rules require submission of extensive plans, regulation of equipment used to collect and process sound and a host of other requirements best left to bureaucrats, engineers or anyone who needs eyestrain or a nap.
If thats you, the AOPA publication, Noise, contains the FAA guidelines along with several interesting articles on the topic. AOPA will gladly send you a copy. Because regulation of airborne craft falls exclusively within the authority of the federal government, municipalities obtain a Letter of Agreement from the FAA approving abatement procedures like special vectors and altitudes.
Those Dirty Decibels
A decibel, for our purposes, is a unit of sound pressure level, or SPL. At Santa Monica airport (SMO), like other airports that collect aircraft noise, microphones sit atop 30-foot poles 1,500 feet from either end of the runway and relay sound to a computer that calculates a single event noise exposure level, known as the SENEL.
The maximum noise your plane makes as it passes closest to the mics is called the Lmax and is plotted on a graph that displays sound level over time in seconds (see chart 1). The computer calculates your airplanes noise, starting when your plane is within 10 decibels of reaching Lmax and ending when your aircraft is 10 decibels past Lmax. All that noise generated over time is called the SENEL and appears as a bell curve on a graph. Because the SENEL reflects accumulated noise made while approaching Lmax, at Lmax and after passing Lmax, the SENEL is always greater than Lmax. If the SENEL exceeds the level set in the statute, youre busted.
Since the computer calculates your noise over time, a fast, noisy plane may generate a lower SENEL than a quieter but slower craft because the louder airplanes noise duration is shorter. Climbing into a stiff wind will cause a greater SENEL than on a calm day because the headwind will slow you down and increase the duration of your noise.
Although you may gain altitude more quickly climbing into a stiff headwind, you will linger longer in the mics zone and generate a higher SENEL than if you can pass through the microphones zone more rapidly. A little extra altitude does not meaningfully diminish the sound of your airplane as heard on the ground.
I Didnt Do It
Microphones merely sense sound and cannot discriminate among noise made by planes, trains or automobiles. Ambient sounds are usually too low to skew the SENEL, but what about sudden uncommon cacophony? If a car alarm blasts near the mic just as you pass into the mics zone it can cause an SENEL that is higher than your airplanes actual noise. Then youre unjustly cited. Fortunately you may be able to prove your innocence with the very evidence used to prosecute your violation. That is the noise graph that will be sent to you along with the official notice of your infraction.
An SENEL due to aircraft noise will create a relatively smooth bell curve beginning when you enter the mics zone, peaking as you pass nearest the mics and declining as you leave the micss zone. A sudden loud noise near the microphone will be interpreted as louder than your airplane and the computer will plot it as Lmax. Because it is a sudden sound that does not fit the smooth, progressive noise your plane is making as it approaches the mics, the Lmax generated by the extraneous sound will appear on the chart as a spike atop the bell curve (see chart 2).
The computer, relying on this erroneously greater Lmax, will generate an SENEL that is greater than the noise your plane actually made and you will be unjustly accused.
It happened to me.
Fighting City Hall
Due process of law requires that you be given an opportunity for a hearing, but you must request your day in court within the time limits indicated on your citation or its accompanying documents. If you believe you were unfairly cited, you may wish to have a qualified engineer review the bell graph to determine whether an airplane could account for its depiction.
I obtained from the airport managers office the name and address of the engineer who installed SMOs system and faxed him the chart. He confirmed that it was not consistent with airplane noise and asked me to have the airport manager call him.
Then, on a hunch, I contacted the citys garbage collection department and discovered that their trucks were operating in the neighborhood surrounding the microphones on the day I was cited. They faxed me a garbage collection map. After the airport manager had spoken to the engineer and reviewed the garbage map, he graciously withdrew the citation and closed my case.
Even without the garbage map, the bell curve proved my innocence. But the map at least provided a plausible source for the errant noise. Theres no telling how many pilots over the years have merely assumed they are guilty and eaten the warning or paid the fine.
If youve been flying out of the same airport in the same way for a while and are suddenly cited, dont assume they are right. The mics dont know what they are hearing, and, when it comes to computers, its garbage in, garbage out. Or, in my case, garbage trucks.
Shhhh
Some pilots do, of course, exceed the maximum allowable SENEL. If your throttle slips back unnoticed or you forget to raise the landing gear, you may depart slower than usual – thereby keeping you in the mics zone just long enough to violate. Here are some flight procedures that will help you stay on the quieter side of the law.
