State noise control regulations for airports will become more restrictive at midnight Dec. 31, but neither Burbank nor Van Nuys airports will be any quieter as the new year begins.
A change in the regulations, however, appears to be setting up one more confrontation in the long-running battle between airport administrators and groups of anti-noise homeowners.
The noise protesters accuse airport executives of manipulating the rules to escape the intent of the state law and to avoid reducing the number of planes using their airports.
Airport administrators say they are doing the best they can, but airport noise is a difficult problem, involving factors from aircraft design to zoning to federal laws, which they cannot resolve by simply issuing commands.
The standard that goes into effect Jan. 1 "is not technologically feasible for a large airport with residences nearby," said Brett Lobner, the Los Angeles deputy city attorney who prepared Van Nuys Airport's request to be exempted from the new standard.
The quarrel probably will end up as the subject of a trial-like public hearing by the California Department of Transportation, providing a new forum for the noise protesters.
"Absolutely, we're going to demand a hearing," said Don Schultz, president of Ban Airport Noise, a group formed to combat noise from Burbank-Glendale-Pasadena and Van Nuys airports.
Richard Close, president of the Sherman Oaks Homeowners Assn., said: "The airports have no intent of ever complying with the law." Close also represents an alliance of five homeowner groups from Burbank, Studio City, North Hollywood, Van Nuys and Sun Valley.
Van Nuys ranks as the third-busiest airport in the nation in the number of takeoffs and landings, which have been running about 500,000 annually. It ranks as the busiest general aviation, or non-commercial, airport anywhere.
Airport executives respond that they have put many anti-noise measures into effect and that aircraft noise will be no greater after the rule change goes into effect, no matter what the change does to legal definitions.
At the heart of the dispute is a change involving the complicated, abstract method by which airport noise is measured under California law. The unit of measurement is the CNEL, or Community Noise Equivalent Level.
A CNEL is the daily average of decibel readings recorded by monitoring stations near airports, weighted by a mathematical formula designed to reflect the fact that noise is more annoying at night. Aircraft noise registered between 7 and 10 p.m. is multiplied three times before being figured into the average, and noises from flights between 10 p.m. and 7 a.m. are multiplied 10 times.
The results are used to draw imaginary lines around airports, a "noise footprint" marking the boundaries of the areas where the average CNEL reaches a common volume. A 70 CNEL line defines the point where noise readings inside the line are higher than 70 CNEL, and those outside are lower.
The footprint is a statistical tool used to come to grips with aircraft noise, which fluctuates from moment to moment. In real life, the footprint has no fixed existence.
A listener moving from one side of the boundary to the other would find it difficult to detect any difference in noise levels. The real footprint shrinks to nothing when no aircraft is landing or taking off, and balloons out to a far larger area when a fully loaded jet with a heavy-handed pilot is climbing rapidly away from the field.
In real life, the footprint shifts with the wind and the direction of aircraft traffic.
The daily CNEL averages are further processed into a quarterly average, which the Aeronautics Division of Caltrans uses to administer the state airport noise law.
The law sets a maximum average CNEL for residential areas and schools near airports. Industrial, commercial and agricultural areas, as well as the airport itself, are exempt.
Set at 80 decibels in 1975, the limit was reduced to 75 in 1976 and to 70 in 1981. The level drops to 65 on Jan. 1, the final stage of the law.
"A decibel reading of 65 is about the level that interferes with your speaking to someone a few feet away, noisy enough to cause you to raise your voice, but not loud enough to drown you out," said Robert Beard, a noise abatement officer for the Los Angeles Department of Airports, which administers Van Nuys Airport.
Passage of the state law, which took effect in 1971, did not necessarily mean airports complied with its stipulations, however, or even that they were obliged to. The law includes a provision for airport operators to petition Caltrans' Division of Aeronautics for a variance--in effect a permit allowing the airport to continue operating even though the CNEL is above the maximum in neighboring residential areas.
The variances are good for one year, but can be renewed.