Airport Noise 101

There are many terms used when it comes to aircraft noise. Here are the definitions for the most commonly used words.

• Airport Operation is the term used by the Federal Aviation Administration (FAA) to define airport activity levels. An operation is an aircraft takeoff or a landing. For example, a “touch and go” conducted by a training aircraft includes both a takeoff and a landing and counts as two operations.
  
  
• Class Bravo Airspace is generally airspace from the surface to 10,000 feet mean sea level (MSL) surrounding the nation’s busiest airports. The configuration of each Class Bravo airspace is individually tailored, consists of a surface area and two or more layers (some Class Bravo airspace areas resemble upside-down wedding cakes), and is designed to contain all published instrument (approach and departure) procedures once an aircraft enters the airspace. Clearance from Air Traffic Control (ATC) is required for all aircraft to operate in Class Bravo airspace. Both the San Carlos and Half Moon Bay Airports are located below the San Francisco International Airport (SFO) Class Bravo airspace.
  
  
• Community Noise Exposure Level (CNEL) is the standard used for environmental noise studies in California and represents Day-Night Average Sound Level (DNL) plus with an additional artificial increase of 5 dB between the hours of 10:00 p.m. to 7:00 a.m.
  
  
• Day-Night Average Sound Level (DNL) is the average noise level over a 24-hour period except that noise occurring at night (between the hours of 10:00 p.m. and 7:00 a.m.) is artificially increased by 10 dB. This weighting reflects the added intrusiveness of night noise events attributable to the fact that community background noise typically decreases by 10 dB at night, and communities are more sensitive to noise during these hours.
  
  
• Decibel (dB) is a measure of the sound pressure of a given noise source relative to a standard reference value, which is the sound pressure level. This reference pressure is typical of the quietest sound that a young person with good hearing is able to detect and is measured in decibels (dB). The conversion of sound pressure to sound pressure level means that the quietest sound we can hear (the reference pressure) has a sound pressure level of 0 dB, while the loudest sounds we can hear without pain have sound pressure levels on the order of 120 dB. Most sounds in our day-to-day environment have sound pressure levels on the order of 30 to 100 dB.
  
  
• FAA (Federal Aviation Administration) is the agency that regulates civil aviation, including aircraft, pilots, and airspace. The FAA has jurisdiction over aircraft in flight.
  
  
• FAR (Federal Aviation Regulations) are the rules governing civil aviation.
  
  
• General Aviation includes flight training, business aviation, public benefit (volunteer, nonprofit) flying, air tours, law enforcement flights, charter flights (less than 10 seats), air ambulance flights, private flights, and more. The FAA defines general aviation as all flights not conducted by the military or airlines with scheduled service using aircraft with more than 10 seats.
  
  
• GPS-Approach is an approach path into the San Carlos and/or Half Moon Bay Airport that is flown by an instrument-rated pilot operating under instrument flight rules. The GPS-Approach can be used during any weather, but it must be used when the weather is less than the FAA defined visual-flight-rule minimums.
  
  
• IFR (Instrument Flight Rules) allow pilots to safely fly in clouds and lower weather minimums. The pilot must have an instrument rating from the FAA and the aircraft and airport must be IFR capable.
  
  
• Reliever Airports are those that relieve congestion at commercial service airports and provide improved general aviation access to the overall community. Reliever airports serve general aviation flights and can accommodate air taxi and charter flights with fewer than 10 passengers.
  
  
• Touch-and-Go is a training maneuver where aircraft practice takeoffs and landings in succession – taking off, turning right back toward the runway to land, then adding power and taking off again without exiting the runway. The touch-and-go is often completed by pilots as part of the FAA’s proficiency requirement for carrying passengers.
  
  
• Traffic Pattern Area is the flight path aircraft fly when arriving, departing, and returning to land for training purposes. The traffic pattern area for the San Carlos and Half Moon Bay Airports can be found on the Voluntary Noise Abatement procedures handout and on this website.
  
  
• Visual Flight Rules (VFR) are a set of minimum weather requirements that pilots (without instrument ratings) must adhere to for day and night operations.
  
  
• Voluntary Noise Abatement Procedures (VNAP) were designed to reduce noise impacts for residents living near the airports. The San Carlos Airport and Half Moon Bay Airport are surrounded by noise sensitive neighborhoods.

The County of San Mateo, pilots associations, airports’ staff, community groups, and the FAA worked together to develop VNAPs as a fly friendly policy that has produced positive results. Adherence by pilots is high.