San Jose Noise Monitoring Center’s Frequently Asked ...

Can the noise office change flight paths?

No. The Federal Aviation Administration (FAA) controls and
regulates the airspace. Any change in departure or arrival flight
paths must be approved and implemented by the FAA. The
noise office is here in large part to help communicate between
the airport, FAA and local community.

Why Do Commercial Aircraft Fly During the Posted Curfew Hours?

Since our curfew program, established by the FAA is a noise-based program, certain aircraft are permitted to operate
between the hours of 11:30 p.m. and 6:30 a.m. During this time, only jet aircraft at or below 89.0 EPNdB average of
takeoff/sideline/approach noise levels, or any “grandfathered” jet aircraft can operate.

The curfew times at Norman Y. Mineta San Jose International Airport are between the hours of 11:30 p.m. and 6:30 a.m.
There is an additional restriction for Stage II, older and louder technology aircraft that prohibits operations between the hours
of 11:00 p.m. and 7:00 am. In addition, if a flight operates between 6:30 a.m. and 11:30 p.m. and cannot meet its scheduled
arrival or departure time because of “factors beyond the control of the airline,” i.e., weather factors, mechanical factors, or
Federal Aviation Administration (FAA) Air Traffic Control factors, the flight is permitted to achieve its scheduled operation
to/from the Airport. This can and does result in some flights occurring during the restricted hours.

Why do aircraft sound louder at night than they do during the
day?

Nighttime noise events seem louder because the ambient noise is
lower. More noise events may be noticed at night compared to
daytime hours when there exists a higher ambient noise level.

What is a Noise Abatement Procedure?

A noise abatement procedure is a recommended flight path aircraft follow to minimize noise over a
populated area. Because this is a recommended procedure, pilots may decline to follow it due to safety
concerns or operating limitations. For some noise abatement procedures, a pilot must be able to see
specific visual cues. If the visual cues are not visible, the pilot will not be able to safely follow the noise
abatement procedure. Other procedures rely on navigational equipment capabilities.

Will noise increase as result of the Mineta San Jose Airport expansion?

The noise impact area for the San Jose Airport has decreased during the past decade and is expected
to continue to decrease as a result of newer and quieter technology aircraft even with the planned
expansion. Development of the next generation of aircraft (Stage 4) is well underway and will bring
quieter planes in the future.

What kind of information should a complaint convey and why?

The Noise Management Office documents noise complaints by obtaining information from the caller about the
nature of the complaint, time of the occurrence and location of the caller’s residence. The noise staff uses this
information to determine the probable activity responsible for the complaint and, when requested, provides a report
or a letter to the caller. The letter or report may include the original complaint and flight track map(s), as well as a
response that identifies the aircraft and activity responsible for the call (arrivals, departures, engine run-up, etc.),
any available meteorological information (an important factor in aviation activities), and runways in use at the time
of the call. Staff may also be able to provide information on unusual noise events and, if appropriate, any action
the Noise Office may take.

What happens when I submit a noise complaint?

The Noise Management Office will log your complaint into its noise complaint database. The Noise Management
Office investigates all complaints by new callers and callers who desire specific information about noise events
and aircraft activity. When appropriate, staff follows up with aircraft operators and/or the FAA to investigate what
action can be taken to minimize noise in the future. Staff does not investigate every complaint made by frequent
callers because they are often repetitive in nature and the staff may have previously spoken to the caller about
their concerns.

Why do some aircraft seem louder than others?

Aircraft operating at San Jose International Airport have a diverse range
of noise levels. These noise levels primarily depend on the type of
engine used by the aircraft, the size of the aircraft and whether the
aircraft is taxiing on the airfield, landing or taking off. The newest so
called "full Stage 3" aircraft tend to be the quietest aircraft in the fleet.
Aircraft that were originally Stage 2 compliant but retrofitted to meet
Stage 3 regulations tend to be the loudest. Departures tend to be louder
than arrivals since the pilot is forcing more power to the engine to
achieve lift.

What are Stage 1, Stage 2 and Stage 3 aircraft?

This is a FAA-established classification system used to
determine the noise level of an aircraft based on weight,
number of engines and, occasionally, its passenger capacity.
Aircraft may be certified as Stage 1, 2 or 3.

Stage 1 aircraft are the oldest and the noisiest and are not
permitted to operate in the United States as commercial
aircraft.

Stage 2 aircraft, over 75,000 pounds take-off weight, include
the older Boeing 737-200, 727 and the DC-9.

Stage 2 aircraft were required by law to be phased out of
service by January 1, 2000.

Stage 3 aircraft meet current standards set by the FAA and
generally are quieter. These aircraft include the Boeing 737-
300,757 and 767; the Airbus 320; and the MD 80/90. Some of
the older Stage 2 aircraft were re-engined or "hushkitted" to
meet the new Stage 3 standards.

When do flight paths change? How do flight paths change?

During the winter months, inclement weather and Southerly winds typically reverse the flight pattern at the airport. When
operations are on runway 12-Right, departures are to the South and arrivals from the North. The weather conditions that
cause the change in departure direction mostly occur during the months of September through March. Because of the
complexity of the Bay Area airspace system, San Jose must maintain prescribed altitudes and separation to/from San
Francisco and Oakland Airports traffic. Aircraft traffic patterns are not within the control of this Airport.

The southern departure pattern occurs about 15% of the time depending on the prevailing winds and weather conditions
that mostly occur during the months of September through March. When winter storms move in, winds generally come from
the South. To accommodate the change in wind direction and for flight safety, the departures and arrivals now must
proceed to the South. As the weather systems pass, we will then return to our Northerly departures. (Weather or wind
patterns at Oakland and San Francisco also affect these patterns even if the weather is better here; The FAA has to
accommodate these airports to maintain the same traffic flow throughout the Bay Area.)

Who tells the pilots where and when to turn?

Commercial pilots fly prescribed routes and general aviation pilots also fly prescribed routes as well as visual flight
procedures (VFR) to and from San Jose International Airport as instructed by air traffic controllers. The FAA is responsible
for managing San Jose’s airspace and for ensuring the safe and expeditious flow of traffic. San Jose Airport Operations is
responsible for operating and maintaining airport facilities and for ensuring that runways (and taxiways and other facilities)
are in good working conditions, meet FAA regulations and are available for use.

Example of the North Flow Example of the South Flow
Departure occurring 85% of the Departure occurring 15% of the
time at SJC time at SJC

How does Mineta San Jose International
Airport track and monitor flights?

Our Noise Management Office uses
software called ANOMS, which stands for
Airport Noise and Operations Monitoring
System. This system collects noise data
from 10 permanent community monitoring
sites in addition to flight track data from the
FAA. It is the main tool used by the noise
office to research complaints and to monitor
noise abatement procedures and programs.

Why do airplanes fly out of the corridors?

There are many reasons, sometimes beyond the airline's control, why a jet may fly out of the noise abatement corridors.
These include traffic conflicts, weather, air traffic control directives, safety considerations, aircraft performance and pilot
technique.

How are Noise Levels Determined?

To more consistently and easily describe and compare noise environment comprised of numerous single events that vary
in duration and magnitude over long periods of time, the U.S. Environmental Protection Agency developed a single
number descriptor. This descriptor is the DNL. It is a noise metric which describes and average day/night sound level.
The DNL metric is used by the FAA to quantify aircraft noise exposure in the vicinity of an airport. Noise contours of
specific DNL levels are developed using the FAA’s Integrated Noise Model (INM). Airport specific data used in the INM
model to develop the contour will result in the depiction on noise exposure in the vicinity of an airport. Airport specific data
used in the INM include: Average Daily Operations, Aircraft Fleet Mix, Runway Use, Flight Corridors and Usage,
Departure Destinations and Day/Night Use.

What is A DNL?

DNL (Day-Night Sound Level) is based on sound levels measured in relative intensity of sound, or decibels (dB), on the
“A” weighted scale (dBA). This scale most closely approximated the response characteristics of the human ear sound. The
higher the number on the scale, the louder is the sound. DNL represents noise exposure events over a 24-hour period. To
account for human sensitivity to noise between the hours of 10 p.m. and 7 a.m., noise events occurring during these hours
receive a “penalty” when the DNL is calculated. Each nighttime event is measured as if ten daytime events occurred.

What are Noise Contours?

Noise contours are a series of lines superimposed on a map of the airport’s environs. These lines represent various DNL
levels (typically 65, 70, and 75 dBA). DNL noise contours are used for several reasons.
Noise contours highlight existing or potential areas of significant aircraft noise exposure (as identified by the FAA).
Noise contours are used to assess the relative aircraft noise exposure levels of different runway and or flight corridor
alternatives.
Noise contours provide guidance to political jurisdictions in the development of land use control measures. These
measures include zoning ordinances, subdivision regulations, building codes and airport overlay zones.
It is the areas within the 65, 70, and 75 DNL noise contours that the FAA considers to be the most impacted by aircraft
generated noise.

Which Is Quieter—An Arrival or Departure?

Arriving aircraft at low altitudes are generally quieter than
departures of the same aircraft type because this mode of flight
requires much less engine power. However, close to the airport,
the relative quietness of an arrival may be offset by the fact that
they are typically lower in altitude that departures over the same

location.

Did you get all of your Noise Questions Answered? If
Not, Please email us at: [email protected]