Just about everything an aircraft does, including the noise it makes, is affected by the weather. Aircraft climb more slowly in warm weather, making operations louder on the ground. On cloudy days, the noise from aircraft rebounds down to the earth’s surface from the bottom of the clouds, making it louder. On windy days, aircraft noise carries further at ground level.

For an explanation of how to navigate the City's Casper Noise Lab website please see the User Manual.  This document provides an overview of the website as well as details about each individual webpage, data browser, and the associated charts.

For safety reasons aircraft always land and take off into the wind.  A headwind decreases the amount of runway needed for an airplane to take off and land by increasing the amount of airflow over the wing, which increases lift, allowing the plane to land or take off at a slower airspeed.  As a general rule, when the wind speed at the airport is measured to be three knots or higher, the prevailing direction of the wind dictates which runways are used for landing and takeoff.

The Federal Aviation Administration (FAA) has the sole authority to determine where aircraft fly and how the airspace in the Bay Area is operated.  The FAA controls the runways and associated airspace to ensure the safe and efficient operation of the skies around Sunnyvale.  Noise complaints are not directly considered when Air Traffic Control (ATC) makes decisions about how to manage the airspace in Northern California.  However, individual airports, various roundtable groups, and city, state, and federal representatives continuously engage with the FAA and work to ensure that noise concerns are considered when the FAA initiates a process to modify or introduce new flight procedures in the Bay Area.

If aircraft noise is bothering you, the best thing that you can do is to contact the appropriate airport to report airplane noise. You can also contact the FAA Aviation Noise Ombudsman.

The City’s NOMS (Noise and Operations Management System) provider Casper collects data from multiple sources to ensure accuracy and to plan for contingencies. The primary source used for most flight tracking is a data feed provided by the FAA known as System Wide Information Management or SWIM. Casper collects data from both a primary and backup FAA SWIM feed center, in the case of an outage. To supplement that data, Casper pulls flight plan information from FlightAware, and further aircraft type specifications from a database known as FlightGlobal. Beginning in December 2022, Casper also integrated data from a network of physical transponders known as ADS-B Exchange. This helps to pick up flight tracks from aircraft that have historically been able to hide their location from most other public feeds. Because these data feeds are all working to supplement each other on the server-side, the end result is a blend of what all of them collected, meaning that the data points in Noise Lab and the flight tracks in Flight Tracker look as though they have come from one single source.

The City does not have direct authority over air space. We are, however, working with regional agencies and federal representatives and authorities to mitigate the effect on our residents. The authority to control aircraft in flight and on the ground is vested exclusively with the Federal Aviation Administration (FAA).

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, which is the dominant source of airplane noise.  However, close to the airport, the relative quietness of arrivals may be offset by the fact that the airplanes are typically lower in altitude than departures over the same location.  Configuring the plane for landing requires the pilot to lower the landing gear and wing flaps which enables the airplane to slow down and the wings to generate greater lift. However, the noise generated by the turbulent airflow over the landing gear and flaps also creates substantial noise that can equal or exceed that produced by the jet engines.  The turbulent airflow also increases the drag on the airplane requiring the pilot to increase engine power to maintain a safe descent path to the runway, which also increases noise. 

During times of inclement weather, some mornings, or during frontal passages, the wind at SJC will blow from the south. For safety reasons, aircraft must take off and land into these southerly winds, requiring the airport to operate in "south flow," an alternate arrival path into SJC that allows aircraft to land and take off into the wind. During these times, aircraft must follow a basic traffic pattern over the area to the west of SJC over Santa Clara and Sunnyvale, before turning east over Moffett Airfield to return to the airport. As these weather systems pass the airport returns to "north flow," our most common configuration, and Air Traffic Control begins directing aircraft to arrive over downtown San Jose.