South Flow

What is South Flow?

During normal operations, aircraft arriving at San Jose Airport (SJC) land from the Southeast. However, when winds at SJC change from their prevailing direction, planes need to land from the Northwest. In this configuration, arriving flights typically overfly Cupertino and Sunnyvale, make a 180 degree right turn over Mountain View or Palo Alto, before beginning their final straight line descent over the Bay into SJC. This picture from SJC shows the general direction of flight taken by airplanes during South Flow. Please note that the picture does not faithfully chart the path:

These south-easterly winds occur predominantly in the winter months and in inclement weather. Because this airport traffic configuration reverses the normal operation, South Flow is sometimes called Reverse Flow. South Flow operations are declared approximately 15% of the time, but usage from year to year varies with the weather.

Why is it a problem?

Historically South Flow traffic into SJC was scattered over a wide area, which kept the noise burden for individual residents small and acceptable. There were few complaints (2,963 in 2014). In 2015, the FAA altered the South Flow procedure as part of its NextGen program to modernize the use of air space for efficiency. This followed a rerouting of traffic in 2012, which paved the way for this change. The result of these changes is a flight path that has been shifted over new neighborhoods with a much increased concentration of aircraft. Finally, in 2016 the speed guidance was increased, enabling planes to fly faster, but louder. What was previously a non-problem became a major nuisance for many residents. Noise complaints to SJC airport increased sharply (859% from 2015 to 2016) and remain at high levels.


Left unaddressed, the South Flow problems will get worse: in 2016, SJC was the fastest growing large airport in the US and the SJC 2016 Master Plan projects that traffic into SJC will double between 2015 and 2027. This plan also shows a four-fold increase in cargo aircraft, which can be especially loud. Fulfilling all this demand would mean a plane almost every two minutes during waking hours. Regularly scheduled flight operations are permitted from 7am until 11pm, with late arrivals often heard past midnight. Quieter aircraft can operate 24 hours a day.

What can be done?

A concerted effort between residents of affected cities and elected officials convinced the San Jose Airport Commission and the San Jose City Council in 2017 to establish an Ad Hoc Advisory Committee to address South Flow (official page). The committee consists of city council members from affected cities who will hear input from residents, the FAA and airport staff to make recommendations to the FAA for addressing South Flow. This is the opportunity to resolve the South Flow problem!


Some of the solutions that should be considered are:

  1. Undo the concentration and shift of aircraft. The low volume of complaints in the past has shown that this is effective and fair.

  2. Reduce speed. The speed has a much greater influence on the noise of a plane than the altitude.

  3. Reduce use of flaps, slats and air brakes. Use of these surfaces are often the biggest source of noise on arrivals.

  4. Increase pilot discretion: ‘One size fits all’ does not work for aircraft -- the quietest arrival procedure differs by aircraft model. Pilots like to land their planes quietly, but automated flight management systems simply follow their programming.

  5. SJC should incentivize quiet operations. For example, a simple, cheap fix to the Airbus whine is available, but implementation is sluggish in the US. The airport could encourage faster implementation of this and other noise reduction measures by charging a nominally higher landing fee for noisier aircraft. (While fines are pre-empted by federal law, airport fees may be acceptable.)

There's more, but solutions that are both safe and effective require the input from professionals such as acoustical consultants and FAA officials, which we are not.

What can you do as a resident?

A lot:

  1. Stay informed: join the distribution list by emailing
    We promise not to spam you, but we will alert you when your voice will help most.

  2. Contact your city council and let them know you care about this issue. You can find which of your city council members is serving on the Ad Hoc Advisory Committee below, along with his or her email address.

  3. Tell your neighbors. More residents getting involved means higher chances of 

  4. Send a short email or, better, show up for a meeting of the Ad Hoc Committee and speak. Community input is critical to make your voice heard. You can find the schedule here.

  5. Report South Flow noise here. An easier web-based interface is available at It’s easier because it can record a flight with a single click and you can create an icon on the home screen of your cell phone or tablet to access it easily. These results are not currently tabulated by SJC staff, but the results are reported by activists at their meetings. The Flightradar24 app can be used to see airplanes in flight and can display information like origin and destination airport, altitude and speed. It’s a great companion to your noise-reporting programs and useful if you just want to see what made so much noise overhead.

Members of the Ad Hoc Advisory Committee On South Flow Arrivals

Mayor Glenn Hendricks — City of Sunnyvale, Committee Chair

Councilmember Charles “Chappie” Jones — City of San José

Councilmember Raul Peralez — City of San José

Mayor Savita Vaidhyanathan— City of Cupertino

Vice Mayor Lisa Matichak — City of Mountain View

Councilmember Lydia Kou — City of Palo Alto

Mayor Gary Waldeck — Town of Los Altos Hills

Councilmember Rene Spring — City of Morgan Hill

Vice Mayor Kathy Watanabe — City of Santa Clara

Mayor Jean (John) Mordo — City of Los Altos

Councilmember Rowena Turner — City of Monte Sereno

Mayor Mary-Lynne Bernald — City of Saratoga

Councilmember Jeffrey Cristina – City of Campbell

Upcoming Events

You can find a list of upcoming events here. Consider adding your voice to a meeting that is rated as HIGH importance by speaking or emailing in your comments.

224 Flights on 12/5/14 vs 224 flights on 3/10/16 - Note the increase in concentration