While, the majority of the current flight paths used at Sacramento International Airport (SMF) have been in place for several decades, on January 8, 2015, the Federal Aviation Administration (FAA) implemented a series of instrument arrival and departure procedures at several Northern California Airports intended to make the air traffic system safer and more efficient. These changes are a part of the FAA’s nationwide air traffic control modernization program commonly known as NextGen.
One arrival procedure and three departure procedures have been implemented at SMF. An additional departure procedure is expected in the spring of 2015. The procedures, called RNAV for Area Navigation, are intended to reduce pilot and air traffic controller communications, reduce distance flown, and to produce more precise and repeatable fuel-efficient aircraft flight paths. The improved fuel efficiency results in reduced air emissions.
Because the new arrival and departure procedures are more precise, aircraft operations are more concentrated along the RNAV flight paths than the previous procedures. As a result, some residents have experienced an increase and others have experienced a decrease in the number and frequency of aircraft overflights.
The images below compare a set of departure and arrival flight tracks for SMF for the third week of January 2014 to the same period in 2015. The flight tracks in the 2014 image appear much more dispersed over nearly the entire image. The flight tracks in the 2015 image appear concentrated along the arrival and departure paths. Although it may seem as though there are fewer flight tracks in the 2015 image, both images have a similar number of flight tracks. The 2015 image illustrates how the new RNAV procedures generate more precise and repeatable flight paths.
Aircraft Flight Tracks – 4th week of January 2014
Aircraft Flight Tracks – 4th week of January 2015
The FAA has the sole jurisdiction over aircraft in flight as well as the sole responsibility for the development and implementation of new flight procedures. Prior to the implementation of these RNAV arrival and departure procedures, the FAA prepared an Environmental Assessment to quantify any environmental impacts. The Environmental Assessment resulted in a finding of no significant impact.
As the operator of SMF, the Department of Airports receives aircraft noise complaints and informs the FAA of community concerns related to aircraft noise.
Changes in wind and weather conditions may result in a change the runways being used at the airport. Many times, residents may interpret this as a change in flight paths when in actuality it is a different runway being used than what may occur most of the time.
You may ask why different runways are used. Aircraft must take off and land into the wind. When airports are constructed, the runways are built to align with the general wind pattern for the area. The runways at SMF are oriented north-south and as a result the Airport operates in either North Flow (take offs and landings to the north) or South Flow (take offs and landings to the south). Aircraft operate to the south, in South Flow, the majority of the time during any given year. This is due to the prevailing winds in the Sacramento region. South Flow occurs approximately 70 percent of the time in a given year; North Flow occurs approximately 30 percent of the time during a given year.
Arrivals from the south fly north past SMF on the Airport’s west side to remain clear of the south flow departures, which generally turn to the southeast due to the position of Sacramento in the USA and most destinations from Sacramento are located to the east. To allow for adequate spacing between each arrival, aircraft may travel further to the west than what may seem necessary. Once past the Airport, aircraft continue flying north until making their turn to the east and then south to line up with the runways for landing. The location where this turn takes place is dependent on the amount of air traffic in the area and the spacing required between aircraft for operational safety reasons.
Typical South Flow Day
Winds from the north result in SMF operating in North Flow, meaning flights approach SMF from the south and land or take off on northbound headings. North Flow conditions occur most frequently during the more variable weather conditions experienced between fall and spring.
For more than 20 years, SMF has also had a nighttime preferential runway system that calls for a North Flow operation, using Runways 34L/R, between 9:45 pm and 7:45 am local time daily as conditions permit (also referred to as North Flow at Night). The areas immediately north of SMF consist primarily of farmland, while the areas south of SMF include residential development. Departing to the north at night when possible reduces the potential of disturbing residents with aircraft noise at night..
Typical North Flow Day
With all of the open or rural areas around Sacramento, such as the Yolo Bypass, why do the airlines fly over the city?
Moving the departure paths to overfly portions of Yolo County is often a suggested solution to unwanted aircraft noise. The majority of the current departure and arrival flight paths at SMF have remained the same since the Airport opened in 1967. One change that occurred after McClellan Air Force Base closed was to turn aircraft headed for northerly destinations such as Portland and Seattle to the east as opposed to the west after departing to the south on Runways 16L and 16R. This change moved the northbound departures over agricultural land east of SMF and away from the residential areas along the Garden Highway west of SMF.
In general, flight paths are defined by the airspace configuration, which in turn is driven by the location of surrounding airports. The concept of departing over the Yolo Bypass was examined and rejected by the Federal Aviation Administration (FAA) in a study completed by the FAA in 1990. The FAA cited the airspace constraints that exist to the south of SMF as the primary reason for rejecting a Yolo Bypass departure. The SMF arrival route is south of the Airport and Travis Air Force Base airspace is just to the southwest of the Airport. The majority of the air carrier jet operations departing SMF are headed for eastbound destinations, which is why most aircraft turn to the southeast shortly after takeoff.
Aircraft used to fly further south; why are arrivals from the east now flying over my West Sacramento home?
It is during North Flow and the Nighttime Preferential Runway Use conditions that locations to the south of SMF may experience more frequent overflights by arriving aircraft. Aircraft from the east and south are aligning with the runways to land to the north. Depending on traffic and weather conditions, aircraft may align with the runways several miles from the Airport in order to fly a stabilized approach down to the runway. Aircraft on approach typically align with the runway at seven to ten miles from the touchdown point. This is typically further away from the airport when compared to where departures may initiate a turn. North Flow conditions occur approximately 30 percent of the time in a given year.
Between 6 a.m. and 8 a.m., the frequency of flights seems to be about every few minutes. Why are there so many flights at this time?
Early morning is a busy time at many airports as business travelers seek to get to their destination at or near the start of the business day. At SMF, the 6:00 a.m. to 7:00 a.m. hour is the busiest hour of the day for departures. This busy departure time is also driven by Sacramento’s location relative to the rest of the country. Many destinations to the east of Sacramento are located in an earlier time zone, especially those located on the East Coast. Departing at an early hour from SMF is necessary to reach those destinations by the end of the day. There are also many business travelers that make day trips to Southern California, necessitating they leave early in the morning to complete their trips in a single day. Airlines recognize business traveler’s needs, as well as the geographic location of Sacramento, and make the decision to operate more flights in the early morning hours. The Sacramento County Airport System has no authority to regulate when the airlines schedule their flights.
The FAA is the agency that has sole responsibility for aircraft movement in the air. Air traffic controllers are part of the FAA and they direct aircraft movements. The FAA is responsible for developing air traffic routes and procedures, including arrival and departure paths. These procedures are then provided by the controllers to the pilots. All air traffic routes and procedures are developed with safety and efficiency of moving aircraft being the most important components. Airports can advocate changes to those routes and procedures to the FAA for noise abatement reasons, as long as safety and efficiency are not compromised and noise is not simply shifted from one community to another. The FAA must approve all changes and is then responsible for implementing those changes.