2003 noise measurements and approach studies

Summary of 2003 noise and approach studies

Several types of data were gathered in 2003:

Noise measurements at multiple points of the two approach paths to Mather
Radar data plotting the vertical approach profiles
Radar data plotting approach tracks
Locations and times of noise complaints
Details of individual approaches, such as type of aircraft and carrier

Mather approach paths and noise measurement sites.

Measurement sites in El Dorado Hills

Site	Address	Approach Path	Elevation (MSL)	Distance to runway, nautical/statute miles
3	354 Glen Ridge Ct.	ILS	1,010 ft	11.17 nm / 12.85 sm
7	435 Platt Circle	VOR/DME	785 ft	10.77 nm / 12.39 sm

(1 nautical mile = 1.15 statute miles)

Site 3 is on the ridge west of El Dorado Hills Blvd, in the area of most-frequent noise complaints for the ILS approach. Site 7 is near the interchange of US 50 and El Dorado Hills Blvd, under the VOR/DME approach.

Site 3 is the immediate area of El Dorado Hills which as produced the most vocal complaints about jet freighter noise prior to the 120-day test of the VOR/DME approach.

Two approach paths were compared:

ILS, the Instrument Landing System approach.
This is a "precision approach", using on-field radio navigational aids.
A "localizer" signal provides lateral guidance to follow a path along the extended centerline of the runway, in this case on a heading of 217 degrees magnetic. A "glide slope" signal provides vertical guidance, permitting pilots to fly the approach on a 3-degree glide slope. Both signals are calibrated to allow flying the approach with very high accuracy.
VOR/DME approach, a nonprecision approach with a flight path located south of the ILS approach. Lateral guidance is provided by a VOR (VHF Omni Range) located at Sacramento Metropolitan Airport for an approach heading of 224 degrees magnetic. This is less accurate than the ILS localizer, but it allows displacing the approach path to the south, with most of the approach not precisely aligned with the runway and with a small left turn near the end of the approach. There is no separate navigational aid for vertical guidance. Instead, flight crews use DME (Distance Measuring Equipment), which operates with the VOR signal, to observe their distance from the VOR. A subtraction translates this to the aircraft's distance from Mather's runway threshold. An FAA-approved and published VOR/DME approach procedure identifies a minimum altitude which must be maintained or exceeded until the aircraft is within a given distance of the runway. In this case, aircraft must stay at or above 2,000 feet above field level until they pass a point 5.4 nautical miles from the runway threshold.

Instrument approaches of both types require that the pilot have the runway in sight before descending below a given minimum descent altitude.

The study collected all data including noise measurements during two 1-week periods, one in February and one in August. In February most traffic used the ILS approach; in August the majority of arrivals used the VOR/DME approach, which was recommended for purposes of a 120-day test to compare noise impacts. At all times a relatively small proportion of arrivals used a visual approach, which does not regulate approach paths or glide slopes as the two instrument approaches do.

Information on this page is based on these public documents, from the Sacramento County Airport System:

August, 2003 report on noise measurements    84 pages, 2.5 MB.pdf file
December, 2003 noise study updates    25 presentation slides, 769 KB .pdf file
VOR/DME Test Jet Cargo Correlated Complaint Summary   6 pages, 790KB .pdf file

Most of the graphics in this set of web pages are extracted from these documents, with permission from and thanks to SCAS. In many cases portions of them have been highlighted to emphasize portions relating directly to El Dorado Hills.

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