The statement very substantially
understates approach altitudes
and somewhat overstates ground elevation in this area.
and somewhat overstates ground elevation in this area.
- Actual
approach altitudes over Shingle Springs are much higher than 3,000
feet. The minimum, average, and maximum crossing altitudes
observed in the data sample gathered from March through June, 2008,
were: 4,524 feet (minimum); 6,342 feet (average); 10,128 feet
(maximum).
- Ground elevation in most of this area is generally in the range of 1,400 to 1,500 feet. Minimum and maximum elevations in the commentor's area appear to be around 1,200 and 1,600 feet, respectively.
The graph above is adapted from an actual glide slope profile recorded
during tests of Continuous Descent Approach (CDA) procedures.
Distances are in nautical miles from Runway 22L at Mather.
Air carrier cargo approach altitudes at two sites:
EDH west ridge and Rescue/Shingle Springs
These two histograms shwo the distribution of approach crossing altitudes at the west ridge in El Dorado Hills and at the Initial Approach Fix (IAF) or its equivalent, usually north of Shingle Springs.
Comparison of these two histograms shows not only that crossing altitudes in Shingle Springs are much higher than stated by the Shingle Springs resident, but also differences due to Air Traffic Control routing.
The IAF/Shingle Springs plot shows higher altitudes and more spread in crossing altitudes dispersion than the EDH west ridge plot.
The shortest description of the reason for more dispersion in Rescue and Shingle Springs than in El Dorado Hills is that arriving traffic is essentially traveling through an invisible funnel in all three dimensions. In the vertical dimension it converges onto a 3-degree glide slope leading to the runway.
| Comparison
of actual approach altitudes and the altitude stated by the Shingle
Springs commentor: "msl" is altitude in feet above sea level, "agl" is altitude in feet above typical ground level in Shingle Springs |
||||
| Approach Altitude | ||||
| Minimum | Average | Maximum | ||
| Stated | Approach altitude, msl | 3,000 msl | -- |
3,000 msl |
| Ground elevation, msl | 2,000 msl | -- | 1,500 msl | |
| Approach altitude, agl (above ground level) | 1,000 agl | -- | 1,500 agl | |
| Actual | Approach altitude, msl | 4,524 msl | 6,342 msl | 10,128 msl |
| Ground elevation, msl | 1,600 msl | 1,450 msl | 1,200 msl | |
| Approach altitude, agl (above ground level) | 2,924 agl | 4,892 agl | 8,928 agl | |
Actual terrain elevations are cited approximately from inspection of the commentor's home area in Google Earth. On the whole it appears that at least 80% of this area is between 1,400 feet and 1,500 feet. The commentor's home is in the area mapped in Assessor's Parcel Book 70.
Actual approach altitude data is taken from the flight track logs posted on this web site. The altitude referenced for Shingle Springs is that shown on the flight track at the Initial Approach Fix (CAMRR), which is designated to be at 6,500 feet msl at a particular distance from the threshold of Mather Runway 22L. This fix is approximately due north of the east/west center of the Shingle Springs area in question, it probably should be considered to be in a rural part of the county immediately north of Rescue, which in turn is due north of Shingle Springs. Some approaches are routed into this area by enroute Air Traffic Control (Oakland Center) on courses arriving from the east or southeast, south of the standard ILS approach path whose extension passes over Squaw Valley and join the ILS locator course at points west of CAMRR, the Initial Approach Fix. For those approaches this altitude was read from flight path data at a location approximately due south of CAMRR.