Cell phones
Theory
9/11 conspiracy theories often assert that cell phones do not work on airplanes, and the cell phone calls from Ed Felt and CeeCee Lyles couldn't have happened.
Fact
These phone calls came at ~9:58 a.m., just a few minutes before the plane crashed near Shanksville. At this point, the plane had dropped its altitude and was flying at approximately 5,000 ft.
As well, several mountain ridges in the Appalachians transverse Westmoreland and Somerset County, with elevations exceeding 3000 ft.[1] The highest point in the state is Mt. Davis, with a summit of 3,213 ft. Even some of the mountain passes, along the Lincoln Highway (Route 30) rise to ~2400-2900 ft in elevation and tend to house cell towers and equipment. The field near Shanksville where United Airlines Flight 93 crashed is at 2200 feet above sea level.
Bald Knob Summit is one such ridge, located no more than 10 miles (to the east) from the Flight 93 crash site. The Lincoln Highway (Route 30) crosses over Bald Knob at 2900 ft. Communications facilities are located at Bald Knob.
Image:Bald knob summit celltower.jpg
On top of a smaller ridge, located 3-4 miles (to the northeast) from the crash site, is this cell tower:
Laurel Hill summit (~2,600 ft) is located ~14 miles to the west of the crash site, at the Westmoreland-Somerset County border. The cell tower is owned by American Towers, which operates towers for the cell phone industry. This tower is 329 ft tall, located at 2701.9 ft, with an overall height of 3060 ft. The second tower is also owned by American Towers.
Near Jennerstown, ~10 miles to the west of the crash site, this tower is owned by Cingular Wireless. It has been here since 1997. The total height of the tower is 275 ft, together with a ground elevation of 2210 ft, the overall height is 2500 ft. The second tower here is owned by Crown Communications, which owns and operates cell towers, and has been here since 1997.
Combine the elevation of the land surface with the low flying altitude, the plane was flying only ~2500 feet above the ground when the cell phone calls were made. For comparison, the World Trade Center north tower was ~1,368 feet tall. It's entirely reasonable that cell phones would work at double that height.
Both phone calls only lasted 1-2 minutes, and then were dropped. That coincides with a sudden ascent up to ~10,000 feet that the aircraft made before it then plummeted to the ground and crashed.
References