Final answer:
United Flight 93 was the fourth plane which crashed in a field in Pennsylvania on September 11, 2001.
Step-by-step explanation:
On September 11th, 2001, one of the most shocking and deadliest terrorist attacks on American soil involved four hijacked airplanes by members of the terrorist group al-Qaeda.
While each plane had a tragic fate, the fourth plane in question, which unfortunately did not reach its intended target due to the heroic actions of its passengers, was United Flight 93. This plane ultimately crashed in a field near Shanksville, Pennsylvania.