A Flight 93 Memorial Ambassador* telling visitors that the official claim is that most of the plane burrowed underground:
"Because where the plane hit the ground, it literally went into the ground! They had to excavate and try and recover what they could and this top picture shows the excavation that they did. They excavated down about 40 to 45 feet and the last pieces were recovered at about 30 to 35 feet."
*The volunteer Ambassadors at the Memorial are trained to recite the official Flight 93 story:
"Today Ambassadors are at the temporary memorial every day of the year and have welcomed over one million visitors from all over the world. They have participated in rigorous educational training to become familiar with details of Flight 93 and the passengers and crewmembers to inform visitors about what happened here on 9/11."
- HonorFlight93.org