The official narrative of the events which have become known as 9/11 includes descriptions of attacks on the World Trade Center towers and the Pentagon by aircraft on 11 September, 2001. The towers were eventually destroyed and the Pentagon was severely damaged. The account of the attack on the Pentagon includes the following: A Boeing 757, operated by American Airlines, took off from Washington Dulles International Airport at 8:20 a.m. At 8:54 it deviated from its assigned route and at 8:56 the transponder was switched off. The plane, under the control of hijackers, headed back toward Washington and descended. As it approached the Pentagon it performed a descending spiral to the right and finally dived toward the Pentagon while accelerating. It hit some light poles and other objects on the ground and then penetrated the west face of the building at 9:37:44,(1) or 9:37:46,(2) depending on source.
Various claims have been made about the attack on the Pentagon. Early claims included damage by a missile or a truck bomb.(3) However, as so many witnesses had reported seeing a large commercial aircraft approaching the Pentagon, these claims received little attention from the public. It was not until the data from the Flight Data Recorder (FDR) was received from the National Transportation Safety Board (NTSB) that serious consideration was given to alternative explanations of the damage. The data was received in two forms, following a number of Freedom of Information Act (FOIA) requests. One form could not be understood by inspection and the other, a readable comma-separated values (CSV) file, had some columns of data missing, a critical omission being radio height.(4) After considerable difficulty, assistance in interpreting the coded file was received and the result came into public hands.(5) Like the CSV file, it appeared to indicate that the flight terminated at a position which was too high to have struck the Pentagon in the described manner.Calibration of altimeter 92