This (right) is the only known photograph of the plume of smoke rising from the impact site of Flight 93 in an uninhabited area near Shanksville, Pennsylvania. It was taken by Val McClatchey from the porch of her home near Indian Lake, as reported by Shanksvillememorial.com and by Post-Gazette.com.
Some conspiracy theorists claim that this photograph suggests that Flight 93 did not crash there. The shape of the cloud is wrong, they say: it's typical of a bomb, not of a plane crash.
This is an allegation made for example by an Italian conspiracy theory site, Luogocomune.net, in a video entitled La verità di cristallo ("Crystal Truth"), broadcast on Italian national TV on September 11, 2006, and by many other similar sites.
Similar allegations are made elsewhere:
"the mushroom cloud in her photo is more reminiscent of an ordnance blast than a jet fuel column" - Lisa Guliani, Wingtv.net.
"It proves that this blast is more likely an ordnance plume" - Killtown.
The implication is that the crater and debris were produced by using a bomb and therefore the tragic crash of the plane was staged. A key element of "evidence" for these claims is obtained, according to conspiracy theorists, by comparing the Flight 93 photograph with images of plane crashes and ordnance blasts, as in this montage used by Killtown:
Left to right: the photo taken at Shanksville, an ordnance blast and a plane crash.
But is it true that a plane crash invariably forms a smoke cloud whose shape is distinctly different from the one shown in Val McClatchey's photograph? No, it isn't. On August 13, 2006, an Algerian Lockheed L100-30, the commercial version of the well-known C-130 Hercules, a four-engine turboprop, crashed near Piacenza, Italy, as reported by local news and government sources (such as the ARPA environmental protection unit).
If you're not familiar with the appearance and size of a Hercules, Wikipedia has the specs and a photograph:
A cloud of smoke rose from the crash site and a local resident, Gianluca Pietta, took a picture of it (shown here with his permission):
The resemblance to the Shanksville plume is striking:
Therefore, it is beyond doubt that sometimes plane crashes do form clouds shaped like the one in McClatchey's Flight 93 photograph. Accordingly, the shape of the plume is not conclusive evidence of conspiracy and any theories or allegations based on such a premise are flawed.