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It appears that there has been a crash at the 2009 Sacred Defense air show over Tehran, involving an IRIAF F-5 and Il-76 Adnan. There appears to be no survivors; initial reports indicate seven crew members killed. [Source: ACIG]
The official IRNA news bulletin stated that a plane crashed into farmlands just south of the Iranian capital, during an exhibition flight over a military parade marking the beginning of the Imposed War [Iran-Iraq War]. However, inexplicably, the bulletin was subsequently removed from IRNA's news website.
Update: Details remain sketch concerning the aircraft type(s) involved. Boeing aircraft have been suggested, as well as a Saeqeh.
Fars News Agency quoted the Iran Red Crescent relief chief Ahmad Esfandiari as saying that relief workers had found the bodies of seven passengers from a plane which crashed in an area called Qarchak, south of Tehran. The report said the crash took place at around 10:00 am (0630 GMT) in Qarchak, an area close to where an army parade was taking place. Fars, however, quoted a statement by the Iranian air force as saying the plane that crashed was not part of the parade, but was a training aircraft.
Update 2: The involved plane was the ex-Iraqi Il-76MD Adnan 1 "Simorgh" - the only AWACS airframe in IRIAF service (5-8208).