Black September

Black September was an alternative version of the September 11 Attacks, in which the Slayerz traveled back in time and avenged the 3,000 Americans killed in 9\11 by hijacking and crashing airplanes into various Islamic terrorist hideouts in the US and the Middle East.

Background (fromalthistory.wikia.com )
Seething with rage over the amount of American casualties in the actual 9\11 event, Slayerz member Lev Ivanovich Raskov sought to avenge the deaths by killing Muslim radicals and their civilian allies. Fellow Slayerz member Olivia Coonzlater went along with it. At the same time, The Marxist Brethren and their leader, a reincarnated Karl Marx, sought to eliminate religion as part of their own war against the Western world and create a Marxist society and had been planning a genocide of Muslim radicals and their allies for years (after Karl Marx grew tired of attacking Christianity). He eagerly accepted The Slayerz's request to assist them in their attack on the Islamic world. For the next five years, The Marxist Brethren help train the Slayerz in time for the operation. As the terrorists had done earlier, the Slayerz are trained to blend into their Middle Eastern environments to avoid arousing any suspicion.

This was the general plan for the hijackers: change their names, pose as tourists, and board the planes. Taking advantage of the less security, they smuggle weapons on board and subdue the crews and passengers at the right time, and then crash the planes into their respective targets.

In addition, Marx instructed that the flights be hijacked in a particular order; once one airplane was hijacked, the hijackers of that flight would text their friends to alert them of the hijacking and that it was "their turn" to hijack their flight. The hijackers of the next flight would then hijack theirs, and alert the buddies on the next flight and so on. Eventually, they were to crash the planes into their respective targets. As for the original flights hijacked during the old time line, they were to simply kill the hijackers and either alert the crew on the ground of a hijacking attempt or crash the planes into Islamist terrorist targets.

In addition to airliners, The Marxist Brethren also utilized suicide bombers; Marxist members loaded explosives onto trucks and drove them into ground targets that the airliners could not reach, killing more people. ==The Attacks==

Just like in the Old Time Line, September 11, 2001 was a clear and sunny day. By 9:00 AM Eastern Time, the attacks began. However, security was upgraded and so the hijackers had to pose as tourists and then hijack the flights at the appropriate time. Despite air marshalls being on the flights, the Marxist Brethren were able to subdue the passengers and crew and crash the planes into their targets.