Apache by Boeing 2
An Apache attack helicopter, built by Boeing Boeing

Syrian activists monitoring the situation in Kobani said fighters with the Islamic State attempted to shoot down U.S.-led coalition airplanes flying over the city. Raqqa is Being Slaughtered Silently, an anti-militant activist group based in Raqqa, said coalition airplanes were bombarding the city with airstrikes Sunday.

About 20 ISIS fighters have been killed so far in the attacks, the activist group reported on Twitter Sunday. In retaliation, ISIS fighters purportedly began shooting "thermal" rockets at coalition aircraft.
There are several kinds of thermal rockets. It is unclear which type ISIS used. But if used correctly, thermal rockets do have the ability to bring down aircraft. In March 2013, Syrian rebels purportedly shot down a government helicopter near Aleppo.
Earlier this week the Iraqi Defense Ministry said ISIS had in its possession anti-aircraft weapons known as MANPADS -- shoulder fired anti-aircraft missiles. Images released Oct. 10 show ISIS shooting down an Iraqi government helicopter with a shoulder fired missile.
The presence of anti-aircraft weapons among the ISIS ranks threaten the U.S.-led coalition. MANPADS are portable systems that are easy to hide. Targetting them in airstrikes is a difficult task, military experts say.
The U.S. is now using Apache helicopters in Iraq, which are easier to target with weapons like MANPADS. ISIS has released a guide to its fighters on how to shoot down the helicopters. It explains explains in detail how to use portable surface-to-air missiles, such as the Russian-made SA-16 and SA-18 and the American FIM-92 Stinger against the attack helicopter.