In April, ash from Icelandic volcano Eyjafjallajokull (pronounced AY-yah-fyah-lah-YOH-kuul) grounded flights across the globe heading to and from Europe for days.
Although no aircraft were actually affected, airline companies kept their planes grounded, based upon government safety policy.
The effects of this cost the airlines billions of dollars, and after being grounded for days, they complained that the government agencies making the decisions overreacted to the problem.
Volcanic ash is formed during explosive volcanic eruptions, which create particles consisting of small tephra, or bits of pulverized rock and glass.
This can be a major hazard to aircraft because it is invisible to aircraft weather radar and is often not immediately noticed by pilots.
Volcanic ash is hard, does not dissolve in water, is extremely abrasive and mildly corrosive, and conducts electricity when wet.
Aircraft avoid any airspace that has volcanic ash in it because the ash can interfere with the function of propeller or jet aircraft.
It is so fine that it will invade the spaces between rotating machinery and jam it.
The silica melts and fuses on to the turbine blades and nozzle guide vanes (another part of the turbine assembly), which in modern aircraft operate at a much higher temperature than that needed for the silica to melt.
Aircraft avionics and electronics can also be damaged.
Flying through the ash cloud presents the danger of engine failure, among other potential problems.
Considering that most airlines are already losing significant amounts of money and we are still not yet out of the woods from the global financial crisis, it is no surprise that they protested having to have tens of thousands of flights grounded for days.
While it is certainly open for debate whether the governments involved in Iceland's ash problems overreacted when confronted with having to decide the best course of action, there are sound reasons for the concern.