A commercial airliner may need to be moved from one airport to another at the end of that day's operations to satisfy the next day's timetable or to facilitate routine scheduled maintenance; this is commonly known as a positioning flight or repositioning flight, and may sometimes carry revenue freight or passengers as local aviation regulations and airline policies allow. They may also be necessary following a major weather event or other similar disruption which causes multiple cancellations across an airline's network resulting in many aircraft and crew being 'out of position' for normal operations; the 2010 eruptions of Eyjafjallajökull or the mass evacuation of US airspace following the &lt;a href="September%2011%20attacks"&gt;9/11 attacks&lt;/a&gt; being significant examples of this.