Answers. Best Answer: FL means Flight Level. It's used above 18.000ft (in the US, in other countries other altitudes are used as the boundary) to indicate the altitude in hundreds of feet. So FL230 is 23.000ft standard altitude.est Answer: FL means Flight Level. It's used above 18.000ft (in the US, in other countries other altitudes are used as the boundary) to indicate the altitude in hundreds of feet.
The nostrils, which form the external entrance of the nose, lead into the two nasal cavities, which are separated from each other by the nasal septum, a partition formed of cartilage and bone. Three bony ridges project from the outer wall of each nasal cavity and partially divide the cavity into three air passages.
The nasal vestibule is the pear-shaped cavity that lies directly behind the nostrils of the nose. Nasal vestibules are constructed from the same materials as human skin with hairs protruding from cells that act as filters to stop dust particles and pollutants passing into the respiratory system.