Transom windows may be fixed or operable. Retractable roofs are sometimes referred to as operable roofs or retractable skylights. Because these lights are all independently operable, different effects can be created within these spaces. There are no controls or operable valves of any kind. These offices used cross-ventilation from operable windows instead of air conditioning for cooling. Perceivable, Operable, Understandable and Robust. However, studies have shown that the system is operable with a severed vagus nerve. Securing an operable machine gun, Sgt. The MD-82 is permitted to fly with just one operable thrust reverser. The ablation releases oxygen from the glass, increasing the pressure beyond an operable level. Each of these major sites is split up into numerous sub-sites known as Operable Units. Dihedral and an operable elevator were also included. Both helper units derailed, but were still operable. The only F40Cs that remain in operable condition are #611 and #614. In 1960 TOA went bankrupt and only four were in operable condition.