Structural limits:
These are the allowed positive and negative g limits of the aircraft. Structural limits are based on the strength of the aircraft structure. Under any loading, even 1 g, the aircraft structure will flex. A large amount of airframe flexure will lead to permanent deformation (a bent airframe) or component failure. A lesser amount of flexure affects the lifetime of the airframe due to metal fatigue, etc. The aircraft structural limits are selected to ensure that g-loading induced flexure will not damage the airframe or shorten its design life. Structural limits are also referred to as acceleration limits or limit load factors. Exceeding the structural limits (overstress of aircraft) may or may not damage the aircraft. Numerous overstresses will shorten the service life of the aircraft.
Rate of turn:
The rate at which an aircraft executes a turn expressed in degrees per second. In turning flight, the number of degrees of heading change per unit of time (usually measured in seconds) is referred to as the rate of turn. By definition, a rate one or standard rate turn is accomplished at 3°/second resulting in a course reversal in one minute or a 360° turn in two minutes. A rate one half turn is flown at 1.5°/second and a rate two turn at 6°/second. The bank angle required to conduct a turn at a specific rate is directly proportional to True Airspeed (TAS). The approximate bank angle required to accomplish a coordinated rate one turn (3°/second) can be calculated by dividing the TAS (in knots) by 10 and then adding 7. Using this formula, an aircraft flying at 80 knots would require 15° of bank for a rate one turn whereas at 160 knots, 23° would be required and at 240 knots a bank angle of 31° would be required to achieve the same rate of turn.As high bank angles are undesirable, especially in IMC, ICAO guidance for holding procedures states that "all turns in nil wind should be at a bank angle of 25 degrees or Rate One, whichever requires the lesser bank". Protected airspace is then based on the radius of turn for the maximum allowable holding speed at 25° of bank.
