Aircraft counter act oscillations. Therefore, lighter aircraft have

Aircraft experiences dynamic modes in longitudinal and lateral-directional planes. Oscillations occur in longitudinal plane consists of two modes namely, short period oscillations and long period oscillations which are also known as phugoid. Dynamic modes in lateral-directional plane consist of three modes. Roll, spiral and dutch-roll falls under that category. When an aircraft operates under different flight conditions, pilot has to preserve the desired control characteristics to ensure safe flight and passenger comfort. In order to achieve this, pilot has to maneuver the controllers effectively to counteract these dynamic modes and that can be done either automatically or manually.Damping rates and frequencies of these dynamic modes that encounter on an aircraft depend upon the geometric properties, mass properties, aerodynamic configurations and the flight conditions of the aircraft. Aircraft designers have significant amount of control over how the aircraft responses to these characteristics of dynamic modes occur in longitudinal and lateral-directional planes. This control is carried off by implementing an active feedback control system which is also known as a stability augmentation system. Larger aircraft are already equipped with stability augmentation systems to reduce the effects of dynamic modes but, majority of lighter aircraft are unassisted and the pilots have to operate control surfaces manually to counter act oscillations. Therefore, lighter aircraft have low degree of damping of dynamic modes.In modern larger aircraft, the required damping ratio is achieved by complex automatic flight control system. This will also reduce the amount of work that has to be done by the pilot while providing precise control during all the flight conditions. Hence, the aircraft will obtain higher stability as the movements done by automatic controllers are more reliable compared to the movements done by the pilot manually. Automatic controls are widely engaged with commercial aircraft due to the vast number of advantages associate with such systems. Reduction of pilot’s workload, improved fuel efficiency, passenger safety and comfort are few among them. It has been shown that greater numbers of aviation accidents that are associated with light weight aircraft are due to its inability of responding to the dynamic modes encounters on the aircraft effectively. This is because the pilot has to maintain the controllers manually since majority of lighter aircraft are unassisted. Hence the effect of human error becomes a vital effect. Since the control is taken by the pilot manually, in situations like take-off, landing, extreme weather conditions and etc., where the control is highly essential, pilot would not be able to ensure a safe flight by him alone. So that in such cases concerns has arisen of having an automatic control system for lighter aircraft as well.In this research, the researchers are focusing on Jetstream 31 Jet airliner where a low level of oscillation damping was found. This aircraft was selected mainly due to the availability of necessary data to achieve researchers’ desired outcomes. Jetstream 31 is a light twin turbo prop airliner which has unassisted mechanical flight controls. Also it was found that many failures were occurred and according to the previous researches as the reason for those they have shown that the damping coefficients of above dynamic modes are not in required and pre-determined levels. Therefore, the pilot has to take command manually in these scenarios. As the recommended solution for this, researchers have shown that an increment in damping ratio through the use of stability augmentation system for yaw damping and phugoid as an excellent solution.The drawbacks that are associated with this system in implementing for lighter aircraft are generally the relatively high weight and the size of this system as the weight factor is considered to be a critical design consideration for lighter aircraft. Besides, the manufacturing and the maintenance cost for automatic control systems are also relatively high. Therefore, in order to overcome above issues, researchers are intended in designing and implementing a more reliable and an accurate electronic stability augmentation system maintaining the discussed flows to a minimum. Such a system can be designed either electronically or mechanically. Mechanical system adds extra weight due to its heavy mechanical controllers and due to the considerable amount of friction losses, there could be a significant amount of a mechanical loss. So in order to avoid these, researchers have meant to design an electronic stability augmentation system over a mechanical system. Jetstream 31 is occupied with an on board flight computer. Therefore that can be used as a processing unit for stability augmentation system. That’s another reason for selecting electronic method in designing stability augmentation system.