Accident is an occurrence associated with the operation of an aircraft that takes place between the time any person boards the aircraft with the intention of flight and the time all such persons have disembarked and which any person suffers a fatal injury, serious injury or the aircraft receives substantial damage. On another part, incident has to happen first like a symptom before sick. Incident is an occurrence other than accident associated with the operation of an aircraft that affects or could affect the safety operations. Incidents are events that can be defined as near to accidents. All accidents started as near accidents.
Accident can cause a fatal injury, serious injury and substantial damage to the aircraft. Fatal injury results in death within 30 days. The examples of fatal injury are on Malaysia Airlines (MAS) flight 653 crashed at Tanjung Kupang, Johor on 4th December 1977. It was the deadliest and first fatal accident for MAS with all 93 passengers and 7 crew was killed. The flight was apparently hijacked when it reach cruised altitude. On another view, substantial damage affects structural strength of aircraft, performance or flight characteristic that need major replacement of affected components. Another example is on 15th September 1995 when Malaysia Airlines (MAS) flight 2133, a Fokker-50 crashed during approach in Tawau, Sabah due to pilot error and 34 people were killed. According to investigation report, the accident was probably caused by the pilot’s poor in flight decision making and failure to follow standard operating procedures. The report also pointed out the failure of the co-pilot to alert the captain of unsafe manoeuvre or take over control of the aircraft.
The various combinations of possibly unsafe acts and conditions that occur each day usually end as incidents rather than accidents. The examples of incidents is Malaysia Airlines flight-124 on 1st August 2005, a Boeing 777-200ER departed Perth for Kuala Lumpur. Climbing through 38,000 feet a faulty accelerometer caused the aircraft's Air Data Inertial Reference Unit (ADIRU) to command changes of altitude. The flight crew overrode the ADIRU and manually returned to land the aircraft at Perth. Subsequent NTSB investigation led the US FAA to issue emergency airworthiness directive 2005-18-51 on the fly-by-wire software. Another example is on 2nd October 2009, MAS Boeing 737-400 (9M-MMR) was substantially damaged when the port main undercarriage collapsed while the aircraft was parked at the gate at Kuching Airport.