**6.2 Airworthiness and flight safety in military aviation**

The phrase 'acceptable level of safety' in the definition of airworthiness is a complex consideration as absolute safety is hypothetical and can be achieved only at infinite cost. Therefore, the airworthiness standards have to balance between safety concerns on the one hand and the cost and practicability from design and manufacture point of view on the other.

In aviation, safety may be defined as freedom from death, injury or damage to people on board and loss property and life on ground (accident). Safety of any flying effort or machine would depend primarily upon, whether we are operating below or above a particular level known as 'risk threshold'. The risk threshold is the level of risk beyond which accidents are inevitable. It also must be appreciated that this 'risk threshold' is not a stationary one and it keeps varying based on the role, function and a host of other associated factors. It needs therefore to be reassessed under each changing scenario. Airworthiness control is to minimize the risk and maximize the effectiveness. All the airworthiness standards, military or civil, whether that of the USA, Europe or Russia, have a common point of reference which is that an inverse relation should exist between probability of occurrence of an event and the degree of hazard inherent in its effect.

For military aircraft in the US Department of Defense (DoD) document, Mil-STD-882 defines the safety requirements during design of an airborne stores. The decision matrix of system safety as per Mil-STD-882 is shown in **Figure 8**. The safety requirement of any failure event is based on the hazard index of the failure which is defined as the product of the probability of the failure and the damage consequent of the failure event. The damage consequences can range from 'catastrophic' (loss life, aircraft and property) to negligible (minor inconvenience). The frequencies of occurrences are grouped under 'frequent' (1 in 10 h of flight) to 'extremely improbable' (1 in 107 flight hours).
