Section 51(2)(b) in The Navy (Pension) Regulations, 1964
(b)without serious negligence or misconduct on his part(i)is killed while on flying duty or parachute jumping duties in a service aircraft or while being carried on duty in a service aircraft, under proper authority, or dies of injuries sustained in such circumstances, or(ii)though not serving in an operational area, dies of a cause attributable to circumstances which, in the opinion of the Central Government, are similar to those encountered on field service or in operations; or