Weather and nightfall play significant roles in accident prevention and unexpected fog or storms may require rerouting, creating more congestion in other areas. Aircraft crashes are especially difficult for disaster management for a variety of reasons. An aircraft may be reported overdue but the precise location is unknown. Rugged and remote terrain may hide aircraft for months, even years. Weather may hinder or even prevent aerial searches.
Injuries are often extremely severe and delay in medical assistance is likely.
The aircraft fuel is highly flammable and often ignites as a result of a crash, further complicating rescue and life saving efforts. If an aircraft crashes in an urban environment, the casualties on the ground may be as numerous and severe as those on the aircraft. The novelty tends to attract as many onlookers as rescuers. Subsequently, one of the primary roles for law enforcement is protecting the scene of the disaster from spectators. One of the worst air disasters in the United States occurred in San Diego on September 25, 1978.