Frequency: The expected number of events that occur or are expected to occur over some
measured interval, such as events per unit time or events per aircraft operation.
General Aviation: As defined by the NTSB in their compilation of accident data and as used in
this standard, all operations involving U.S. registered aircraft that are not conducting air carrier
revenue operations (i.e., not air carriers or air taxis).
Global Response: Response of the overall target structure, as measured by its state of strain
or displacement, which may result in global structural failure due to collapse or excessive
structural deformation. Global response may also result in the functional failure of SSCs.
Hazard: An inherent physical or chemical characteristic that has the potential for causing harm
to people, property, or the environment. It is the combination of a hazardous material, an
operating environment, and certain unplanned events that could result in an accident.
High Altitude (Jet) Route: The designated route between VOR (very high frequency
omnidirection radio) or VORTAC stations for aircraft flying between 5486 m or 5.5 km (18,000 ft)
mean sea level (MSL) and 13,716 m or 13.7 km (45,000 ft) MSL.
IFR Flight: As defined by the FAA, flight conducted in accordance with Instrument Flight Rules.
Immediately Dangerous to Life or Health (IDLH): The maximum concentration of a (chemical)
substance in air from which healthy male workers can escape without loss of life or irreversible
health effects under conditions of a maximum 30-minute exposure time.
Impact Frequency: The frequency, per unit time, of an aircraft impacting a facility of interest.
In-flight Flight Phase: Refer to "Flight Phase" for definition.
Jet Route: Same as high altitude route.
Landing Flight Phase: Refer to "Flight Phase" for definition.