Hoverlane--A designated aerial traffic lane for the directed movement of helicopters between a helipad
or hoverpoint and the servicing and parking areas of the heliport or airfield.
Hoverpoint--A prepared and marked surface at a heliport or airfield used as a reference or central point
Imaginary Surfaces. Surfaces in space established around airfields in relation to runway(s), helipad(s),
or helicopter runway(s) that are designed to define the obstacle free airspace around the airfield. The
imaginary surfaces for DoD airfields are the primary surface, the approach-departure clearance surface,
the transitional surface, the inner horizontal surface, the conical surface (fixed-wing only), and the outer
horizontal surface (fixed-wing only).
Ingress/Egress, Same Direction--One approach-departure route to and from the helipad exists. The
direction from which the rotary-wing aircraft approaches the helipad (ingress) is the only direction
which the rotary-wing aircraft departs (egress) from the helipad. Typically, the helipad is surrounded by
obstacles on three sides which make approaches from other directions impossible. For example, if the
rotary-wing aircraft approaches from the southwest, it must also depart to the southwest.
Ingress/Egress, Two Direction--Rotary-wing aircraft can approach and depart the helipad from two
directions (one direction and the opposite direction). (See also Ingress/Egress, Same Direction.)
Instrument Runway--A runway equipped with electronic navigation aids for which a precision or
non-precision approach procedure is approved.
Instrument Flight Rules (IFR)--Rules that govern the procedure for conducting instrument flight.
Also see Instrument Meteorological Conditions.
Instrument Landing System--A system of ground equipment designed to provide an approach path
for exact alignment and descent of an aircraft on final approach to a runway. The ground equipment
consists of two highly directional transmitting systems and, along the approach, three (or fewer) marker
beacons. The directional transmitters are known as the localizer and glide slope transmitters.
Instrument Meteorological Conditions--Meteorological conditions expressed in terms of visibility,
distance from cloud, and ceiling; less than minimums specified for visual meteorological conditions.
Intermediate Area--The area between runways and between runways and taxiways that is graded or
cleared for operational safety.
Joint/Shared Use Airfield--Those airports that are shared by a civilian DoD agency covered under the
"Airports and Airway Improvement ACT of 1982 (Public LAW 97-248, Sep 3, 1982, 49 USC, APP
2201.) Only those facilities (i.e., runways/taxiways) that are used by both civilian and DoD agencies are
considered "Shared/Joint Use." All other facilities (parking ramps, hangars, terminals, and so forth) are
the sole property of the using agency. A US Air Force installation where agreements exist among the
Air Force, civil, and host nation authorities for joint use of all or a portion of airfield facilities.
Landing Area--See Take-Off and Landing Area.
Landing Field--Any area of land consisting of one or more landing strips, including the intermediate
area, that is designed for the safe takeoff and landing of aircraft.
Landing Lane--A defined lane on the airfield used for simultaneous takeoff and landings of multiple
(up to four at one time) helicopters. Landing lanes are used at airfields or heliports when a high density
of helicopters are parked on an apron, or in the process of takeoff and landings.