INCERFA (Uncertainty Phase) [ICAO]- A situation wherein uncertainty exists as to the safety of an aircraft and its occupants. 

INCREASED SEPARATION REQUIRED (ISR)– Indicates the confidence level of the track requires 5 NM separation. 3 NM separation, 1  NM separation, and target resolution cannot be used. 

## INCREASE SPEED TO (SPEED)- 

(See SPEED ADJUSTMENT.) 

INERTIAL NAVIGATION SYSTEM (INS)- An RNAV system which is a form of self-contained navigation. 

(See Area Navigation/RNAV.) 

INFLIGHT REFUELING- (See AERIAL REFUELING.) 

INFLIGHT WEATHER ADVISORY- (See WEATHER ADVISORY.) 

INFORMATION REQUEST (INREQ)- A request originated by an FSS for information concerning an overdue VFR aircraft. 

INITIAL APPROACH FIX (IAF)- The fixes depicted on instrument approach procedure charts that identify the beginning of the initial approach segment(s). 

(See FIX.) 

(See SEGMENTS OF AN INSTRUMENT APPROACH PROCEDURE.) 

INITIAL APPROACH SEGMENT- (See SEGMENTS OF AN INSTRUMENT APPROACH PROCEDURE.) 

INITIAL APPROACH SEGMENT [ICAO]- That segment of an instrument approach procedure between the initial approach fix and the intermediate approach fix or, where applicable, the final approach fix or point. 

INLAND NAVIGATION FACILITY- A navigation aid on a North American Route at which the common route and/or the noncommon route begins or ends. 

INNER MARKER- A marker beacon used with an ILS (CAT II) precision approach located between the middle marker and the end of the ILS runway, transmitting a radiation pattern keyed at six dots per second and indicating to the pilot, both aurally and visually, that he/she is at the designated decision height (DH), normally 100 feet above the touchdown 

zone elevation, on the ILS CAT II approach. It also marks progress during a CAT III approach. 

(See INSTRUMENT LANDING SYSTEM.) 

(Refer to AIM.) 

INNER MARKER BEACON- (See INNER MARKER.) 

INREQ- (See INFORMATION REQUEST.) 

INS- (See INERTIAL NAVIGATION SYSTEM.) 

INSTRUMENT APPROACH- (See INSTRUMENT APPROACH PROCEDURE.) 

INSTRUMENT APPROACH OPERATIONS [ICAO]- An approach and landing using instruments for navigation guidance based on an instrument approach procedure. There are two methods for executing instrument approach operations: 

a. A two-dimensional (2D) instrument approach operation, using lateral navigation guidance only; and 

b. A three-dimensional (3D) instrument approach operation, using both lateral and vertical navigation guidance. 

Note: Lateral and vertical navigation guidance refers to the guidance provided either by: 

a) a ground-based radio navigation aid; or b) computer-generated navigation data from ground-based, space-based, self-contained navigation aids or a combination of these. 

(See ICAO term INSTRUMENT APPROACH PROCEDURE.) 

INSTRUMENT APPROACH PROCEDURE- A series of predetermined maneuvers for the orderly transfer of an aircraft under instrument flight conditions from the beginning of the initial approach to a landing or to a point from which a landing may be made visually. It is prescribed and approved for a specific airport by competent authority. 

(See SEGMENTS OF AN INSTRUMENT APPROACH PROCEDURE.) 

(Refer to 14 CFR Part 91.) 

(Refer to AIM.) 

a. U.S. civil standard instrument approach procedures are approved by the FAA as prescribed under 14 CFR Part 97 and are available for public use. 

