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.  INERTIAL NAVIGATION SYSTEM (INS)- An  RNAV system which is a form of self-contained  navigation.  (See Area Navigation/RNAV.)  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 [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  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.  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.  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:  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.  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.  Pilot/Controller Glossary Pilot/Controller Glossary  8/15/19 12/31/20  PCG I-3  (See SEGMENTS OF AN INSTRUMENT  APPROACH PROCEDURE.)  (Refer to 14 CFR Part 91.)  (Refer to AIM.)  (See ICAO term INSTRUMENT APPROACH  PROCEDURE.)  zone elevation, on the ILS CAT II approach. It also  marks progress during a CAT III approach.  (See INSTRUMENT LANDING SYSTEM.)  (Refer to AIM.)  INCREASE SPEED TO (SPEED)- INFLIGHT REFUELING- (See AERIAL REFUELING.)  INFLIGHT WEATHER ADVISORY- (See WEATHER ADVISORY.)  INSTRUMENT APPROACH- (See INSTRUMENT APPROACH  PROCEDURE.)  INS- (See INERTIAL NAVIGATION SYSTEM.)  INREQ- (See INFORMATION REQUEST.)  INNER MARKER BEACON- (See INNER MARKER.)  (See SPEED ADJUSTMENT.)  INITIAL APPROACH SEGMENT- (See SEGMENTS OF AN INSTRUMENT  APPROACH PROCEDURE.) 