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Flight Regularity Messages and Flight Safety Messages

Flight Regularity Messages They include the messages that require immediate action on the part of flight crews, aircraft operators, or agencies acting for aircraft operators for the efficient and expeditious utilization of aircraft to avoid serious delays or travel interruptions to passengers and/or cargo, or to avoid situations that could cause the aircraft operator to

Compass Locator

When a radio beacon is used in conjunction with the ILS markers, it is called compass locator. Compass locator is low or medium frequency NDB  co-located with MM or OM beacons to help establish the pilot on localizer for ILS approach. Also check: ILS Critical and Sensitive Area

Cyclic Redundancy Check (CRC)

CRC is defined as mathematical algorithm applied to digital expression of data that provides level of assurance against loss or alteration of data. Also Read: Part 1: PBN – Performance Based Navigation

Approach Procedure With Vertical Guidance (APV)

APV is defined as instrument procedure which utilizes lateral and vertical guidance but does not meet the requirements established for precision approach and landing operations. Part 4: PBN – RNP APCH, RNP AR APCH, RNP AR DP and A-RNP

Hot Spots

Hot Spots are defined as the intersection of complex and confusing taxiways and runways in any combination. These areas have history or potential for runway incursions or surface incidents due to variety of causes not limited to airport marking, traffic flow, signage and airport lighting.


TACAN stands for Tactical Air Navigation. It is used for military or naval operations. TACAN ground equipment consists of either fixed or mobile transmitting unit also TACAN does not operate through conventional VOR equipment. TACAN is pulse system and operates in Ultrahigh Frequency (UHF) band of frequencies. Also Read: Frequency Bands and Frequency Allocation for

Takeoff Funnel

Takeoff funnel represents the area surrounding the take off flight path, withing which all obstacles must be cleared, assuming they are all projected on the intended track.

Obstacle free zone (OFZ)

Obstacle free zone is the airspace above the inner approach surface, inner transitional surfaces, and balked landing surface and that portion of the strip bounded by these surfaces, which is not penetrated by any fixed obstacle other than a low-mass and frangible mounted one required for air navigation purposes.

Runway Incursion

Runway incursion is occurrence at an aerodrome involving the incorrect present of person, aircraft or vehicle  on the protected area of surface designated for the landing and takeoff of aircraft.

Preventive Maintenance

Preventive maintenance is programmed maintenance work done in order to prevent failure or degradation of facilities. Example: preventive maintenance of ALS preventive maintenance of navigation aids etc.