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.

Approach Lighting System Explained!

Approach light system(ALS) is part of aviation ground lighting patters primarily used for identification and aircraft alignment with runway center line. ALS is made of several parts collectively working to serve the said purpose. Availability of ALS category for runway depends on its licensing category and need for continuous operation during period of poor visibility.

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.

Runway Reference Code Numbers and Code Letters

Runway Code Numbers Runway Code Runway Length Code 1 Runways less than 800 metres long Code 2 Runways 800-1199 metres long Code 3 Runways 1200-1799 metres long Code 4 Runways 1800 metres long Runway Code Letters Code Letter Wingspan Outer main gear wheel span A < 15 m < 4.5 m B 15 m but