Instrument flight rules (IFR) Non-directional beacon (NDB) Precision approach radar Secondary surveillance radar VHF omni-directional range (VOR) Notes References Winner, Karl (2002). Application of the Transponder Landing System to Achieve Airport Accessibility Barbeau, Charles (2002). Flight Inspection of the Transponder Landing System Background section explains operation and use of a TLS. External links ANPC (Advanced Navigation & Positioning Corporation) – developers of the TLS FAA AIM Section 1-1-22c "Transponder Landing System (TLS)" Aircraft landing systems Runway safety Radio navigation