SDF

SDF. See simplified directional facility.
Selective availability (SA).

SDF-
(See SIMPLIFIED DIRECTIONAL FACILITY.)
SEA LANE- A designated portion of water outlined by visual surface markers for and intended to be used by aircraft designed to operate on water.

SDF may be either 6 or 12 degrees wide.
Runway alignment within 3-degrees
Centred SDF needle has localizer accuracy.
16 of the SDF approaches require use of ADF. ADF is required even having IFR GPS.
Even if vectored ADF may be needed to locate marker.

Simplified directional facility (SDF)
Simultaneous Offset Instrument Approach (SOIA)
Special flight permit ...

Simplified Directional Facility or SDF
GPS - Global Positioning System
TACAN
SRA - Surveillance Radar Approach (known in some countries as an ASR approach)
ASR - Airport Surveillance Radar (Military designation for SRA) ...

See also: Landing, ILS, MLS, Radar, Air traffic