A Simplified Directional Facility (SDF) provides a final approach course similar to that of the ILS localizer although is not as precise as Localizer. It does not provide glide slope information.
The SDF transmits signals within the range of 108.10 to 111.95 MHz.
The approach techniques and procedures used in an SDF instrument approach are essentially the same as those employed in executing a standard localizer approach except the SDF course may not be aligned with the runway and the course may be wider, resulting in less precision.
Usable off-course indications are limited to 35 degrees either side of the course centreline. Instrument indications received beyond 35 degrees should be disregarded.
SDF is not explicitly mentioned in PANS-AIM. Hence, for the purpose of this coding guidelines the specific requirements are derived form those specified for the Localiser in PANS-AIM.
The diagram below shows the AIXM classes, including the relevant data types, needed to encode that information The main class is the SDF which is a specialisation of the NavaidEquipment.
Frequency
The SDF.frequency attribute is used to code the value of the frequency.
Localiser Course (bearing)
The magnetic bearing of a SDF (or SDF course) is the measured angle between the localizer beam and Magnetic North at the SDF antenna is coded using the SDF.magenticBearing attribute. In additio the is used to provide the corresponding accuracy value. In general this information is published on an approach chart.
At some locations of the world rather a true than a magteic bearing may be publsihed for the SDF course. The SDF.trueBearing attribute is used to code that information.
In case either the true or the magnetic bearing is provided for the other attribute a nilReason should be provided.
Coding Rules for SDF
TBD
Coding Examples
TBD