Title 14 - Aeronautics and Space

Volume: 3Date: 2021-01-01Original Date: 2021-01-01Title: Section Â§ 171.107 - Definition.Context:
Title 14 - Aeronautics and Space. CHAPTER I - FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION (CONTINUED). SUBCHAPTER J - NAVIGATIONAL FACILITIES. PART 171 - NON-FEDERAL NAVIGATION FACILITIES. Subpart F - Simplified Directional Facility (SDF).

§ 171.107
Definition.
As used in this subpart:
SDF
(simplified directional facility) means a directional aid facility providing only lateral guidance (front or back course) for approach from a final approach fix.
DDM
(difference in depth of modulation) means the percentage modulation depth of the larger signal minus the percentage modulation depth of the smaller signal, divided by 100.
Angular displacement sensitivity
means the ratio of measured DDM to the corresponding angular displacement from the appropriate reference line.
Back course sector
means the course sector on the opposite end of the runway from the front course sector.
Course line
means the locus of points along the final approach course at which the DDM is zero.
Course sector
means a sector in a horizontal plane containing the course line and limited by the loci of points nearest to the course line at which the DDM is 0.155.
Displacement sensitivity
means the ratio of measured DDM to the corresponding lateral displacement from the appropriate reference line.
Front course sector
means the course sector centered on the course line in the direction from the runway in which a normal final approach is made.
Half course sector
means the sector in a horizontal plane containing the course line and limited by the loci of points nearest to the course line, at which the DDM is 0.0775.
Point A
means a point on the front course in the approach direction a distance of 4 nautical miles from the threshold.
Point A1
means a point on the front course in the approach direction a distance of 1 statute mile from the threshold.
Point A2
means a point on the front course at the threshold.
Reference datum
means a point at a specified height located vertically above the intersection of the course and the threshold.
Missed approach point
means the point on the final approach course, not farther from the final approach fix than Point “A2”, at which the approach must be abandoned, if the approach and subsequent landing cannot be safely completed by visual reference, whether or not the aircraft has descended to the minimum descent altitude.

Code of Federal Regulations /
Title 14 - Aeronautics and Space /
Vol. 3 / 2021-01-01819