[Code of Federal Regulations]

[Title 14, Volume 3]

[Revised as of January 1, 2006]

From the U.S. Government Printing Office via GPO Access

[CITE: 14CFR171.107]



[Page 227-228]

 

                     TITLE 14--AERONAUTICS AND SPACE

 

CHAPTER I--FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION 

                               (CONTINUED)

 

PART 171_NON-FEDERAL NAVIGATION FACILITIES--Table of Contents

 

             Subpart F_Simplified Directional Facility (SDF)

 

Sec. 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



[[Page 228]]



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.