[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: 14CFR171.253]



[Page 240-241]

 

                     TITLE 14--AERONAUTICS AND SPACE

 

CHAPTER I--FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION 

                               (CONTINUED)

 

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

 

       Subpart I_Interim Standard Microwave Landing System (ISMLS)

 

Sec. 171.253  Definitions.



    As used in this subpart:

    Angular displacement sensitivity (Glide Slope) means the ratio of 

measured DDM to the corresponding angular displacement from the 

appropriate reference line.

    Collocated ground station means the type of ground station which 

transmits two or more guidance signals simultaneously from a common 

location.

    Course line means the locus of points nearest to the runway 

centerline in any horizontal plane at which the DDM is zero.

    Course sector (full) 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.

    Course sector (half) 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 DDM is 0.0775.

    DDM means difference in depth of modulation. The percentage 

modulation depth of the larger signal minus the percentage modulation 

depth of the smaller signal, divided by 100.

    Displacement sensitivity (Localizer) means the ratio of measured DDM 

to the corresponding lateral displacement from the appropriate reference 

line.

    Facility Performance Category I--ISMLS means an ISMLS which provides 

guidance information from the coverage limit of the ISMLS to the point 

at which the localizer course line intersects the ISMLS glide path at a 

height



[[Page 241]]



of 200 feet or less above the horizontal plane containing the threshold.

    Glide path means that locus of points in the vertical plane 

containing the runway center line at which the DDM is zero, which, of 

all such loci, is the closest to the horizontal plane.

    Glide path angle ([thetas]) means the angle between a straight line 

which represents the mean of the ISMLS glide path and the horizontal.

    Glide path sector (full) means the sector in the vertical plane 

containing the ISMLS glide path and limited by the loci of points 

nearest to the glide path at which the DDM is 0.175. The ISMLS glide 

path sector is located in the vertical plane containing the runway 

centerline, and is divided by the radiated glide path in two parts 

called upper sector and lower sector, referring respectively to the 

sectors above and below the glide path.

    Glide path sector (half) means the sector in the vertical plane 

containing the ISMLS glide path and limited by the loci of points 

nearest to the glide path at which the DDM is 0.0875.

    ISMLS Point `A' means an imaginary point on the glide path/localizer 

course measured along the runway centerline extended, in the approach 

direction, four nautical miles from the runway threshold.

    ISMLS Point `B' means an imaginary point on the glide path/localizer 

course measured along the runway centerline extended, in the approach 

direction, 3500 feet from the runway threshold.

    ISMLS Point `C' means a point through which the downward extended 

straight portion of the glide path (at the commissioned angle) passes at 

a height of 100 feet above the horizontal plane containing the runway 

threshold.

    Interim standard microwave landing system (ISMLS) means a ground 

station which transmits azimuth and elevation angle information which, 

when decoded and processed by the airborne unit, provides signal 

performance capable of supporting approach minima for V/STOL and CTOL 

operations and operates with the signal format and tolerances specified 

in Sec. Sec. 171.259, 171.261, 171.263, 171.265, and 171.267.

    Integrity means that quality which relates to the trust which can be 

placed in the correctness of the information supplied by the facility.

    Mean corrective time means the average time required to correct an 

equipment failure over a given period, after a service man reaches the 

facility.

    Mean time between failures means the average time between equipment 

failure over a given period.

    Reference datum means a point at a specified height located 

vertically above the intersection of the runway centerline and the 

threshold and through which the downward extended straight portion of 

the ISMLS glide path passes.

    Split type ground station means the type of ground station in which 

the electronic components for the azimuth and elevation guidance are 

contained in separate housings or shelters at different locations, with 

the azimuth portion of the ground station located at the stop end of the 

runway, and the elevation guidance near the approach end of the runway.