SUBPART G
Obstacle Restriction and Removal
139.317
Obstacle Restriction and Removal
Note 1: The objectives of the specifications in this Subpart are to define the airspace around aerodromes to be maintained free from obstacles so as to permit the intended aeroplane operations at the aerodromes to be conducted safely and to prevent the aerodromes from becoming unusable by the growth of obstacles around the aerodromes. This is achieved by establishing a series of obstacle limitation surfaces that define the limits to which objects may project into the airspace.
Note
2: Objects which penetrate the obstacle limitation surfaces contained in this
Subpart may in certain circumstances cause an increase in the obstacle
clearance altitude/height for an instrument approach procedure or any
associated visual circling procedure or have other operational impact on flight
procedure design.Criteria for flight procedure design Criteria for flight
procedure design are contained in ECAR Part 174.
Table 4-1: Dimensions and slopes of obstacle limitation surfaces-Approach runways
Approach runways
a. All dimension are measured
horizontally unless specified otherwise
b. Variable length (see .3179b)(9) or
.317(b)(17)).
c. Distance to the end of strip.
d. Or end of runway whichever is less.
e.Where the code letter is F (Column
(3) of Table 1-1), the width is increased to
(a) Obstacle
limitation surfaces:
Note 1: See Figure 4-1.
Note
2: Guidance on the need to provide an outer horizontal surface and its
characteristic is contained in EAC 139-23.
(1) Description of conical surface: A surface
sloping upwards and outwards from the periphery of the inner horizontal
surface.
(2) Characteristics of conical surface: The
limits of the conical surface shall comprise:
(i) A lower edge coincident with the periphery
of the inner horizontal surface; and
(ii) An upper edge located at a specified height
above the inner horizontal surface.
(3) The slope of the conical surface shall be
measured in a vertical plane perpendicular to the periphery of the inner
horizontal surface.
(4) Description of inner horizontal surface: A
surface located in a horizontal plane above an aerodrome and its environs.
(5) Characteristics of inner horizontal surface:
The radius or outer limits of the inner horizontal surface shall be measured
from a reference point or points established for such purpose.
Note. The shape of the inner horizontal
surface need not necessarily be circular. Guidance on determining the extent of
the inner horizontal surface is contained in EAC 139-23.
(6) The height of the inner horizontal surface
shall be measured above an elevation datum established for such purpose.
Note:
Guidance on determining the elevation datum is contained in EAC 139-23.
(7) Description of approach surface: An inclined
plane or combination of planes preceding the threshold.
(8) Characteristics of approach surface: The
limits of the approach surface shall comprise:
(i) An inner edge of specified length,
horizontal and perpendicular to the extended centre line of the runway and
located at a specified distance before the threshold;
(ii) Two sides originating at the ends of the
inner edge and diverging uniformly at a specified rate from the extended centre
line of the runway; and
(iii) An outer edge parallel to the inner edge.
The above surfaces shall be varied when
lateral offset, offset or curved approaches are utilized, specifically, two
sides originating at the ends of the inner edge and diverging uniformly at a
specified rate from the extended centre line of the lateral offset, offset or
curved ground track.
(9) The elevation of the inner edge shall be
equal to the elevation of the mid-point of the threshold.
(10) The slope(s) of the approach surface shall be
measured in the vertical plane containing the centre line of the runway and
shall continue containing the centre line of any lateral offset or curved
ground track.
(11) Description of inner approach surface: A
rectangular portion of the approach surface immediately preceding the threshold.
(12) Characteristics of inner approach surface: The
limits of the inner approach surface shall comprise:
(i) An inner edge coincident with the location
of the inner edge of the approach surface but of its own specified length;
(ii) Two sides originating at the ends of the
inner edge and extending parallel to the vertical plane containing the centre
line of the runway; and
(iii) An outer edge parallel to the inner edge.
(13) Description of transitional surface: A complex
surface along the side of the strip and part of the side of the approach
surface, that slopes upwards and outwards to the inner horizontal surface.
(14) Characteristics of transitional surface: The
limits of a transitional surface shall comprise:
(i) A lower edge beginning at the intersection
of the side of the approach surface with the inner horizontal surface and
extending down the side of the approach surface to the inner edge of the
approach surface and from there along the length of the strip parallel to the
runway centre line; and
(ii) An upper edge located in the plane of the
inner horizontal surface.
(15) The elevation of a point on the lower edge
shall be:
(i) Along the side of the approach surface equal
to the elevation of the approach surface at that point; and
(ii) Along the strip- equal to the elevation of
the nearest point on the centre line of the runway or its extension.
Note: As a result of (ii) the
transitional surface along the strip will be curved if the runway profile is
curved, or a plane if the runway profile is a straight line. The intersection
of the transitional surface with the inner horizontal surface will also be a
curved or a straight line depending on the runway profile.
(16) The slope of the transitional surface shall be
measured in a vertical plane at right angles to the centre line of the runway.
(17) Description of inner transitional surface: A
surface similar to the transitional surface but closer to the runway.
Note. It is intended that the inner
transitional surface be the controlling obstacle limitation surface for
navigation aids, aircraft and other vehicles that must be near the runway and
which is not to be penetrated except for frangible objects. The transitional
surface described in .317(a)(13) is intended to remain as the controlling
obstacle limitation surface for buildings, etc.
(18) Characteristics of inner transitional surface: The limits of an
inner transitional surface shall comprise:
(i) A lower edge beginning at the end of the
inner approach surface and extending down the side of the inner approach
surface to the inner edge of that surface, from there along the strip parallel
to the runway centre line to the inner edge of the balked landing surface and
from there up the side of the balked landing surface to the point where the
side intersects the inner horizontal surface; and
(ii) An upper edge located in the plane of the
inner horizontal surface.
See Figure 4-2 for inner transitional and balked landing obstacle
limitation surfaces and EAC 139-59 for a three-dimensional view
Figure 4- 1: Obstacle limitation surfaces
(19) The elevation of a point on the lower edge
shall be:
(i) Along the side of the inner approach surface
and balked landing surface: equal to the elevation of the particular surface at
that point; and
(ii) Along the strip: equal to the elevation of the nearest point on the
centre line
of
the runway or its extension.
Note: As a result of (ii) the inner transitional surface along the strip
will be curved if the runway profile is curved or a plane if the runway profile
is a straight line. The intersection of the inner transitional surface with the
inner horizontal surface will also be a curved or straight line depending on
the runway profile.
(20) The slope of the inner transitional surface
shall be measured in a vertical plane at right angles to the centre line of the
runway.
(21) Description of balked landing surface: An
inclined plane located at a specified distance after the threshold, extending
between the inner transitional surface.
Figure 4-2: Inner approach, inner transitional and
balked landing obstacle limitation surfaces
(22) Characteristics of balked
landing surface: The limits of the balked landing surface shall comprise:
(i) An inner edge horizontal and perpendicular to
the centre line of the runway and located at a specified distance after the
threshold;
(ii) Two sides originating at the ends of the inner
edge and diverging uniformly at a specified rate from the vertical plane
containing the centre line of the runway; and
(iii) An
outer edge parallel to the inner edge and located in the plane of the inner
horizontal surface.
(23) The elevation of the inner edge shall be equal
to the elevation of the runway centre line at the location of the inner edge.
(24) The slope of the balked landing surface shall
be measured in the vertical plane containing the centre line of the runway.
(25) Description of take-off climb surface: An
inclined plane or other specified surface beyond the end of a runway or
clearway.
(26) Characteristics of take-off climb surface: The
limits of the take-off climb surface shall comprise:
(i) An
inner edge horizontal and perpendicular to the centre line of the runway and
located either at a specified distance beyond the end of the runway or at the
end of the clearway when such is provided and its length exceeds the specified
distance;
(ii) Two
sides originating at the ends of the inner edge, diverging uniformly at a
specified rate from the take-off track to a specified final width and
continuing thereafter at that width for the remainder of the length of the
take-off climb surface; and
(iii) An
outer edge horizontal and perpendicular to the specified take-off track.
(27) The elevation of the inner edge
shall be equal to the highest point on the extended runway centre line between
the end of the runway and the inner edge, except that when a clearway is
provided the elevation shall be equal to the highest point on the ground on the
centre line of the clearway.
(28) In the case of a straight take-off flight
path, the slope of the take-off climb surface shall be measured in the vertical
plane containing the centre line of the runway.
(29) In the case of a take-off flight path
involving a turn, the take-off climb surface shall be a complex surface
containing the horizontal normals to its centre line, and the slope of the
centre line shall be the same as that for a straight take-off flight path.
(b) Obstacle
limitation requirements:
Note:
The requirements for obstacle limitation surfaces are specified on the basis of
the intended use of a runway, i.e. take-off or landing and type of approach,
and are intended to be applied when such use is made of the runway. In cases
where operations are conducted to or from both directions of a runway, then the
function of certain surfaces may be nullified because of more stringent
requirements of another lower surface.
(1) Non-instrument
runways: The following obstacle limitation surfaces shall be established for a
non-instrument runway:
(i) Conical
surface;
(ii) Inner
horizontal surface;
(iii) Approach
surface; and
(iv) Transitional
surfaces.
(2) The
heights and slopes of the surfaces shall not be greater than, and their other
dimensions not less than, those specified in Table 4-1.
(3) New
objects or extensions of existing objects shall not be permitted above an approach
or transitional surface except when, in the opinion of the ECAA, the new object
or extension would be shielded by an existing immovable object.
Note:
Circumstances in which the shielding principle may reasonably be applied are
described in EAC 139-23.
(4) New
objects or extensions of existing objects should not be permitted above the
conical surface or inner horizontal surface except when, in the opinion of the
ECAA, the object would be shielded by an existing immovable object, or after
aeronautical study it is determined that the object would not adversely affect
the safety or significantly affect the regularity of operations of aeroplanes.
(5) Existing
objects above any of the surfaces required by .317(b)(1) should as far as
practicable be removed except when, in the opinion of the ECAA, the object is
shielded by an existing immovable object, or after aeronautical study it is
determined that the object would not adversely affect the safety or
significantly affect the regularity of operations of aeroplanes.
Note.
Because of transverse or longitudinal slopes on a strip, in certain cases the
inner edge or portions of the inner edge of the approach surface may be below
the corresponding elevation of the strip. It is not intended that the strip be
graded to conform with the inner edge of the approach surface, nor is it
intended that terrain or objects which are above the approach surface beyond
the end of the strip, but below the level of the strip, be removed unless it is
considered they may endanger aeroplanes.
(6) In
considering proposed construction, account should be taken of the possible
future development of an instrument runway and consequent requirement for more
stringent obstacle limitation surfaces.
(7) Non-precision
approach runways: The following obstacle limitation surfaces shall be
established for a non-precision approach runway:
(i) Conical surface;
(ii) Inner horizontal surface;
(iii) Approach surface; and
(iv) Transitional surfaces.
(8) The
heights and slopes of the surfaces shall not be greater than, and their other
dimensions not less than, those specified in Table 4-1, except in the case of
the horizontal section of the approach surface (see .317(b)(9)).
(9) The
approach surface shall be horizontal beyond the point at which the 2.5 per cent
slope intersects:
(i) A horizontal plane 150 m above the threshold
elevation; or
(ii) The horizontal plane passing through the top
of any object that governs the obstacle clearance altitude/height (OCA/H);
whichever is the higher.
(10) New objects or extensions of existing objects
shall not be permitted above an approach surface within 3000 m of the inner
edge or above a transitional surface except when, in the opinion of the ECAA,
the new object or extension would be shielded by an existing immovable object.
Note:
Circumstances in which the shielding principle may reasonably be applied are
described in EAC 139-23.
(11) New objects or extensions of existing objects
should not be permitted above the approach surface beyond 3000 m from the inner
edge, the conical surface or inner horizontal surface except when, in the
opinion of the ECAA, the object would be shielded by an existing immovable
object, or after aeronautical study it is determined that the object would not
adversely affect the safety or significantly affect the regularity of
operations of aeroplanes.
(12) Existing objects above any of the surfaces
required by .317(b)(7) should as far as practicable be removed except when, in
the opinion of the ECAA, the object is shielded by an existing immovable
object, or after aeronautical study it is determined that the object would not
adversely affect the safety or significantly affect the regularity of
operations of aeroplanes.
Note:
Because of transverse or longitudinal slopes on
a strip, in
certain cases the inner edge or
portions of the inner edge of the
approach surface may be
below the corresponding elevation of the strip. It is not intended that the
strip be graded to conform with
the inner edge
of the approach
surface, nor is it
intended that terrain or objects which are
above the approach
surface beyond the end of the
strip, but below the level of the
strip, be removed
unless it is considered they may endanger aeroplanes.
(13) Precision approach runways: The following
obstacle limitation surfaces shall be established for a precision approach
runway category I:
(i) Conical surface;
(ii) Inner horizontal surface;
(iii) Approach surface; and
(iv) Transitional surfaces.
Note
1: See 139.335(i) for information regarding siting and construction of
equipment and installations on operational areas.
Note
2: Guidance on obstacle limitation surfaces for precision approach runways is
given in EAC 139-23.
(14) The following obstacle limitation surfaces
should be established for a precision approach runway category I:
(i) Inner approach surface;
(ii) Inner transitional surfaces; and
(iii) Balked landing surface.
(15) The following obstacle limitation surfaces
shall be established for a precision approach runway category II or III:
(i) Conical surface;
(ii) Inner horizontal surface;
(iii) Approach surface and inner approach surface;
(iv) Transitional surfaces;
(v) Inner
transitional surfaces; and
(vi) Balked landing surface.
Table 4-1: Dimensions and slopes of obstacle
limitation surfaces-Approach runways
Approach runways
a. All dimension are measured
horizontally unless specified otherwise
b. Variable length (see .3179b)(9) or
.317(b)(17)).
c. Distance to the end of strip.
d. Or end of runway whichever is less.
e. Where the code letter is F (Column
(3) of Table 1-1), the width is increased to 155 m See ICAO circular 301-
AN/174 New larger Aeroplanes- Infringement of the Obstacle Free Zone.
Operational Measures and Aeronautical Study for information on code letter F aeroplanes equipped with digital avionics
that provide steering commands to maintain an established track during the go-
around manoeuvre.
(16) The
heights and slopes of the surfaces shall not be greater than, and their other
dimensions not less than, those specified in Table 4-1, except in the case of
the horizontal section of the approach surface (see .317(b)(17)).
(17) The
approach surface shall be horizontal beyond the point at which the 2.5 per cent
slope intersects:
(i) A
horizontal plane 150 m above the threshold elevation; or
(ii) The
horizontal plane passing through the top of any object that governs the
obstacle clearance limit;
whichever
is the higher.
(18) Fixed
objects shall not be permitted above the inner approach surface, the inner
transitional surface or the balked landing surface, except for frangible
objects which because of their function must be located on the strip. Mobile
objects shall not be permitted above these surfaces during the use of the
runway for landing.
(19) New
objects or extensions of existing objects shall not be permitted above an
approach surface or a transitional surface except when, in the opinion of the
ECAA, the new object or extension would be shielded by an existing immovable
object.
Note: Circumstances in which the
shielding principle may reasonably be applied are described in EAC 139-23.
(20) New
objects or extensions of existing objects should not be permitted above the
conical surface and the inner horizontal surface except when, in the opinion of
the ECAA, an object would be shielded by an existing immovable object, or after
aeronautical study it is determined that the object would not adversely affect
the safety or significantly affect the regularity of operations of aeroplanes.
(21) Existing
objects above an approach surface, a transitional surface, the conical surface
and inner horizontal surface should as far as practicable be removed except
when, in the opinion of the ECAA, an object is shielded by an existing
immovable object, or after aeronautical study it is determined that the object
would not adversely affect the safety or significantly affect the regularity of
operations of aeroplanes.
Note: Because of transverse or longitudinal slopes
on a strip, in certain cases the inner edge or portions of the inner edge of
the approach surface may be below the corresponding elevation of the strip. It
is not intended that the strip be graded to conform with the inner edge of the
approach surface, nor is it intended that terrain or objects which are above
the approach surface beyond the end of the strip, but below the level of the
strip, be removed unless it is considered they may endanger aeroplanes.
(22) Runways
meant for take-off: The following obstacle limitation surface shall be
established for a runway meant for take-off:
take-off climb surface.
(23) The
dimensions of the surface shall be not less than the dimensions specified in
Table 4-2, except that a lesser length may be adopted for the take-off climb
surface where such lesser length would be consistent with procedural measures
adopted to govern the outward flight of aeroplanes.
(24) The
operational characteristics of aeroplanes for which the runway is intended
should be examined to see if it is desirable to reduce the slope specified in
Table 4-2 when critical operating conditions are to be catered to. If the
specified slope is reduced, corresponding adjustment in the length of take-off
climb surface should be made so as to provide protection to a height of 300m.
Note: When local conditions differ widely from sea
level standard atmospheric conditions, it may be advisable for the slope
specified in Table 4-2 to be reduced. The degree of this reduction depends on
the divergence between local conditions and sea level standard atmospheric
conditions, and on the performance characteristics and operational requirements
of the aeroplanes for which the runway is intended.
(25) New
objects or extensions of existing objects shall not be permitted above a
take-off climb surface except when, in the opinion of the ECAA, the new object
or extension would be shielded by an existing immovable object.
Note: Circumstances in which the shielding
principle may reasonably be applied are described in EAC 139-23.
(26) If
no object reaches the 2 per cent (1:50) take-off climb surface, new objects
should be limited to preserve the existing obstacle free surface or a surface
down to a slope of 1.6 per cent (1:62.5).
(27) Existing
objects that extend above a take-off climb surface should as far as practicable
be removed except when, in the opinion of the ECAA, an object is shielded by an
existing immovable object, or after aeronautical study it is determined that
the object would not adversely affect the safety or significantly affect the
regularity of operations of aeroplanes.
Note: Because of transverse slopes on a strip or clearway, in certain
cases portions of the inner edge of the take-off climb surface may be below the
corresponding elevation of the strip or clearway. It is not intended that the
strip or clearway be graded to conform with the inner edge of the take-off
climb surface, nor is it intended that terrain or objects which are above the
take-off climb surface beyond the end of the strip or clearway, but below the
level of the strip or clearway, be removed unless it is considered they may
endanger aeroplanes. Similar considerations apply at the junction of a clearway
and strip where differences in transverse slopes exist.
(c) Objects outside the obstacle limitation
surfaces:
(1) Arrangements should
be made to enable the ECAA to be consulted concerning proposed construction
beyond the limits of the obstacle limitation surfaces that extend above a
height established by that authority, in order to permit an aeronautical study
of the effect of such construction on the operation of aeroplanes.
(2)
In areas beyond the limits of the obstacle limitation surfaces, at least those
objects which extend to a height of 150 m or more above ground elevation should
be regarded as obstacles, unless a special aeronautical study indicates that
they do not constitute a hazard to aeroplanes.
Note: This study may have regard to the
nature of operations concerned and may distinguish between day and night
operations.
(d) Other objects:
(1) Objects which do not project through the
approach surface but which would nevertheless adversely affect the optimum
siting or performance of visual or non-visual aids should, as far as
practicable, be removed.
(2) Anything which may, in the opinion of the
ECAA after aeronautical study, endanger aeroplanes on the movement area or in
the air within the limits of the inner horizontal and conical surfaces should
be regarded as an obstacle and should be removed in so far as practicable.
Note: In certain circumstances, objects
that do not project above any of the surfaces enumerated in .317(a) may constitute
a hazard to aeroplanes as, for example, where there are one or more isolated
objects in the vicinity of an aerodrome.
Table
4-2: Dimensions and slopes of obstacle limitation surfaces
runways
meant for take-off
a. All dimensions are measured horizontally
unless specified otherwise.
b. The take-off climb surface starts at the end
of the clearway if the clearway length exceeds the specified distance.
c. 1 800 m when the intended track includes
changes of heading greater than 15° for
operations conducted in IMC, VMC by night.
d. See .317(b)(24) and .317(b)(26).