AC 120-29 Appendix 2 9/25/70 Page 7 Obstruction Clearance. No obstruction shall penetrate the applicable final approach surface specified in paragraph 4.c. When obstructions penetrate the final approach area transitional surfaces, and when deemed necessary, consideration will be given to an adjustment in the Decision Height (DH) commensurate with the degree of interference presented by the particular obstruction or obstructions.
SPECIAL OBSTRUCTION CLEARANCE AREAS. Because of the lower flight altitudes which occur in the immediate vicinity of the runway during ILS Category II approach and missed approach, it is necessary to specify certain areas in which obstructions must be eliminated or controlled.
These special areas are the Approach Light Area, the Touchdown Area, the Transitional Surfaces, and the Missed Approach Area.
6. APPROACH LIGHT AREA. (See Figure 2) Definition. An area longitudinally centered on the extended centerline of the ILS Category II runway, and extending outward from the end of the Touchdown Area (See Paragraph 7) to a point 200 feet beyond the last approach light fixture, and having a total width of 400 feet.
Obstruction Clearance. No obstruction shall penetrate the approach light plane. Further, no obstruction, including the approach light structure or fixtures, shall penetrate a 50:1 surface which originates at the same point as the final approach area (See Paragraph
4.b(1) at the elevation of the runway threshold. The 50:1 surface over the Approach Light Area remains a constant requirement even when other portions of the final approach surface are adjusted for glide slope angles greater than 2-1/2 degrees. However, where glide slope angles of less than 2-1/2 degrees are established, no obstruction in the Approach Light Area shall penetrate the associated approach surface.
400 Ft
FINAL RUNWAY
APPROACH AREA Length oF AIS 3000 200 Ft (50:1 Surface) FIGURE 2. Approach Light Area Par 6
Appendix 2 AC 120-29 9/25/70
7. TOUCHDOWN AREA. See Figure 3.
Definition. An area longitudinally centered on the runway centerline, extending from a point 200 feet outward from the runway threshold (normal or displaced) for a distance of 3200 feet in the direction of landing, and having a total width of 1000 feet.
Obstruction Clearance. The only obstructions permitted in the Touchdown Area are those objects which are fixed by their functional purpose or which are required for precision approaches to the Category II ILS runways. All objects except visual aids and frangible functional objects shall be appropriately marked and lighted unless shielded by a properly lighted and marked functional object. The identity and height limits of acceptable objects are as follows:
(1) Visual Aids. Unless flush-mounted, all visual aids shall be installed on frangible mounts. Maximum height is 14 inches above the surface where the fixture is located. Except that taxiway guidance signs may be installed in accordance with Advisory Circular 150/5340-18.
(2) Glide Slope Antenna. The mast or monitor mast shall be no closer than 400 feet to the ILS Category Il runway centerline, and should not exceed 55 feet in height above the elevation of the runway centerline nearest it. A mast of over 55 feet may be permitted if the minimum distance from the runway centerline is increased by 10 feet for each foot the mast exceeds 55 feet in height.
Structures. Those structures which are elements of the Glide Slope, PAR, or RVR systems (except GS antenna or monitor masts) should not exceed 15 feet in height above the elevation of the runway centerline nearest them, and in addition may be no closer to the runway centerline than 400 feet. When such structures are more than 15 feet high, they may be permitted if the minimum distance from the runway centerline is increased 10 feet for each foot the structure exceeds 15 feet. Frangible PAR reflectors are not considered to be obstructions.
Pat 7
AC 120- 29 Appendix 2 9/25/70 Page 9
8. TOUCHDOWN AREA TRANSITIONAL SURFACES (See Figure 3) Definition. Transitional Surfaces sloped at 7:1 extend outward and upward from the edges of the Touchdown Area and Section 1 of the Missed Approach Area (See Paragraph 9) to a height of 150 feet above the elevation of the runway centerline at the end of the touchdown 1050' Section 1
MISSED APPROACH AREA Touchdown Area 3100 Ft 1000' 40:1 Surface 1050 ' 7:1 Transitional Surface → 3200 Fts - 6000 Ft FIGURE 3. OBSTRUCTION CLEARANCE AREAS: ILS Category II.
Obstruction Clearance. When an obstruction penetrates the 7:1 transitional surfaces and when deemed necessary, adjustment in the RVR minimum will be made commensurate with the degree of interference presented by the obstruction. Such adjustment will be approved by Flight Standards Service. A caution note will be added to the approach procedure to identify obstacles which penetrate the 7:1 surfaces.
MISSED APPROACH AREA. A missed approach will be specified to commence at the DH if the required visual reference has not been established.
However, it is possible that aircraft will còntinue to descend through the decision height while initiating the missed approach, or that a decision to land may be altered by circumstances and the approach aborted at a lower altitude. In either case the missed approach obstruction clearance criteria must consider aircraft which have progressed into the touchdown area to heights below the decision height, perhaps even to a momentary touchdown. There are two Sections to the Missed Approach Area, and a special treatment for the turning missed approach is also necessary.
a. Missed Approach Section 1. This portion of the area begins at the end of the Touchdown Area at the height of the runway, and is longitudinally centered on the runway centerline. It has the same width as the touchdown area at the point of beginning (1,000 feet) and the width increases uniformly to 3,100 feet at 6,000 feet from the point of beginning. (See Figure 3) Par 8
Appendix 2 AC 120-29 Page 10 9/25/70 Missed Approach Section 2. This portion of the area starts at the end of Missed Approach Section 1 and is centered on a continuation of the Section 1 course. The width increases uniformly from 3100 feet at the beginning to 8 miles at a point 15 miles from the runway threshold. When positive course guidance is NOT provided for the missed approach procedure, secondary areas which are zero miles wide at the point of beginning and increase uniformly to 2 miles wide at the end of Missed Approach Section 2, must be added to the edges of Section 2. (See Figure 4) Turning Missed Approach Area. (Applies to turns of over 15 degrees).
The design of the turning missed approach area assumes that aircraft missing an approach will climb straight ahead until reaching a height of at least 300 feet above the elevation of the runway centerline at the end of the Touchdown Area. The procedure will identify the obstruction if a turn toward a significant obstruction has to be made. The turning flight track radius shall be 1.75 miles, and it shall be plotted to begin at the end of Missed Approach Section 1. The outer boundary of Missed Approach Section 2 shall be drawn with a 3.5 mile radius. The inner boundary line shall commence at the outer edge of the transitional surface opposite the end of the Touchdown Area. The outer and inner boundary line shall terminate at points 4 miles each side of the assumed flight track 15 miles from the runway threshold. (See Figures 5 and 6).
Where secondary areas are required, they shall commence after completion of the turn. Turns in the missed approach area are normally specified to commence after reaching a height of 300 feet. Where an operational requirement exists to continue the climb of the aircraft to a height of more than 300 feet prior to commencing a turn, Missed Approach Section l will continue to increase uniformly in width, and will be extended longitudinally 4000 feet for each 100 feet of height over 300 feet. In addition, the 7:1 Transitional Surface (Paragraph 8.a.) is also extended laterally on the inside of the turn to a height equal to the elevation attained by the extension of Missed Approach Section 1.
NOTE: Where a positive course guidance is provided in Section 2 consideration may be given to reducing the width of this Section.
d. Obstruction Clearance.
Straight Missed Approach. No obstruction in Sections 1 or 2 may penetrate a 40:1 surface. This surface originates at the beginning of Section 1 at the elevation of the runway centerline at the end of the touchdown area, and overlies the entire Missed Approach Area.
Par 9
AC 120-29 Appendix 2 9/25/70 3000' 6000' Secondary Area 2 NM 12:1 Surface 4 NM
MISSED APPROACH COURSE
13.5 NM (15 miles from runway threshold, T 40:1 Surface 4 NM Secondary Area 2 NM FIGURE 4. STRAIGHT MISSED APPROACH AREA. Section 2.
<iF Secondary Area a 1 surface | 2 NM Section 2 40:1 PRIMARY AREA 4 NM Assumed Flight Track r=3.5 Missed Approach Course r=1.75 (15 NM from Runway Section 1 Threshold) ≤ NM Missed Approach surface Runway Threshold 12:1 Surface 2 NM _! I FIGURE 5. TURNING MISSED APPROACH AREA Section 2
Appendix 2 AC 120-29 CHG 1 Page 12 15 Dec 71
(2) Turning Missed Approach. Section 1 obstruction clearance is the same as that for straight missed approach. To determine the obstruction clearance requirements in Section 2, the lines A-B and B-C are identified in Figures 5 and 6. The height of the missed approach surface over any obstruction in Section 2 is determined by measuring the distance from the obstruction to the nearest point on the line A-B or B-C and computing the height according to the 40:1 ratio starting at the elevation of line A-B or B-C. Note that lines A-B and B-C are always at the same elevation as the end of Section 1. (See Figure 6).
(3) Secondary Areas. Where secondary areas are considered, no obstruction may penetrate a 12:1 surface which slopes outward and upward from the missed approach surface.
* 10. GLIDE SLOPE ANGLE. The maximum angle is 3.0 degrees. An angle less than 2.5 degrees will be established only to satisfy a unique operational requirement, and must be jusitifed by special study for consideration of approval by Flight Standards Service, Washington, D.C.
GLIDE SLOPE THRESHOLD CROSSING HEIGHT. The optimum glide slope threshold crossing height is 50 feet. The maximum is 60 feet. A height as low as 47 feet may be used at locations where special consideration of the glide path angle and antenna location are required. Heights are measured at the landing threshold. See TERPS' Appendix 1, paragraph 10, *NOTE: Use of glide slope crossing heights as low as 47 feet are predicated on the vertical distance between the aircraft glide not exceeding 19 feet with the aircraft in its normal landing + slope antenna and the lowest part of the main landing gear wheels approach attitude.
ALJUSTMENT TO CATEGORY II ILS MINIMUMS. The decision height is measured from the highest elevation of the runway in the touchdown area. The lowest minimums permitted by the Category Il system are a decision height of 100 feet and RVR 1200. Application of Category II obstruction clearance criteria may identify objects which exceed the allowable height in the touchdown area or penetrate the approach light surface.
In such cases, adjustment to the decision height shall be made as follows:
Final Approach Surface - Requires a special study of local features and doing by standards Serve, Bane authorized by Flight Standards Washington, D.C.
Approach Light Surface - Adjust the DH upward one foot for each one and foot an object exceeds the allowable height.
Touchdown Area The RVR value will then be adjusted as indicated in the table:
Par 12
AC 120-29 Appendix 2 9/25/70 Page 13 Adjusted Decision Height RVR 101-140 feet 1200 141-180 feet 1600 181-199 feet 1800 Outer Boundary Section 2 Extended Outer Boundary Extended Flight Track / Assumed Flight Track (A), (B), (C) are extended points. They are plotted turning missed approach commences above Nos Seation 1 Extension 300 feet.
_ (B)
- - 40:1- MObstruction
• - 40:1 - Line AB is end of Section 1 Section Approach Area Missed Line BC is equal in length to section 1 and parallel to the
- 40:1--Mobstr runway centerline.
(C)
- Inner Boundary Section 2 Extended Transitional Surface TDZ Area Transitional Surface FIGURE 6. TURNING MISSED APPROACH AREA CONSTRUCTION DETAIL. ILS Category II.
470 fpm/150K, 630 fpm/200K, no wind conditions." approach area require a rate of climb of at least 315 fpm/100K, The caution note should read as follows: Obstructions in the missed 200K - 630 150K - 470 100K - 315 ground speeds this becomes: obstruction by 50 feet. Expressed in feet-per-minute for a range of approximately 190 feet per mile is required to clear this 900-foot surface starts and 900 feet above this point. A climb gradient of An obstruction is 30,000 feet from the point where the missed approach required to clear the controlling obstruction by 50 feet. For example: note which specifies a rate of climb in feet per minute which is 40:1 surface the missed approach procedure will contain a caution surface are not considered a hazard. When an object penetrates the the need approach area. Objecte with do not pee OBSTRUCTIONS IN THE MISSED APPROACH AREA. 13. Page 14 Appendix 2 Feet Per Minute The 40:1 missed approach 9/25/70 AC 120-29