Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
26 Key Insights The process of identifying imaginary surfaces involves considering not only the protection of existing airport and airspace surfaces, but also the protection of planned approaches and changes to airport design based on the approved airport layout plan. While FAR Part 77 provides an initial âscreenâ of potential obstruction issues, the absence of FAR Part 77 impacts does not preclude the possibility of an impact on other airport design or operational criteria that may be more restrictive. Under certain circumstances, instrument procedure design, instrument departure, or air carrier planning surfaces may be lower and more critical than FAR Part 77 surfaces and result in operational impacts on the facility. Key Definitions Airport layout plan (ALP): A set of drawings that provide a graphic representation of the sponsorâs long-term development plan for an airport, including property boundaries, exist- ing and proposed airport facilities and structures and the location of existing and proposed nonaeronautical areas. Decision altitude (DA) or decision height (DH): The altitude on final approach at which a missed approach must be conducted if the runway environment cannot be seen. Decision altitude is expressed above mean sea level, and decision height is expressed above ground level. Final approach fix/precision final approach fix: A specified point on a precision or a nonprecision instrument approach that identifies the commencement of the final approach segment. Final approach segment: The part of the instrument approach procedure in which alignment with the runway and descent for landing are accomplished. Instrument approach procedure (IAP): A series of predetermined maneuvers for the orderly transition of an aircraft under instrument flight conditions from the beginning of the initial approach to a landing or a point from which a landing may be visually made. Lateral splay: The lateral widening of an imaginary or design surface used for obstruction management that occurs at the surface and extends away from its designed point of origin. Missed approach: A procedure followed by a pilot when an instrument approach cannot be completed to a full-stop landing. C H A P T E R 3 Identifying the Applicable Airspace Surfaces and Criteria
Identifying the Applicable Airspace Surfaces and Criteria 27 Obstacle identification surface (OIS): The sloped surface used to identify the lower limit of the airspace to be protected from obstacles. One engine inoperative obstacle identification surface (OEI OIS): An imaginary surface used by air carriers operating under the provisions of FAR Parts 121 or 135 or ICAO Annex 6, which allows operators to analyze the net takeoff flightpaths at airports for obstruction impacts during engine-out departures. Runway visual range (RVR): Represents the horizontal distance a pilot can expect to see down the runway, based on visibility, background luminance, and runway light intensity. Visual area surface: The obstacle identification surface that covers the segment of a final approach between the approach procedure decision altitude and landing threshold point, during which a pilot visually descends to the runway touchdown point. 3.1 Applicable Surfaces As described in Chapter 2, there are multiple surfaces an airport sponsor must assess to find the critical or most limiting surfaces for their airport. This is necessary in order to identify the appropriate areas to protect. While FAR Part 77 is the central regulation for airspace protection, its primary purpose is to provide notice to the FAA of the proposed construction or alteration of structures. As FAA design requirements have evolved, FAR Part 77 must be used in conjunction with the other requirements to fully protect all the required surfaces. The types of surfaces applicable to an airport and the sizes and slopes of such surfaces are dependent on the type of approach procedure and its minimums, the sizes of aircraft served at the airport, and whether the airport supports commercial air services. For airports without commercial service, there are three regulations applicable to the airportâs airspace: â¢ FAR Part 77: Safe, Efficient Use and Preservation of the Navigable Airspace â¢ FAA AC 150/5300-13A: Airport Design â¢ FAA Order 8260.3D: United States Standard for Terminal Instrument Procedures (TERPS) For air carriers, the OEI criteria defined by FAA AC 120-91 and ICAO Annex 6 should also be considered by the airport to protect the interests of its users. 3.2 FAR Part 77 Surfaces In addition to establishing the standards for providing notice to the FAA of a proposed development, FAR Part 77 identifies the baseline surfaces to protect in airport obstruction management. However, FAR Part 77 alone will not identify all the critical surfaces for an airport. FAR Part 77 has five types of surfaces to be protected that must be considered. For a federally obligated airport, these surfaces are depicted on the airport airspace drawing in the ALP set. The surfaces outlined in Â§77.19, 77.21, or 77.23 include the following: â¢ Primary surface: A surface longitudinally centered on a runway. When the runway has a specially prepared hard surface, the primary surface extends 200 feet beyond each end of that runway; but, when the runway has no specially prepared hard surface, the primary surface ends at each end of that runway. The elevation of any point on the primary surface is the same as the elevation of the nearest point on the runway centerline. The surface width ranges from 250 feet to 1,000 feet, based on the runway category and approach type.
28 Best Practices for Airport Obstruction Management Guidebook â¢ Approach surface: A surface longitudinally centered on the extended runway centerline and extending outward and upward from each end of the primary surface. An approach surface is applied to each end of each runway based on the type of approach available or planned for that runway end. â¢ Transitional surface: These surfaces extend outward and upward at right angles to the runway centerline and the runway centerline extended at a slope of 7 to 1 from the sides of the primary surface and from the sides of the approach surfaces. Transitional surfaces for those portions of the precision approach surface that project through and beyond the limits of the conical surface extend a distance of 5,000 feet measured horizontally from the edge of the approach surface and at right angles to the runway centerline. â¢ Horizontal surface: A horizontal plane 150 feet above the established airport elevation, the perimeter of which is constructed by swinging arcs of a specified radii from the center of each end of the primary surface of each runway of each airport and connecting the adjacent arcs by lines tangent to those arcs. The radii of the arcs are 5,000 or 10,000 feet, depending on runway category or approach type. â¢ Conical surface: A surface extending outward and upward from the periphery of the horizon- tal surface at a slope of 20 to 1 for a horizontal distance of 4,000 feet. The complex geometrical shape that combines the various FAR Part 77 imaginary surfaces is unique to each airport. It is recommended that an airport sponsor develop and keep current a graphic of airport-specific imaginary surfaces for the purposes of communicating obstruction management concerns to elected officials, zoning and planning officials, and members of the public. Table 3.1 summarizes surface size by type of runway and approach visibility minimums. A sample graphic of FAR Part 77 surfaces is shown in Figure 3.1. Source: Obstruction Identification SurfacesâFederal Aviation Regulations Part 77. Available at https://www.ngs.noaa.gov/AERO/oisspec.html Table 3.1. FAR Part 77 surface sizes.
Identifying the Applicable Airspace Surfaces and Criteria 29 3.3 FAA AC 150/5300-13A: Design Surfaces In addition to considering FAR Part 77 surfacesâor in cases where there are impacts on FAR Part 77 surfacesâthe design standards in FAA AC 150/5300-13A should be considered. The design standards in FAA AC 150/5300-13A generally align more closely with TERPS standards than FAR Part 77, to account for the new instrument approach capability using a global positioning system (GPS). When preparing an ALP, typically the TERPS surfaces are not depicted; only the FAR Part 77 and FAA AC 150/5300-13A surfaces are shown. This is in part because the requirements in TERPS design standards provide for adjustments that can be made to an approach or departure procedure to avoid an obstruction, whereas the standards in FAR Part 77 and AC 150/5300-13A identify the surfaces to be kept clear of obstructions. The key surfaces in FAA AC 150/5300-13A for landing aircraft include the following: â¢ TSSs: Runway threshold siting criteria, based on runway approach type and airplane design group. FAA design standards require the runway threshold to be positioned so that there Source: Hanson Professional Services Inc., 2017 Figure 3.1. FAR Part 77 surfaces graphic.
30 Best Practices for Airport Obstruction Management Guidebook are no obstacle penetrations to the appropriate approach surface. Impacts on the TSSs may result in threshold displacements or the implementation of declared distances on the runway (specified available runway length for a particular operation such as a takeoff or a landing), reducing runway utility. â¢ The approaches with vertical guidance surface (VGS): An imaginary 30:1 surface, appli- cable to precision approach or approaches with vertical guidance, extending from the runway threshold along the runway centerline to the DA point. Impacts on the VGS may require nonstandard glide path angles or approach discontinuation. Figure 3.2 shows the TSS defined in FAA AC 150/5300-13A, and Table 3.2 shows the cor- responding values. For airports with IAPs, regardless of commercial service availability, the FAA also establishes an instrument departure. Figure 3.4 of FAA AC 150/5300-13A depicts the instrument departure surface, as shown in Figure 3.3 of this report. Notes: 1. See Table 3-2 for dimensional data. 2. The starting elevation of the approach slope begins at the elevation of the runway threshold. For displace thresholds, the approach slope begins at the runway elevation at the displaced threshold. Source: FAA AC 150/5300-13A, Figure 3-2 Figure 3.2. Threshold siting based on approach slope.
Identifying the Applicable Airspace Surfaces and Criteria 31 3.4 FAA Order 8260.3D: United States Standard for Terminal Instrument Procedures (TERPS) IAPs are designed to provide aircraft access to an airport in all weather conditions. There are different types of IAPs using different types of navigational aids (NAVAIDs). These IAPs range from procedures that only provide horizontal guidance to the airport or to a specific runway end to procedures that provide vertical and horizontal guidance all the way to touch down. The more precise the guidance provided by the IAP, generally the lower the minimums, meaning the aircraft can use the airport in conditions with lower ceiling and visibility. Minimums are defined in terms of the following: â¢ Visibility: the average forward horizontal distance from the cockpit of aircraft in flight at which objects can be identified â¢ Ceiling: the height of the base of the lowest clouds that cover more than half of the sky The lower the minimums are for an IAP, the larger the area that must be protected, because aircraft will fly lower to the ground and slower in landing configuration before the pilot is required to establish visual contact with the runway environment. FAA Order 8260.3D (TERPS) defines critical surfaces and criteria used to design instrument procedures at an airport. Because the specifics of the approach procedure design are based on facility conditions and critical aircraft, the precise dimensions of individual surfaces are unique to the facility and particular approach. While TERPS is used to design IFPs, it is helpful to under- stand what surfaces need to be protected to support the IAP design. It is important to consider the criteria for existing and planned airport flight procedures to protect those procedures and airport operations from potential impact. The following TERPS surfaces are closest to the air- port and can have a direct impact on IAP availability and minimums for an airport: â¢ Approach segments: The approach is made up of the initial, intermediate, and final approach. Table 3.2 notes are available at https://www.faa.gov/airports/engineering/engineering_briefs/media/ EB-99-Airport-Design-Tables-3-2-and-3-4.pdf. Source: FAA AC 150/5300-13A, Table 3-2, as updated by FAA Engineering Brief 99, September 20, 2018 Approach Table 3.2. Approach/departure standards.
32 Best Practices for Airport Obstruction Management Guidebook â¢ Initial approach segment: The aircraft has departed the en route phase and is maneuvering to enter an intermediate phase. There may be more than one initial approach procedure. These are typically located some distance from the airport. â¢ Intermediate approach segment: Connects the initial and final approach segments. In this segment, the aircraft speed and position are configured to enter the final approach segment. â¢ Final approach segment: This is the segment of an approach procedure in which alignment and descent for landing are accomplished. The segment begins at the precise precision final approach fix and ends at the missed approach point (MAP), which coincides with the DA or DH. The dimensional criteria or slope varies, based on airport conditions and approach type. Objects that penetrate this segment must be lowered or removed or the approach must be modified through higher minimums to maintain adequate clearance. If adequate clear- ance cannot be provided, the approach would need to be deactivated. â¢ Missed approach segment: If an aircraft is unable to complete a full-stop landing, it executes a missed approach. This segment of the approach procedure protects the safety of aircraft when executing a missed approach procedure and climbing away from the runway. Like the Source: FAA AC 150/5300-13A, Figure 3-4 Figure 3.3. 40:1 departure surface for instrument runways.
Identifying the Applicable Airspace Surfaces and Criteria 33 final approach segment, the dimensional criteria for this surface will vary from procedure to procedure. The area considered for obstacles generally will have a width equal to that of the final approach segment at the missed approach (or DA point) and will uniformly expand to the width of the initial approach segment at a point 15 nautical miles from the MAP. These TERPS approach segments are shown in Figure 3.4. Visual Area OIS The visual area OIS underlies the visual portion of the final approach segment from the DA or visual descent point (VDP) to 200 feet before the runway end on a straight-in approach and from 10,000 feet to 200 feet before the runway end for circling approaches. The purpose of the visual area OIS is to protect the aircraft on approach as the pilot transitions from flight by reference to instruments to using visual cues to land. As the sides of the visual area trapezoid splay outward from the extended runway centerline, the width of the visual area varies based on the distance from the runway threshold. IAF = initial approach fix, IF = intermediate fix. Source: FAA Order 8260.3D, Figure 2-1-5 SEGMENTS OF AN APPROACH PROCEDURE Figure 3.4. Segments of an approach procedure.
34 Best Practices for Airport Obstruction Management Guidebook For runways with straight-in approach procedures, the visual area OIS is aligned with the extended runway centerline. The surface beginning width is 400 feet (200 feet on each side of the runway centerline), while the width of the area at a specific distance from the area origin is calculated as shown in Figure 3.5. The length of the area varies as the area extends to the calculated DA/DH point or VDP for the approach, the point where the pilot needs a visual identification of the runway environment to continue the approach to land. As those points vary based on the approach specifics, the length of the surface will vary accordingly, not to exceed 10,000 feet. The height of the OIS for the visual area is determined by a slope from the visual areaâs origin. The vertical component (ratio) of the surface is 34:1 (34 feet horizontally for each 1 foot verti- cally) for all runways with visibility lower than 3/4 statute miles or 4,000 feet RVR, a distance over which a pilot can see the runway surface markings delineating the runway, as measured in horizontal feet, and 20:1 for all other category types. The height of the visual area surface at a specific point can be calculated using the formula in Figure 3.5. Protecting this visual area OIS is important to establishing and keeping approach minimums. When using TERPS to design the approach, if there are penetrations to the OIS 34:1, the IAP visibility will be limited to no lower than Â¾ statute miles or 4,000 feet RVR. If the 20:1 OIS is penetrated, the IAP visibility will be limited to no lower than 1 statute mile or 5,000 feet RVR. Additionally, if the obstruction is not lighted, night IAPs to that runway end (straight-in and cir- cling) may be denied. Under certain circumstances, and in coordination with the FAA, a visual glide slope indicator (VGSI) [e.g., VASI or precision approach path indicator (PAPI)] may be used in lieu of obstruction lighting. If new obstacles are developed or grow into the OIS surface, the minimums may need to be raised to align with standards or restrictions on instituted nighttime instrument procedures. While all the airspace surfaces for an airport need to be protected, the FAA has focused first on the TERPS visual approach segment. The FAA has established a Surface Analysis and Source: FAA Order 8260.3D, Figure 3-3-2 1/2W = (0.15 Ãd ) + 200 where: Â½W = Perpendicular distance (feet) runway centerline to area edge d = Distance (feet) measured along runway centerline from area origin 20:1 OIS Height= d/20 34:1 OIS Height=d/34 Where d=distance from visual area origin along runway centerline Figure 3.5. Circling and straight-in visual area.
Identifying the Applicable Airspace Surfaces and Criteria 35 Visualization (SAV) tool that can be used by airports to help monitor the 20:1 visual area surface. This tool is discussed in more detail in Chapter 5. In the past, the impacts to the visual area OIS were categorized as high risk (more than 11 feet above the surface), medium risk (3 feet to 11 feet above the surface) or low risk (less than 3 feet above the surface). High-risk surface penetrations required immediate action on the airportâs part. The airport was immediately required (as promptly as practicable but in no more than 30 days) to remove, lower, or light the obstruction. Impacts of medium or low severity required less urgent action, but nonetheless had to be addressed by the airport through removal, lowering, or marking or lighting within a longer time frame. At this time, the FAA is reassessing the policy and has not issued any follow-up guidance. VGS There is one additional surface that must be kept clear: the VGS. Originally associated with approaches with vertical guidance, this surface is now analyzed and evaluated for all precision and nonprecision straight-in aligned approaches. The VGS is a narrow, inclined trapezoid sur- face centered on the runway centerline. It is evaluated for obstructions between the DA or VDP and the landing threshold point on IAPs. The origin of the VGS is based on the runway threshold crossing height (TCH). The runway crossing height is an aircraftâs elevation above the runway end when it crosses. Larger aircraft with taller landing gear need a higher crossing height than smaller aircraft. For â¢ Runways with TCH below 40 feetâthe VGS originates before the runway threshold â¢ Runways with TCH 40 feet or more but less than 50 feetâthe VGS originates at the runway threshold â¢ Runways with TCH above 50 feetâthe VGS originates at the runway threshold, but at an AGL height equal to the TCH height over 50 feet As is the case with the visual area OIS, the surface dimensions are dependent on where the DA point or VDP is located. Therefore, the dimensions of this surface vary for each runway based on the minimums for a particular approach. The surface width at its point of origin is 100 feet on each side of the runway centerline. The ultimate width of the surface is based on the location of the approach DA or VDP, with the TERPS order specifying formulas to calculate the surface width in Section 2-6-6 of the order. To address VGS penetrations, the FAA Flight Procedures team will adjust the glidepath angle or TCH for the approach to accommodate the obstacle while trying to keep the descent angles and TCH values within allowable limits. If the angle exceeds the maximum established in the TERPS order for the particular aircraft approach category and the obstacle still penetrates the VGS, straight-in minimums will not be authorized for that approach. It is possible to have multiple VGS surfaces for each runway for approaches designed for dif- ferent aircraft categories. Therefore, it is critical to evaluate the most restrictive or lowest VGS. Departure Obstacle Clearance Surface (OCS) Similar to approaches, FAA Order 8260.3D defines the surfaces for instrument depar- ture surfaces. A 40:1 OCS originating at the location and elevation of the departure end of the runway (DER) is used to evaluate the required climb performance from a particular departure runway end to the nearest (shortest distance) obstacle in the segment. Impacts to this surface may result in the addition of required climb gradient restrictions to the DER. Figure 3.6 shows the departure OCS.
36 Best Practices for Airport Obstruction Management Guidebook Final Approach Segment This procedure design element is the segment of the IAP in which the pilot completes runway alignment and commences the final descent for landing, either as a straight-in approach or as a circling approach. Generally, the final approach segment begins at the IAP final approach fix and terminates at the MAP or DA point. The standards and criteria for design and obstacle clearance evaluation of the final approach segments vary widely based on the approach type and are beyond the scope of this guidance. As an example, Figure 3.7 shows a comparison of an instrument landing system (ILS) and required navigation performance (RNP) approach to the same runway. The areas required to be clear of obstacles vary in the final and missed approach sections. Each type of approach (ILS, lateral navigation [LNAV], localizer performance with vertical guidance [LPV], nondirectional beacon, RNP, very high Source: FAA Order 8260.3D, Figure 14-1-2 DER 40: 1 O CS Figure 3.6. Departure surface starting elevation and 40:1 OCS. Source: Graphic by Planning Technology Inc. 2017, based on ILS surface definition in FAA Order 8260.3C and RNP surface in FAA Order 8260.58; map source credits: Esri, HERE, Garmin, USGS, Intermap, INCREMENT P, NRCan, Esri Japan, METI, Esri China (Hong Kong), Esri Korea, Esri (Thailand), NGCC, Â© OpenStreetMap contributors, and the GIS User Community Figure 3.7. ILS versus RNP final approach segment comparison.
Identifying the Applicable Airspace Surfaces and Criteria 37 frequency omnidirectional ranges, etc.) has its own OCSs based on the precision of the instru- mentation used to fly the procedure. The final approach segment must accommodate the maximum vertical descent angle with- out obstacle penetrations, based on the aircraft approach category for the specific approach evaluated. Impacts on the final approach segment between the final approach fix and the MAP will result in higher approach minimums or the FAA making the approach not available if the obstruction impact cannot be mitigated. Missed Approach Segment Similar to a departure surface, the surface associated with a missed approach is designed to protect an aircraft departing the runway environment, in this case after an aborted landing. The missed approach is part of the design of every instrument procedure and is just as important to protect as the landing portion. The missed approach segment begins at the MAP or DA located before the landing end of the runway. The missed approach surface has a width equal to that of the final approach area at the MAP or DA and uniformly expands to the width of the en route approach segment, as shown in Figure 3.8. The primary area considered for obstacles varies based on the type of approach analyzed. Within the primary missed approach area, no obstacle may penetrate the missed approach surface. This missed approach area begins over the MAP at a height that meets the required final approach obstacle clearance for the approach. In most cases, the sur- face increases at a 40:1 ratio to a height equaling 1,000 feet below the missed approach altitude for the approach (highest missed approach obstacle clearance altitude or minimum holding altitude). The secondary area slopes up at a rate of 12:1. If the missed approach segment is penetrated by any obstacles, the FAA will address the impact by increasing the approach mini- mums, adjusting the MAP or procedure, or making other operational adjustments. Figure 3.9 shows the missed approach OCS. Clearing the final approach and missed approach segment surfaces of obstructions is critical to the procedure. Any penetration of the final approach segment between the final approach fix and the MAP, or any penetration to the missed approach surface, will cause an increase in NM = Nautical mile Source: FAA Order 8260.3D, Figure 2-8-1 Figure 3.8. Straight missed approach area.
38 Best Practices for Airport Obstruction Management Guidebook landing minimums or may make the approach not authorized. In some cases, the FAA may mitigate penetrations to the final approach segment between the MAP and the runway if they donât penetrate the VGS, visual area OIS, or missed approach surfaces. 3.5 OEI OIS The primary difference between a non-air-carrier airport and an air carrier airport is the need to consider the OEI OIS. While regulations related to the OEI surfacesâ criteria are not directly applicable to the airport sponsors, they have an indirect impact on the airportâs current and planned operations. The OEI OIS is a term that describes the generic trapezoid surfaces with a 62.5:1 ratio created in response to the requirements of FAA AC 120-91 and ICAO Annex 6. These criteria are applicable to air carriers operating under the regulations of Parts 121 or 135 or ICAO Annex 6 as operational safety planning criteria. However, the impact of encroachment on any of those surfaces by obstacles can affect the airport as capacity impacts. The OEI OIS starts at the location and elevation of the DER, as shown in Figure 3.10. The generic FAA OEI OIS criteria specify an overall length of 50,000 feet from the DER. The inner width is 300 feet on each side of the runway centerline with a 15-degree lateral splay, NM = Nautical mile Source FAA Order 8260.3D Figure 3.9. Straight missed approach OCS. Source: FAA AC 120-91 Appendix A, Figure 1 Figure 3.10. Obstacle accountability area for straight-out departures.
Identifying the Applicable Airspace Surfaces and Criteria 39 until the width reaches and remains at 6,000 feet on each side of the runway centerline. It is important to note that this is an obstacle identification surface, not an obstacle clearance surface. The objective of identifying penetrations to this surface is to provide air carriers with the information necessary to develop obstacle accountability areas or splays, as described in Section 2.2. 3.6 No Individual Surface Controls All criteria and regulations that define airspace surfaces must be considered during the obstruction evaluation to have a complete picture of what surfaces are the lowest and most critical to be protected. Tables 3.3 and 3.4 summarize the surfaces to be considered for non-air-carrier airports, based upon the type of approach and its minimums. Table 3.3 is for airports that serve aircraft weighing more than 12,500 lb maximum takeoff weight (MTOW). Table 3.4 is for air- ports that only serve aircraft with MTOW of 12,500 lb or less. These tables show a comparison of the sizes and slopes of the surfaces based on the three sets of standards: FAR Part 77, FAA AC 150/5300-13A, and TERPS. Table 3.5 includes a set of additional criteria and considerations for air carrier airports, including departure and OEI OIS criteria. 3.7 Special Considerations in Obstruction Surface Identification Although FAR Part 77 surfaces may be more restrictive and identify a greater number of objects as potential obstructions, there are circumstances, as shown in Tables 3.4 to 3.6, in which the FAA AC 150/5300-13A or TERPS surfaces cover a larger area than an FAR Part 77 surface or have a more restrictive (shallower) vertical ratio, resulting in a larger surface, lower surface, or both. Particular attention must be given to the following conditions: â¢ Utility runways (runways designed to serve small aircraft only, with MTOW of 12,500 lb or less) with a vertically guided instrument approach â¢ Runways with a nonprecision approach that also have instrument departure procedures â¢ Part 139 (air carrier) facilities that aim to protect the OEI OIS surfaces â¢ Missed approach segment Utility Runway with Vertically Guided Instrument Approaches Utility runways that are equipped with vertically guided instrument approaches require spe- cial considerations. In accordance with FAR Part 77.19, the approach surface for those runways extends at a slope of 20:1 for 5,000 feet horizontally. These criteria include those runways having vertically guided IAPs with vertical guidance, such as LPV, LNAV, or vertical navigation. The FAR Part 77 approach surfaceâs 20:1 ratio is less restrictive and captures fewer objects than the VGS, which has a 30:1 ratio. In addition to having a less restrictive vertical component, the FAR Part 77 approach surface has a horizontal length of only 5,000 feet as compared to the VGS, which can horizontally extend up to 10,000 feet. The FAR Part 77 surface and the FAA AC 150/5300-13A and TERPS VGS surfaces have slightly different points of origin. When adjusted for a TCH of less than 40 feet, the VGS may start before the runway end, or at the runway end in all other cases. The approach surface starts 200 feet beyond the end of the runway. As a result of the different points of origin, the approach CHALLENGES TO RELYING ON TERPS FOR OBSTRUCTION MANAGEMENT â¢ Accurate mapping of TERPS surfaces is time-consuming and can be costly. â¢ Any errors made in mapping may result in flaws in analysis, which can subsequently mismatch the findings of the OE/AAA process and the actual FAA determination and can result in significant liability for an airport. â¢ When the airport develops a static map of existing TERPS surfaces, it represents existing and planned conditions at that time. The static map will not remain accurate unless it is regularly maintained by the airport or its consultant. â¢ Changes to the airportâs surfaces may occur due to changes to any of the elements of a particular approach (such as the approach fix or approach minimums) or to TERPS criteria. â¢ Existing or planned procedures may be cancelled or rendered obsolete due to technological advances. Source: ACRP Report 38: Understanding Airspace, Objects, and Their Effects on Airports
40 Best Practices for Airport Obstruction Management Guidebook surface is generally lower for the first 600 feet but extends above the VGS surfaces thereafter, while the VGS remains lower and more critical. Both surfaces need to be considered to avoid an operational effect on the airport, such as higher approach minimums, a threshold displacement, or the loss of the IAP until the obstruction is removed. Nonvertically Guided Approaches Nonvertically guided approaches, which use a step-down procedure, also need special con- sideration. The approach surface criteria, as defined in Part 77.19, are based on a continuous, progressively sloped surface. However, the TERPS criteria for instrument approaches without vertical guidance, such as a localizer, LNAV, nondirectional beacon, or very high frequency omnidirectional ranges approach are based on a step-down method. That is, when a pilot reaches a certain waypoint, he or she may immediately descend to a lower altitude and level off and do so again when arriving at the next waypoint, continuing to step down until reaching the approach DH or minimum descent altitude. As shown in Figure 3.11, once inside the final approach fix (SNOWL in Figure 3.11), there is a 250-foot required obstacle clearance beneath the minimum descent altitude for each step down. When allowing for the required obstacle clearance below the aircraft after it levels off and is approaching the next waypoint, the airspace that is required to be clear of obstacles to allow or Airspace Protection Criteria GA Precision Approach or Visibility <3/4 Mile GA Vertically Guided Approach Visibility 3/4 Mile GA Nonvertically Guided Approach Visibility 3/4 Mile GA Visual Flight Rules Only FAR Part 77.13 notification, height standards, and surfaces 100:1 for 20,000 feet 100:1 for 20,000 feet or 50:1 for 10,000 feet if runway <3,200 feet 100:1 for 20,000 feet or 50:1 for 10,000 feet if runway <3,200 feet 100:1 for 20,000 feet or 50:1 for 10,000 feet if runway <3,200 feet FAR Part 77.25 obstruction height standards 10,000 feet at 50:1 and 40,000 feet at 40:1 10,000 feet at 34:1 10,000 feet at 34:1 5,000 feet at 20:1 FAA AC 150/5300-13, Table 3-2 threshold siting surface 200 feet offset, inner width 800 feet, outer width 3,400 feet, 10,000 feet long at 34:1 200 feet offset, inner width 400 feet, outer width 3,400 feet, 10,000 feet long at 20:1 200 feet offset, inner width 400 feet, outer width 3,400 feet, 10,000 feet long at 20:1 0 feet offset, inner width 400 feet, outer width 1,000 feet for 1,500 feet then 1,000 feet wide for 8,500 feet at 20:1 FAA AC 150/5300-13, Table 3-2 instrument approaches with vertical guidance Inner width runway width +200 feet, outer width 1,520 feet, 10,000 feet long at 30:1 Inner width runway width +200 feet, outer width 1,520 feet, 10,000 feet long at 30:1 N/A* N/A FAA AC 150/5300-13, Table 3-2 departure surface Inner width 1,000 feet, outer width 6,466 feet, 10,000 feet long at 40:1 Inner width 1,000 feet, outer width 6,466 feet, 10,000 feet long at 40:1 Inner width 1,000 feet, outer width 6,466 feet, 10,000 feet long at 40:1 N/A TERPS departure surface 40:1 missed approach course 40:1 missed approach course 40:1 missed approach course N/A TERPS approach surfaces Straight-in approach Straight-in approach Straight-in approach* N/A *As of Oct. 1, 2017, all straight-in nonprecision approaches are evaluated for the visual glide slope Source: 14 CFR Part 77, FAA AC 150/5300-13A as updated by FAA Engineering Brief 99 and FAA Order 8260.3D Table 3.3. Approach airspace protection criteria for non-air-carrier airport (existing or planned approach)âaircraft with more than 12,500 lb MTOW.
Identifying the Applicable Airspace Surfaces and Criteria 41 Airspace Protection Criteria GA Precision Approach or Visibility <3/4 Mile (All Aircraft) GA Vertically Guided Approach (Small Aircraft Only) Visibility 3/4 Mile GA Existing or Planned Nonvertically Guided Approach Visibility 3/4 Mile GA Visual Flight Rules Only FAR Part 77.13 notification, height standards, and surfaces 100:1 for 20,000 feet 100:1 for 20,000 feet or 50:1 for 10,000 feet if runway <3,200 feet 100:1 for 20,000 feet or 50:1 for 10,000 feet if runway <3,200 feet 100:1 for 20,000 feet or 50:1 for 10,000 feet if runway <3,200 feet FAR Part 77.25 obstruction height standards 10,000 feet at 50:1 and 40,000 feet at 40:1 5,000 feet at 20:1 5,000 feet at 20:1 5,000 feet at 20:1 FAA AC 150/5300-13, Table 3-2 threshold siting surface 200 feet offset, inner width 800 feet, outer width 3,400 feet, 10,000 feet long at 34:1 200 feet offset, inner width 400 feet, outer width 3,400 feet, 10,000 feet long at 20:1 200 feet offset, inner width 400 feet, outer width 3,400 feet, 10,000 feet long at 20:1 0 feet offset, inner width 250 feet, outer width 700 feet for 2,250 feet then 7,000 feet wide for 2,750 feet at 20:1 FAA AC 150/5300-13, Table 3-2 instrument approaches with vertical guidance Inner width runway width +200 feet, outer width 1,520 feet, 10,000 feet long at 30:1 Inner width runway width +200 feet, outer width 1,520 feet, 10,000 feet long at 30:1 N/A* N/A FAA AC 150/5300-13, Table 3-2 departure surface Inner width 1,000 feet, outer width 6,466 feet, 10,000 feet long at 40:1 Inner width 1,000 feet, outer width 6,466 feet, 10,000 feet long at 40:1 Inner width 1,000 feet, outer width 6,466 feet, 10,000 feet long at 40:1 N/A TERPS departure surface 40:1 missed approach course 40:1 missed approach course 40:1 missed approach course N/A TERPS approach surfaces Straight-in approach Straight-in approach Straight-in approach* N/A *As of Oct. 1, 2017, all straight-in nonprecision approaches are evaluated for the visual glide slope. Source: 14 CFR Part 77, FAA AC 150/5300-13A as updated by FAA Engineering Brief 99 and FAA Order 8260.3D Table 3.4. Approach airspace protection criteria for non-air-carrier airport (existing or planned approach)âaircraft with MTOW of 12,500 lb or less. Airspace Protection Criteria Precision Approach or Visibility <3/4 Mile (All Aircraft) Vertically Guided Approach (All Aircraft) Visibility 3/4 Mile FAR Part 77.13 notification, height standards, and surfaces 100:1 for 20,000 feet 100:1 for 20,000 feet FAR Part 77.25 obstruction height standards 10,000 feet at 50:1 and 40,000 feet at 40:1 10,000 feet at 34:1 FAA AC 150/5300-13, Table 3-2 threshold siting surface 200 feet offset, inner width 800 feet, outer width 3,400 feet, 10,000 feet long at 34:1 200 feet offset, inner width 400 feet, outer width 3,400 feet, 10,000 feet long at 20:1 FAA AC 150/5300-13, Table 3-2 instrument approaches with vertical guidance Inner width runway width +200 feet, outer width 1,520 feet, 10,000 feet long at 30:1 Inner width runway width +200 feet, outer width 1,520 feet, 10,000 feet long at 30:1 Departure Criteria FAA AC 150/5300-13, Table 3-2 departure surface Inner width 1,000 feet, outer width 6,466 feet, 10,000 feet long at 40:1 TERPS standard departure surface Inner width 1,000 feet at DER, 15-degree increase in width each side for 2 nautical miles at 40:1, then all directions from that height OEI OIS Inner width 600 feet, outer width 6,000 feet at 62.5:1 Source: 14 CFR Part 77, FAA AC 150/5300-13A updated by FAA Engineering Brief 99 and FAA Order 8260.3D Table 3.5. Checklist of airspace protection criteria for air carrier airport (existing or planned approach).
Surfaces Effect of Impact Monitoring Responsibility FAR Part 77 Primary Needs further evaluation Airport and tall structure proponent Approach Needs further evaluation Airport and tall structure proponent Transitional Needs further evaluation Airport and tall structure proponent Horizontal Needs further evaluation Airport and tall structure proponent Conical Needs further evaluation Airport and tall structure proponent FAA AC 150/5300-13A Threshold siting surface Threshold displacement or runway end relocation Airport Instrument approaches with vertical guidance surface Increased minimums or approach discontinuation Airport FAA Order 8260.3D TERPS Initial approach segment Increased minimums or approach discontinuation FAA Final approach segment Increased minimums or approach discontinuation FAA Missed approach segment Increased minimums or approach discontinuation FAA Visual area OIS Night instrument approaches not authorized Airport/FAA Vertical guidance surface Increased minimums or approach discontinuation FAA Departure OCS Increased required climb-out performance or instrument departures not authorized FAA FAA AC 120-91 and ICAO Annex 6 OEI OIS Reduced passenger or revenue cargo capacity, fleet down-gauging, limitation on air carrier service range and air carrier service discontinuation Air carriers Table 3.6. Summary of critical airspace surfaces, effect of impacts, and monitoring responsibility. MDA = minimum descent altitude. Source: Planning Technology Inc., 2018 Figure 3.11. Final segment step-down fix.
Identifying the Applicable Airspace Surfaces and Criteria 43 authorize that procedure is often well below the Part 77.19 surfaces. For reference, if this were classified as a utility runway, the LNAV surfaces would be the same; however, the 5,000-foot radius of the FAR Part 77 horizontal surface (at 1,530 feet), plus the 4,000-foot conical (rising to 1,730 feet), would end prior to the step-down fix (ORIYE in Figure 3.11). Any penetration of the OCS for the nonvertically guided approach will result in higher mini- mums for that segment and may render the approach unacceptable for straight-in procedures if the pilot is not in a position to land when passing the obstacle. Departure Surfaces at Airports with Nonprecision Approaches An instrument departure procedure permits aircraft to depart an airport when IFR weather conditions prevail. To protect the safety of flight, the FAA analyzes runway departures and mitigates impacts on the instrument departure surface by implementing measures such as non- standard climb gradients for departing aircraft. The surface is assumed to be applicable to all runways with an IAP until otherwise precluded. The Part 77 approach surface for all utility runways with a nonprecision instrument approach has a slope of 20:1, whereas the approach surface for all other-than-utility runways with a non- precision approach has a slope of 34:1. The standard instrument departure surface has a slope of 40:1 and is based on a departing aircraft climbing at a rate of 200 feet per nautical mile. The surface is not only more vertically restrictive; it has a larger horizontal footprint, as shown in Figure 3.12. The instrument departure surface starts at the runway end and extends for 10,200 feet. Ini- tially, the approach surface will be lower and more restrictive than the departure surface because the approach surface starts 200 feet from the runway end. However, because the instrument departure surface is larger, once the approach surface extends above it, the instrument departure surface remains more restrictive. Thus, both surfaces must be considered in obstruction man- agement. If impacts on the instrument departure surface cannot be removed, some mitigation measures may be available to the airport through the FAA. Depending on the obstacleâs loca- tion, height, or both, the FAA will typically increase the required climb gradient for that runway departure end; develop a departure procedure; or label it a low, close-in obstacle and list it in the takeoff minimums for pilot reference (or a combination of these measures). While these mea- sures may offset the existing departure impacts, the overall goal of the airport sponsor should be to protect the surface from any additional impacts. Part 77 Precision Instrument Runway (PIR) Approach Surface and OEI OIS Most air carrier airports have at least one precision instrument approach, such as an ILS with its associated FAR Part 77 50:1 approach surface, as a necessity to support air carrier operations. However, this most restrictive and lowest of all FAR Part 77 imaginary surfaces does not capture the potential impacts on another OIS critical for air carrier operationsâthe OEI OIS. It is criti- cal for airport sponsors to understand these criteria, because the OEI surfaces are often more restrictive than the Part 77 and TERPS surfaces and are related to the amount of payload that can be transported on each air carrier flight. For airport planning purposes, the FAA uses a 62.5:1 OEI OIS, although the airlines or Part 135 operators are permitted to utilize an OIS that more closely reflects their actual operation at the specific facility. Therefore, FAR Part 77 analysis of the airportâs imaginary surfaces will likely fail to capture any potential impacts on the 62.5:1 OEI OIS. The dimensional criteria of the OEI OIS are intended to help airports plan for air carrier operations or evaluate the potential impact
44 Best Practices for Airport Obstruction Management Guidebook Source: Hanson Professional Services Inc., 2018 Figure 3.12. Departure surface and nonprecision approaches.
Identifying the Applicable Airspace Surfaces and Criteria 45 on air carrier operators because the OEI OIS is wider and larger than the obstacle evaluation areas used by air carriers. Air carriers are required to mitigate impacts on the OEI OIS by ensuring that during depar- tures from a particular air carrier runway, an aircraft can clear all obstacles in its path by at least 35 feet vertically or 300 feet horizontally in the event of an engine loss. To resolve impacts on an OEI OIS, an air carrier may need to reduce the available runway length for its operation. To operate on the reduced runway length, the air carrier may need to reduce its load by decreasing fuel, passengers, or both. This reduction may happen more frequently in warm weather condi- tions, when the lower air density reduces aircraft climb performance. Reducing the amount of revenue cargo, fuel, or passengers on flights, even if only at certain times of the year, will make those routes less profitable. Such reductions may eliminate certain existing or future destina- tions (due to fuel load limitations) or may increase the cost to fly to those destinations, with the potential for complete loss of service to a particular destination. Additional effects may include the following: â¢ Reduction in range due to fuel load limitations â¢ Reduction in enplanements or cargo tonnage due to lower passenger or cargo capacity â¢ Down-gauging of the fleet operating to and from the airport to fit within the available runway length The 62.5:1 OEI OIS is a starting point for OEI impact analysis because each air carrier oper- ating to and from the airport will have specific OEI OIS surfaces for internal operating and emergency procedure development purposes. The airport should collaborate with air carriers operating at the airport and determine which obstacles are used as critical or controlling for the purposes of their individual OEI procedure planning. The discussion should determine what the air carrier would operationally gain (in takeoff weight capacity) by clearing the obstacles to a specific slope and how that need corresponds with the airport runway length and weight-bearing capacity, the passenger or cargo market, and other factors. Such discussions would permit the airport to establish the extent to which the FAR Part 77 PIR 50:1 approach surface is less or more vertically and horizontally restrictive than the air carrier operational OEI surfaces. While the FAA has guidance for OEI planning, the FAA still considers air carrier OEI OIS impacts an economic issue rather than a safety or capacity issue. However, in certain instances, the agency has considered these surfaces on some obstruction evaluations due to the airport making a strong case for the surface protection and justifying it with the anticipated degradation of runway capacity. 3.8 Summary The multiple sets of regulations and criteria that affect the design and structure of air- port and en route airspace are complex. The role of various stakeholders in monitoring and managing obstructions affecting various criteria, as well as the effect that impacts on criteria have on airport operations, often are confusing. Table 3.6 presents all the surfaces discussed in Chapter 3, the effect of impacts on those surfaces and who is responsible for monitoring the surfaces and managing impacts to them.