SBO (Selection of Bypassing Obstacle) in Aviation Operations

Definition and Scope

Selection of Bypassing Obstacle (SBO) in aviation is the comprehensive, methodical process that ensures aircraft maintain safe separation from obstacles during all critical phases of flight. SBO includes identifying, assessing, and integrating obstacle clearance strategies. It is grounded in international and national regulatory frameworks (like those from the FAA and ICAO) and technical standards. SBO’s primary objective is to guarantee that, regardless of the operational scenario—including engine-out or abnormal conditions—flightpaths are planned and managed to maintain required obstacle clearance margins, thereby protecting both aircraft and occupants.

The SBO process starts as early as the airport planning phase and extends through takeoff, climb, en route, approach, missed approach, and even emergency procedures such as rejected takeoffs or landings. SBO is vital in both instrument and visual flight conditions, but its criticality is heightened in low-visibility, non-standard, or degraded performance situations. While regulatory bodies define minimum standards, many operators and airports implement additional safeguards and analyses for enhanced safety.

SBO’s effectiveness depends on integrating authoritative data sources, advanced analytical methods (area-based and track-based), and a thorough understanding of aircraft performance, airspace structure, and regulatory requirements. SBO is continuously updated and validated as new obstacles are identified or as operational and regulatory requirements change. It is also a vital part of safety management systems, flight crew training, and airport operational planning.

Regulatory Foundation

FAA Regulations

In the United States, SBO is regulated primarily under 14 CFR Parts 121 and 135, which define operational standards for scheduled air carriers and commuter/on-demand operations. For example:

• 14 CFR Part 121.189: Requires aircraft to be able to clear all obstacles by a minimum of 35 feet along the net takeoff flightpath in the event of an engine failure.
• Part 121.177, 135.367, 135.379, 135.398: Outline additional performance and obstacle clearance criteria for various operational situations, including OEI (one-engine inoperative) scenarios.

FAA Advisory Circular 120-91A is the principal guidance document for airport obstacle analysis, outlining acceptable compliance methods, detailed methodologies for area and track-based analyses, and requirements for engine-out procedures (EOPs).

Instrument procedure design (for departures and approaches) falls under FAA Order 8260.3 (TERPS), which defines obstacle clearance surfaces and flightpath protection under all engines operating assumptions. 14 CFR Part 97 governs the notification and approval of instrument procedures, incorporating obstacle clearance requirements.

ICAO Standards

Internationally, SBO is governed by ICAO standards, especially:

• Annex 6, Part I: Sets operational requirements for aircraft, including mandatory obstacle clearance margins and performance criteria for normal and abnormal operations.
• ICAO PANS-OPS (Doc 8168): Provides global criteria for the design of instrument flight procedures, including obstacle assessment, protected airspace definition, and calculation of minimum obstacle clearance (MOC) values.

ICAO standards typically harmonize with national regulations but may differ in technical details (e.g., OAA width, lateral splay, use of PBN). ICAO also emphasizes risk management, data quality, and coordination among airport operators, ANSPs, and regulators.

Related Regulatory Documents

Other important references include:

• NBAA Airport Runway Obstacle Analysis Guide: Industry best practices for integrating SBO in Part 135 and business aviation.
• ACRP Report 195 – Best Practices for Airport Obstruction Management: Comprehensive methodologies for obstacle identification, assessment, mitigation, and documentation.
• FAA InFo 23009 and Federal Register notices on SIAPs**: Contextualizing SBO within broader regulatory and procedural frameworks.

Core Concepts and Terminology

Obstacle

An obstacle is any object—natural or man-made—that extends above a defined surface intended to protect aircraft in flight or on the ground. This includes:

• Terrain (mountains, hills, cliffs)
• Permanent structures (buildings, towers, antennas)
• Temporary objects (cranes, vehicles)
• Vegetation (trees, brush)

Obstacles are cataloged by location, elevation (AGL or MSL), and their relationship to protected airspace surfaces. Their identification triggers SBO methodologies to ensure clearance or safe rerouting.

Obstacle Clearance

Obstacle clearance is the minimum vertical and/or lateral distance required between an aircraft and an identified obstacle. It is defined by:

• Vertical clearance: Usually at least 35 feet above any obstacle for OEI takeoff scenarios (per 14 CFR 121.189, ICAO Annex 6, PANS-OPS).
• Lateral clearance: Defined by the OAA or protected airspace corridor, which varies depending on analysis method, aircraft performance, and available navigation.

Clearance calculations consider aircraft performance (climb, turn radius), navigation accuracy, and environmental factors (wind, temperature).

Obstacle Accountability Area (OAA)

The Obstacle Accountability Area (OAA) is a geographic zone surrounding the intended flightpath within which all obstacles must be identified and assessed. OAA width is defined by:

• Regulatory standards (FAA: typically 200 ft each side on the airport, 300 ft or more outside)
• Maximums (FAA: up to 2000 ft, ICAO: up to 3000 ft depending on procedure and navigation)

OAA dimensions may be tailored for specific procedures, aircraft performance, and navigation precision.

Engine-Out Procedures (EOP)

EOPs are departure procedures designed to ensure that, in the event of an engine failure during takeoff or initial climb, the aircraft can continue flight and maintain obstacle clearance. Key features:

• Tailored to aircraft and airport
• Developed by operator, accepted by regulators
• Not designed using TERPS, but must provide an equivalent level of safety
• Documented in operational manuals, reviewed and validated regularly

One-Engine Inoperative (OEI)

OEI refers to flight with one engine inoperative in a multi-engine aircraft. It is a critical scenario for obstacle clearance due to reduced climb and maneuvering capability. SBO for OEI includes:

• Net takeoff flightpath analysis
• Degraded performance (climb gradient, turn radius)
• Aircraft-specific data, environmental conditions
• Integration in EOPs, manuals, and crew training

Runway Obstacle Analysis

A systematic evaluation of all obstacles near a runway and its flightpaths to determine:

• Maximum allowable takeoff/landing weights
• Safe operational configurations
• Escape procedures (normal and abnormal scenarios)

Uses data from FAA DOF, airport records, charts, and surveys. Results are documented and reviewed regularly.

SBO Process and Methodology

Data Sources for Obstacle Identification

Reliable SBO depends on accurate, current obstacle data from:

• FAA Form 5010 (Airport Master Record)
• Digital Obstacle File (DOF) and Digital Vertical Obstacle File (DVOF)
• Aeronautical charts (Jeppesen, Lido, etc.)
• National Flight Data Digest (NFDD)
• NOTAMs for temporary/new obstacles
• USGS terrain data
• Aeronautical Information Publications (AIP)
• Area Navigation Approach Surveys (ANA)
• National Geodetic Survey (NGS)
• Local surveys and GIS data

Data validation protocols include field surveys, reconciliations, and proactive engagement with local stakeholders.

Analysis Methods

1. Area Analysis Method

Defines a standard OAA around the flightpath for obstacle collection and clearance assessment. OAA width is:

• 200 ft each side of centerline (within airport)
• 300 ft or more outside airport
• Up to 2000–3000 ft maximum

All obstacles within the OAA are analyzed; the most limiting obstacle governs procedural requirements.

2. Flight Track Analysis Method

Focuses on the intended ground track, considering navigation accuracy and guidance system reliability. Lateral course allowances depend on navigation aid:

• Localizer: ±1.25°
• VOR: ±3.5°
• ADF: ±5°
• DME: ±0.25 NM minimum

Visual guidance may be used with documented conditions (e.g., daylight, visibility).

Procedural Steps

1. Identify applicable regulations and surfaces
2. Collect and validate obstacle data
3. Define OAA or track corridor
4. Analyze obstacle clearance
5. Develop and document procedures
6. Implement and monitor
7. Review and update regularly

SBO in Flight Procedures

SBO is integral to:

• Standard Instrument Departures (SIDs)
• Obstacle Departure Procedures (ODPs)
• Visual Departure Procedures (VDPs)
• Missed Approach Procedures
• Engine-Out Procedures (EOPs)
• Special departure procedures for challenging airports

Operators must ensure SBO considerations are reflected in flight planning, crew briefing, and operational manuals.

Challenges and Trends

Challenges

• Rapidly changing obstacle environments (construction, vegetation)
• Data quality and validation
• Integration of diverse data sources
• Balancing operational flexibility with safety
• Crew training and procedural adherence

Trends

• Increased use of digital terrain and obstacle databases
• Integration of SBO in advanced flight planning and EFB apps
• Use of GIS and high-resolution LIDAR for real-time updates
• Performance-based navigation (PBN) enabling narrower OAAs
• Proactive airport and operator collaboration for obstacle management

SBO and Safety Management

SBO is a core component of Safety Management Systems (SMS) for airlines and airports. It supports:

• Proactive risk identification and mitigation
• Regulatory compliance
• Incident and accident prevention
• Continuous improvement through review and feedback

Conclusion

Selection of Bypassing Obstacle (SBO) is a cornerstone of modern aviation safety and operational efficiency. By integrating regulatory standards, advanced data analytics, and rigorous procedural controls, SBO ensures that aircraft can safely navigate complex obstacle environments under both normal and abnormal conditions. Its effectiveness relies on accurate data, robust analysis, and a culture of continuous review and improvement.

Further Reading and Resources

• FAA Advisory Circular 120-91A (Airport Obstacle Analysis)
• ICAO Doc 8168 PANS-OPS
• NBAA Airport Runway Analysis Guide
• FAA Digital Obstacle File (DOF)
• ACRP Report 195 – Best Practices for Airport Obstruction Management

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Frequently Asked Questions

What is SBO in aviation?
SBO (Selection of Bypassing Obstacle) is the process of ensuring safe aircraft separation from obstacles during all phases of flight by systematically identifying, assessing, and integrating regulatory and procedural controls.

What does OAA stand for and why is it important?
OAA is the Obstacle Accountability Area—a defined corridor around the flightpath where all obstacles must be identified and assessed for impact on obstacle clearance.

Why are Engine-Out Procedures (EOP) critical?
EOPs ensure that, in case of an engine failure during takeoff or climb, the aircraft can still clear all obstacles safely, complying with regulatory requirements and protecting passengers and crew.

How often should SBO analyses be updated?
SBO analyses should be updated regularly—at least annually or whenever new obstacles are identified, airport infrastructure changes, or regulations are updated.

Where can I find more information on SBO?
Authoritative references include FAA AC 120-91A, ICAO PANS-OPS, NBAA runway analysis guides, and your regulatory authority’s official publications.