12.1 Obstacle Departure Procedures (ODP) & Standard Instrument Departures (SID)

Obstacle Departure Procedures (ODP) & Standard Instrument Departures (SID)

Quick Answer: Standard TERPS instrument departure design criteria require crossing the Departure End of Runway (DER) at >= 35 ft AGL, climbing straight ahead to 400 ft AGL before turning, and maintaining a minimum climb gradient of 200 ft/NM (approx 3.3%). The 40:1 Obstacle Identification Surface (OIS) rises at 152 ft/NM, leaving 48 ft/NM Required Obstacle Clearance (ROC). Obstacle Departure Procedures (ODPs) are designed strictly for obstacle clearance and can be flown by Part 91 pilots without explicit ATC clearance unless an alternative departure is assigned. Standard Instrument Departures (SIDs) are designed for ATC traffic management and pilot workload reduction, requiring an explicit ATC clearance and published chart/text in hand (or "NO SID" in flight plan remarks). Climb rate is calculated as: $\text{FPM} = (\text{Groundspeed} \div 60) \times \text{Climb Gradient (ft/NM)}$.

Departing an airport under Instrument Flight Rules (IFR) in Instrument Meteorological Conditions (IMC) represents one of the most critical phases of flight. Between liftoff and reaching the Minimum En Route Altitude (MEA) or Minimum Vectoring Altitude (MVA), an aircraft operates close to terrain and obstacles while accelerating, configuring, and navigating in zero-visibility conditions.

To ensure positive terrain separation during this transition, the Federal Aviation Administration (FAA) establishes rigorous criteria under United States Standard for Terminal Instrument Procedures (TERPS) (FAA Order 8260.3) and publishes two primary types of instrument departure procedures: Obstacle Departure Procedures (ODP) and Standard Instrument Departures (SID).

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TERPS Departure Design Criteria & Obstacle Clearance Standards

Every published instrument runway in the United States undergoes an extensive obstacle clearance assessment by FAA procedure designers. The design criteria rest on specific geometric and performance baselines:

+-----------------------------------------------------------------------------------------+
|                        TERPS INSTRUMENT DEPARTURE DESIGN BASELINE                       |
|                                                                                         |
|                      Standard Climb Gradient: 200 ft/NM (approx 3.3% / 30:1)            |
|                     ▲ -------------------------------------------------------------     |
|                    /|                                                                   |
|                   / | ◄--- Required Obstacle Clearance (ROC): 48 ft/NM (24% of gradient)|
|                  /  |                                                                   |
|                 /   ▼                                                                   |
|                / 40:1 Obstacle Identification Surface (OIS) = 152 ft/NM                 |
|               /                                                                         |
|              / ◄--- Turn permitted ONLY after reaching 400 ft AGL                       |
|  [35 ft]    /                                                                           |
|     ▲      /                                                                            |
|  ---|-----/-----------------------------------------------------------------------      |
|   Runway Surface           | Departure End of Runway (DER)                              |
+-----------------------------------------------------------------------------------------+

1. Crossing Departure End of Runway (DER) at >= 35 Feet AGL

• Unless otherwise specified, the procedure assumes the aircraft crosses the departure end of the runway (DER) at an altitude of at least 35 feet Above Ground Level (AGL).
• On certain military procedures or specialized civil runways, this crossing height may be designated as 0 feet AGL (screen height at the runway threshold), but the standard civil baseline is 35 feet.

2. Climbing Straight Ahead to 400 Feet AGL Before Turning

• The aircraft must climb straight ahead on runway heading to at least 400 feet AGL before initiating any turn.
• This allows the aircraft to gain sufficient vertical buffer and lateral stability before introducing bank angles, which decrease the vertical component of lift and increase stall speed.

3. The 40:1 Obstacle Identification Surface (OIS)

• Procedure designers evaluate obstacle hazards using an imaginary inclined plane termed the 40:1 Obstacle Identification Surface (OIS).
• A 40:1 slope means the surface rises 1 foot vertically for every 40 feet horizontally. In aviation units ($1\text{ NM} = 6,076.1\text{ ft}$):

$\text{OIS Slope} = \frac{6,076.1\text{ ft}}{40} \approx 152\text{ ft/NM}$

• The 40:1 OIS begins at the DER at an elevation of 35 feet AGL and extends outward along the departure track.

4. Standard Climb Gradient and Required Obstacle Clearance (ROC)

• The standard minimum climb gradient required for all IFR departures is 200 feet per nautical mile (ft/NM) (a 30:1 slope or approximately 3.28% / 3.3% grade).
• The difference between the 200 ft/NM standard climb gradient and the 152 ft/NM 40:1 OIS provides a safety buffer known as Required Obstacle Clearance (ROC):

$\text{ROC} = 200\text{ ft/NM} - 152\text{ ft/NM} = 48\text{ ft/NM}$

• Under TERPS, ROC equals 24% of the total climb gradient ($0.24 \times 200\text{ ft/NM} = 48\text{ ft/NM}$). The remaining 76% ($152\text{ ft/NM}$) accounts for the obstacle surface.

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Diverse Departures & Obstacle Penetrations

When procedure designers survey an airport, they assess whether any natural terrain or man-made structures penetrate the 40:1 OIS:

+-----------------------------------------------------------------------------------------+
|                         IFR DEPARTURE ASSESSMENT FLOWCHART                              |
|                                                                                         |
|                    Does any obstacle penetrate the 40:1 OIS?                            |
|                                  │                                                      |
|                 ┌────────────────┴────────────────┐                                     |
|                 ▼ NO                              ▼ YES                                 |
|        [ DIVERSE DEPARTURE ]            [ OBSTACLE MITIGATION REQUIRED ]                |
|       • Turn any direction             • Non-Standard Takeoff Minimums                  |
|       • Climb 200 ft/NM to MEA/MVA     • Non-Standard Climb Gradient (>200 ft/NM)       |
|       • Climb to 400 ft AGL first      • Obstacle Departure Procedure (ODP)             |
|                                        • Visual Climb Over Airport (VCOA)               |
+-----------------------------------------------------------------------------------------+

Diverse Departure (No Obstacles Penetrate OIS)

• If no obstacles penetrate the 40:1 OIS within 25 NM (flat terrain) or 46 NM (designated mountainous areas), the airport qualifies for a Diverse Departure.
• An IFR aircraft can depart on any heading after crossing the DER at 35 ft AGL, climbing to 400 ft AGL on runway heading, and climbing at a standard gradient of 200 ft/NM until reaching the minimum IFR altitude (MIA/MEA/MVA).

Non-Standard Takeoff Minimums and Higher Climb Gradients

• If obstacles penetrate the 40:1 OIS, the FAA must publish one or more mitigating procedures:
  1. Non-Standard Takeoff Minimums: Higher ceiling and visibility requirements (e.g., "Standard with minimum climb of 320 ft/NM to 4,500 ft, or 1200-2 for VCOA").
  2. Non-Standard Climb Gradient: A required climb gradient exceeding 200 ft/NM up to a specified altitude where the obstacle is cleared (e.g., "Climb of 380 ft/NM to 6,200 ft").
  3. Specific Routing / Ground Track: Requiring the aircraft to fly a specific heading or radial away from terrain.

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Obstacle Departure Procedures (ODP): Safety of Flight

An Obstacle Departure Procedure (ODP) is an instrument departure procedure designed solely to provide obstacle clearance from the terminal area to the en route structure.

+-----------------------------------------------------------------------------------------+
|                     OBSTACLE DEPARTURE PROCEDURES (ODP) AT A GLANCE                     |
|                                                                                         |
|  • Primary Purpose: OBSTACLE CLEARANCE ONLY (Safety of Flight).                         |
|  • Publication Formats:                                                                 |
|    - Textual: Found under 'IFR Takeoff Minimums and Departure Procedures' (Trouble T).  |
|    - Graphical: Charted pictorially with '(OBSTACLE)' in the title.                     |
|  • ATC Clearance: NOT required for Part 91 operators unless an alternative clearance   |
|    (e.g., radar vectors or a SID) is assigned.                                          |
|  • Regulatory Mandate: Mandatory for 14 CFR Part 121/135; highly recommended for Pt 91. |
+-----------------------------------------------------------------------------------------+

The "Trouble T" Symbol

• On FAA instrument approach charts and terminal publications, an inverted black triangle containing the letter "T" (known as the Trouble T symbol $\mathbf{T}$) in the notes section signifies that non-standard IFR takeoff minimums and/or published departure procedures (ODPs) exist for that airport.
• Pilots must consult the "IFR Takeoff Minimums and (Obstacle) Departure Procedures" section in the front of the Terminal Procedures Publication (TPP) for specific instructions.

Textual vs. Graphical ODPs

• Textual ODPs: Described in written paragraph form (e.g., "Rwy 16: Climbing left turn heading 040° to intercept OAK VOR R-120 to 4000 before proceeding on course...").
• Graphical ODPs: Charted as a full pictorial diagram. To distinguish a graphical ODP from a SID, the FAA includes the word "(OBSTACLE)" in the procedure title (e.g., RENO TWO DEPARTURE (OBSTACLE)).

ATC Clearance & Regulatory Status

• Part 91 Operators: 14 CFR Part 91 does not establish legal takeoff minimums for non-commercial general aviation flights ($0/0$ visibility is legally permitted, though perilous). Furthermore, a Part 91 pilot does not require a specific ATC clearance to fly a published ODP from an uncontrolled airport or when cleared as filed, unless ATC assigns a different departure instruction (such as radar vectors or a SID).
• Best Practice: If flying an ODP at a towered airport or when talking to ATC, the pilot should inform ATC: "Departing via the published ODP."
• Part 121/135 Operators: Compliance with published takeoff minimums and ODPs is mandatory by regulation.

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Standard Instrument Departures (SID): ATC Flow & System Efficiency

A Standard Instrument Departure (SID) is an Air Traffic Control (ATC) procedure designed to expedite traffic flow, reduce pilot-controller communication workload, and provide separation between departing and arriving aircraft in high-density airspace.

+-----------------------------------------------------------------------------------------+
|                    ODP vs. SID COMPARISON MATRIX                                        |
|                                                                                         |
|  Characteristic       | Obstacle Departure Procedure (ODP) | Standard Instrument Dep (SID)|
|  -------------------- | ---------------------------------- | ---------------------------  |
|  Primary Purpose      | Obstacle & Terrain Clearance       | ATC Traffic Flow & Efficiency |
|  Design Authority     | TERPS Obstacle Evaluation          | ATC / Airspace Management    |
|  ATC Clearance Req.?  | NO (Part 91 may fly autonomously)  | YES (Mandatory ATC clearance)|
|  Format               | Textual or Graphical               | Always Graphical (with text) |
|  Procedure Title      | Includes '(OBSTACLE)' if graphical  | e.g., CHATY TWO DEPARTURE    |
|  Filing 'NO SID'?     | N/A (Cannot file 'NO ODP')          | Allowed in flight plan remarks|
|  Obstacle Clearance   | Always guarantees obstacle buffer  | Guarantees obstacle + ATC req|
+-----------------------------------------------------------------------------------------+

Types of SIDs: Pilot Navigation vs. Vector SIDs

1. Pilot Navigation SIDs (Pilot NAV): The chart provides full lateral and vertical navigation guidance (radials, bearings, or RNAV waypoints) allowing the pilot to navigate independently along the departure route from DER to the en route transition fix.
2. Vector SIDs (Radar SIDs): ATC provides initial takeoff runway headings or magnetic turns, followed by radar vectors to join an en route airway. Obstacle clearance along radar vector tracks is monitored by ATC radar controllers.

Clearance & Documentation Requirements

• Mandatory ATC Clearance: An aircraft cannot fly a SID without an explicit ATC clearance (e.g., "Cleared to Chicago O'Hare via the DEEZZ FIVE DEPARTURE, ELX TRANSITION, then as filed...").
• Possession Requirement: The pilot in command must possess at least the textual description or graphic chart of the approved SID to accept it.
• Filing "NO SID": If a pilot does not have the charted SID, lacks aircraft equipment capability (e.g., RNAV 1 certification), or simply does not wish to accept a SID, they must enter "NO SID" in the Remarks section (Item 18 or Field 11) of the IFR flight plan.

"Climb Via" vs. Conventional Altitude Clearances

• "Climb Via [SID Name] Departure": Authorizes the pilot to navigate laterally along the SID and vertically climb, complying with all published altitude and speed constraints at every charted waypoint up to the published top altitude of the SID.
• "Climb and Maintain [Altitude]": Clears the pilot directly to the assigned altitude, overriding published altitude constraints on the SID (unless ATC specifically adds "comply with restrictions"). However, published speed restrictions remain mandatory unless explicitly canceled by ATC ("Delete speed restrictions").

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Diverse Vector Areas (DVA) & Visual Climb Over Airport (VCOA)

In addition to standard ODPs and SIDs, two specialized departure procedures exist in the National Airspace System:

1. Diverse Vector Area (DVA)

• A Diverse Vector Area (DVA) is a designated volume of terminal airspace where ATC radar controllers may assign radar vectors to IFR aircraft immediately upon departure below the Minimum Vectoring Altitude (MVA) or Minimum IFR Altitude (MIA).
• Procedure designers survey the entire DVA to guarantee that assigned radar vectors provide the required 48 ft/NM obstacle clearance over all obstacles in that sector without requiring a published ODP routing.

2. Visual Climb Over Airport (VCOA)

• A Visual Climb Over Airport (VCOA) is an alternative departure option designed for multi-engine or single-engine aircraft unable to meet required steep climb gradients under IMC.
• Procedure: The pilot remains in visual meteorological conditions (VMC) and executes a visual climbing spiral over the airport to reach a specified safe altitude before proceeding on course on the IFR flight plan.
• Published Format: Published in the TPP notes under Takeoff Minimums (e.g., "Rwy 22: For climb in visual conditions, obtain ATC approval when requesting IFR clearance. Climb in visual conditions to cross Lake Tahoe Airport at or above 8,500 ft MSL before proceeding on course.").
• Weather Minimums: Requires specific published ceiling and visibility minimums (e.g., 2,500 ft ceiling and 3 SM visibility).

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Climb Gradient Calculations & Conversions

Instrument departure charts publish climb requirements in feet per nautical mile (ft/NM) (a measure of climb angle over ground distance). However, aircraft cockpits are equipped with vertical speed indicators (VSI) calibrated in feet per minute (FPM) (a rate of climb over time).

+-----------------------------------------------------------------------------------------+
|                        CLIMB GRADIENT CONVERSION FORMULA                                |
|                                                                                         |
|                       Groundspeed (knots)                                               |
|       Climb Rate (FPM) = -------------------  x  Climb Gradient (ft/NM)                 |
|                                60                                                       |
|                                                                                         |
|       Example: 360 ft/NM required climb gradient at 120 knots groundspeed:              |
|                FPM = (120 / 60) x 360 = 2 x 360 = 720 FPM                               |
+-----------------------------------------------------------------------------------------+

Mathematical Derivation

Since $1\text{ hour} = 60\text{ minutes}$, an aircraft traveling at a groundspeed ($GS$) of $V\text{ knots}$ covers $\frac{V}{60}$ nautical miles per minute. Multiplying ground distance per minute by feet climbed per nautical mile gives vertical speed in feet per minute:

$\text{Climb Rate (FPM)} = \left(\frac{GS}{60}\right) \times \text{Climb Gradient (ft/NM)}$

$\text{Alternative Fast Rule:} \quad \text{FPM} = GS \times \left(\frac{\text{Gradient}}{60}\right)$

Worked Calculation Examples

Example 1: Standard 200 ft/NM Gradient

• Aircraft Groundspeed: $90\text{ knots}$
• Required Gradient: $200\text{ ft/NM}$ $\text{FPM} = \left(\frac{90}{60}\right) \times 200 = 1.5 \times 200 = 300\text{ FPM}$

Example 2: Steep Mountainous ODP (420 ft/NM)

• Aircraft Groundspeed: $150\text{ knots}$
• Required Gradient: $420\text{ ft/NM}$ $\text{FPM} = \left(\frac{150}{60}\right) \times 420 = 2.5 \times 420 = 1,050\text{ FPM}$

Comprehensive Groundspeed vs. Climb Gradient Conversion Matrix

The Wind Effect on Required Climb Rate

• Climb gradient is relative to ground distance, not airspeed.
• A headwind decreases groundspeed, requiring a lower vertical climb rate (FPM) to achieve the same ft/NM gradient.
• A tailwind increases groundspeed, requiring a significantly higher vertical climb rate (FPM) to clear the same obstacle profile. Always calculate climb rate based on expected groundspeed!