Departure Procedures: ODPs and SIDs
Key facts on obstacle departure procedures, standard instrument departures, and climb gradient math.
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Questions Covered in This Set
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What is the purpose of an ODP vs. a SID?
ODPs exist solely to provide obstacle/terrain clearance (a pilot tool); SIDs primarily organize traffic for ATC and may also provide obstacle protection.
What two baseline assumptions underlie every instrument departure design?
Crossing the departure end of the runway (DER) at least 35 ft AGL and climbing at least 200 ft/NM to the minimum enroute altitude.
What is the 40:1 obstacle clearance surface?
An imaginary surface sloping up from the DER at about 152 ft/NM; if no obstacle penetrates it, no ODP is needed.
How much obstacle clearance margin does the 200 vs. 152 ft/NM gap give?
About 48 ft per NM flown (roughly 24 ft/NM after the DER) — a thin margin.
What three tools does a TERPS designer use when an obstacle penetrates the 40:1 surface?
(1) Publish a higher climb gradient, (2) publish a routing that avoids the obstacle, or (3) raise takeoff minimums so it can be seen and avoided.
What chart symbol indicates published takeoff minimums and/or an ODP?
An inverted black triangle containing a white T (▼T) on the approach plate/airport diagram.
Formula to convert a charted climb gradient into a VSI rate?
Required FPM = (gradient ft/NM × groundspeed in knots) / 60
Why does groundspeed — not airspeed — drive climb gradient performance?
The requirement is feet per nautical mile over the ground, so a higher groundspeed (e.g., from a tailwind) demands a higher rate of climb in fpm.
Useful sanity baselines for gradient math?
At 60 kt GS, ft/NM = ft/min exactly; at 120 kt you need double the gradient number; 200 ft/NM at 120 kt = 400 fpm.
Are Part 91 pilots required to fly an ODP?
No — 91.175 requires DPs/takeoff minimums only for Part 121/125/129/135, but the FAA strongly recommends them; tell ATC if you'll fly one at a radar/towered field.
Difference between pilot nav and vector SIDs?
Pilot nav SIDs have a charted route and transition you fly yourself (e.g., CHANL3.PMD); vector SIDs give an initial heading and then radar vectors.
How are textual vs. graphic ODPs published?
Textual ODPs appear in the front section of the TPP booklet; graphic ODPs are charted like SIDs with '(OBSTACLE)' in the title.
