Many VFR-only pilots are familiar with how instrument approaches offer the safe paths that take us from the air to the ground. Each approach gets a snazzy chart, rich with black lines, zigging arrows and lots of numbers, and the skill at decoding said charts is a time-honored right of passage into the IFR illuminati.
New IFR students also learn there is departure equivalent from some airports called the Obstacle Departure Procedure (ODP) designed to get them safely around obstacles on their journey from the runway to the sky. ODPs are rarely charted. Instead, they are published in a somewhat cryptic text that requires study and visualization, plus cross-reference to instrument Enroute Charts (the IFR equivalent of the Sectional Chart) to really work out.
It’s like they’re a test: If you can read this and depart without killing yourself, we’ll let you in the IFR club and provide radar services to your destination. If not, well, at least we weeded you out at the beginning of the flight.
What’s confusing to many an IFR inductee is what to do when the airport doesn’t have an ODP. You’re standing on the ramp looking at the low overcast skies and thinking, “I know there’s stuff out there somewhere, yet there’s no procedure to avoid it. Can I just take off and climb without worrying about it?”
Well, almost, but not entirely.
The first question you must ask when departing is whether the airport you’re departing has at least one published instrument approach. If so, the airport has been surveyed for obstacles on departure as well. Unlike an approach where the designers have to find just one viable path to the runway, you could potentially go any direction on departure, so the survey team evaluates a full 360-degree cylinder of space around the airport. If they discover unyielding, aircraft-eating objects, they publish an ODP. If not, the airport qualifies for a diverse departure.
The diverse departure is the default IFR departure procedure. That is, if you haven’t been assigned a departure procedure in your clearance or a departure instruction from ATC, and there’s no ODP published for your airport, and the airport has at least one published instrument approach, then you can take off and climb on course as cleared, provide you meet a few requirements.
The first one is trivial for most aircraft: You must fly runway heading to at least 400 feet AGL and cross the departure end of the runway at least 35 feet AGL. All IFR departures, be they published, diverse or by ATC instruction, begin that way.