On Instruments: Launch rules

Look at the flip side of a Jeppesen 11-1 approach plate, or the “Takeoff Minimums and (Obstacle) Departure Procedures” entry for government-issued terminal instrument procedures, and there you’ll find them. Some use text descriptions, and some post graphical depictions to help us understand the courses, fixes, and altitude restrictions for a departure procedure (DP), standard instrument departure (SID), or an obstacle departure procedure (ODP). These procedures often are specific to certain runways, and they may include climb-gradient performance requirements.

The standard climb-gradient requirement is 200 feet per nautical mile after crossing the departure end of the runway (DER) at a height of 35 feet agl. After that, climb gradients can increase if terrain or obstacles are factors surrounding, or within, the designated departure-path surface. The typical objective is to provide at least 48 feet per nautical mile of clearance above what’s known as the obstacle clearance surface (OCS), an imaginary surface that rises at a 40:1 ratio—this equates to a slope rising at a rate of 152 feet per nm. Again, if high terrain or obstacles are factors, then the OCS can rise more steeply.

To find out if your airplane can manage a published minimum climb gradient, check out a rate of climb table. There, you’ll see the climb-gradient rate plotted against groundspeed. For the airplanes most of us fly, for example, you’ll see that at a climb groundspeed of 90 knots, you’ll need to climb at 300 fpm to meet a 200-foot-per-nm climb-gradient requirement. Ordinarily, that’s no problem for most of the piston singles and light twins we fly. Maybe that’s why departure procedures don’t get heavy emphasis in instrument training.

What if the government’s surveyors determine that obstacles do enter the 40:1 OCS? That’s when an obstacle departure procedure is published. Be advised that required climb gradients may be higher than standard. ATC will clear you for an ODP only if traffic is a factor; otherwise, pilots operating under FAR Part 91 can fly an ODP at their discretion—even if the weather is below visual flight rules minimums. Even so, it’s a good idea to put “departing via ODP” in the remarks section of your flight plan, for ATC’s information.

There’s yet another option that many may not know exists. It’s the visual climb over airport (VCOA) technique. Simply climb in visual conditions, remaining over the departure airport until reaching a safe altitude, before departing on the flight’s en route segment.But beware: ODPs can be complicated, and they have many turns, fixes, and altitude restrictions. They are riskier than your run-of-the-mill DPs—because terrain and obstacles are closer to the airport. They can be harder to find, too, and not many are published as graphical charts.

Now let’s say that you’re at a high-elevation airport, temperatures are toasty, and you’ve consulted the rate-of-climb table. A check of the performance section in your pilot’s operating handbook reveals there’s no way you can meet climb-gradient requirements. What can you do? Refuse the departure clearance, that’s what! Wait until temperatures drop, lighten your load, or both.

There’s yet another option that many may not know exists. It’s the visual climb over airport (VCOA) technique. Simply climb in visual conditions, remaining over the departure airport until reaching a safe altitude, before departing on the flight’s en route segment.

VCOAs are intended for use at airports where no SID, DP, or even ODP could ever meet standard criteria. If an obstacle more than three statute miles from the DER requires more than a 200-foot-per-nm climb gradient, then it’s a candidate for a VCOA. Again, look in the takeoff minimums and departures section of your terminal instrument procedures for a departure procedure mentioning a “climb in visual conditions” for details.

A VCOA removes the extra layer of hairiness that instrument conditions impose on other departure procedures, but risks still abound. After all, it wouldn’t be published unless there was some pretty impressive, close-in scenery surrounding the airport.

Before we depart this subject (intentional pun), it’s worth a final reminder for pilots of twin-engine airplanes, including turboprops and jets. The mandatory, minimum climb gradients we’ve been discussing assume that both engines are operating. With one engine inoperative, it’s doubtful that some underpowered piston twins could meet that 200-foot-per-nm target—especially if conditions are hot, high, and heavy.

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