Saturday, September 6, 2014

IFR departures - Visual Climb Over Airport?

"For Climb in Visual Conditions...." wait, aren't I IFR?

Ever see these words on an instrument departure procedure and wondered what they mean? There's a little-taught (and probably even lesser flown) type of instrument departure procedure called a VCOA - Visual Climb Over Airport. I know it wasn't covered at all in my instrument training - of course that was in coastal Virginia, so with the terrain being very flat there wasn't much in the way of actual departure procedures to fly anyway.

So what is this? It's an instrument departure, but involves a VISUAL climb to an altitude at which you can then proceed into IMC along your cleared route. Kind of the opposite of a visual approach in that regard, and typically would only be used in an area without radar coverage. When this is an option, you will see it in either the takeoff minimums/textual departure procedure listing at the front of the approach chart book, or in the takeoff minimums section of a graphic obstacle DP, and it looks something like this:


These VCOA procedures are only published when there is an obstacle greater than 3 sm from the airport that causes a required climb gradient of greater than 200 ft per nm to clear. Here's what the FAA's Instrument Procedure Handbook has to say about them (page 1-38):

Visual Climb Over Airport (VCOA)
A visual climb over airport (VCOA) is a departure option for an IFR aircraft, operating in VMC equal to or greater than the specified visibility and ceiling, to visually conduct climbing turns over the airport to the published "climb-to" altitude from which to proceed with the instrument portion of the departure. A VCOA is a departure option developed when obstacles farther than 3 SM from the airport require a CG of more than 200 FPNM.

These procedures are published in the Take-Off Minimums and (Obstacle) Departure Procedures section of the TPP. [Figure 1-36] Prior to departure, pilots are required to notify ATC when executing the VCOA.

Okay, so there's a specified ceiling and visibility requirement for this VCOA. The intent is for the pilot to take off, spiral up over the airport until reaching a certain altitude, and then it's safe to fly the cleared route even if entering IMC at that point, assuming the climb continues to an appropriate altitude in the clearance. In our example from California, you would make gradual, climbing turns up to 8300 MSL (3400 AGL) and then continue climbing on your cleared route.

At first glance, that almost seems a little silly, doesn't it? The required ceiling is 3500 AGL, and that's pretty solid VFR, so why not just depart VFR? However, the threat that the procedure is designed to avoid is really those times when the ceiling is high enough over the airport, but obstacles (like mountaintops) are still obscured by cloud. This is reflected in the design methods for these procedures.

Briefly, a "cylinder" of airspace is evaluated around the airport, with a radius determined by the elevation (higher elevations needing a greater turn radius due to increasing TAS). In our example, the radius used is 3.4 nm (source - FAAO 8260.3B, Vol 4, Chapter 4).

The highest obstacle in this cylinder is used to establish the "climb-to" altitude. If there are other obstacles outside the cylinder, a 40:1 slope is then evaluated to see if it clears the obstacles. If it does not, then the "climb-to" altitude is increased appropriately. Notice that the "climb-to" altitude also provides for a minimum of 250 feet of obstacle clearance, growing as you get further from the cylinder.

A VCOA can also have a "route" attached to it, like at Craig, Colorado (CAG), where you would climb up over the airport then proceed on a radial to the nearby VOR. This departure procedure also incorporates a "normal" departure if you can make the climb gradient (of 510 ft per nm off runway 7!) but the parts we're interested contain the words "for climb in visual conditions".

This is a pretty complicated textual departure procedure, so it definitely takes some review before takeoff! Note that once you get to the VOR, you're not done - you need to follow the "thence ..." instructions in the last paragraph, which can consist of a climb in a holding pattern depending on your route of flight.

Certainly if you need to execute a maneuver like this it's important to inform ATC when you get your clearance so everybody knows what you're doing and there are no surprises. But flying them is admittedly pretty rare, so let me know how it went if you have actually flown one!

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