Getting Down From On High

Being in Washington's sensitive airspace, I assumed the approach controller had his reasons for hanging me high like that; and as it was a warm summer day, I wasn't excessively concerned about shock-cooling. But there have been several other times I've had to prompt a controller to grant his blessing to start my descent. Vertical navigation in the IFR environment is a bit of a touchy issue; but there are some guidelines.

Now, I have my GPS navigator set with one of the data windows showing 'vertical speed to target.' If it starts showing more than 700 feet per minute, I consider speaking up. Before I had this nifty data block available as part of my scan, I would perform a rough calculation of how many miles I needed at my groundspeed to bleed off altitude at 500 feet per minute. At 120 knots (two miles per minute) I needed four miles to lose 1,000 feet. At 180 knots it would be six miles per 1,000 feet. One hundred-fifty knots would split the difference -- five miles per 1,000 feet. In my VFR days, I could even roughly figure those out with a sectional chart using landmarks.

If you are starting to get antsy about whether ATC has forgotten that you need to return to Mother Earth sometime that day, you can add a postscript, "Looking for lower," to the end of one of your routine transmissions. If they seem to have forgotten you -- perhaps due to lots of other chatter -- you can find a break and ask. Frequently, if there is a good reason for keeping you where you are, they will give you a quick explanation that can help you anticipate when and where you'll be able to pull the plug.