Getting Down From On High

Anticipating your descent profile makes for a more comfortable transition.

Approach Control had vectored me onto what seemed like a wide downwind leg to Washington Dulles International. My problem was he still had me at 5,000 feet. When I was abeam the numbers, waiting for an answer to the mystery, he turned me over to the tower controller who said, "cleared to land." I replied, "That's a long way down;" to which he responded, "Roger." Since I wasn't flying a Stuka dive bomber at the time, it took gear extension, full flaps and an extra long downwind leg to get me down in the same time zone as the airport.

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.