The Slam Dunk

 

If you’ve done much flying into busier airports—and even some not so busy but with defined arrival and departure procedures—you know all about the dreaded “Slam Dunk.”  The Slam Dunk happens when you are held much higher close in to the airport than you’d like to be, and then are finally given a descent to the altitude you wanted, only now with an airport right underneath for a visual approach, or with the localizer right in front of you and the glide slope underneath you.  Why do they have to make this so hard?

The most common assumption is that it is for noise abatement: trying to appease all those people on the ground who knew they were buying a house next to a busy airport and then complained about all the noise.  So we get The Slam Dunk.

Noise abatement is a factor, but it isn’t a big one.  The real reason is air traffic control.  Let’s take a look at that.

Separating arrivals and departures at airports that aren’t very busy isn’t hard.  There seldom are more than one or two aircraft in the local area and they are coming and going in different directions, so separation can be as simple as assigning vectors to keep them apart, maybe holding one at one altitude while the other climbs or descends through it, or a speed adjustment—something simple that doesn’t affect the descent profile substantially.  A lot of that is done at busy airports too, to get everyone in line and sequenced properly.  But it isn’t enough.  Standard departure and arrival patterns have to be created to organize and simply the controllers duties, and one of the most important component of those procedures is to hold departures down to one altitude until they have gotten some distance from the airport, and to keep arrivals above that altitude until they’ve gotten to the point where they are past the traffic departing.  Once the departure is out past the arrival, he is allowed to climb and the arrival (finally) is allowed to descend.  Otherwise you’d have traffic climbing and descending right into each other.  In order to not hold the departure down any longer than necessary, they keep the arrivals above the departures until that point where the arrival has just enough airspace to get on down.  That’s The Slam Dunk.

Now you could say, “’Just enough’ according to whom?” According to Airways Standards personnel who don’t have to actually fly them in real world conditions? According to standards for turbine powered aircraft, disregarding the concerns of recip pilots who don’t want to shock cool their engines?  Both good points, but the situation isn’t so bad if: 1, You know The Slam Dunk is coming and you don’t try to fight it but are ready for it; and 2, You know you have tools available and are ready to use them, all of them, as necessary.  So let’s go over that.

The first point is the easy one.  There isn’t any point in requesting lower over and over in this situation.  Unless you have an emergency, or are arriving late at night with only a few freight dogs around, it just isn’t going to happen.  All you’re doing is wasting time that could be spent getting ready for the descent when it does come.  So that leaves the tools.  Let’ talk about engine shock cooling.  Mike Busch, who writes a maintenance column for the EAA magazine “Sport Flying”, and who runs a business managing maintenance for GA pilots, someone I respect very much, says there is no hard evidence that rapid engine cooling damages engines, but plenty of evidence that hot cylinder head temps does.  Of course, it’s still better to manage engine temps and not subject them to rapid changes, but pulling an engine that has been coasting along at 50% power or so back to idle is probably not going to do a lot of harm.  So if that’s what it takes, that’s one tool.

But remember, you don’t have to come all the way back to idle every time.  A recip at idle creates a lot of drag.  At idle the propeller has changed from pulling the aircraft to turning the engine, pumping a lot of air and overcoming a lot of internal drag, while a turbine at idle is still generating thrust. (For turbine aircraft, their ace in the hole is speed brakes, and not being able to generate drag with the engines is why they have them.)  You can duplicate that by bringing power back to whatever power setting equates to zero thrust. (Listen for it—the sound changes as the engine starts to “back pedal”.) That’s a good place to start and won’t shock cool the engine as much as coming all the way back to idle does.

The other tools are pretty obvious: gear and flaps.  Gear should probably go out first—it creates a lot of drag and has to go down sooner or later—flaps next.  Flaps don’t add much drag until you get down to landing flaps, but you can start with the first notch of flaps once the speed is below the flap extended limit.  So now you have power at zero thrust, gear down, approach flaps.  In many cases that will be enough.  If not, reduce the power to idle and when slow enough go to full flaps.  If you know The Slam Dunk is coming and you start aggressively configuring drag the second you get your descent clearance, it should work out just about right, with a level off just before localizer intercept and underneath the glide slope.  Acting immediately and aggressively, throwing everything at it if you have to—power to idle, full flaps—is the key.

Once you understand that Slam Dunks are not some evil joke that controllers like to pull on pilots just because they can, but are an inevitable part of air traffic control at airports with more than local traffic, you’re well on your way to dealing with them.  And it feels pretty good when you know what to do, are ready for it, and it all works out, sitting on the porch with the big dogs, and looking pretty good doing it.