The Stabilized Approach

The pilots of a Boeing 737 recently attempted to land on a relatively short runway in Burbank, California, after a high-speed, unstabilized approach. Twenty seconds after touchdown, the baby Boeing punched through a fence and came to rest in a Chevron station off the end of the runway.

The crew's attempt to land in Burbank followed a request by air traffic control to "maintain at or above 3,000 feet until the Burbank VOR," six miles from the airport. By accepting this clearance, the pilots put themselves in a difficult position from which the Boeing would have to be flown steeply to the runway. It might have worked—but only if the airplane was slowed to approach speed early and configured with gear and flaps before reaching the VOR. The captain, who was flying the jet, apparently did not do this and ended up "high and hot" on the approach—touching down some 40 knots above normal landing speed, well past the normal touchdown point of the 6,082-foot runway. At that moment, the crew became the Year 2000 poster pilots for stabilized approaches.

The concept of stabilized approaches was first advocated in turbine aircraft in the late 1950s and early 1960s when pilots learned that their new jet transports were "slipperier," or harder to slow, than the large piston and turboprop aircraft they were used to. The early generation jet engines also didn't respond to power changes as quickly as airplanes with props, and undershoot accidents, where jets land short of the runway, became common.

Later accidents with turbine aircraft showed that we were having trouble with overshoots, or landing long on a runway, often running off the end. These accidents were caused by pilots failing to slow their aircraft to approach speed and configure for landing early enough to land on the runways that they were using.

In response, the airline industry adopted a procedure called the stabilized approach. This means that at some predetermined point on the approach, usually 500 or 1,000 feet agl, the aircraft will be at the correct final approach speed, configured (landing gear down, final flaps), on glide path (or a "normal descent angle for a normal landing"), and spooled (all engines are at the final power setting for landing). Thus, everything is complete. Since instituting the program, undershoot and overshoot accidents have been mostly eliminated—yet a few crews occasionally test the limits by ignoring the stabilized approach procedure. Unfortunately, the 737 crew at Burbank chose to ignore the benefits of the stabilized approach—and paid the price with their careers.

Most of us don't have to worry about the vagaries of turbine aircraft and their response to power and speed changes on approach. But there are plenty of good reasons to fly stabilized approaches regardless of whether you fly a Cessna Skyhawk or Golden Eagle, Beech King Air or Piper Super Cub. Here are a few:

• It reduces workload. How many of us have come screaming onto a final approach course in our Beech Bonanza only to have the controller assign a final intercept and approach clearance while we were still at cruise speed? We don't need controllers' help to screw it up, either; we can do ourselves in by having too much speed when intercepting the inbound ADF approach bearing with the gear tucked neatly into the wells.
• It gives us more opportunity to see the big picture. If you are concentrating mightily on details such as that ILS needle sweeping across the indicator face, you are less likely to see that 172 naively crossing the localizer in front of your nose, for example. Situational awareness improves greatly when we can see the big picture.
• It slows the aircraft down earlier, allowing more time to think. Most of us have a speed at which we can comfortably process information—anything faster and something, possibly something important, will be neglected.
• It allows more time to react. It's much easier to complete checklist items or respond to a minor problem with a landing gear light or circuit breaker at 70 or 80 kt than while flying at 130 or 200 kt.
• It makes it easier to fly the VOR, ILS, or ADF needles. Let's face it, stabilizing and slowing early is better when trying to corral those recalcitrant, wobbly needles.
• It allows the pilot more opportunity to detect changes in the wind on approach. By configuring earlier, we have more time to assess the effect of wind on our aircraft; we are also more likely to catch such things as wind shear or crosswind.
• It reduces the variables and thus reduces our required reactions to these changes. When you have the airspeed nailed early, you have one less variable to worry about, freeing you to focus on other things. If we can set the power and mostly forget it, we don't have to constantly change power in response to our configuration and speed changes.
• It creates the time to finish your before-landing checklist and to really look around the airplane for other things you might have missed or neglected when rushed. We're better prepared for things such as turbulence, which destabilizes the approach, or for wet runways, which increase landing distance.
• It makes the approach—and thus the landing spot—predictable because you do it the same every time.

Notice that time is the major benefit when we fly a stabilized approach. Time allows us to more easily perceive changes and then make corrections to course, altitude, or airplane management.

This doesn't mean we have to fly our Skyhawk at 60 kt from the outer marker to the runway at Atlanta Hartsfield, creating an Excedrin moment for some unlucky Georgia controller; instead, we might consider flying the approach at a comfortable 100 to 110 kt, then slowing to our final approach speed and adding flaps, stabilizing at 500 feet above ground.

To do that, you must first know how long it takes to decelerate your airplane while descending on the glideslope or on a nonprecision approach path. Does it take you two miles? Three? Or can you do it in a mile? What power setting do you use? Some airplanes are harder than others to slow down and configure because of their cleanliness or low gear/flap speeds. You should know how many miles or feet to add to your target stabilized approach point in order to make it work. This is something to practice before trying it live. Note that tailwinds on approach will make it even tougher to make the airplane slow to your flap or gear speed.

Most airlines set the stabilized approach point at 500 feet in visual conditions and 1,000 feet when the weather is IMC. These 500- and 1,000-foot target points might be a good starting place when establishing your own stabilized approach minimums. You might also want to use 1,000 feet for night approaches and landings because the fewer visual cues at night reduce your ability to perceive differences and changes.

If the airplane is not stabilized by those 500- or 1,000-foot marks, many airlines mandate a go-around. Should you fail to stabilize at the required point, the mandatory go-around does two things: It reduces the chance of finding yourself wrestling for gear or flap speed while chasing an ADF or ILS needle, or reading the before-landing checklist as you cross the approach lights. Second, it motivates you to get the airplane stabilized on the second attempt.

When flying some of the simpler airplanes in busy terminal areas, you might want to consider leaving flaps up to allow more compatible speeds for mixing with faster aircraft. Most runways at major airports are five to seven times longer than we really need, and flaps don't do much to decrease stall speed for these airplanes, anyway.

A major contributor to the accident at Burbank was the captain's acceptance of a clearance that increased the crew's workload, and was neither comfortable nor prudent. Don't allow ATC to fly your airplane. If you sense that you will have to increase your workload dramatically or perform magic to fulfill an ATC request (remember they're all requests until you accept them), just say no. This goes especially for those times when ATC asks you to "keep the speed up as long as possible." Translated to wise pilot-speak, this clearance becomes: "Fly the airplane as fast as you can safely and within your limitations, but have it stabilized, on speed, power set, and final flaps and gear at your 500- or 1,000-foot point." Don't bend that rule to make the controller happy. Plan where you will be stabilized and stick to it. Getting creative at the middle marker is not wise.

The key to a stabilized approach is to slow the pace of the critical final segment. If you're doing it right and stabilize early, it seems that there is nothing left to do; time expands as you sit observing the airplane during the final minute to the runway. At this time on the approach you are primarily monitoring, not manipulating, and that is better for situational awareness during the approach.

Remember, if you can't make your stabilized approach goals, go around. Had the 737 crew done that, they would have been at most 10 minutes late, instead of seriously endangering 137 passengers and three other crewmembers.

Michael Maya Charles, AOPA 1082652 , of Erie, Colorado, is an aviation writer and frequent contributor to Pilot .