A Solid Foundation For Landing

Flying A Stabilized Approach

When I was a young boy, I helped my father to build an addition to our house. In reality, I'm sure I was more of a liability than an asset, but I did learn some important lessons. My father was a perfectionist, and everything had to be exactly right, starting with the foundation. The excavation had to be to the proper depth, even if making it a little shallower would have been easier. The foundation had to be precisely level. The studs has to be perfectly vertical, and the corners were checked and rechecked to make certain that they were all square. As my father explained, small errors made along the way added up to major problems later. If the end product was to look good and be safe, we needed to build it right from the foundation up.

Landing an airplane is, in one respect, similar to building an addition to your house. Minor errors are additive, and if we let them accumulate, we will have major problems at the end. Our landing begins well before we flare for touchdown. In fact, the entire approach forms the foundation upon which we frame our landing. If we pay attention to details and fly the approach with precision, the end result will be a prettier, safer landing.

As The Pros Fly

One way to ensure that the foundation for our landing is solid is to fly a stabilized approach to the runway at the proper speed and descent rate. The concept of the stabilized approach has been around for a long time, and it is used extensively by professional pilots. However, a stabilized approach is just as important to the pilot of a single-engine trainer as it is to the captain of a Boeing 747, and the FAA has recently reiterated the importance of the stabilized approach for general aviation pilots.

What Is A Stabilized Approach?

As explained in the FAA Air Transportation Operations Inspector's Handbook, the stabilized approach concept involves maintaining a stable speed, descent rate, vertical flight path, and configuration during the final stages of the landing approach. Doing so makes it easier for us to spot deviations from the desired course and glidepath. It allows us to develop a mental picture of the aircraft's flight path and make the appropriate control inputs to maintain the desired approach path. Perhaps more importantly, the ability to constantly assess the progress of an approach for landing is critical to the decision-making process. This is particularly crucial as we reach a point where the decision to land or go around must be made.

Clear Advantages

A stabilized approach offers numerous advantages. A primary advantage is consistent landing performance. The process of landing involves literally hundreds of variables, and we must quickly assimilate these variables and make the proper control inputs to transition the aircraft from flight to a controlled taxi. If we can limit the number of variables involved in an approach by always using the same airspeed, descent rate, and configuration, the transition (and landing) will go much more smoothly and easily.

Another advantage of the stabilized approach is a more predictable point of touchdown. By flying our properly configured aircraft along a predefined flight path and arriving at the right place at the right airspeed, we consistently touch down on the right spot on the runway, thus minimizing the potential for landing long (see "Beyond the Numbers," p. 46)

The stabilized approach also makes it easier to identify problems as we fly the approach to the runway. By knowing the proper power setting for a no-wind approach, we can more readily recognize a headwind or tailwind on the approach. By flying at the proper airspeed, we can quickly identify the abrupt airspeed changes that signal an encounter with wind shear, and we can make the appropriate control inputs to counter its effects.

The stabilized approach decreases our workload, and that spells an in-creased margin of safety throughout the approach and landing. When the difficulty of flying the approach decreases, our situational awareness increases. We have more time to scan for traffic and identify hazards in the air and on the ground. We're more likely to hear important radio calls that provide critical information, such as traffic calls, wind changes, and other warnings. We're also more likely to anticipate problems, such as terrain-induced turbulence or wind shear, wind shear that is associated with a temperature inversion, or the effects of virga, wake turbulence, or approaching gust fronts.

Finally, the use of a stabilized approach procedure helps to prepare for the transition to instrument flying and to complex and high-performance aircraft. Developing good flying skills, habits, and procedures, such as the use of a stabilized approach procedure, forms not only the foundation for safe landings, but also for a professional career in aviation.

Defining the Parameters

One way of defining the stabilized approach procedure is in terms of a flight profile. This is how airlines teach their pilots the parameters and procedures for making stabilized approaches. The profile tells the pilot when to complete checklists and identifies the specific key locations to make aircraft configuration changes. The profile also spells out the power settings and airspeeds to be used throughout each phase of the approach.

Approach profiles can also be developed for small general aviation aircraft, and doing so provides an effective tool for mastering stabilized approaches. A typical approach profile for a Piper Archer might resemble Figure 1. The profile identifies the configurations used in the approach and target airspeeds and specifies the key points where configuration changes are made.

In this example, the transition from cruise or cruise descent is made before entering the pattern, typically while on the 45-degree leg to the downwind. By slowing the aircraft to an appropriate approach speed and completing the prelanding checklist before entering the pattern, we can spend more time scanning for traffic. The profile identifies the power setting (approximately 1,900 rpm), airspeed (90 kt), altitude (1,000 feet agl-a fairly standard pattern altitude), and configuration (flaps up, level pitch) for this portion of the approach. Understand that the power setting is approximate because changes in aircraft weight and density altitude may require slightly different power settings to attain the desired airspeed.

Abeam the touchdown point, the configuration is again changed. Airspeed is reduced to 80 kt, and one notch of flaps (10 degrees) is added. A power reduction to approximately 1,700 rpm results in a shallow descent (about 400 feet per minute).

The third configuration change is made during the base leg, with the second notch of flaps (25 degrees) added and speed reduced to 75 kt. Altitude should be approximately 700 feet agl as the turn to base is initiated.

On a one-mile final at approximately 300 feet agl, the pilot adds the remaining flaps (as required) and reduces speed to the manufacturer's recommended approach speed of 66 kt plus any additional margin required for wind shear or gusty conditions. Power settings on short final will range roughly from idle to 1,500 rpm, de-pending on the conditions.

Of course, we don't always fly a standard traffic pattern. Particularly at controlled airports, we may be required to enter the pattern on base, crosswind, or even straight in. When this occurs, we must adjust our profile accordingly. Some instructors and pilots may develop specific profiles for nonstandard pattern entries and for instrument approaches.

When improvising a change to the profile to accommodate a nonstandard situation, remember to complete the prelanding check early-always before entering the pattern. As a rough guide, we can use the key altitudes to determine when to make our configuration changes. When in doubt, make your configuration changes early. The sooner you're stabilized in the landing configuration, the less likely you are to have problems.

Taking Aim On The Runway

The objective of the stabilized approach is to smoothly guide the aircraft to the touchdown zone at the proper configuration and airspeed. While the power settings identified in the profile will be useful in establishing the target airspeeds and descent rates, the pilot must also monitor the approach and make the appropriate control inputs to stay on the desired glidepath. Visual approach aids such as the visual approach slope indicator (VASI) and precision approach path indicator (PAPI) are designed to assist the pilot in this process. These devices are designed to guide the aircraft along a safe approach path (usually a 3-degree glideslope) to the appropriate touchdown zone, which begins roughly 500 feet beyond the end of the runway threshold.

When flying an approach to a runway not equipped with a VASI or PAPI, the pilot must use another means to maintain the proper glidepath. The most common method is called the spot landing method. By keeping a reference landing target in a fixed position on the windscreen, we maintain a flight path that takes us to that spot.

Setting The Limits

An important aspect of the stabilized approach concept is defining minimum altitudes at which the approach must be stabilized and setting the standards or limits for the various parameters. For example, the stabilized approach criteria for one major airline requires that on a VFR approach, the aircraft must be stabilized by a minimum altitude of 500 feet above the touchdown zone elevation. That means the prelanding checklist must be completed, and the aircraft must be established in the landing configuration. The aircraft also must be on the proper glidepath without an excessive descent rate, and the airspeed must be within 5 kt of the target airspeed for the particular landing. When flying an instrument approach, the same airline requires that the aircraft be stabilized no lower than 1,000 feet above the field. Whether VFR or IFR, if the aircraft isn't on a stabilized approach by the minimum altitude, the flight crew is obligated to go around.

The same philosophy can be adopted when flying any aircraft. Using our example of the Piper Archer, we can define our stabilized configuration as: prelanding checklist complete, airspeed within 5 kt of our approach speed (plus any additional airspeed needed to compensate for wind shear or gusts), and on glidepath as determined by the available glidepath indicators (VASI, PAPI, etc.).

With this in mind, we can set our own limits. If we aren't stabilized by the time we reach a minimum altitude of 300 feet agl (about one mile from touchdown), we will execute a go-around.

For an instrument approach, we'll use the same criteria, but the instruments will determine our glidepath. For an ILS approach, the localizer and glideslope must be within two dots (half-scale) of centered by the time we reach 1,000 feet above field elevation. For a nonprecision approach, we must be within 5 kt of our target airspeed and at our predetermined descent rate before reaching 1,000 feet above field elevation. In addition, we must reach our minimum descent altitude within one-and-one-half miles of the airport (or within one minute of our missed approach timing). If we don't meet these criteria, we go around.

A Solid Foundation

The addition to our house turned out to be beautiful. Because we took the time to do it right from the beginning, the end product was easier to complete. And so it is with landing an airplane. If we lay a solid foundation in the form of a stabilized approach, the flare and touchdown not only look better, but also are easier to master.

The Spot Landing Method

A good way to judge your approach is the spot landing method. Choose the spot on the runway where you want to begin your flare, and note where that spot lies on your windscreen. As you continue your descent, the spot should stay fixed at that same point on the windscreen. If the spot begins to rise on the windscreen, you are undershooting, so add power to shallow the approach path. If the spot begins to sink, you are overshooting, so de-crease power and/or add flaps to steepen the approach path.

The spot landing technique takes practice to master, but it is tremendously useful. When learning the technique, be sure you are flying an appropriate approach by cross-checking with a VASI or PAPI or an ILS glideslope for instrument procedures. After a few sessions, you'll learn to recognize the picture corresponding to the proper approach angle.

Guides To Getting Down

The easiest way to fly the approach to the runway is to follow the VASI or PAPI while maintaining the proper approach speed. These visual aids bring us in at the proper angle and help us avoid obstacles that may be present on the approach to the runway. If we're flying at the proper airspeed, our rate of descent will also be correct. When such aids are not available, pilots can use other means to determine the proper rate of descent to the runway.

The standard glideslope is 3 degrees for VASIs, PAPIs, and instrument approaches. Following a 3-degree glideslope, we descend approximately 300 feet per nautical mile. If our aircraft is GPS-, loran-, or DME-equipped (and there's a DME on the field), we can do some simple math to determine if we are on the glideslope. Five miles from the touchdown point, we should be about 1,500 above field elevation. On a three-mile final we should be roughly 1,000 feet above the field, and on a three-quarter-mile final we should be about 200 feet above the field.

A rough guide for determining the rate of descent needed to maintain a 3-degree glidepath is to multiply our groundspeed in knots by five. At 80 kt, that gives us 400 feet per minute. At 60 kt we get 300 feet per minute, and at 100 kt it's 500 feet per minute.

The Right Speed

While various instructors will suggest slightly different approach speeds for the same aircraft, the following rule of thumb is a good guide.

The initial approach speed used on downwind should be no greater than the flap extension speed (V_FE) and no slower than 1.4 times the stall speed in the landing configuration (V_SO). Airspeed should be at least 1.4 V_SO until the aircraft is on final approach. On short final, speed can be reduced to 1.3 V_SO, or the manufacturer's recommended final approach speed for the type of landing being planned (normal, short field, etc.).

The approach speed should be adjusted to compensate for turbulence, wind shear, and gusty wind conditions. In general, half the gust speed should be added to the approach speed. For example, if the wind is 10 knots gusting to 18 kt, you should add at least 4 kt to the approach speed (8/2).