Safety Publications/Articles


Are you stable?

Approach parameters to use in your flying

The implications are many, but here stable concerns flying your final approach. The concept is simple: a safe touchdown is the result of proper airspeed and glidepath control. The FAA and airlines have codified this concept, added well-defined parameters, and call it the stabilized approach.

Of course, this isn't anything new. Even my 1980 Flight Training Handbook addresses stabilized approaches. "After aligning the airplane with the runway centerline, the final flap setting should be completed and the pitch attitude adjusted as required for the desired rate of descent." The Handbook's language seems pretty clear, so why the discussion? Because about half of all general aviation accidents are landing accidents. If that sounds incredible, you can look for yourself: The AOPA Air Safety Foundation's Accident Database is easy to search.

Simply put, every approach provides a new challenge, and even the most experienced pilots can make errors. The Handbook addresses this: "Occasionally it may be advisable for safety reasons to discontinue the landing approach and make another approach under more favorable conditions.... Although the need to discontinue a landing may arise at any point in the landing process, the most critical go-around will usually be one started very close to the ground." Again, the language is clear: If the aircraft isn't within the desired parameters, then go around. Every pilot knows this, yet the majority of accidents still occur on landing. Why? Fatigue, distractions, and/or weather-related factors can result in the pilot failing to properly monitor and fly the approach. Pilot proficiency is also a key factor in most of these accidents.

"The objective of a good final approach is to descend at an angle and airspeed that will permit the airplane to reach the desired touchdown point at an airspeed which will result in a minimum of floating just before touchdown," states the 1980 Handbook, without specifically mentioning stabilized approach. Today, Part 121 and 135 flight operations manuals address the stabilized approach and define specific tolerances. Should the aircraft deviate from the stated parameters, the approach should be aborted and a go-around initiated.

Since the stabilized approach concept was the result of a cooperative effort between the FAA and commercial carriers, it makes sense that airlines use common guidelines. Generally speaking, the sapproach is stabilized by 1,000 feet above ground level. By this altitude, the aircraft must be in its final landing configuration, all briefings and checklists accomplished, the engines at operating power appropriate to the configuration (for example, jet engines spooled), and the descent angle and rate appropriate to the type of approach being flown using all available landing aids (ILS, VASI, PAPI, and the like).

In addition, the sink rate should not exceed 1,000 feet per minute, the airspeed should not exceed VREF plus 20 knots, and the airplane should cross the threshold within plus five knots of target airspeed to make a normal landing within the touchdown zone. For two-pilot crews, at 1,000 feet agl, the pilot monitoring is required to verbally state either "stable" or "not stable" and if not stable, identify the parameter. Captain's discretion does permit an "unstable approach" to continue, so long as the adjustments are minor and the aircraft will be within parameters shortly after the "not stable" call.

Some general aviation pilots may point out that most of these parameters don't apply to their aircraft. That's true. Obviously, a light airplane won't deviate 20 knots from its target speed. Also, an airplane flying final approach at 75 knots won't require a thousand-feet-per-minute sink rate to maintain a normal glidepath. However, the Handbook's discussion of "Final Approach" and GA landing accident statistics should make it clear that the stabilized approach concept can be helpful to all aircraft, not just commercial carriers.

With that in mind, consider how monitoring final approach parameters can improve your landings. For simplicity, we'll use a generic propeller-driven aircraft that flies base leg at 85 knots and final approach at 75 knots. Since propeller aircraft usually fly a 1,000-foot-agl traffic pattern and the aircraft must descend on base leg, we must adjust our "stabilized altitude" to 500 feet agl. So which stabilized approach parameters are applicable to our generic aircraft? I suggest the following:

  • Configuration. This means gear down and flaps in the final setting. Does this mean you can't delay your final flap setting? Not at all, but if you choose to lower your flaps below 500 feet, have a reason.
  • Descent angle or glidepath. Always fly the visual approach slope indicator glidepath, if available. Since your groundspeed determines the required sink rate to maintain glidepath, pay attention to the winds. Generally speaking, you should not exceed 500 feet per minute with a 75-knot final approach speed.
  • Airspeed. Maintain speed within five knots of the target.

Recognize that the intent of the redefined stabilized approach is to reduce accidents by providing guidelines on when to abort an approach. In other words, if the airplane isn't doing what you want it to do, then go around before it's too late. There is no shame in making a second approach under more stable conditions.

Mark W. Danielson is a retired Navy pilot who currently flies for FedEx. He has been a CFI for 26 years and has flown more than 11,000 hours.

By Mark W. Danielson

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