In response to the recent Air Safety Institute blog about the Asiana crash at San Francisco, I am addressing the point of developing basic “stabilized approach” skills and how they are used in flight training.
Bruce Landsberg wrote:
I absolutely agree that students will be working it all the way down and that is part of their learning what “good” is but there’s that judgment thing on teaching when an approach has become unsalvageable. Not so good to allow them to “attempt to save it” when the risk is rising rapidly.
Given that a light single-engine airplane needs to make turns and configuration changes below 1,000 feet above ground to complete a traffic pattern, at what point does one decide to not even attempt the flare and landing? Do I need to make that decision at a fixed height such as 500 feet? Do I need to meet specific criteria such as stable airspeed, stable descent angle, and stable configuration?
Let’s think about a few examples. These are the scenarios I can remember where I made that decision not to land after making the turn to final approach (or even earlier).
Downdraft Exceeding Climb Performance
This was a moderately bumpy day in the pattern. It was one of those days where establishing a power-on descent from the key position was not adequate to get a stabilized approach. As Bruce put it, I was “working it all the way down”. I was practicing short field landings with my flight instructor. To achieve the short field level of precision in turbulent, gusty crosswind, I was moving the throttle continuously to keep the descent angle stable.
All of the patterns and landings worked well that day, with one exception. After making the turn to a final approach leg and fighting the turbulence down to about 100 feet, I needed to bring the descent up just a bit further past the threshold to reach my aiming point.
As I applied forward pressure to the throttle, I suddenly realized that it was already full forward, and we were descending to the threshold with climb power. At that point, I said to my instructor, “I don’t think we should land now if we can avoid it.” A full-throttle landing would be a precarious and unusual maneuver that I did not care to attempt.
This was the beginning of the go-around maneuver. With a negative rate of climb we couldn’t risk retracting the landing gear. With our approach speed nearly identical to the best-rate-of-climb speed, we couldn’t do much with the airspeed but monitor it and attempt a flare over the runway.
Fortunately, we flew out of the effects of the downdraft around 20 feet above the runway. The airplane leveled off, still at the approach speed, and then I was able to perform a normal go-around maneuver from there.
Updraft Exceeding Descent Performance
On a more amusing note, I have also encountered the opposite problem. Practicing power-off 180s on a hot summer day, there was one attempt in particular where I remember turning to final with the power idle and adding full flaps, to attempt a precision landing. Instead of landing, we glided gracefully along the runway center line still hundreds of feet above, with zero vertical rate. If I had attempted to force the descent and land in this situation, I would have exceeded the stable approach speed by a considerable margin. The appropriate decision was to enjoy the glide and execute a go-around over the departure end of the runway.
Low Level Wind Shear
There have been two occasions when I decided a turbulence encounter exceeded my personal limits during traffic pattern approaches. Both of these happened during solo flights, so there was no instructor or co-pilot to use as a resource.
The first one that comes to mind happened on a day when the weather was becoming increasingly turbulent. Each landing was noticeably more challenging than the one before, and I had reached the point where I felt the next landing should be my last one for the day, to play it safe. The downwind leg was bumpy but normal. I reduced the power setting at the key position, added 10° flaps, and started a smooth 20° banked left turn to the base leg. At that moment the airplane rocked rapidly to the right, and the next thing I knew, I was in a nose-low 60° banked turn away from the field. My instincts from unusual attitude training kicked in: level the wings, then lift the nose. After adding full power and returning to the clean configuration, I called the tower controller and told him I was going to continue my downwind leg. This enabled me to make longer, shallower turns, and more importantly, to take a deep breath before trying that approach again.
On another bumpy day, I remember having a consistent 20 or 30 knot wind at pattern altitude, but only a few knots below 500 feet. This was acceptable because as the wind speed would gradually change throughout the pattern, I would get valuable practice adjusting to the changes in ground speed and track. On one of my final approach legs, though, the wind changed quickly on me. Instead of seeing a slight change in my descent angle, I saw both my airspeed and altimeter needles suddenly rotating counter-clockwise. I had no desire to wait for the indications to stabilize, so I pushed the throttle forward and had an uneventful go-around.
Conclusions
While students strive to achieve a stabilized approach from the turn to final, all the way to the runway threshold, every pilot in the training environment must be prepared to abort an approach at any time and for any reason. This is part of the continual decision-making process. The approach must be evaluated, adjustments made, and if the desired performance is not achieved then a go-around is often the best corrective action. In my examples above, the decisions to not land were made at various altitudes ranging from just turning toward the base leg, to only 100 feet above the touchdown zone. Problems with stabilizing the airspeed or runway alignment must be corrected as early as possible during the approach. Both airspeed and runway alignment are monitored continuously by both pilots. Any deterioration of these skills in any pilot needs to be detected and remedied to maintain the highest level of safety.