Recognizing that a surface should be considered glassy is the first step to safely landing on it, and I point this out because every so often a glassy water mishap occurs when a pilot fails to treat a surface as glassy. In some situations it is not entirely obvious whether or not you need to use a glassy water procedure, and a good definition of glassy water is a starting point for any discussion of the procedure.

In one word, the defining characteristic of glassy water is reflections. If you can see any reflections at all, that tells you that your sense of height above the water will be compromised to some degree. With that said, it is important to note that not every glassy surface is the same. There is perfectly glassy water, a completely flat surface that makes perfect mirror-like reflections, and this can completely eliminate depth perception. This condition once resulted in touching down at a mountain lake when I would have sworn I was still a hundred feet above it. But there is also what might be called partially glassy water; a slightly wavy surface that supports distorted reflections that may only partially compromise depth perception. In this case you may have some sense of height above the water, but not necessarily enough to rely on for a normal flare. It isn't until the smooth surface is broken into wind ripples that reflections are completely destroyed and the water is definitively not glassy.

Having defined glassy water, the next question is how to deal with it. Given that there are varying degrees of glassy water, should they all be treated the same or can they be addressed by varying degrees of glassy-water technique? There is no doubt that a completely smooth surface with perfect reflections requires the full textbook long stabilized glassy water approach. But what about ‘partially glassy' water? Do we need to take all the same precautions when approaching a wavy surface with distorted reflections that provides some sense of height? Is the long stabilized approach really necessary when your depth perception is ‘just a little off'? Many pilots answer no to this, and instead do a more-or-less normal approach to partially glassy water, which is not necessarily unreasonable provided that you acknowledge the potential depth perception problem and at some point in the approach, transition to a glassy water attitude to feel out the water with a slow speed and a nose-high pitch. Of course if there is any doubt about what to do, you can't go wrong by doing the full stabilized glassy water approach.

Of the varying degrees of glassy water, the partially glassy water may present the more insidious hazard because it can lull you into thinking you have more depth perception than you actually do. The problem with even partially glassy water is that if your sense of height is off by any amount, it is impossible to know exactly how much it is off. Every so often a pilot has a problem because they mis-judge the extent of the glassy water illusion. Keep in mind that the glassy water illusion makes you think you are higher above the water than you actually are, which can entice you close to the surface with an inappropriately nose-low attitude. Even if your depth perception is off by only a small amount, this can be enough to cause problems. However we treat partially glassy water, we should be careful not to treat it too casually.

My solution to this goes back to the definition of glassy water. Regardless of what kind of depth perception I think I have, the presence of any kind of reflections triggers caution and points out the need for some sort of glassy water landing. Whether or not that is the full textbook glassy water procedure is a matter of judgment, but the potential hazard should be acknowledged and taken seriously. Some glassy water caution should be used any time any kind of reflections are present.