The human brain is capable of truly remarkable feats. It can deduce the laws of nature and devise methods to manipulate those laws. It can process of an endless stream of data in real-time. Most amazing, it can contemplate the implications of its own existence. What it cannot do operate with absolute precision. The brain keeps up with the firehose of information streaming into the five senses by selectively ignoring the information it deems unimportant (my wife complains constantly about my brain's well-honed ability in this regard). It produces output (a decision) based on incomplete input by filling in the blanks with extrapolations based on available information and past experience. If one of the blanks filled-in turns out to be the hang-check, however, the results can be less than desirable.
Almost doesn't count in many sports, and hang gliding is most definitely one of them. Whenever we decide to commit aviation, we must force our brains to operate with greater precision. Several techniques have evolved as the result of over 80 years of aviation experience, of countless mistakes made and the best efforts of aviation pioneers to find workable solutions. These techniques work as well as anything can, and we should add these tools to our arsenal. They include: 1) The use of written memory aids (checklists), 2) Directed assistance from another crew member (wire crew), 3) Redundancy, 4) Habit pattern, 5) Interlocks, and 6) Standardization. It is ultimately the pilot's responsibility to effectively manage all of the resources at his or her disposal in order to conduct a safe and successful flight.
Checklists are the first line of defense against mistakes of omission. Checklists may be run from memory (most pilots do this even with incredibly complex checklists) provided that the accomplishment of all checklist items is confirmed by reference to a written checklist. This helps prevents the pilot from falling victim to a fill-in-the-blank type error (I could have sworn I checked that!).
If a wire crew is available, they should be directed to confirm each checklist item as it is performed. This helps prevent the pilot from falling victim to a performance related error (I could have sworn that I checked that correctly!). Note that this does not make the wire crew responsible for backing-up every pilot they help launch. The responsibility for safe conduct of flight always resides solely with the pilot.
To be most effective a checklist should be run in a linear fashion, from A to Z, without interruption. The wire crew should never attempt to run the checklist for the pilot. The wire crew should never interrupt the flow of the pilot's checklist unless directed to do so by the pilot as part of the check. I have seen launches where well intentioned wire crew members would prompt the pilot to check (or double-check) for their favorite important items. This only disrupts the flow of a well-run checklist. If the pilot is not conducting a well-run checklist, the wire crew should point this out and let the pilot take corrective action: ideally by running the whole thing over again starting with item #1. Our checklists are not so long that this represents a significant burden.
Another line of defense is to build redundancy into your system. Critical items should be checked independently, at different times. If the odds are 1 in 20 that you will miss something on any single check, they increase to 1 in 400 that you will miss that item after two independent checks, and 1 in 8,000 that you will miss that item after three independent checks. As you can see, redundancy can be a powerful tool! This principle works in space as well as time. Four independent sets of eyes, used properly, are far less likely to miss something that one set. Responsibility for the effective use of all those eyes lies solely with the pilot. Make effective use of you wire crew.
Establishing a habit pattern is another good technique. There is a great deal of controversy about this in the hang gliding community. It works well in other forms of aviation due to the consistency of most other operations. We, by contrast, often fly at a different site every day. We fly under an incredibly wide range of conditions. Our crew composition changes with every outing, and often with every launch on any given outing. We fly on a highly irregular basis. Distractions are legion. Nevertheless, if it can be accomplished, a well established habit pattern may help warn the pilot that something has just been missed. Any break in your pattern should trigger the immediate response: Ok, let's start over again from the beginning.
Interlocks are physical devices designed to prevent mistakes of commission. Some have suggested that we should hook the harness into the glider before getting into the harness, as a way of making it more difficult to launch unhooked. This makes a great deal of sense, really. Currently accepted practice has us building our wing and then walking around for an hour wearing our cockpits. We finish building the aircraft just prior to launching. Sounds kinda dumb when you put it that way. Many harness designs make this scheme impossible or extraordinarily difficult, however, but where it is practicable this technique for preventing launches while not hooked should be given serious consideration.
Perhaps the most controversial technique is standardization. We should all be reading from the same page. Certain checklist items will vary in detail depending on glider and harness design, but if everyone were accustomed to performing the same basic checks in the same order it would be virtually impossible to miss something. Any errors of omission would stick out like a sore thumb, virtually guaranteed to be noticed by someone and brought to the pilot's attention.
Below is a strawman Before Takeoff checklist, based on the one I run (soon to be with written backup):
Educational Resources for Hang Gliding