On Thursday, January 25, 2018 at 1:11:13 PM UTC-8, Steve Koerner wrote:
John: I agree that it would be possible to set a numeric criteria and use your flight recorder like we do for other SUA numbers. I do need to state the issue in different terms...

The class A SUA is effectively set in terms of pressure measurement at nominal 17,500. It doesn't matter that one's flight recorder is reading wrong by +/- 500ft. For SUA, we simply all agree and understand that we are going by a known faulty pressure measurement. In fact, the expectation that it will read wrong by 500 ft at some probability is the reason that it's not an 18,000 ft contest criteria. When we are at the start cylinder, our altimeters have been recently referenced to field elevation; so in that case the measurement is fairly accurate. Not so out on course, 100 miles away late in the day. There will not be a suitable relationship between what is measured and where the ground actually is.

You would have to incorporate an expectable measuring uncertainty into your hard deck. The hard deck would have to be set to avoid the obvious problem that would be created by a false confidence scenario wherein the rules indicate that I'm not outside safety limits so I must be safe enough to keep circling.

You will end up with a hard deck number not very acceptable to very many people. Pilots will prefer to eyeball what is a safe circling height rather than have a faulty measurement dictate when it is not safe according to the rules. To state the problem differently: being scored as landing out due to an unreasonably high "hard deck" when you in fact, make it around without compromising your safety, will seem objectionable to most. I know it would be objectionable to me.

What's more, pilots will ultimately change their circling behavior only minisculely due to a hard deck land out rule -- they still need to get back to the airfield for plenty of good reasons.

There are two reasons for the hard deck: one is to keep idiots from being idiots. But the more important one is to keep the sensible pilots from having to be idiots to compete. I guy who frequently circles very low might continue to do so with a hard deck rule. But the more sensible pilot who stays above the hard deck and goes slower as a result would not lose to the idiot.. This isn't really about protecting the idiot, it's about protecting the responsible pilot who must otherwise become an idiot, or lose.

Modern flight computers will easily be able to warn you when you are getting close to the deck, exactly as they do now for the ceiling.

John has it exactly right that the argument is really "I want to keep circling at 300 ft". All we are doing is creating a virtual ground slightly above the real ground to insure everyone's margin for error is equal, so their chances of winning on this basis are equal. It does not change the competition at all other than this.

It as amusing that the same arguments are used by some of the same individuals against motorgliders: that the motor allows continuing low over unlandable terrain and this is unfair. All you need in a non-motorized glider to do that is a high risk tolerance, this is equally unfair. The hard deck makes both of those arguments moot.