On Friday, May 24, 2013 10:21:58 AM UTC-4, wrote:
On Friday, May 24, 2013 9:04:27 AM UTC-5, Evan Ludeman wrote:

Man, what a pain in the ass at Mifflin.







Returning on the back side of Jacks with weak ridge and no thermals, you leave the ridge at 1900-2000 because you *cannot* get higher and fly through a ton of sink (netto 4 - 6 kts down is common). The closest point of the ridge to the edge of the finish cylinder is 1.6 SM and the 700' agl finish is 1520. You'd probably prefer to cut the corner if energy allows, but that makes the distance more like 3 miles. Twice I was hanging on my flaps at 42 kts at what I guessed to be the edge of the cylinder (when the gps says 1.0 mile, you've generally finished several seconds earlier). Eyes on the panel, about 1530 feet, right in the GA traffic pattern (amazing how many GA pilots don't read Notams and show up at closed airports!). This is safer than an eyes out finish at lower altitude? I don't think so. I fly a '20. What's a Libelle pilot supposed to do in that situation? We never found out because none of the low performance guys had to try to make this work.







I don't have a problem with penalizing actual unsafe flying. However, we're now erring on the side of penalizing (severely) *potentially* unsafe flying. Two guys I know of (there may have been others) drew no speed points after hitting the cylinder below 1320 agl. In both cases the airport arrivals were reasonable energy and safe.







Evan Ludeman / T8



The finish altitude is set by the CD to whatever he or she feels is appropriate for the airport, surrounding terrain, traffic issues, weather, etc. There is no rule regarding its value.



The guidance -- guidance, not rule -- to 700' AGL (Which means 500' AGL for speed points) has in mind thermal flight, reasonable surrounding terrain, and a normal airport. The point is to reduce the otherwise strong incentive to try marginal glides that either pop over the fence at the last moment, or result in a hasty off field landing 1 mile out and "planned" from about 100 feet AGL.



The guidance suggests even higher altitudes for rough surrounding terrain, airports with little room for multiple landings, or airports with power traffic.



The situation at Mifflin on a backside ridge day certainly seems plausibly appropriate for a lower altitude. There is no temptation to squeak low final glides -- you're all coming off the back of the ridge at the same point and altitude, and your only choice from then on is to push or float. 500' AGL has worked fine in the past in this situation.



But... I can naturally see a harried CD not thinking about this ahead of time. It's a subtle point. Did you or any of the pilots notice this might be a problem ahead of time and suggest a lower finish altitude to the CD for that day only? The rules give a lot of flexibility for a reason, but you can't expect rules to foresee every possibility, especially if wise CDs, task advisers, and pilots in place aren't seeing that possibility! Really, I don't think you get to complain unless pilots and task advisers saw the problem, explained this issue to the CD ahead of time, and the CD refused the request.



Otherwise, let's all file in the lesson learned category. 500' finish for backside ridge days. Check.



John Cochrane

We understand all those points. The thing is, people will tend to go with guidance by default.

It isn't just the "classic" back side sailplane time trial days at Mifflin, either. The back side ridge came into play one other day when no one would have forecast such a thing. It was weak, the angle stunk, the thermals were gone. Given the terrain around Mifflin, there really isn't any good reason to set the finish height above 1320 at any time.

As far as tasking goes... talk about harried! Nothing like getting the Mifflin special "no repeat MAT" for 4 hours, about 20 minutes before launch! If anyone was thinking ahead to the finish gate height, it certainly wasn't me. I didn't even realize we were using 700 agl (we'd discussed on practice day and what I'd heard was that we'd use 500 / 1 mile cylinder or a 50' gate if tasking allowed) until I approached the first finish and wondered why 600 over the airport on my 303 display was showing 100 low on ClearNav.

T8