Hi
John_Tullamarine,
This thread is running a bit cold now, but to address the questions posed in you recent post…………
Yup, Red Vs Blue, you got it in one, the chess piece was (and is) a bit more cryptic.
I can agree with you that for the odd-ball occasions where an RTOW is invalidated a simple (and comfortable) single deduction to STOD/TODA might be desirable, but, oh boy!, the variation is enormous even for the same OCG and S1 length, for a variety of Runway slopes. As has been covered (by both of us in fact), when discrete analysis is unavailable and we have to revert to RDS data ‘on the day’ we need to keep the 1st segment above the Runway and the OCP, but what of considerations for steeply sloping runways. Your namesake’s RWY 34 comes to mind here. As we’ve both pontificated, S1 length and Delta G1/G2 is quite constant, and even the use of the worst case data here will only be a minor penalty if applied to the best case. The big factor in this one is the runway slope. Irrespective of the geometric techniques used, a simple one page table of RWY Slope Vs OCG does it all, including the steep runway slope case. (I’d love to post an example here but there goes the anonymity).
H3 problems for the odd-ball days are monitored by ‘Ops Watch’ in my absence, I’ve provided them with a table of highest tolerable obstacles for each runway procedure and the closed (not open) areas that the Takeoff Area covers beyond the worst S2 distance. We use a standard 1000 ft AFL H3, and as most MAA’s are well below this, operational restrictions are rare. If the ‘new’ obstacle is higher than that listed, I get a phone call. I don’t get many phone calls. When the MAA is above 1000 ft (e.g. Albury RWY 07) and a new lump appears, I get a phone call. Similar procedures apply for S2 in the area not covered by Type’A’ charts or the RDS surveyed area.
The 0.4% margin on G1…. Lines drawn in the sand (by me). I cannot accept the allowance that G1 need only be positive (both aircraft that I answer to CASA for are 2 engined), and the line drawn in the sand is the minimum 1.2% capability required throughout the OEI procedure degraded by the 2 engined aircraft decrement of 0.8%, et voila! 0.4%. In it’s application, G1 minimum must be 0.4% to the horizontal, G1 OCP plus 0.4%, or Runway Slope plus 0.4%, whichever is the greater. In practice, it’s rarely limiting. “My” 2 aircraft have about a 0.9% Delta G1/G2, and as we’re often looking at a minimum Net G2 of 1.6%, at least 0.7% is achieved in any case….. except at your namesake’s 34.
Re TORA and TORA+60…… Another line drawn in the sand, but with manufacturer and CASA concurrence. A bit of simplification at work here, TORA+60M is used as the maximum useable ASDA to preserve the RESA. Protection is needed for the continued Takeoff to ensure that 50% of the airborne portion from Vloff to V2 be over the TORA, and in the interests of simplification and commonality with the ASDA case, 60M use of the Clearway was considered. AFM data from the manufacturer was virtually non-existent here, but I was successful in gaining an official (FAA approved) statement from both manufacturers that Vloff to V2 was ALWAYS more than 120M in any set of circumstances, thus, ‘my’ CASA guy accepted the 60M use of Clearway. Thus, the greatest credit taken for Stopway or Clearway is 60M.
Thanks for the simplified geometric calculation, Yep, it works the same, but as I did my original post developed it on a piece of paper beside me as I typed the post (too lazy to dig through my programmes). I’m always worried when throwing formulae at people not using mathematics every day to exercise great care with Gradient, Gradians, Radians, and Degrees, which is why I went through the more laborious process of first converting everything to degrees. You always could simplify to a simple one-liner couldn’t you?
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A bit of a thumb nail sketch, there’s much more, that’s the gist of it, includes a fair bit of personal policy to enable better sleeping habits by me.
Yes, it continues to be jolly good fun, does it not?
Regards,
Old Smokey