4Dogs,
Much better that you leave that one to
John_Tullamarine, he's an extraordinary engineer, but just as extraordinary in twisting the legislator's tails, something I'm not good at.
Permafrost_ATPL,
You describe the nightmare scenario. I'm well familiar with ZRH, and as I read your post I get goose bumps. ZRH is definately NOT a good place to turn in ANY safe direction following engine failure on the RWY 28 Left-Turn SID (or just about any of the ZRH SIDs for that matter). I don't want to sound as though I'm beating my own drum, but I've advocated over hundreds of posts in these forums that if SIDs are to be used - Fine, but FORMALLY establish procedures for MAA and a "break-off" point from the SID following engine failure. It's
NOT difficult to do, it just costs your operator extra money. I do it for all of the "critical" SIDs that my clients use. I define critical as a turn during the SID before the aircraft has achieved a safe altitude should an engine fail after the SID turn.
galaxy flyer,
The principals involved in establishing MAA and the length of the 3rd segment are quite similar to the protocols used for Gross Vs Net performance in the 2nd segment. Using a 2 engined aircraft as the example, Gross climb gradient is estableshed by flight testing, and arbitrarily degraded by 0.8% to achieve the Net performance. (3 and 4 engined aircraft use the same principle, but the increments differ).
As an example, consider a Sea Level Runway which requires a 2.0% climb gradient to clear a 2nd segment obstacle. The aircraft should, if in new condition and flown by the Test Pilot, achieve an actual Gross Gradient of 2.8%. Therefore, the ratio of Gross to Net is 2.8 : 2.0, a factor of 1.4 (a comfortable margin).
Now, let's say that the highest obstacle in the Takeoff Area is 1000 Ft above the runway. The Net flight path need only clear this obstacle by 35 ft, not acceptable to anyone! Thus, the Minimum Acceleration Altitude (MAA or 3rd Segment Altitude) is factored in exactly the same way as was the 2nd segment glimb, i.e. 2.8 : 2.0 or 1.4. The "base" MAA will then be 1000 X 1.4 or 1400 Ft. To this is added the screen height of 35 ft (or 50 ft for a turning manoeuvre) plus the Airport elevation, yielding a MAA of 1435 ft (as we used a Sea Level Runway). If you want to put this into a long-hand formula -
MAA = Obstacle Height above the lowest point on the Runway X (Required Net Gradient + 0.8%) divided by Required Net Gradient + Screen Height + Highest Runway Elevation.
3rd Segment horizontal Distance is similarly factored. If the actual (Gross) 3rd Segment distance was, for example, 20,000 M, this is multiplied by the same factor (1.4 used here) to achieve a Net 3rd Segment distance of 20,000 X 1.4 = 28,000 M.
After all of this, you're PROBABLY still below MSA, so you'd better go lookin' for a safe place to climb to MSA. A FAR 25 principle developed "safe climb" holding pattern is this person's preferred choice here.
Sadly, there are still people "out there" who want to 'eye-ball' it!
A personal viewpoint - The Gross Vs Net margins for the continued Takeoff following engine failure are generous. With FPA / FPV displays available on most modern aircraft, I've observed even average pilots tend to fly closer to the "Test Pilot's" Gross gradient than the Net. It lends great strength to the
GO case, as the margins for Accelerate Stop are much much less.
Regards,
Old Smokey