livin'thesim
Well-known member
- Joined
- Apr 6, 2005
- Posts
- 926
Read Advisory Circular 120-71A and get back to us.
3.2 degree glidepath and 140kts approximate groundspeed for this approach results in 792 FPM.
First, as I stated earlier, this was not an approach requiring VS>1000.
But, how would you handle a steeper final segment, with a notably higher corrected ref than that with a tailwind that becomes a crosswind upon landing?
I've seen ref speeds in the high 140s, plus 5, plus 15 knots of tailwind aloft, changing to direct crosswind.
Call it 160 knots groundspeed. At the max published gradient per Terps (400 ft/nm) that yields a descent rate of 1100 fpm.
Now, the 400 ft/nm is measured from the FAF crossing altitude to threshold plus 50 ft. This means that on some approaches, to get an effective chance at visual contact, you may need to beat 400 ft/nm slightly, depending on whether the MDA and "approximate" VDP falls above or below the average descent gradient.
Also, the 1100 fpm I referenced earlier is the required average rate of descent, which means unless you are capable of instantaneously achieving that rate and leveling off instantaneously, some additional descent rate will be required in order to account for initiating and ending the descent.
In short, there is nothing magic about VS-1000, other than that for 99+% of flights, it serves as a useful limit for descent rate.
However, the right mix of ref additives, winds, and approach gradient/MDA geometry can push the required rate higher.
Brief it, be aware, and use sparingly.
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