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Old 24th Feb 2006, 15:40
  #41 (permalink)  
chuks
 
Join Date: Apr 2003
Location: Germany
Age: 76
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Things have moved on...

When I learned to fly on instruments I was taught to get down to the MDA and then motor along to the MAP, hoping to spot the approach lights before the time was up. We didn't call that 'Dive and Drive,' but I guess it was the same thing.

Thinking later changed to the use of a stabilised 3 degree approach slope, just as on a precision approach. Figure out your groundspeed and apply an appropriate rate of descent (for example: G/S 120 knots, ROD 646 feet per minute for 3 degrees) to arrive at the VDP (Visual Descent Point) at the MDA. If you do not have the lights or the runway in sight at that VDP then you will not be able to make a stabilised approach to land, so that you might as well go around rather than hope to see something from over the threshold at the MDA. Of course it makes a big difference if you are in a Twin Otter at 80 knots or perhaps a jet doing double that, so that this is not a given for all situations.

What I usually do in practice is to hit the MDA just a bit short of the VDP so that the PNF can take a good long look for the lights. Too, if you are just a little bit off on your rate of descent it's much easier to cope with being a bit low on the slope compared to being a bit high. And, after all, this is a non-precision procedure.

We used to amuse ourselves holding at Lagos, Nigeria when the weather was bad and the VOR was the only approach aid available by watching for the next BAC 1-11 to come blasting out of the murk at nought feet. 'Stabilised Approach? No idea what you are talking about, mate!'

Of course another problem with 'dragging it in' is the way it can be very difficult to land the aircraft on the fixed distance markers. You will be very shallow as you come across the threshold. So it would be a case of 'Here he comes! There he goes!' with the occasional landing that would end in tears.

I became a convert to this newer way of doing things. Plus, as previously pointed out, it is now mandatory in many places.
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