Originally Posted by
justapax
'non-precision approach final segments or ground speed from DME'. I know that DME means Distance Measuring Equipment but the rest is a foreign language to us pax........
It takes 18 months of study; 16 two hour classroom exams and 5 major flying examinations to complete the full ATPL course and training at a full-time flight school. We cover A LOT of subjects - including how human bodies work and weather patterns throughout the globe, as well as flying in 3D space by sole reference to small cockpit instruments.
A precision approach means following specific path guidance on cockpit instrumentation. This can be the ILS - instrument landing system, where two radio "beams" are transmitted from the runway up along the approach path. By sole reference to the instrumentation, we can see if we are too far to the left or right, or too high or too low from the slope. Thus we can approach in cloud and keep on exactly the correct path, as long as we come out below the clouds at a certain point to enable us to see and make the very fine corrections needed to land in the correct place.
There is a third "beam" (not actually a beam), called DME - Distance Measuring Equipment that pings a radio facility and gives us a very accurate distance from the landing point as well.
And there is a fourth navigation aid called a RadAlt - radio altimeter, which pings the ground directly below the aircraft and measures the distance to give us a very accurate height read-out.
A non-precision approach does not have such accurate "beams" or instruments, but relies on us pilots tracking a particular radial from a beacon. This is less accurate than, say, an ILS, so we cannot fly a non-precision approach in cloud as low as we can an ILS - we need to be visual at a higher and safer position, in case we are too far off course.
This is why the amount of cloud and its 'base' height is of such interest to us. We cannot legally approach to land if the cloud is too much or too low - depending what navigation aids are available for the landing.
For 'autolands', the 'plane follows very accurate guidance and lands using both, (or three), autopilots working together, and only after very accurate checks by the pilots and close monitoring all the way down the approach. So we can land in fog if the approach aids; the aircraft; and both pilots, are equipped and qualified to do so.
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