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Guest JHG

Use of Altitude Range Arc

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HiI am using the PMDG 737 800/900 and need some information relating to the use of the Altitude Range Arc. ie. The green arc that appears on the ND showing where the A/C will reach the altitude selected in the MCP.I am not sure what triggers the appearance of the Arc which is not visible all the time.I would like to use it to assist with flying non precision approaches, for example established on final I would like to select airfield elevation in the MCP and adjust the V/S on the MCP positioning the arc over the runway threshold giving me an indication of the rate of descent required for the approach.My problem is that the Arc will not always appear when I need it.What triggers it's appearance? It doesn't always appear when i select a new altitude on the MCP or adjust the V/S on the MCP.Any help would be much appreciated.RgdsJohn Gayford

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The green banana is useful for descents to a target altitude at a fix but I wouldn't use it as a guide for approach descent. It only appears when the target is within range and then when the range is ahead of the aircraft some distance. Not exactly the precision you're hoping for.Try this for non-precision approaches: Cross the final approach fix at the altitude shown on the chart (usually a at or above but cross at the altitude) with gear down and 15 flaps at the appropriate speed for your Vref and on autothrottle, on crossing the FAF set up landing configuration in a 800 fpm descent. Descend to the published minima for the approach, use the VASI or PAPI if you have it. Land if the picture looks good and landing is assured. With some practice, you can nail the approach quite easy. You might practice handflying an ILS with GS guidance used for reference instead of autopilot to gain experience with how the plane reacts to pitch changes. A little pitch change leads to differences in sink rate after a slight delay so it takes getting used to.This is one of the best parts of flying. Have fun with it.

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Thanks Dan very useful information will put it to good use.Much appreciated.RgdsJohn Gayford

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Dan, in the method you describe would I descend from the FAF in V/S mode, or just push the stick forward, or does either method work equally well?RegardsGeoff

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I descend from the FAF hand flying attitude (pitch and roll) with autothrottle engaged. I cut throttles below 100 ft agl and flare about 50 ft agl. I cut the throttles with the F1 key, then after touchdown extend spoilers with the / key and use F2 for reverse thrust. There are other ways of doing this, but this works for me.The challange is in learning not to overcontrol pitch changes. A small adjustment in pitch results in a marked difference in descent rate after a delay. Getting used to the delay and amount of pitch change to use is the key.I use Vref+5 for final, sometimes lowering it to Vref if wind is light below 500 ft agl.

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Hi Dan, so you prefer to hand-fly down rather than use V/S. I've been experimenting and find I can only descend at a constant 800 fpm using V/S - I find it really difficult to do this just by watching the descent rate (B737 NG). Is there a magic button I've missed that expands the descent rate scale by 10 ;-) ?Geoff

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Don't chase the vertical speed. If you are on a visual approach, use the VASI or PAPI and runway environment as your glide slope reference. If you are hand flying a ILS, use the GS indication. The vertical speed indication is only a reference, I'm sorry if I mislead you, it will vary with groundspeed.No magic button for pilot skill, it takes practice.Set up a flight at a familiar airport on the runway with no wind. Takeoff and climb to 2000 agl, fly a local pattern (cross wind, down wind and base legs) to intercept the localizer at a 30 deg angle about three miles outside the final approach fix. Get on the localizer and start hand flying the approach. After landing keep rolling and do a go around to do the pattern again. Do it over and over. There's a lot of things going on that you need to become proficient with including attitude, speed, and aircraft configuration. If you still can't get it, maybe you should practice with the King Air B350, it is a good stable airplane.

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