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What is the maximum rate of descent approved in an instrument approach procedure non-precision? Basically what is the maximum rate of descent (Fpm) that I use during the approach?

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ICAO Doc 8168 stipulates that for a non-CDFA non-precision approach, the aircraft should not exceed 15% gradient when descending from FAF to MDA.

1.7.4 Stepdown descent The third technique involves an expeditious descent and is described as “descend immediately to not below the minimum stepdown fix altitude/height or MDA/H, as appropriate”. This technique is acceptable as long as the achieved descent gradient remains less than 15 per cent and the missed approach is initiated at or before the MAPt. Careful attention to altitude control is required with this technique due to the high rates of descent before reaching the MDA/H and, thereafter, because of the increased time of exposure to obstacles at the minimum descent altitude.

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There cannot possibly be a maximum descent rate because the rate depends on the ground speed.

Instrument approaches are based on a fixed glide path with a typical slope of $ 3^\circ $ (but can be higher). Your descent rate will depend on the ground speed during the approach. E.g. flying at $ 150 \, \mathrm{kt} $ ground speed down a $ 3^\circ $ glide slope will result in $$ \tan(3^\circ) \cdot 150 \, \mathrm{kt} \approx 796 \frac{\mathrm{ft}}{\mathrm{min}} $$

Non-precision approaches may not have any vertical guidance available, but the chart should still specify the gradient and target altitudes at various points. When flying this approach at a given true airspeed, the descent rate will still vary with the wind because the gradient is fixed with respect to the ground, e.g. adding $ 10 \, \mathrm{kt} $ of headwind to the example above will result in $$ \tan(3^\circ) \cdot 140 \, \mathrm{kt} \approx 743 \frac{\mathrm{ft}}{\mathrm{min}} $$

The maximum descent rate will therefore depend on the airspeed you want to fly at during approach, the glide slope angle and the wind speed.

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    $\begingroup$ Actually, the angle of the approach can be from 3 to as much as 5.5 degrees, depending on the airport, but individual aircraft must be certified to be able to use the steeper approaches. $\endgroup$ – Juan Jimenez Aug 27 '18 at 13:21
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    $\begingroup$ Lugano (LSZA) even has 6.65 degrees, so coming in at 100 kt ground speed (more realistic for a small airport) would result in 1181 ft/min. $\endgroup$ – Bianfable Aug 27 '18 at 14:02
  • $\begingroup$ Wow. That's steep! I wonder if there are any other published approaches that are steeper than that... $\endgroup$ – Juan Jimenez Aug 28 '18 at 7:56
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    $\begingroup$ By the way, this is good information on a target rate of descent, but I don't think that it really answers the question of what the maximum descent permitted is. $\endgroup$ – Lnafziger Sep 24 '18 at 15:57
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    $\begingroup$ The question does not have an answer for the reasons stated in this answer. There is no maximum rate of decent. In the USA the maximum would only be a rate considered safe and in control for the equipment, crew training, and conditions. Decent angles are fixed to the ground and not aircraft vertical or horizontal airspeeds or relative airflow angle. $\endgroup$ – Max Power Aug 1 at 18:02
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Basically you should not exceed 1000 feet per minute after you have passed the initial approach fix. The actual rate of descent will vary with speed, the approach angle and type of approach as well as met conditions. Please see this article.

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There is no "approved" legal maximum. As a general rule of thumb, 500 fpm is the target rate you should use for IFR descents on non-precision approaches.

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    $\begingroup$ 500 fpm corresponds to 3° glide-slope at 100 knots over ground. Higher speed or steeper approach need higher rate of descent. $\endgroup$ – Jan Hudec Aug 26 '18 at 15:23
  • $\begingroup$ Which at the typical approach speed of a typical light twin used in training is about where you want to be unless you are diving because you started late. In a high perf aircraft it is closer to 7-800 fpm. 500 fpm is also roughly the limit for passenger comfort in unpressurized aircraft (and is the max rate that pressurization systems use for the same reason). $\endgroup$ – John K Aug 26 '18 at 21:28
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The standard descent angle is three degrees. Assuming no wind, your sink rate is given by airspeed * sin 3 degrees, and it works out to about 5 ft/min/knot. For a Cessna on final at 60 knots, the sink rate will be about 300 ft/min. For a 737 on final at 150 knots or so (I'm used to seeing Vref30 + 5 = 148 knots in the simulator), you're looking at about 750 ft/min.

With wind, you'll have to calculate your along-track groundspeed component, and use tan 3 degrees instead of sin 3 degrees. However, tan(3 degrees) and sin(3 degrees) are just about equal, and more than close enough for this particular flavor of government work.

According to a convenient calculator, sin 3 degrees = 0.0523, and tan 3 degrees = 0.0524. That's close enough...

Incidentally, you CAN work this all the way through on an E6B computer.

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In the USA the maximum rate would only be that considered safe and in control for the equipment, crew training, and conditions. Decent angles are fixed to the ground and not aircraft vertical or horizontal airspeeds or relative airflow angle. Each segment of an approach has different slope and clearance requirements as they expect different aircraft configuration and technique in addition to local hazards(including odd wind patterns) and political rubbish like noise limitations. The details of a modern approach are calculated by computer due to the number of variables and the details of the formulas take up at least three 500 page FAA orders.(8260.3D, 8260.19H, TI8200.52, along with several other miscellaneous rules.)

There are maximum design descent angles but these depend on the approach segment, approach type, and aircraft category. For example a non-precision final approach segment for straight in landings with category A aircraft at 80knots or less can be up to 6.4degrees, while the slope is limited to 3.5 degrees for approaches that allow category D aircraft. The minimum decent angle is 2.75 degrees and 3.0 is preferred, but the angle should also be within 0.2 degrees of the visual slope indicator (ie. papi, vasi)(FAA order 8260.3D section 2-6)

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enter image description here

If the Descent Gradient exceeds 400 ft per nm, the approach will be designated a circling approach, even if the course is straight-in.

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    $\begingroup$ -1 for pasting a screenshot. $\endgroup$ – bogl Dec 11 '19 at 7:18
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    $\begingroup$ Please add the actual text (which is then searchable) instead of the screenshot (which is not searchable). Also, please post the link to what you screenshotted, so that those who are interested can go to that page if they're interested in reading more. $\endgroup$ – Ralph J Dec 11 '19 at 7:23
  • $\begingroup$ Also, the question is asking about descent RATE (i.e. feet per minute) rather than descent GRADIENT (i.e. feet per nm). This post addresses the latter, but not the former. $\endgroup$ – Ralph J Dec 11 '19 at 7:25
  • $\begingroup$ Hi and welcome to aviation.SE. You may take a tour in the help center, especially the page named how do I write a good answer? to understand why your answer is not well received and how you can improve it. $\endgroup$ – Manu H Dec 11 '19 at 15:55

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