# The Minimums on landing...How do I know them?

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Hello everyone, Its been a while since Iv'e posted a topic on AVSIM and this time I'm a little confused on the 'Minimums' callout upon landing.

I already know that the Minimums is the lowest altitude you can get before touching down on the runway (correct me if I'm wrong). However, I was watching a video and the guy in it was landing and while doing so, said that he forgot to set the minimums and began to do that. I never knew you had to set minimums. So the question is: How do I know my minimums and how to set them (on the 737 like PMDG)?

JWMuller

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Minimum altitude info is always given in approach maps, i recommend to buy Navigraph subscription.

this one can help u i think ( the guy is real pilot )

In short:

The minimum for a particular instrument approach is the lowest height you can descend to at which you must be able to see the runway to continue. If you cannot see the runway (or approach lighting etc -- the exact requirements for a particular approach are laid down in law) you must go around.

For a precision approach (i.e. an ILS) the minimums will be in the form of a Decision Altitude/Height (DA/DH). If you do not see the runway you must initiate a go around no later than DH (and it is expected that the aircraft's momentum will result in it sinking slightly -- up to about 50ft -- below the DH as the go-around is initiated).

For a non-precision approach (RNAV, VOR, NDB etc etc) the minimums will be in the form of a Minimum Descent Altitude/Height (MDA/MDH). This differs slightly from the precision approach DA because there is no allowance for the aircraft sinking below this height during the go-around -- in other words, if you are descending at the time you must initiate the GA slightly above the MDA in order to not sink below it (think of it as a hard floor). Note some operators have approval to treat MDAs as DAs but don't worry too much about that for now...

In more depth...

The minimums vary depending on the approach category of the aeroplane, which in turn depends on Vref at the maximum certified landing weight (i.e. - an aircraft can only be in one category, it doesn't change depending on your actual weight/Vref). Most airliners fall in to category C (121-140 knots) or D (141-165 knots).

The minimums for a particular approach can be found on the approach chart. Commercially-produced charts like Lidos or Jepps (i.e. those you get from Navigraph/Aerosoft etc) will have the DAs/MDAs pre-calculated so you use them straight from the chart (just select the correct category for your aircraft type). State-produced charts will usually only display the Obstacle Clearance Altitude/Height (OCA/OCH) for each category and thus some extra work is required: essentially, this involves comparing the OCA/OCH with the system minimum for a particular approach and taking the higher of the two.

The system minimum is set for each type of approach and the basic rule is that the more accurate the approach aid the lower the minimums. So for a standard Category I ILS the system minimum is 200 ft AGL; for a VOR/DME approach it is 250 ft AGL; for a VOR approach it is 300 ft AGL and for an NDB approach it is 350 ft AGL and so on. Thus if you are flying an ILS approach and the chart says the OCH is less than 200 ft, you would use 200 ft AGL as your DH.

It is important to note that for all normal instrument approaches the DA/MDA is referenced to the barometric altimeter. The radio altimeter is only used for Category II and III ILS approaches.

Hope that helps!

• 2

4 hours ago, JWMuller said:

So the question is: How do I know my minimums and how to set them (on the 737 like PMDG)?

JWMuller

On a Boeing 737 NG (such as the PMDG one), you need to use the EFIS panel to set the decision height. I'm sure you know the EFIS panel is the small grey one just to the left of the Mode Control Panel (aka autopilot) on the pilot's side, and duplicated to the right of the MCP on the co-pilot's side.

On the EFIS panel you will see four large rotary control knobs, labeled from L-R: RST, CTR, TFC, STD. Specifically, we're going to use the control knob on the left of the EFIS panel, which is labeled RST which has the word , MINS above it and can be switched between two selections, RADIO and BARO. Put that switch on RADIO.

That RST knob is two concentric knobs on one spindle, one of them being a two-position selector switch and the other one a rotary control, so make sure you are using the right one. As noted, you'll usually want that RST selector set on RADIO for a DH minimum, since it will use the radio altimeter to bounce a signal off the ground and detect the return, thus giving you your exact height above the terrain rather than one based on a pressure reading. Then you can use the outer control wheel to adjust the DH value in feet, which you'll find is displayed on the Primary Flight Display. Depending on which version of a 737 you are in, the DH displays in different places on the PFD, it's on the lower left in an older 737, in an NG, it's displayed on the right of the PFD.

The DH for an airfield can be found on the charts for a specific type of approach, and most such charts can be found online, although if you want to just go for a shotgun approach and are not bothered about doing things mega-accurately, setting the DH to 200 feet will do and is in fact the default setting on many aeroplane systems.

You should note that it is worth looking at the side profile of any such approach, since there will often be information relating to the use of a radio altimeter when on approach, for example, on Runways 05L at Manchester EGCC, there is a warning on the approach chart that the terrain briefly drops away on short finals, since this can be misinterpreted as the aircraft climbing on a radio altimeter reading, when it would in fact on the correct profile for the approach. This is why you can have the decision height display on the PFD be based on the Barometric settings if you choose, which is what that selector switch on the EFIS is there for.

Note that the procedure for using the DH is quite specific in terms of who does what in a commercial airliner, although it's actually a contention point in terms of safety, since that procedure can cause spatial disorientation if not done absolutely correctly. In a flight sim, because you have a pause button, you can actually do both the co-pilot and pilot jobs if you like. That would be, the pilot flies the approach by referencing the Primary Flight Display ONLY, and the co-pilot looks out of the window for the visual. Only when the co-pilot spots the runway reference (NOT THE AIRPORT), he calls out 'runway in sight', the pilot can then visually transition from watching the PFD, to watching the view out of his window to perform the actual flare and landing. Normally when the DH is reached, the pilot flying will call that he is continuing the landing if he can see everything he needs to see. If not, it's a go around.

This is where problems can occur, since the pilot's focal distance has to switch from looking at a PFD a foot in front of him, to a reference point outside the window several hundred feet away. Thus if the co-pilot makes the call too early and says something like, 'airport in sight', it could lead to the pilot looking up from his PFD and becoming spatially disoriented by any lights or stuff other than the runway approach lights, markers etc, and getting confused when in low visibility, so this is why it is done in a very specific way, with the co-pilot only saying something when he has the runway itself in sight. On occasions where that has not been done, it has led to undershoots in poor visibility, where the pilot flying has looked up, seen some lights and thought 'damn, I've gotta stick this thing down', and flown the thing into the approach lights instead.

This is exactly what happened on an Air Canada A320 a couple of years ago when it was landing in poor visibility at Halifax Nova Scotia, resulting in the aeroplane ploughing through all the approach lights and coming to a halt as complete write off on the runway, fortunately with only minimal injuries to all on board.

11 minutes ago, Chock said:

You'll  want that RST selector set on RADIO for a DH minimum,

No - as I said above, the only time you should ever be using the radio position is where the minimums on the chart are specifically noted as radio minima, and in practice this will only ever be on a CAT II or CAT III approach. This is because the terrain under the approach will have been surveyed in order to produce a radio height which corresponds to a specific point along the glidepath.

If the terrain under the approach is at a different level to the threshold (as it will be almost 100% of the time) then (eg) 200 ft radio height will not correspond to 200 ft aal. The difference may be small or it may be very large indeed.

Of note, the Bollin Valley is the reason that Manchester 05L has CAT III minimums but not CAT II: the CAT II radio DH would lie over the valley where the radalt is unreliable, whereas the CAT IIIA DH is over the runway where the radalt once again provides useful information.

• 1

10 minutes ago, skelsey said:

No - as I said above, the only time you should ever be using the radio position is where the minimums on the chart are specifically noted as radio minima, and in practice this will only ever be on a CAT II or CAT III approach. This is because the terrain under the approach will have been surveyed in order to produce a radio height which corresponds to a specific point along the glidepath.

Yup, true. Although for a flight sim such as P3D or FSX (which one assumes the OP is using based on asking about the PMDG NG), the accuracy of the mesh comes into play and the tesselation setting etc, but more critically since nearly every airport in P3D and FSX is plonked on an unrealistic flat plane for quite a way around the airport, the radio altimeter will do the job in your flight sim, even if that isn't actually what is required for many approach plates, which is why I said check the approach plate profile and anything specific relating to the use of the RA.

33 minutes ago, Chock said:

In a flight sim, because you have a pause button, you can actually do both the co-pilot and pilot jobs if you like

Or use "R - -" to slow down time and avoid the immersion-breaking pause.

• 1

7 minutes ago, Holdit said:

Or use "R - -" to slow down time and avoid the immersion-breaking pause.

Or, fly the FSL A320 with all the sliders over to the right and land at Aerosoft's Heathrow with all the AI traffic on full, which will end up making your sim run at 1 frame per second anyway lol. Or, a blistering 5 frames per second if using the UK2000 version of Heathrow.

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I'm so tempted to buy that plane, but I'm still on FSX:SE and I'm not mad about having no other traffic in the sky.

Actually, I was being a bit facetious, I have the FSL A320 in FSX-SE and I've never had it do an OOM or been really bad on FPS, and that's with commercial traffic on about 30 percent departing and coming into from a lot of UK 2000 airports. As long as you don't go mad with the sliders in FSX-SE, it'll run okay, no worse than the PMDG NG to be honest, although if you have some absolutely mental scenery, such as VFR France's Isle de France (which could bring down a NASA supercomputer with all the sliders over on the right hand side lol), you can obviously expect to get problems with something like the FSL A320 or any other fancy add-on aeroplane.

• 1

Thank you so much for replying  everyone. Unfortunately, I am currently very busy and so it will take me time to read through everything (I'm not saying make your answers shorter) so please I may take a while to reply so please don't think Iv'e just ignored everything.

Thank you so much for your effort in answering to my topic.

All the best,

JWMuller

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