Hi People,

 

Please let me know if I've posted this article in the wrong area... I'm new to the forum! But here goes my query: When using the Boeing 747-200/300 Series (Just Flight product by CLS) with MS FSX as my basepack, I'm getting a difference in height readings between the Pressure Altimeter and Radar Altimeter. Whatever altitude clearances I'm given from ATC, my Radar Alt always produces a reading MUCH LOWER, even when I input the given Altimeter/Baro settings by ATC (eg; 29.94). This is obviously very dangerous, particularly when setting up a landing approach in areas of high terrain. So, I increase my height, in order that my Radar Alt reaches the final approach height given by ATC (and to avoid danger), but then because my Pressure Alt reading has increased by about 600-800ft more (sometimes by a couple of thousand!!), ATC then instructs me to descend before it transmits any further! I don't seem to have a problem when using any other programme, only this one... so I'm wondering if someone out there can shed some light on this issue??

 

Thanks.

I'm getting a difference in height readings between the Pressure Altimeter and Radar Altimeter. Whatever altitude clearances I'm given from ATC, my Radar Alt always produces a reading MUCH LOWER, even when I input the given Altimeter/Baro settings by ATC (eg; 29.94). This is obviously very dangerous, particularly when setting up a landing approach in areas of high terrain. So, I increase my height, in order that my Radar Alt reaches the final approach height given by ATC (and to avoid danger),

 

You do realise that the Radar Altitude is the altitude above ground (AGL) don't you? Unless you are over the sea or a land depression below sea level (as in Holland, Dead Sea or some desert in the U.S.) it will always be less than the true AMSL altitude. And it isn't affected by the pressure settings because it is determined by the time it takes radar waves to bounce back off the ground.

 

ATC never give radar altitudes for any clearances or instructions. Radar altitudes are used for altitude call outs on final approach, for Decision Height checks ("minimums" call out when RADIO is selected for DH instead of "BARO" for MDA), and of course your own situation awareness.

 

Regards

Pete

Hi Pete,

 

Thanks for your prompt reply. Yes, I am aware of how a Radar Altimeter basically works, and I understand it provides a more accurate reading of height, compared to a Pressure Altimeter. However, couple of things here I wasn't aware of: I didn't realise a Radar Alt would only give a reading over land. I imagined the radio waves of this device would bounce off any surface, be it solid land or water - and at any height?

 

Of course, if you are flying over water or, as you said, a desert or an area of flat land depression below sea level, all those surfaces are level terrain... so you're Pressure Alt should provide an accurate reading of AMSL. However, when making an approach into an airport situated on regular terrain (ie; an uneven surface, like surrounding hills and buildings), you're still making your descent as per ATC instructions. And the height settings you input to the Auto Pilot are still being read by the Pressure Alt, which is still giving an AMSL reading... not good when you're trying to make an approach into an airport with surrounding high terrain and you're Radar Alt is telling you something different!!

 

So what am I missing here? What am I doing wrong (or not doing), when I'm making an approach to land, but can't descend to the altitudes given by ATC, as my Radar Alt is indicating that I'm 'dangerously' low??

Regards,

 

Ned.

All instructions by ATC are pressure altitudes. The radar altimeter is not used for these things. What you are missing is the charts. You need to read the charts and follow the instructions for your arrival. The arrivals have been designed so that you wont fly into a mountain side.

 

You might want to not use colors when you post, its really, really annoying for the reader. Personally I normally dont even reply to posts where the poster have used colors to attract attention to himself. Using colors is considered bad etiquette

I didn't realise a Radar Alt would only give a reading over land.

 

I don't think I said that or implied it. Although the term "AGL" is of course short for "Above Ground Level" it really refers to whatever the surface is below the aircraft.

 

However, when making an approach into an airport situated on regular terrain (ie; an uneven surface, like surrounding hills and buildings), you're still making your descent as per ATC instructions. And the height settings you input to the Auto Pilot are still being read by the Pressure Alt, which is still giving an AMSL reading.

 

 

Well, not strictly "presure alt" which is a term reserved for meaning the altitude corresponding to the standard prerssure 29.92" or 1013.25 hPa. But yes, if you mean the altimeter driven by barometric pressure that is always what the A/P is using.

 

. not good when you're trying to make an approach into an airport with surrounding high terrain and you're Radar Alt is telling you something different!!

 

I still think you are misunderstanding something. ATC will always command altitudes, AMSL, not radar altitudes, AGL. You as the pilot are responsible for avoiding terrain and the Radar Altitude assists you in this (as would charts of course).

 

So what am I missing here? What am I doing wrong (or not doing), when I'm making an approach to land, but can't descend to the altitudes given by ATC, as my Radar Alt is indicating that I'm 'dangerously' low??

 

In the real world that wouldn't happen except by error, but FS ATC is stupid. You are in charge of the aircraft and you must disobey ATC if otherwise you'd put the flight in jeopardy. That actually applies in the real world too!

 

Pete

All instructions by ATC are pressure altitudes. The radar altimeter is not used for these things. What you are missing is the charts. You need to read the charts and follow the instructions for your arrival. The arrivals have been designed so that you wont fly into a mountain side.

 

You might want to not use colors when you post, its really, really annoying for the reader. Personally I normally dont even reply to posts where the poster have used colors to attract attention to himself. Using colors is considered bad etiquette

 

Gosh, really??

 

Perhaps some people may find reading coloured text a little hard, but I had no idea it's regarded as bad etiquette!! My motive on this site is genuine and in good spirit... and certainly not an attempt to 'draw attention to myself'. Using a different coloured text, especially when quoting on someone's post, in my opinion breaks up the continuous black text and therefore, thought would make for some easier reading? But maybe not... so black it is then.

 

So anyway, when you say 'charts', what charts do you mean? NDB and VOR/DME Approach Plate charts, or other? And where would I obtain these charts to use with MS Flight Simulator?? Thanks.

I still think you are misunderstanding something. ATC will always command altitudes, AMSL, not radar altitudes, AGL. You as the pilot are responsible for avoiding terrain and the Radar Altitude assists you in this (as would charts of course).

Yes Pete, I understand that ATC will always command altitudes in AMSL. The problem is, that when I'm making an approach into an inland airport surrounded by high terrain, I am suddenly finding that I'm in fact way too low for the correct approach... as indicated by the (AGL) Radar Altimeter. And when carrying out a flight using the standard Flight Planner in FSX, the stupid ATC will keep instructing you to descend to the (AMSL) Barometric altitude it requires you to, before giving you your Vectors To Final and eventually, the clearance to land.

 

Yes, of course, as you mentioned, in real world aviation, that wouldn't (or at least shouldn't!) happen... as you would also consider what your eyes are telling you too. Along with aviaton charts for reference, in reality, I'm sure that Approach Centres and Control Towers would know the ground clearances required for pilots making an approach. And they would provide vectors to flight crews, in guiding them around high terrain and in for their final approach for a safe landing.

 

So maybe this issue is just one of those sticking points with Microsoft's FS programme... I don't know. But I've yet to find a solution.

I mean all the charts, from ground taxi charts all the way up to enroute. Obstacle charts seem to be very relevant for your problem. Other charts like arrival charts / departure charts might also be very useful, as the arrivals / departures have been designed to avoid mountains and other objects.

 

As for where to find charts, this is highly dependant on where you fly. I see that your nickname on AVSim is Speedbird70, so I assume that you are from the UK. You can find charts for UK airports / airspace at http://www.nats-uk.ead-it.com/public/index.php%3Foption=com_content&task=blogcategory&id=6&Itemid=13.html

So maybe this issue is just one of those sticking points with Microsoft's FS programme... I don't know. But I've yet to find a solution.

 

The solution is to check the charts or only fly to such airports in VFR conditions so you can see what you are doing.

 

Pete

One of the other problems it sounds like you are having, is with ATC itself, and it is one which is fairly well known to many FS users - ATC vectoring you into terrain. When I got sick of that happening on radar controlled approaches to LEAM, with ATC continuously vectoring my airliners into the Sierra Nevada mountain range when in IMC, I bought the payware ATC program, Radar Contact, and I have found that such issues no longer occur when using that for my ATC, because it seems to be better aware of keeping you clear of terrain amongst other things. Although as others have noted, it is also the pilot's responsibility to be aware of such dangers, and have a general idea of whether there is some granite in the middle of that cloud they are descending through, which is where either charts, or aircraft with terrain warning systems on board them will help.

 

But it is not the only issue you can find with the default FS ATC, for example, since for the purposes of ATC commands, FS takes a guess at what aeroplane you are flying (based on reading the config file) and then it commands the ascents and descents on flight plans based on what it determines is appropriate. With payware add-on aircraft, the guess FS makes at what aircraft you have is not always appropriate. For example, you may be flying an old DC-2 and ATC may start chivvying you to expedite your climb instead of understanding that a heavily-loaded DC-2 might not be able to climb at 800 feet per minute when up near ten thousand feet, or again, it might start your descent when eighty miles from the destination, which would possibly be appropriate for a 747 at 40,000 feet, but probably not ideal for a Cessna 150 cruising along at 8,000 feet.

 

Again, payware ATC programs usually handle that kind of thing better, since you can customise many aspects of them to gain more appropriate performance. The point here being that whilst the default FS ATC is not desperately bad, and can be helped a little by having a decent flight plan, if you want to do more complex and realistic procedures, the default FS ATC is not always the best choice.

 

Al

I mean all the charts, from ground taxi charts all the way up to enroute. Obstacle charts seem to be very relevant for your problem. Other charts like arrival charts / departure charts might also be very useful, as the arrivals / departures have been designed to avoid mountains and other objects.

 

As for where to find charts, this is highly dependant on where you fly. I see that your nickname on AVSim is Speedbird70, so I assume that you are from the UK. You can find charts for UK airports / airspace at http://www.nats-uk.e...&Itemid=13.html

 

You assume correctly... and thank you. I shall take a look on the link you've provided and comment on this matter in due course

If you look at the UK Final Approach charts to, say EGLL, you will find that altitudes are given above mean sea level (QNH) and above threshold (QFE). These are both barometic readings: neither has anything to to with radio altitude,

One of the other problems it sounds like you are having, is with ATC itself, and it is one which is fairly well known to many FS users - ATC vectoring you into terrain. When I got sick of that happening on radar controlled approaches to LEAM, with ATC continuously vectoring my airliners into the Sierra Nevada mountain range when in IMC, I bought the payware ATC program, Radar Contact, and I have found that such issues no longer occur when using that for my ATC, because it seems to be better aware of keeping you clear of terrain amongst other things. Although as others have noted, it is also the pilot's responsibility to be aware of such dangers, and have a general idea of whether there is some granite in the middle of that cloud they are descending through, which is where either charts, or aircraft with terrain warning systems on board them will help.

 

But it is not the only issue you can find with the default FS ATC, for example, since for the purposes of ATC commands, FS takes a guess at what aeroplane you are flying (based on reading the config file) and then it commands the ascents and descents on flight plans based on what it determines is appropriate. With payware add-on aircraft, the guess FS makes at what aircraft you have is not always appropriate. For example, you may be flying an old DC-2 and ATC may start chivvying you to expedite your climb instead of understanding that a heavily-loaded DC-2 might not be able to climb at 800 feet per minute when up near ten thousand feet, or again, it might start your descent when eighty miles from the destination, which would possibly be appropriate for a 747 at 40,000 feet, but probably not ideal for a Cessna 150 cruising along at 8,000 feet.

 

Again, payware ATC programs usually handle that kind of thing better, since you can customise many aspects of them to gain more appropriate performance. The point here being that whilst the default FS ATC is not desperately bad, and can be helped a little by having a decent flight plan, if you want to do more complex and realistic procedures, the default FS ATC is not always the best choice.

 

Al

 

Hi Al and thanks for your reply.

 

I'm not sure that my navigation problem on approaches is much to do with ATC itself, as it is with the whole FSX programme. As you pointed out, with FS taking into account the type of aircraft you are using and then ATC calculating your approach. But also, in addition to surrounding terrain, there's aircraft location, speed, height, weight and weather... quite a lot of information for the programme to compute there! Not to mention a whole load of other addons you may have plied your FSX basepack with. I appreciate that Microsoft and other associated flight sim software manufacturers, have put a lot of reasearch and hard work into the production of their programmes - and I guess you can forgive them for missing a few things out! Hence the deficiency of FSX's ATC I've mentioned.

 

Charts or no charts, yes pilots do have a duty of also considering what their eyes are telling them, and reacting appropriately to avert danger. But it does drive me nuts when making an approach on FSX, where ATC is repeating the same message over and over again to descend, but I keep having to climb and go around, in order to avoid the impending threat of close proximity terrain! Needless to say, because I ignore ATC guidance in these cases, clearance to land never comes!

 

However, on the FSX Flight Planner, when loading a default flight route, you can obviously change it to your personal liking, by clicking/holding your PC's mouse and dragging the 'line' between Waypoints. Having said that, like most flight sim enthusiasts I imagine, I'd like to make my simulation experience as real as I can get it. So I'm open to various suggestions, as you've made one here: Payware 'ATC Radar Contact'. Where would I obtain this from? And is it similar to the programme 'AirNav Radar Box-3D', which I've seen advertised on the back of various aviation magazines??

Regards,

 

Ned.

I recommend flying online on one of the big networks (vatsim and ivao) with real humans as ATC, it vastly improves the experience in my opinion. Nothing beats interacting with humans when it comes to ATC, controlling traffic is too complex to program into a piece of consumer software. The ATC business is so dynamic and complex, so its hard to get it right.

I mean all the charts, from ground taxi charts all the way up to enroute. Obstacle charts seem to be very relevant for your problem. Other charts like arrival charts / departure charts might also be very useful, as the arrivals / departures have been designed to avoid mountains and other objects.

 

As for where to find charts, this is highly dependant on where you fly. I see that your nickname on AVSim is Speedbird70, so I assume that you are from the UK. You can find charts for UK airports / airspace at http://www.nats-uk.e...&Itemid=13.html

 

Also, do you have any suggestions for finding charts of international airports? Thanks.