Hello all!I've been learning how to use GPS for airports and runways that don't have ILS. I'm currently using the Garmin GPS 500 in the Mooney M20J and there's something that's confusing me. When the GPS gets me to my final approach should it automatically start descending as well or does ILS only do that?I have a feeling that GPS only gets you from point A to point B via waypoints and then when you're on approach and lined up with the runway you need to take it off auto-pilot and descend to land, but I want to make sure I'm not missing something.Thanks,Mark

mark:GPS is for lateral navigation only.--

Short answer is no.GPS descents to airfields with no ground-based aids are something that is now possible with the right avionics in a real aircraft, but by default it is not something FSX simulates, since the technology for it is relatively new and was certainly not common at the time FSX was released.So the default GPS, when slaved to the autopilot, will only fly you from point to point and not take you up or down to a specific altitude. The best you could do with it to assist on landing, would to look on the map in the flight planner and include a waypoint on your flight plan which is a few miles away from the end of a runway, then note the heading of the runway and see if there is some sort of navigational beacon in that direction. If such a beacon was then included that as the next waypoint, you could have the GPS line you up onto it, then you could start a descent on the autopilot until you were at perhaps 500 feet above the ground and then disengage the autopilot to fly the last bit yourself, but you would have to be sure that there were no tall obstructions or hills in the way!That is in fact basically what is going on with a GPS approach.As an aside, I'll tell you a funny story about GPS approach technology: A few years ago, I had a marketing person on my copywriting training course who worked for a well known avionics company. Knowing the kind of thing she would want to write press releases on, I planned some exercises for her on how to write press releases and such. Since I had to do that in advance of the course, I made up some fictional aviation products her company might make, in order that I could demonstrate how one goes about advertising such things and highlighting them in interesting ways for a press release. One of the products I 'invented' for the purpose of this, was a zero visibility cockpit GPS-based landing aid, which could get an aircraft down onto a runway with no ground-based beacons. When I pulled out the exercise sheet for this on the course, she was somewhat shocked and said: 'How do you know about this product we are developing? it's supposed to be a secret!' I then had to explain to her that, in addition to running the copywriting course, I was a keen pilot, and it was fairly common knowledge such technology was something that was being worked towards.Al

Thanks for the info guys! I thought that was the case, but now I know for sure I will plan my flights better. My FS Passengers will be much happier now that I don't end up nose-diving into the runway at the last minute! :( Al, thanks for the info and the little story..very interesting!...can always depend on you! :(

Once the GPS lines you up at the runway, you should let the nav1 radio take over. You should have entered the ils frequency for the appropriate runway in to nav1.Once the GPS lines you up with the runway, switch the NAV/GPS toggle back to nav and click APPR. This assumes you have ALT hold on.Watch the GPS map - once you get in to the green area that depicts the GS, ALT hold will shut off and you will begin to descend

Thanks Jeff! I'm OK with ILS frequencies and landings, although I haven't tried GPS/ILS landings yet. It's the airports and runways that have no ILS frequencies that were confusing me. Now I know I'm not supposed to rely on the GPS to bring me down on a glidescope like ILS does, I think I'll be OK. At least it will give me good practice at manual landings as long as the GPS will get me nicely lined up with the runway!

The FAF for an ILS is usually about 5 miles from the threshhold and the GS intercept altitude is around 2000' AGL (this are just ballpark numbers). If you have a waypoint on a GPS approach that is close to that, just plan on turning inbound around that point, then start a 500-600 FPM descent and you should be close to the correct descent angle. Most airports in FS also have 'VASI' lights to give you the proper glidepath, just keep them 'red/white and follow them down, a normal descent angle is about 3-3.5 degrees, adjust pitch/power to maintain the glidepath and you should be fine, assuming it ain't solid IFR and you can see the lights You can also check the approach plates for the MDA/DH, fly down to that, and hope the runway shows up where it's supposed to be, but it's seldom 0/0 in FS

Thanks Jeff! I'm OK with ILS frequencies and landings, although I haven't tried GPS/ILS landings yet. It's the airports and runways that have no ILS frequencies that were confusing me. Now I know I'm not supposed to rely on the GPS to bring me down on a glidescope like ILS does, I think I'll be OK. At least it will give me good practice at manual landings as long as the GPS will get me nicely lined up with the runway!

It actually depends on which GPS unit you are using. The default FSX GPS does not do vertical approaches, but the RXP 530W unit does...

I didn't know about those VASI lights, so I'll take more notice of them. I'm getting a bit better at landing...now I can touch down without crashing, but I keep overshooting the runway! Although in my defense, it's a very small island with a short runway. I figure if I can crack landing at places like that then landing at major airports will be a cynch! :( I do like the sound of that RXP 530W!! I really need to be able to descend and land on my own though.

In actual fact, if you keep overshooting, that's not necessarily a bad trait in the grand scheme of things, since it means you are aware of the importance of keeping height above the terrain. If you are too high, you have some options, if you are too low, you can find yourself in trouble. It would be a far worse trait to be constantly undershooting the runway, and so you are doing better than you perhaps might imagine. An instructor would be far more concerned with you being too low, than too high.If you are too high on approach, in reality you can sideslip the height off, by applying crossed controls (that is, aileron one way and rudder the other), which considerably reduces the amount of lift by making the aerofoil less efficient as well as using the fuselage to block airflow to part of the wing on one side, all of which makes you lose height. Note that it is normally safer on approach to stick the nose down first to get a bit more speed on before sideslipping, since at very low speeds it could cause a spin owing to the fact that one wing will lose more lift than the other, and keep in mind that if you have autorudder selected in the FSX preferences, you won't be able to try a sideslip, since autorudder will always apply rudder 'properly' for coordinated control deflections, which a sideslip is of course not.Unfortunately, FSX doesn't model sideslipping very well, although some payware aircraft do simulate it better than others. In a real sideslip, the altitude comes off pretty quickly and the noise of the wind over the airframe rises to a very obvious 'wind rushing' sound (neither of which happen in most FS aircraft, although one or two do have that feature). So in FSX, you might find it doesn't work too well to lose height on approach.However, there is a solution: If you are too high, you can hit P to pause the sim, then hit Y to enter 'slew' mode, and then hit Z to slowly slew your aircraft down a bit. When things look good, you can hit either F2 to stop slewing, or Y to come out of slew mode, then unpause the sim and off you go. Control+spacebar is another slew command worth knowing, as it resets the slew mode, but you can of course look up all these slew commands in the FSX preferences for yourself and set them to any keys you like.This might seem a bit like cheating, but since you generally cannot sideslip effectively in FSX, you can regard slewing down a bit as a way to emulate having done a sideslip. Incidentally, if you ever fly a real aircraft and use sideslip to lose height on approach, be sure to have a fairly large extra margin of speed on, because accidentally spinning on approach through stalling a wing in a sideslip, will probably be the last mistake you ever make!lOne last thing. Although I admire your thinking in wanting to crack really tough landings on short runways, be sure you don't make life too tough for yourself, as that can lead to frustration. I will say that from what you wrote, it sounds like you are doing pretty well though, so congratulations on that score.Some info on PAPI/VASI lights: http://en.wikipedia.org/wiki/Precision_App..._Path_IndicatorAl

I didn't know about those VASI lights, so I'll take more notice of them. I'm getting a bit better at landing...now I can touch down without crashing, but I keep overshooting the runway! Although in my defense, it's a very small island with a short runway. I figure if I can crack landing at places like that then landing at major airports will be a cynch! :( I do like the sound of that RXP 530W!! I really need to be able to descend and land on my own though.

If you are still flying the Mooney (not a beginners airplane) and trying to land on short runways, be sure you are using full flaps and your approach speed isn't too fast. It hates to slow down, it's one of the fastest single engines planes made. Having said that, its still a single engine airplane and FAA regs apply so it's stall speed is about the same as any other single. Fly the approach at no more than 80kts, then slow to 65-70kts for landing, and as soon as your wheels touch, retract the flaps, it will dump the lift and increase brake effectiveness. You shouldnt have any problem stopping on any runway in FS. One trick in real life which is easy to demonstrate but hard to explain here: when descenfing on the approach, pick a spot on the runway and watch it. If it moves under the instrument panel, you are going to overshoot it, if it moves away from you, you will land short, try to keep it at the same spot and thats where you will land. Practice a few times and you will get the hang of it. If you are flying in the VC, hit 'Shift+Enter' a few times to move your view up so you get a clear view over the nose of the plane.Re: GPS approaches in FS, before you buy an addon GPS, be aware most airports do not have GPS approaches, in fact most small airports don't have any at all, they are all VFR/visual. GPS is good for situational awareness but dont expect an approach installed using it.Hope this helps keep you on the runway

Thanks guys for the feedback...very helpful as always!Al, that does make me feel a bit better, knowing that overshooting is better than coming in too low. I did some more practicing today using FS FlyingSchool and I feel like I'm improving....I'm getting higher flying and landing scores, so I must be! :( I think like PIC007 said, it's the Mooney and its speed! I just can't seem to slow down in time and I always end up coming at the runway at around 100-120knots! I haven't been using full flaps....must remember to do that! I land and think I'm going to be OK, but then because I'm going so fast I can't break in time and end up going off the end of the runway! One of the first things I did when I got the Mooney was look up how to raise the seat because at its default setting you just can't see the runway at all on approach. Now I just raise the seat as soon as I start. I wonder if there's a way of changing the default somehow.....Al, that bit about sideslipping sounds complicated for me and I'm still just using a controller so I have autorudder set in settings. I think if I work on getting the Mooney slowed down earlier and use full flaps then I'll be OK.One thing I find with the Mooney as well...not sure if you guys have this plane, but when I press F2 to reduce throttle it seems to take quite a few presses before it responds and the gauges are on the right hand side of the panel, which doesn't make them very convenient to look at. I've noticed that when I reduce throttle in say a Cessna then I can see the revs come down, but when I do that in the Mooney the revs stay the same, but the manifold pressure decreases instead and I'm not sure if that has the same effect. The speed does eventually decrease, but it doesn't seem to be as easy to control as a Cessna....hope that makes sense!OK...back to the cockpit! Thanks again for the help...really appreciate it!Mark

I've noticed that when I reduce throttle in say a Cessna then I can see the revs come down, but when I do that in the Mooney the revs stay the same, but the manifold pressure decreases instead and I'm not sure if that has the same effect. The speed does eventually decrease, but it doesn't seem to be as easy to control as a Cessna....hope that makes sense!Mark

The Mooney and the Cessna are 2 different animals. I would really suggest you stick with the 172 until you get the basics down, and using a yoke/rudder pedals will make things a whole lot easier. The 172 you only have to use the throttle, in the Mooney as you have found out, you now have an extra contol, the RPM's. Manifold pressure is the same as the 172 throttle, the RPM's control the pitch of the prop. The 172 is a basic plane used for training, the Mooney is a high performance single that requires a bit more training to fly.For landing the Mooney you need the RPM's (prop) full 'forward', and the manifold pressure at idle. To help slow down, start reducing speed early, and drop the gear and flaps. Once under 100kts, push the RPM's full forward, then use MP to control speed. Have the plane configured for landing at least 3 miles from the runway, then just monitor speed and descent and adjust as needed.

Al, that bit about sideslipping sounds complicated for me and I'm still just using a controller so I have autorudder set in settings. I think if I work on getting the Mooney slowed down earlier and use full flaps then I'll be OK.

Easy way to understand sideslipping is to hold your hand out flat in front of you (like fighter pilots do when describing a move), now, tilt your hand over a bit to the left (that's what your ailerons would do), at the same time, swivel you hand to the right (that's what your rudder would do). Your aircraft would still fly in the direction your arm is pointing, but it will lose height. Cockpit and external videos of a sideslip on approach to landing:

Al

what does flap setting have to do with brake strength?