Sign in to follow this  
martinlest2

ILS landings fall short of runway

Recommended Posts

I have never found out why so many instrument landings I make (withall jet aircraft as far as I can tell) end up with the glidescope bringing the aircraft down too fast and consequently wanting to land well short of the airport. The approaches are normal in all other respects, and the PAPI look good at the time the aircraft picks up the glidescope. But descent is then too rapid and the PAPI change to all red before long. If I don't disengage the AP, AT, FD.... and pull up (panic!) I land amid houses and trees (or whatever). Am I doing something wrong? Maybe, but if so, why are 50% of my instrumental landings fine, the aircraft being lead down more or less to the runway threshold point by the glidescope?I find that setting flaps to only 15 - 20 degrees sometimes helps a bit - touchimg down at about 150-160KIAS, for a B737. But the coming down short happens with PM2's Concorde too, so it can't really be a flaps problem.Advice here much appreciated ! Thanks.Martin S.

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

I fly the PMDG 737 also, and have no problem tracking the ILS, which I use all the time.

Share this post


Link to post
Share on other sites

Martin,My hunch is that your airspeed isn't correct for the weight and flap setting. First, landing flaps-30 should be set on all Boeing jets from the B727 thru the B777, according to all of my flight notes. Second, approach speed is not a single number that comes out of the Flight Sim documentation; it must be based on the weight of the aircraft at that time.My first recommendation is to get some V-speed charts for the aircraft that are giving you trouble. Do a file search for "Matt Zagoren". He has compiled performance charts for many of the large jet aircraft.When all else fails and a speed chart isn't available, here's how I pick an approach speed for these aircraft:- While still in level flight, well before intercepting the glide slope, adjust the airspeed so the aircraft is slightly nose up.- When stabilized on the GS, this should give you a slightly nose down attitude.- When 1000 feet above the field, reduce the throttle so the speed across the threshold is about 10 KIAS slower.- Nearing touchdown, the aircraft should be close to a level attitude (i.e., negative 3 deg glide slope and positive 3 deg angle of attack)- Last, give it a little flare and a smooth touchdown.To summarize: If you're on the GS with a near level attitude, the airspeed is probably about right. If the nose is pitched up very much then airspeed is too low, the aircraft (autopilot) is struggling to maintain lift and may fall through the GS, as you described. Nose down means too fast and likely to overshoot the GS.For me, the best way is to know the weight and use a speed chart to determine approach speed. Next best is to hope I can get the attitude adjusted before reaching the glide slope.Please let us know if any of these ideas were helpful.Regards,JerryH

Share this post


Link to post
Share on other sites

Thanks for this. Yes, Jerry, perhaps it's a weight thing - that's one aspect of the flight sim I tend to give too little consideration too, I admit. (I often end up landing with 80% of fuel left, having forgotten to adjust the amount before take off). Your comments about nose angle/attack angle are useful too - I'll check these too, though I've never been aware of excessive nose-up attitude. I should also check what happens if I re-run a landing (I have saved a dozen or more approaches so they are easy to retry) that came down short, but increase the airspeed substantially (just as an experiment). That said, I think I tend to touch down on the fast side in any case - about 160KIAS for a 737. I'll let you know how I get on. As I say, many ILS landings go perfectly, so I don't think it's my 'technique' per se that's at fault!Martin

Share this post


Link to post
Share on other sites

Martin - Too much fuel, too little flaps, and too much airspeed for a 737. The autopilot can't control an aircraft configured like that. Try 10% fuel, full flaps, and 130 KIAS. That's much closer to how it should be and everything should be OK then.Doug

Share this post


Link to post
Share on other sites

hard to understand here if youre saying that youre landing short due to pilot error OR an inaccurate G/S. The first thing i would do before messing with your landing technique/style is to make sure the G/S on the ILS is indeed accurate...ive seen certain airports/runways where the G/S was grossly inaccurate and would have you touch down halfway down the runway :-)...that being said though, ive never seen one of these "bad" ILS's make you land short, but it wouldnt surprise me...most ILS in fs2004 are pretty darn perfect but SOME really are way off the mark. Typically i fly the ILS down down to about 500ft then fly in viusally using the PAPI lights to guide my descent. This is of course is only possible if weather permits (+1 mile vis 4000RVR min).Dave

Share this post


Link to post
Share on other sites

Hello All,I'll give you a prospective from a real world pilot who has flown a vast variety of Military, cargo and civi aircraft . . . and they all seem to respond to the same technique, IF, the AP on the aircraft, (yes, some respond different in FS due to .air file and .cfg files)is any way close to being right.1.Aircraft are flown by the numbers. There are proceedures for every single aircraft out there that MUST be followed, IF you desire to make a consistant, good landing time after time. They consist of checklists, CG cfg, fuel dist, total weight, payload, temp, humidity . . . the list goes on. Each one of those factors contribute to the landing phase of the aircraft. Screw up one or two, or just ignore them and your landing is NOT going to be pretty.Add in weather, which never seems to cooperate at the most demanding time and you have a recipe for diaster.2.Alot of NON real world pilots are under the assumption that the AP means that you 'don't have to fly the aircraft'. (those of you who do know this, kindly ignore me. I'm only acting as an information giver here, nothing else). I'll give you an example of 'fly the aircraft'. At your pre determined decision height, you kill the AP and fly the aircraft to the runway. I prefer a DH of 300-500 feet depending upon the aircraft. This give me plenty of time to either accept the landing or call a missed approach and go around. I have talked to hundred of simmers who are NOT real pilots who think that you fly the aircraft down to 100 ft and then kill the AP . . . I don't think I would like to try that in the real world with a heavy aircraft which was not in its proper landing attitude.There is NOTHING wrong with going around! It happens every day to even the best pilots, and those who would rather GA than muff a landing are the bright ones . . . trying to FIX a bad approach, at the last moment and manhandling the aircraft has gotten many a real world pilots killed or at least bent their birds in a bad way.3.The developers of the aircraft for FS, who offer us the nicer aircraft include charts, performance figures and the like for a reason . . . they are to be read, and used as part of flying the aircraft. An aircraft may handle and perform perfectly at a give weight, but become a monster, at just a wee bit over that . . . if the developer has done his job, those numbers really mean something.Probably a good example of this is a simmer, I wont' mentione his name but he will see himself, { we since have become good friends] who really did nothing but fly around the airports, one or two pass's and then do landings and touch and go's. On one particular aircraft he just couldn't make it to the runway . . ."but I'm right at the suggested approach speed . . ." yep he was, but he was 25,000 pounds too heavy. He never adjusted or burned off his fuel, and the aircraft just was too heavy for his flap settings, approach speed and weight. When I finally got him to ck the charts and his fuel, he was amazed at the results. "wow . . . I'm not too bad after all, now!" Yep, he wasn't too bad after all, it just took a wee bit of research, reading and doing it by the numbers.Hope I haven't bored any of you . . . just my thoughts and ramblings this morning.BestClay

Share this post


Link to post
Share on other sites

Yes, thanks for the interesting replies. A couple of comments:I will certainly experiment with fuel loads, flaps and speeds. (With flaps and speeds, I have done so already of course - fuel is something I haven't paid enough attention too. That said, surely an ILS landing should be possible even when fairly heavy with fuel, if the speed is appropriately higher??). In at least 50% of landings though, at least a minute or more before touchdown, I can see that the GS is bringing me down far short of the airport (let alone the runway!) - it's not a last second thing. The PAPI go four red when they are still quite a way in the distance. I know that the plane will not 'land itself', but disengaging the AP that early means I can drift off the flight path, especially in cross-wind. That's something real-world pilots have to deal with of course, but in the end I am not a real world pilot and would prefer not to have to panic at the last minute to disengage all the AP controls, bring the nose up, making sure I'm not stalling as I do so (so much to do with no co-pilot!) ... once in a while the excitement (?) of it all is 'fun' (I'm not talking about the real world here, just FS!!), but not when it's happening for over 50% of my landings.As I say, I'll post back when I've had time to experiment more with flaps/speed/fuel combinations. (Or it might be due to poor flight models in some of the add-ons I have - too many variables!). I'm sure the fault must be mine, or lots of other people would be complaining of the same thing....Martin

Share this post


Link to post
Share on other sites

Martin,I have never had the G/S bring me down anywhere other than it is supposed to.If you can see the G/S indication failing off, and the PAPI lights are 4 red (too low) then something is up somewhere.How do you confirm your ILS radio settings?, are you sure you are not flying the BC?Dan.

Share this post


Link to post
Share on other sites

Dan, No, I definitely use the APR button - and check with the GPS that the ILS frequencies are right. I'm pretty sure that the mechanics of what I am doing is correct... It's really mystifying when I hear other people say they have never ever had this problem!!M. :-)

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this