Staying on that ILS! (Especially Glideslope!)

[ba195]

Hi,

I am having real troubles staying on the glideslope during short finals as it just goes everywhere! (The indicator that is, not the plane!). As I am about 500ft off the ground (Radar Alt) the glideslope becomes so sensitive I nearly always get a glideslope warning as it just "jumps" out of position, whereas the PAPI/VASI lights show 2red/w white, the glideslope nearly always tells me I'm too high/too low!!. I always look up what my descent rate should be according to my landing weight, and I always use that descent rate, it's just the final stages I need to hack! Boeing 767-300ER I'm talking about here...

Also, rudder use on the final approach??? I always thought that you had to use rudder adjustments to stay on the LOC during the final stages.....is this true as it looks a bit "wrong" or "odd" if you seed an aircraft banking all over the place on final approach...just to stay on the loc. It seems more sensible to use the rudder for small adjustments. Anyones opinions, rants, suggestions accepted and appreciated.

Thanks
Ben Alexander-Brown

[SFly]

One of these PIC/FS2000 questions again, eh?

Well I don't know exactly what's happening here because I wasn't there but it seems to me that it's a standard case of "ILS-itis". When you get very close to the source the beam tends to begin to "flail" and go crazy at the smallest deviation. This is normal (though I don't know exactly how much it "goes everywhere"). It depends on the amount of deviation really. It if is just minimal deviation then try to avoid the habit of following the ILS up and down like a lost sheep (especially if you are in good visual contact with the runway) because as soon as you begin to climb/descend etc you will find yourself lunging the opposite way again because of the indicator going the other way. Again, it matters how much deviation we are looking at. The VASI/PAPI are much less sensitive which is why they will tell you if you are correct or not. As you get closer to the runway the ILS will begin to move more, which is sometimes worrying in IFR low visibility conditions! But if the ILS is close to the centre and changing up and down, generally you are on course.

As for the LOC, again, these are quite general questions and so it is difficult to answer. Variables include how much crosswind, position in relation to the runway etc. If it goes beyond rudder usage and bank is necessary, then that is what is necessary. If not, then not (que sera sera). Bank inputs into the wind works in stronger situations, but you need the rudder to line back up once at touchdown point.

My mind works in mysterious ways so I hope somebody else understood that except me.

I believe I'm rambling so I will stop now.

Hope this helps to any extent, :)
SFly

[fireflybob]

Not sure what type of aircraft you are flying but here is my advice based on a lot of experience!
Broadly speaking, it's power to control speed and attitude to control glideslope (on the approach, that is). Near the ground think of glideslope as an "attitude demand indicator" - the instant it shows a deviation make a small adjustment to the attitude. Remember also the effect of aircraft inertia.
My advice would be to NEVER use the rudder to change heading to maintain the localiser - if you have to make a (mini) turn then use the controls as you would normally - i.e. aileron and, perhaps, a tad of rudder to balance. Flying just a small amount out of balance affects your physiology (Vestibular apparatus in ears etc.) and leads to a feeling of insecurity!
Hope this helps.

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[Sensible]

I'm assuming that we are talking flight sims here of which I have no experience, However, here's my experience of spam cans for what it's worth: Use aileron only to correct untill below decision height. Close to the ILS just a one one thousand, two two thousand count during adjustment of the aileron will generally be sufficient to bring the needle back to centre. Any adjustment should be done well before the needle becomes very far off centre anyway. It is a great temptation to try to centre the needle too quickly and in doing so, over compensate resulting in a snaking approach path with the wings dipping back and forth. If this is a flight sim we are talking, you may not have had the benefit of a flight instructor and be fixating on one particular aspect of the approach especially if as you say you are trying to go visual at the same time.

[deltahotel]

Don't chase the ILS indications. If there's an error (GS or LOC) make an adjustment (small pitch change or small hdg change - use aileron) and let it take effect. Trim - always. Expect to have to make corrections as you get closer to the ground - think about how the wind changes between 2000' and the ground and how this will affect both head and cross wind components. Keep practising, and relax Bloggs! Good luck.