The ATC says approach 15 miles from the marker fly heading X, I fly heading x, and hit the app hold button, am I simply hitting it too early?

Hi, Dragonmount,

 

You need to explain what is or isn't happening that is causing a problem.  It would also be helpful to know what type of aircraft, what airport and what runway are involved.

 

Mike

Lancair legacy (real air) KGSP runway 22. It turns, but nowhere near the actual airport, I've never used APP hold before a few days ago, and have only a vague understanding of what it does.

Here is a test flight I use to check the limits and proper operation of ILS/AP systems. Any aircraft can be used.

ILS Procedure for FSX (practice) at KSEA (B738 <39% fuel):
 
Set COM1 to Tower 119.9.
Set NAV1 to ILS RWY 34 RT 110.3.
Set NAV2 to ILS RWY 34 LT 117.1. (Both DMEs the same)
Set GPS/NAV switch to NAV.

1. Taxi to position and hold Rwy 34 RT.

2. Don't call the tower and they will ignore you. ATC/Tower procedures come later.

3. Set AP HDG to 343, ALT to 5000, and AT AS to 250.Turn HSI CRS to 343 just for correct card situation.

4. Takeoff. Set AP/HDG/ALT/AT to ON.

5. Turn HDG to 168. Aircraft will turn to 168 and level off at 5000.

6. At 23 miles DME, turn HDG to 010 and AT AS to 190. (The LOC needle will stay active to about 25 Miles. When the DME reads about 20 miles the Glideslope (GS) needle will go active and peg to the top of the guage and the BELOW G/S light will come ON).

7. When the LOC needle comes off the right peg, set APP to ON. The aircraft will turn to center the LOC needle and HDG will dis-engage. The GS needle will slowly come down and center (~18 NM). The ALT will dis-engage.

8. Drop 3 clicks of flaps, Set AT AS to 160. Drop gear. The aircraft will fly 2.5 degree slope.

9. Drop gear and set AT AS to 150. Add flaps slowly to Full DN.

10. At 100 feet, dis-engage AT and AP, close power levers.

11. Flare/land.
 
Do a touch and go to try it again.
 

Good site for basic info:

 http://www.navfltsm.addr.com/
 

Have fun
Dave

Do you have the correct LOC frequency tuned in?

From how I understand it, ATC will give you a heading so that you can intercept the localizer signal at a proper angle. If you're in reach of that signal and you press the APP button(provided that a: the freq is correct and b: you're in NAV mode rather than GPS) the aircraft will align with the course of the LOC. As you come cloesr to the ariport the glideslope of the ILS will be captured, which will then lead your aircraft down to the runway (although you're supposed to diconnect and hand-fly from a certain altitude, hence the RWY has to be in view by then).

 

In case you don't know, here's a rough description of how the LOC and G/S work:

The localiser sends a radio signal - similar to a VOR beacon, but only on one specific direction - which works a a horizontal guideance for the pilot. In most cases the course of the LOC is identical to the RWY heading (with a few famous exemptions such as Kai Tak of Innsbruck). The glideslope works pretty similar, except that it's a vertical guideance. Combined they make an ILS.

I'm not familiar with that aircraft.  Generally, if you are using the autopilot to direct the aircraft on a course to intercept a line extending out from the runway, when you press APProach Hold it should arm.  However the previously selected mode -- heading hold for example -- should still be active.  When you cross that runway extension line, APProach Hold will take over and the aircraft should turn toward the runway and follow the localizer toward it.   KGSP runway 22 also has a glideslope - when the vertical dot  or horizontal line showing the glideslope lines up with the center of the VOR 1 indicator, the aircraft should descend on the glideslope.  It's best to approach the glideslope from below.

 

Some things to check:

 

1)  Is the Nav 1 radio tuned to the ILS/GS frequency?  On my system runway 22 is 110.70 (but you should check the FS X map to make sure it's the same for yours).   It's also helpful to set the VOR 1 course to the runway heading (218 for runway 22).    If you have inadvertently tuned the frequency of a different ILS or VOR, the plane might head toward that runway instead.

 

2)  Are you on a course to intercept the line extended out from the runway?  If you are following an FS X IFR flight plan it should vector you pretty well to intersect this line.   

 

Mike

 ... you're in NAV mode rather than GPS) the aircraft will align with the course of the LOC.

 

 

That's a very important point that I forgot to mention:  If you have a NAV/GPS switch and it is in GPS the aircraft probably won't lock onto the localizer and glideslope and will turn in an unexpected direction. However with a more complex aircraft that has LNAV, it should switch to approach mode (localizer & glideslope) when crossing the extended runway line. 

 

Mike

The clue to push the APP button is the Glideslope moving downward assuming you have followed the instructions of ATC correctly. Before you push the button you should have your speed, landing gear, flaps and lights already set.  Note too that you must keep the Localizer center unless your plane has a LOC button in which case it should have been pushed already and it is already auto laterally controlling you airplane. Also, you should use the GPS to get a visual idea if your approach is going within landing expectations. Good luck.

 

Cheers,

 

MAB

 

 

The clue to push the APP button is the Glideslope moving downward assuming you have followed the instructions of ATC correctly.

 

Sorry, I don't agree.  You might have already crossed the extended runway line before the glideslope dot or line starts to move.  In other words you will activate approach mode too late.  It's OK to arm Approach mode when you are on a course that will intersect the extended runway line; indeed you want to do so well before you cross the extended runway line or the glideslope indicator starts to move.

 

Mike

The Approach button will set you up for landing at the runway. As stated above several times, you MUST have the runway ILS-freq set in your NAV1 radio for it to work. It will tell the plane if you are inline with the runway (localizer) and if you are on the glidepath or not (Glide scope).

 

Also, you have to dial in the course of the runway (like 341 degrees). In the lancair you twist the yellow knob on the NAV1 guage if i remember correctly (next to theorange heading bug you use to fly the heading ATC gives you).

 

Before you pass the imaginary éxtended runway line, you press APP on your autopilot and the plane will turn when you intercept the localizer to set you up in line with the runway.

Then it will auto descent when the glidescope is alive.

 

So this only works on runways wih an ILS!

 

 

you MUST have the runway ILS-freq set in your NAV1 radio for it to work.

That's an essential piece of information, too.

 

 

 

Also, you have to dial in the course of the runway (like 341 degrees).

That's not necessary (in FSX, that is, don't know about real life), at least as far as I remember. It is helpful to have it set approximately to the right heading, though, because then the needles show your position relative to the LOC correctly, which takes away a stress factor and a source of error in that phase of flight.

 

 

7. When the LOC needle comes off the right peg, set APP to ON. The aircraft will turn to center the LOC needle and HDG will dis-engage. The GS needle will slowly come down and center (~18 NM). The ALT will dis-engage.

 

Probably the issue - you need to wait until the localizer needle moves (you can anticipate this if there is an NDB anywhere along the extended centerline of the runway you are using).

 

Remember to disengage the autothrottle if you are using this - does not disengage when you disengage the autopilot.

Probably the issue - you need to wait until the localizer needle moves (you can anticipate this if there is an NDB anywhere along the extended centerline of the runway you are using).

 

I don't see why you need to wait for the localizer needle to start to move.  You might be busy with something else and miss it until you have overshot the extended runway center line.  You can arm approach mode once you are on an intercept course to the extended runway line.  The only way "early" arming will cause a problem is if you are so far away from your destination airport, that you accidentally are near another ILS using the same frequency.   Very unlikely if you are 20-30 miles from your intended destination.

 

However one thing to be aware of is that sometimes the opposite-direction runway uses the same ILS frequency (not the case at KGSP).  So if you are approaching from the opposite side of the airport from your intended runway, you could pick up the wrong ILS.  So you would not want to arm Approach then.  But, again, if you wait until you are on an intercept course to your intended runway, you can set the Approach Hold.  It will arm and become active when it detects the localizer.  An intercept course typically will be about 45 degrees or less from the approach direction, 218 for KGSP runway 22.  So for that runway if you approach the imaginary extended center line at a course between 263 degrees and 173 degrees you will be OK.

 

 

 

Remember to disengage the autothrottle if you are using this - does not disengage when you disengage the autopilot.

 

I think what TXHills is getting at is that for many aircraft you need to manually turn off the autothrottle or it will try to maintain approach speed after you land, and prevent you from stopping.  However you do not want to shut off the autopilot until you are close to landing (or leave it on if you are doing an autoland).

 

One other "fine point:"   After you press Approach, some aircraft will start to descend on the glideslope even if they are not yet lined up with the runway.  This can be dangerous, as there might be high terrain to one side of the runway approach path.  So rather than pressing Approach (which includes locking onto the glideslope), it is better to press LOC (localizer).   This will allow the aircraft to capture the horizontal path to the runway, but it won't capture the glideslope.  After the aircraft has captured the localizer, then press Approach, which will keep the aircraft on the runway approach path and also capture the glideslope at the correct time.

 

Mike

Will try the flight again in a few minutes and tell exactly what I did and exactly what happened. Thank you for the interesting reading.

A much more specific answer by Mike777 - and had my RW GA pilot pants showing with the 'wait til the needle moves' - true that if you are flying a 7xx or Airbus 3xx you will likely overshoot the localizer (which may happen anyway).

 

So Dragonmount, to quote Hercule Poirot - "We wait with the breath that is bated" - hope it works out, anxious to hear!

 

 

So Dragonmount, to quote Hercule Poirot - "We wait with the breath that is bated" - hope it works out, anxious to hear!

 

My sentiments exactly, but TXHills said it much better!

 

Mike