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uberwolfe

Overshooting runway during autoland

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Hey all,

 

I'm having a rather frustrating issue trying to land the 737 with ILS at various aerodromes.

 

The issue seems to occur randomly. Sometimes it will work flawlessly - and then other times it will fail even under exactly the same conditions.

 

Thankfully, the failure is the same each time... the autopilot completely overshoots the runway. The little bug on the HGS will start by pointing to the correct point on the runway during approach, and then as I get closer it will point to the far end of the runway and sometimes even beyond. Then I end up sailing high over the runway (up to 500ft agl).

 

I have everything configured correctly, as like I mentioned sometimes it will work perfectly... My speeds are correct, everything is armed as it should, the little diamonds indicating the glidescope and lateral position are lined up perfectly - there are no disconnects or warnings... the plane thinks it's doing everything correct... and it will still overshoot.

 

Could the altimeter be reporting incorrect values? Is it likely that the aerodromes are configured incorrectly? I use various OrbX scenery and airports but the issue occurs exactly the same whether it's a default FSX airport or an OrbX...

 

When the problem occurs the plane seems to be coming in high - so I disengage APs and end up putting it down manually. My confusion/misunderstanding as to what's going on really puts a downer on what are otherwise perfect flights!

 

I searched around for similar threads on this forum, and while there are some with similar issues none seem to provide a solution for me.

 

Any assistance would be greatly appreciated, thanks! :)

 

Note: I use Active Sky Next.

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I'm having a rather frustrating issue trying to land the 737 with ILS at various aerodromes.

 

The first thing is to (and I know this is gonna sound stupid, but you'd be surprised how many people don't know this) ensure the airport has an ILS.  You cannot autoland at any field without an ILS approach (that means no VOR, no RNAV, no NDB autolanding).

 

Additionally, ensure your hardware throttles are all the way back at their idle stop, and that you have your autobrake set to a value above 0.

 

Have you tried the tutorial flight?  Did the autoland function work when you landed at EHAM?  If you haven't tried the tutorial, please try it and report the results.

 

One final note: ILS and landing are two completely separate topics.  While you need an ILS to autoland, the autoland function is a different concept, and it's best to refer to it as autoland instead of ILS landing (or land with ILS, etc).

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Thanks for clarifying correct use of terminology - as you can tell I'm not an expert on the aviation side of things!

 

The airports I am referring to do indeed have ILS. I have the real charts with all information I need. For the particular runways I generally set autobrakes to 2 and hardware throttles are back in idle position.

 

Here are the charts to the aerodrome and approach that last failed for me.

YBBN (rwy 19): http://www.airservicesaustralia.com/aip/current/dap/BBNAD01-137.pdf

ILS-Y rwy 19: http://www.airservicesaustralia.com/aip/current/dap/BBNII02-139.pdf

 

I did do the tutorials a while back and was able to autoland without a problem. Maybe I should try it again... could be a configuration issue?

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What do you mean by "Overshoot".

 

In Aviation this has several meanings including:

  1. The aircraft touches down on the runway and fails to stop before the end of the runway, running off into the grass at the end.
  2. The aircraft doesn't turn fast enough to capture the centreline and 'balloons out' to the opposite side before returning back to a stabilized approach

From your discription it seems it's either above glideslope or not continuing on glideslope, and getting "high" on approach.

I'm assuming you have APP mode armed, so it's starting to descend to maintain glideslope to begin with.

 

Do you have "Both" autopilots running after glideslope capture? I believe Autoland becomes unavailable if you have just 1 autopilot active below a certain altitude (800ft by memory, but that might be the 767 value) - however it will still follow glideslope, just not go into "RETARD/FLARE" mode.

 

Speed?
 

 

Just general info: Altimeter has nothing to do with how ILS works, just with the presence or absence of config warnings, altitude callouts etc. The ILS/Glideslope still track down the slope as defined by the radio transmission system on the airfield. The slope is always the same, and always originates from the transmitter, GPS, altimeter and even IRS not required.

 

 

Here's a check for YBBN :

  • Flight Director is ON (should have been since takeoff)
  • Auto Throttle is on and in a mode (VNAV is a good one)
  • FMC has your aircraft weight, and has a final approach flap/speed selected in PERF/INIT, or the Landing Flap manual mode is set with a Vref/flap setting (those are the knobs above the EICAS/Engine instrument screen you can use if the CDU is malfunctioning or if you worked for SouthWest Airlines in the previous decade when they still pretended 737-700's were 737-200's.)
  • ILS Frequency set into both NAV radios (technically you can get away with just NAV1, but that will throw out errors and warnings)
  • Course value set to the ILS inbound course (196 for YBBN rwy 19) - Both sides. (Can get away without this, but again, errors, warnings, loud beeping noises).
  • Descend to 2500ft in LNAV/VNAV - preferably with a descent wind forecast entered... or a headwind during descent.
  • Reduce speed in the speed window to cross SINNK at 2500 (and not a foot higher) and at 180 knots (or 200kts, but no higher)
  • Before reaching SINNK by about 3 miles, confirm the ILS indications on the PFD are active (purple dots). Click "APP" to arm the approach LOC/GS modes.
  • The aircraft will turn to intercept the ILS localizer. You want flap 5 out before/while this happens.
  • When the Glideslope centres in the PFD, check that the Announciator on the PFD show the GS and LOC are captured (see yellow rectangle below)
    mqdefault.jpg

     
  • When the descent starts (MCP still set to 2500ft, Autopilot following Glideslope down below 2500) lower the landing gear, reduce speed to the minimum flap speed.
  • Once the glideslope and ILS are tracking and active (Green), select the other autopilot so both are active (A+B )
  • Keep lowering flap and reducing speed till you get to the chosen landing flap, usually either flap 30 or flap 40 (Choose this in the FMC's PERF-INIT page).
  • Pull your hardware throttle quadrant (if you have one) to idle null zone during the descent to avoid random throttle increases from control spikes/jitters.
  • Be fully configured (Gear down, flap at least 15) before reaching 1000ft.

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Thanks hopskip - apologies again for using incorrect terminology. You will have to go easy on me, I'm pretty new to this stuff and don't come from an aviation background!

 

From your description high on approach is exactly what is happening. My process is exactly as you describe, though my speed at SINNK may have been a little over 200kts from memory.

 

The odd thing is that the ILS indications on the PFD are still lined up perfectly, this shouldn't be the case if I'm high on approach correct?

 

I'll give the landing another go tonight and see what comes of it, I really appreciate the info!

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Thanks for clarifying correct use of terminology - as you can tell I'm not an expert on the aviation side of things!

 

You're welcome.  Just want to get people pointed in the right direction.  Aviation is a complex beast, that's for sure, and knowing the proper terms truly helps if you ever want to try Googling various topics.

 

 

 


The airports I am referring to do indeed have ILS. I have the real charts with all information I need. For the particular runways I generally set autobrakes to 2 and hardware throttles are back in idle position.

 

So it seems you have everything set up properly.  That's a good start!

 

 

 


I did do the tutorials a while back and was able to autoland without a problem. Maybe I should try it again... could be a configuration issue?

 

That points to either procedure or config.  Trent (hopskip) has alluded to more of a procedural issue (forgetting to engage the second AP before the config test).  What you might try is to use the tutorial as a guide for your flights around OZ.  Just follow the procedures in the tutorial, specifically those parts right at the end, when it's talking about the autoland setup and procedure.

 

Try again and let us know how it goes!

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Ok, so I worked out the problem. As you guys were alluding to, it was an issue with my procedures :blush:

 

What I was doing wrong was trying to activate the second autopilot before G/S and LOC were captured, so I was alternating between CMD A & B and wondering why I couldn't activate both. I read in the FCOM that when this happens APP is deactivated, and has to be reactivated - which I never did... so that explains why I wasn't correctly following the G/S.

 

I've since done two perfect autolands. Huge thanks to Kyle and Trent for their assistance!!!

 

Now as soon as my yoke arrives I can practice some serious manual landings and will undoubtedly hassle you guys with a new set of noob problems, haha! :P

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I've since done two perfect autolands. Huge thanks to Kyle and Trent for their assistance!!!

 

Awesome!  You're welcome!

 

 

 


Now as soon as my yoke arrives I can practice some serious manual landings and will undoubtedly hassle you guys with a new set of noob problems, haha!

 

haha - bring it.  Doing things by hand is definitely a fun/different challenge.  You'll be flying the River Visual to Runway 19 in no time  :P

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