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737-800YV ILS Landing

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737-800YV ILS Landing

Postby Ivan-Pekar » Fri Jun 08, 2018 2:50 pm

When pressing 'LOC' and 'APP' etc. on the 737-800YV FCU or Autopilot --> Autopilot Settings (F11) , the aircraft does not execute any turns or descents towards the runway, as if nothing happens. I have put in the correct ILS frequency and it is shown on the map just like with any other aircraft. Does anyone know what the problem might be?

Thanks
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Re: 737-800YV ILS Landing

Postby it0uchpods » Sat Jun 09, 2018 10:26 pm

Hello.
As the developer of this autopilot, I will explain you what happen.

737-800YV has a realistic way of switching modes, so when you press LOC or APP, the LOC and G/S modes become armed. Then, once you intersect the ILS path (can see it in cyan on the map), the autopilot will capture the LOC signal, and then G/S signal. If you are already inside this path, the LOC and G/S modes will become immediately active instead of armed.

Best Regards,
Josh
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Re: 737-800YV ILS Landing

Postby Ivan-Pekar » Sun Jun 10, 2018 11:14 am

Thank you very much, Josh. I will try to follow this and make a successful landing.

Regards
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Re: 737-800YV ILS Landing

Postby Ivan-Pekar » Sun Jul 22, 2018 6:33 pm

When switching the modes, the G/S and LOC did appear on the autopilot, however the aircraft suddenly descended, until the descent became very rapid and it crashed. What happened?
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Re: 737-800YV ILS Landing

Postby Ivan-Pekar » Fri Jul 27, 2018 5:18 pm



This is what happens when I press 'APP' (LOC and G/S being armed, but not active, despite me being inside the cyan circle).
What's happening? Could you suggest what I'm doing wrong?
Thanks
Ivan
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Re: 737-800YV ILS Landing

Postby tdammers » Fri Jul 27, 2018 10:05 pm

It's not enough to be inside the cyan circle. Realistically, this is how you'd normally fly an ILS approach (unless the approach plate says otherwise):

1. From the IAF (Initial Approach Fix), maneuver such that you fly towards the ILS beam at an angle of about 90 degrees, at an altitude of about 2000 ft above the airport.
2. As you get closer to the beam (say 2-5 miles), turn onto a 45 degree intercept course.
3. Once you're stabilized on the 45 degree intercept course, and on the correct altitude, push the "APP" button. The aircraft will maintain heading and altitude until you start crossing the ILS beam, and then turn to follow it.
4. A while later, the glideslope indicator will start moving, and the aircraft will pitch down to descend on the glideslope. Keep an eye on your airspeed throughout, and set flaps and lower gear appropriately.
5. Disconnect the autopilot at 500ft AGL, or earlier at your discretion, and land visually.

Now, things can go wrong under some circumstances.

First, if you intercept at more extreme angles, the autopilot will have trouble turning the aircraft onto the localizer beam; especially, if the intercept angle is too sharp, you will overshoot the beam, and the autopilot needs to make an extra turn to go back onto the beam.

Second, if you're flying at the wrong altitude, you might intercept the glideslope too early, or too late, and this can mess things up - if you intercept the glideslope before you're locked on the localizer, then the glideslope needle may move all over the place, and the autopilot will try to follow it. This can easily get you outside the safe flight envelope, and if you're also banked at that moment, you could throw the aircraft into a spin.

Third, if your course intercepts the beam too close to the runway, then the above problems will be made worse: overshooting will require more extreme correction maneuvers, or might not work at all; and the glideslope errors that result from being off the localizer beam get worse the closer you are to the runway. Additionally, intercepting too close to the runway gives you less time to configure the aircraft and stabilize the approach. But even if you don't end up in a spin, just overshooting with insufficient space left to get back on the localizer will produce strange autopilot behavior: you overshoot the localizer beam to the left, so the autopilot banks right to correct; but by the time you're closing in on the localizer again, you've already flown past the runway, and so the autopilot tries to steer you back, in the direction opposite your approach path, and then it tries to intercept the localizer again, but the turn radius is too large, so it overshoots again, and the whole cycle repeats.

Fourth, if you don't watch your airspeed, you can end up flying too slow, and that of course makes you more prone to stall and spin.
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Re: 737-800YV ILS Landing

Postby it0uchpods » Fri Jul 27, 2018 11:12 pm

Good info, but that isn't the problem. Do you see how the LOC and G/S are in the lower lines, not inline with MCP SPD? They are armed not active. Just becuase the CMD A is on, doesn't mean the autopilot is active, you need to enable a mode as well. What happens is you disabled the currently active modes before arming them, so no modes were active = Autopilot doesn't do anything, and controls are yours again.

Best Regards,
Josh
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Re: 737-800YV ILS Landing

Postby Ivan-Pekar » Sat Jul 28, 2018 11:19 am

Thank you very much tdammers and Josh for the help. Your detailed instructions have helped a lot! I do hope the ILS landing will be much easier to carry out now. So, just to confirm, the modes 'LNAV' and 'ALT HLD' (or whatever the modes are) must be active when arming 'APP', correct? And do I have to disarm LNAV and ALT HLD at any point after intercepting the ILS?
Thanks
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Re: 737-800YV ILS Landing

Postby it0uchpods » Sat Jul 28, 2018 11:45 am

They don't have to be, but if there is no active mode, then the controls are yours to keep the plane flying. As long as there is some lateral and vertical mode engaged, the A/P will keep control. HDG and ALT for example, to hold heading for intercept angle, and altitude.

My pleasure,
Josh
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Re: 737-800YV ILS Landing

Postby Ivan-Pekar » Sat Jul 28, 2018 12:22 pm

One last question please! How do I change the 'APP' (LOC and G/S) from being armed to active? I leave LNAV and ALT HLD, arming APP when required, but nothing happens when the aircraft intercepts the ILS.
Thanks
Ivan
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Re: 737-800YV ILS Landing

Postby it0uchpods » Sat Jul 28, 2018 12:53 pm

You don't, they will become active automatically once you enter the beam properly........................ In FG, the beam goes out too far, to get a proper lock on the signal, so you may need to be closer for LOC to activate. LOC activates once the LOC diamond starts to move towards the center, and G/S activates when the G/S diamond gets within 1/2 dot of center.

Josh
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Re: 737-800YV ILS Landing

Postby Ivan-Pekar » Sat Jul 28, 2018 12:59 pm

OK, Josh, thank you so much once again for your work that is helping unsure pilots, I really appreciate it.

Ivan
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Re: 737-800YV ILS Landing

Postby it0uchpods » Mon Aug 06, 2018 8:18 pm

Absolutely no problem :D

J
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