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Either I'm missing something, or this article clearly suggests, that pilots are using ILS for landing only in bad weather conditions. Which could lead to an assumption, that in perfectly clear weather they're landing always or nearly always in visual.

Even though I'm completely new to aviation, I was always sure that ILS is used on every landing procedure, no matter if weather conditions are good enough to do it visually. ILS landing seems to be faster, more precise, more safe, and thus -- in my naive opinion -- should be used whenever it is available (i.e. whenever ILS is commissioned and operational).

What am I missing?

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    $\begingroup$ Visual approaches are still sometimes made when weather conditions are favourable - if the ILS fails, for example, you'd want to know that your pilot regularly practices visual approaches! $\endgroup$ – Jon Story Nov 2 '15 at 12:21
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    $\begingroup$ And when a pilot is unable to fly a Visual in clear conditions, bad things happen $\endgroup$ – abelenky Nov 2 '15 at 15:05
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    $\begingroup$ I think the point you're missing is the difference between navigation systems (include ILS) and manual/autopilot. You can land following the ILS glideslope/ localizer either piloting manually or using the autopilot. $\endgroup$ – Manu H Nov 2 '15 at 16:47
  • $\begingroup$ @JonStory "Sometimes", right. But cited article clearly states (at least I understand it like that), that ILS is used only in foggy / bad weather, which may lead to an assumption (at least it leads me), that ILS in clear weather isn't used at all or even using it is prohibited. That was strange to me. $\endgroup$ – trejder Nov 3 '15 at 8:53
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    $\begingroup$ @trejder - it's just ambiguous wording. ILS must be used in IMC, and it may be used at any other time. Airlines/airports may also have policies that state it should/shouldn't be used at other times, and in VMC it comes down to those policies and the choice of the pilot/controller. $\endgroup$ – Jon Story Nov 3 '15 at 9:47
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I don't think that the article suggests "pilots are using ILS for landing only in bad whether conditions". it simply says that under foggy (i.e. in bad weather), ILS is used as visual approach is not possible.

The use of ILS is at the discretion of pilots with ATC permission. The ILS localiser and glideslope can still be used as a reference during the visual approach (even if the landing is not ILS). The decision is the pilots' as the visual indicators and glideslope may not match.

While it is true that ILS is much more precise and safer, you are forgetting the human factor- the pilot may want to 'fly' the aircraft rather than letting the computer do it.

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    $\begingroup$ Even if it's a CAVU day I like to dial in the ILS frequency (when available) just as an extra sanity check. Nobody wants to be the guy that lands at the wrong nearby airport... $\endgroup$ – Brian Knoblauch Nov 2 '15 at 19:54
  • $\begingroup$ @BrianKnoblauch Like those guys from Czech Airlines, in common joke (joke?), which confused Prague with Vienna, because they confused week days (they're landing in Prague every Tuesday and Friday and in Vienna in all other days), right? :> $\endgroup$ – trejder Nov 3 '15 at 9:01
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The relevant question is not whether or not the ILS system is used at all, but when the pilot switches from ILS to visual.

At the beginning of an ILS approach, the ILS signals function as a navigation aid, helping to make sure that the aircraft is lined up correctly with the runway from a longer distance out than the runway itself would be visible clearly enough to the naked eye even in good weather.

At some point during the approach, the runway will be clearly enough in sight that the pilot can actually land the plane visually. The latest point at which this is allowed to happen is the "decision height" -- if the runway is not reliably in sight by then, a go-around must be executed.

The lower the decision height, the larger demands are placed on the accuracy and reliability of the ILS equpiment -- losing the ILS signal due to interference for a few seconds while still six miles out is much less critical than losing the signal for a few seconds right before touchdown.

It is possible (if all the involved equipment is maintained and certified to high enough standards) to have a decision height of 0 feet so the ILS/autopilot flies the aircraft all the way to touchdown, but doing this requires all other aircraft moving around on the airport surface to observe extended safety distances to the runway to minimize the risk of radio signals bouncing off their fuselages and sending a blind-landing aircraft astray. This can have bad effects for capacity, so in normal operation landings are done with a nonzero decision height.

In fact, most airports don't spend the additional maintenance cost needed to certify their ILS systems for zero decision height ("category III" ILS operation), or do it only for some of their runways. In case of bad weather at busy times, some flights will just have to divert to other airports.

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  • $\begingroup$ This incident is good demonstration what can happen if a plane follows ILS below the minima without the protected areas being observed. $\endgroup$ – Jan Hudec Nov 2 '15 at 16:37
  • $\begingroup$ Thanks for a detailed answer. However, you have focused on explaining (to a newbie like me), how ILS works and how pilots operates during landing with or without ILS. While I was actually asking, if my conclusion from cited article (that using ILS in clear weather is something odd, as in my opinion that article suggests, that ILS is use only in bad weather) is true? So it was rather, who is wrong (article author or me, making wrong assumptions), not: how does ILS works. $\endgroup$ – trejder Nov 3 '15 at 8:58
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    $\begingroup$ @trejder: Using the ILS in clear weather is not odd -- it is practically always being used for the beginning of the approach. What would be odd (or at least require a particular reason to happen) is to let the autopilot fly all the way to touchdown in clear weather, because (a) the safety precautions needed to make this safe harms airport capacity, and (b) even with all the respect distances being observed, there's still a lot more redundancy in visible light and two pairs of Mk 1 eyeballs than there is in a narrow-band ILS signal with one antenna. $\endgroup$ – hmakholm left over Monica Nov 3 '15 at 9:29
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Pilots don't (usually) do autoland, i.e. having autopilot follow the ILS all the way down to the ground, in good weather.

Using autoland requires that no other aircraft or vehicles pass in designated protected area around the ILS transmitters, because they could disturb the signal and cause the aircraft to land outside the runway like this Singapore Airlines B777 in Munich when they tried autoland in good weather for practice and did not tell ATC/ask them for cooperation.

Because these procedures restrict operations, the tower controller won't normally apply them if the weather is good enough to use visual or CAT I approaches in which the final part of the approach must be flown by pilot.

However, visual approach just means that the pilot must have visual reference to the runway. They are still free to use any additional reference and pilots will often tune the ILS (or the FMS will even tune it automatically when the approach procedure is selected) to verify they are approaching the intended runway and for cross-checking the glide-slope.

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  • $\begingroup$ It's my understanding that sometimes the crews do still need to autoland in good weather just for currency, but, for the reasons you mention, they should cooperate with the tower in order to do so. I'd assume they try to avoid doing that at busy times at busy airports, though. $\endgroup$ – reirab Nov 2 '15 at 19:50
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    $\begingroup$ I'll have to dig up the reference, but our FOM required us to use any and all available electronic guidance on an approach. That meant on a visual approach, if there was a localizer (and glideslope), it was tuned as well. That was also a good sanity check to make sure you were lined up with the right runway and at the right airport. $\endgroup$ – casey Nov 3 '15 at 3:36
  • $\begingroup$ @reirab, yes, they do. It is what the Singapore crew was trying to do. And unfortunately there are not many airports that would have a CAT II or III ILS and not be busy. $\endgroup$ – Jan Hudec Nov 3 '15 at 6:01
  • $\begingroup$ @casey That makes sense. Helps to avoid really embarrassing mistakes. $\endgroup$ – reirab Nov 3 '15 at 6:21
  • $\begingroup$ @JanHudec Yes, they'll usually be busy airports, but they won't usually be busy 24/7. Even Atlanta is pretty quiet late in the day. $\endgroup$ – reirab Nov 3 '15 at 6:23
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ILS is sometimes used in clear weather, it's at the discretion of the pilots and company policy (if it's commercial). Most pilots I know would prefer to fly a visual approach because flying is what they do - what's the point if the airplane does all the fun stuff? Even in instrument conditions pilots will often manually fly the ILS approach rather than using autopilot to keep up their skills.

ILS is only one out of several approach systems which exist. There are NDB, VOR, surveillance radar, and now GPS approaches which can be used.

I fly light aircraft from an airfield which has no approach aids whatsoever, when I fly from there it's always visual as it cannot be anything else.

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As a student pilot that isn't IFR trained yet, we always fly visually and don't use the ILS. How I land depends on if it's at a towered airport, non-towered airport, or if I'm coming in from 10 miles out or if I'm already in the vicinity of the airport.

TL;DR what you're missing is that most pilots start out as VFR only and the last thing you want is to be distracted by things inside the cockpit like GPS devices, tuning an OBS, loads of instructions from tower controllers, etc. Every pilot needs to able to fly the airplane without the assistance of an ILS or a GPS.

General Final Approach

On final approach, if flying visually, we power up if the aiming point is descending in the windscreen and we power down if it's climbing. Power is altitude, but may require a corresponding pitch adjustment.

If we get slow, we nose down and vice-versa if our speed is a little high. We adjust power as necessary based upon our pitch adjustment.

Non-towered Landings

These are fairly straightforward. We enter the pattern for the runway we've chosen at a 45-degree angle to the downwind leg. We then turn base then final and end up 1-2 NM out on final, ideally 500-600 feet AGL and descending at 500 FPM. Again, this is a purely visual landing where we're focusing our aiming point in the window and trying to keep it steady by using power.

Towered Airport Landings

Most of the towered landings I've done the controller has said to advise when 2 miles out and told us to aim for a base leg for runway X. We then fly a decently long base leg, turn final ideally at 500-600 feet AGL, and land just like at non-towered airports.

The controller could instruct us to do a 10-mile straight in, enter on the downwind, enter on base, etc., but it just depends on traffic and controller load.

I have yet to be instructed to use the ILS as a visual (VFR) pilot and I wouldn't want to b/c as a student, it's very helpful to learn ground references, ground track, crosswind correction, etc. without the assistance and distraction of in-the-cockpit devices.

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