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ILS, with or without the Glideslope

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Well-known member
Mar 23, 2002
This question response to the discussion going on on the regular board about the ILS and the glideslope.

If the glidelsope fails while already cleared and established, is it possible to finish the intended approach? Is it legal to finish the intended approach? If so,what if anything is necessary to finish the intended approach?

*who loves a healthy discussion
If the glide slope fails you must go missed. The only reason you start your time is to know where the MAP is. You need to think of that plate as two seperate approaches.
If the glide slope fails you must go missed. The only reason you start your time is to know where the MAP is. You need to think of that plate as two seperate approaches.

There are also loc only approaches without timing. A DME distance can define the MAP as well. In case The GS would fail, I would ask the controller if he can clear me for the Loc only app. and then continue according to the appropriate approach.

Any comments on this taught are welcome.

Take care.
If the glide slope fails, you most certainly do not need to go missed. In many cases it's the best thing to do, but there are times and places where it's completely acceptable to continue the approach.

Last year I experienced a glide slope failure in the soup while shooting an approach. I had prebriefed the localizer approach, and on elected to continue localizer only. It was a parallel approach, and shortly the localizer flagged. After querying ATC, we were offered the parallel, and we took it. The glide slope flagged. We queried ATC, and were advised that "everything is going down due to the storm."

We continued localizer only, and it failed about the time we got the runway. We landed (and our T/R's failed to arm...it was one of those days).

Aircraft behind us ended up having to divert. The weather wasn't good, and there were no close alternates. When we filed, an alternate wasn't even necessary, but things had gone from bad to worse.

Preparation is essential if one is to modify the approach while performing the approach. Certainly being familiar with the proceedures is important. I say proceedures because the loc only and the full gs approach may vary considerably. One must be fully oriented to the approach and aware of position and capability to finish the approach. The loc only had better not be overly complicated, as some tend to be. There are many factors which may affect the operation (not the least of which are your own capabilities, the aircraft, the proceedure(s), the facilities, etc).

If performing a full ILS and experiencing a failure at or below loc only minimums, then no effort should be made to continue the approach unless the field is in sight. Simply execute the missed.

Not all ILS approaches have a marker to identify the missed approach point. Timing may be necessary for identification, as well as specific airspeed control to validate the timing effort.

Ali, yes, it's both safe and legal if done properly. However, going missed and executing the full loc only proceedure is also safe, and legal. If you're already burned up your reserves and are at your alternate now...perhaps it's not so safe to go around and try it again. Use best judgement based on all the factors, and it's just another tool in your reportoire.
Loss of glideslope

If the glideslope does fail depending on where you are and what you can see you are permitted to finish the approach. If on the way down, you do see the VASI's they are acceptable for vertical guidance.

I've seen "if the GS goes out you most go missed." OK maybe, but then the question is, where do you go missed????? Do you miss as soon as the GS quits???? Remember that missed approaches start at the MAP or DA on a ILS (time, DME, waypoint) on a LOC. DON'T go missed before getting to that point, I will fail someone on a checkride for that.

I've also seen "ask the controller for a clearance for a LOC approach." He can't do that, it is an ILS with the GS OTS. That means you fly it to LOC minimums but it is still an ILS approach; remember that the approach title tells what kind of approach it is.

My personal fellings, and the way I learned flying Part 135 and teaching part 135 is this: ALWAYS start your time. If the GS quits fly to LOC MDA only and wait for the MAP, approach lights (able to decend to 100' above TZE), or r/w envorinment then continue and land using a normal rate of decent to the r/w.

If you have to miss the only safe place to do it from is the MAP. That's not to say if a GS quits at 1300AGL that you can't level off until the r/w threshold (speaking genaricly {sp?}) then go missed, just don't start a missed approach procedure befor the MAP..... PLEASE.
When you are saying you can't start your Missed until the missed approach point I hope you are only refering to any turns that are required. I'm not 100%, but I think it is acceptable to climb prior to the MAP.
One may initiate a missed approach at any time during the approach. However, one may not begin the missed approach proceedure until the MAP. One may begin a climb early, but may not make any turns until the MAP, unless given by ATC.

I was behind a slotation two weeks ago that caused us to go missed. We slowed up as much as possible, and he slowed up even more. The controller told us to go missed, and on our request, gave us a right 360 back to the localizer to continue the approach. It worked nicely.

However, in general circumstances, no turns before the MAP. This does not preclude initiating the missed approach prior to the MAP by climbing; the proceedure itself is predicated on being initiated with respect to lateral guidance, at the MAP. If one is going to execute a missed approach, there is no need to level off and wait for the MAP before beginning a climb to the appropriate altitude.
The best reason not to climb before the MAP is other traffic. You may be at an airport that is vectoring or holding aircraft over your approach. The controllers wouldn't expect you to climb and if you did, you may do so into traffic.
Not so. If approaches are in progress, aircrart will not be vectored across the final approach course during your approach. You are free to climb, but not to turn. If you are executing a missed approach, there is no reason to stay low all the way to the MAP. You may, at any time, begin the climb to the altitude specified in the missed approach proceedure.

The exception to this is a practice IFR approach, in which the missed approach proceedure is not part of the clearance to conduct the approach, unless specifically approved.

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