# Are there ILS approaches where descending by the glide slope outside final might be dangerous?

Are there ILS approaches out there where descending by the glide slope on a segment of the approach that's outside the final approach segment would cause the aircraft to descend below the no lower than altitude for the segment?

Here's why I'm asking. It's not uncommon for pilots to intercept the glide slope before the published glide slope intercept point and then to track it all the way down. If doing this could be dangerous or might not provide the protections ILS approach are designed to provide, it might be a better procedure to descend using step downs to the no lower than altitude for each segment only intercepting the glide slope at the published point for all approaches.

• As your answer says, it is never safe to descend below the MDA published for the particular segment you are tracking, regardless of you having a glideslope signal. Think about coming into an airport in mountainous terrain. You may hit a peak that the MDA step-downs are published to avoid if you just follow glideslope. – Ron Beyer Mar 9 '16 at 16:15
• The answer is simple - every single one – GdD Mar 9 '16 at 17:19
• I would (and do) teach pilots to intercept and follow the glideslope before the precision FAF. I also teach them they need to be aware of the MEA's for the segments up to the FAF and to level off, if necessary, to keep from descending too early especially in warmer weather. – wbeard52 Mar 10 '16 at 20:02
• The vote to close is entirely misguided... this question isn't asking about false glideslopes, which is the topic of the "duplicate" question. Entirely different questions!!! – Ralph J Mar 14 '16 at 4:00
• @RyanBurnette You probably won't find one of those (at least in the US), because if intercepting the GS is likely to run you into or near the rocks, the FAA probably won't install as GS there. (Or they might raise the angle.) There may be a case where an airport is in enough of a "bowl" where that could be the case, and I'd expect bold print warnings on the approach chart. That said, some approaches WILL have you clip the stepdown altitude when tracking the GS. LAS 25L did, although I think the last redesign fixed this. Most won't, though. – Ralph J Mar 14 '16 at 4:06

Are there ILS approaches out there where descending by the glide slope on a segment of the approach that's outside the final approach segment would cause the aircraft to descend below the no lower than altitude for the segment?

Yes. See InFO 11009.

In part the InFO reads:

On ILS approaches, stepdown fixes are established for obstacle or traffic separation. For all practical purposes, the glide slope remains stationary regardless of atmospheric temperature and pressure. Conversely, stepdown fixes are published for a pilot to fly using indicated altitude, which varies with temperature and pressure changes. Therefore, the proximity of stepdown fixes in reference to the glide slope, changes with the weather.

We know the old adage:

From high (hot) to low (cold) look out below.

What isn't obvious about that adage is the perspective of that statement. It is from the perspective of the pilot to the ground. A glide slope's perspective, if you will, is from the ground to the pilot. Thus what you will experience is this. In warm weather, the stepdown altitudes will be higher than the glideslope and you will need to level off to remain above the MEA until crossing the next stepdown fix.

You must remain above the MEA at all times till crossing the precision final approach fix.

• From the InFO Examples of airports where multiple altitude deviations have occurred include, but are not limited to; LAX, ORD, ATL, SLC – wbeard52 Mar 10 '16 at 16:16
• This information seems to suggest that descent via glideslope I might be dangerous to one's career, but not to safety of flight. – J Walters Mar 12 '16 at 22:20