6
$\begingroup$

I am a brand new Instrument Pilot and the answer that I am looking for is related to good technique and not necessarily not what is legal or not. My instructor taught me that when flying an approach from the IAF that I should get below the glideslope, meet my minimum crossing restrictions at the intermediate fixes, and intercept the glideslope at the lightning bolt symbol depicted on FAA charts. However when I took my checkride, the DPE did not want me to go below the glideslope before the glideslope interception point.

My instructor taught me that by leveling off at the Final Approach Fix altitude I can slow the plane down to final approach speed and do the before landing checklist. I will then intercept the glideslope at the glideslope interception altitude and follow that down. It seemed the DPE wanted me to follow the glideslope all the way down from where I intercepted the localizer from the IAF.

In practice, and I am looking for answers from experienced IFR pilots, what is the best technique; to intercept the glideslope at the lightning bolt symbol or when you intercept the localizer?

$\endgroup$
2
  • $\begingroup$ Does this question help? $\endgroup$
    – Pondlife
    Aug 30 at 17:10
  • $\begingroup$ @Pondlife: I have found that question before and was very helpful for my IFR training. I know that I can't descend below the minimum fix altitudes even when following a glideslope. I think both my instructors method and the DPE method are legal. I just want to know in practice what is typically done especially for airline operations because I hope to go to the airlines some day. $\endgroup$
    – DLH
    Aug 30 at 17:18
6
$\begingroup$

There isn't much point in following step-down altitudes intended for a non-precision approach when flying an ILS. It just adds to workload. You want to capture the glide slope as far out as possible, where the sensitivity is lowest, and make the transition from level flight to glide slope descent once.

So if I crossed an IF at the crossing altitude, and inside the IF I could theoretically descend another thousand feet prior to the FAF before picking up the GS, I've just increased my workload because I'm descending, then leveling off, and descending again at GS capture at or near the FAF, and now it's more challenging because things are happening faster, being closer in. It makes little sense and there is no benefit that I can see.

When you cross the IF at the minimum crossing altitude, you will be 10-15 miles from the runway and well below the GS. Keep it simple; just maintain that altitude to GS capture and then start down. The higher you are, the farther out on the beam you are, and the easier it is.

If ATC is positioning you, which is the case most of the time flying a STAR in a busy terminal area, the controller will either descend you to the IF crossing altitude or some other altitude, possibly lower if the controller's vectoring altitude allows, and you just fly that to LOC and GS capture (note that the vectoring alt the controller may place you at is unpublished - so if you are below a published alt due to an ATC instruction, and you have a comms failure, you are supposed to immediately climb to the applicable published altitude).

So, when flying an arrival in a busy terminal area in an airliner, you will typically fly some of the STAR segments, then at some point close in, the controller will put you on vectors and have you descend to whatever altitude the controller is using for traffic stream using that ILS, eventually placing you on an intercept heading for the localiser, clear you for the approach, and you just maintain that altitude for Localiser capture and Glide Slope capture. The controller will always make sure that you are placed with ample margin below the glideslope path and if they don't, they've messed up.

I can't speak for Heavies, but in the CRJs I flew we would drop gear and go to flaps 20 to 30 (landing flap is 45, selected farther down), and call for part of the landing checklist, at GS capture. The drag from the gear and flap selection would get you started on the descent, along with the speed reduction for the flap setting, pretty much automatically and you didn't have to make large thrust reductions or trim changes. Full landing flap was selected above 1500 ft, usually just before the FAF.

The most important skill for hand flying ILS approaches is use of trim and (gentle) manipulation of thrust. I used to have simulator access outside of scheduled training, and used to spend a lot of time practicing ILS approaches on "raw data", that is, Loc/GS needles only, with the Flight Director turned off. Quite a concentration challenge in a jet going 130kt, but if you got it trimmed hands off on slope and on speed, it wasn't too difficult.

$\endgroup$
6
$\begingroup$

In my opinion, your instructor is essentially correct. However, (again my opinion) you should strive for a "continuous" descent so as to pass the step-down fixes at an altitude not below the minimum published. You can do this by using the glideslope as a reference for your descent angle but ensuring that you don't go below any published minimum step-down altitudes in the process. Leveling off at the faf altitude (glideslope intercept altitude) should not be necessary or even practical if making a continuous descent which provides for a more stabilized approach. Slowing and configuring the aircraft can be done during the approach.

Descending below a published minimum step-down altitude prior to reaching the ILS glideslope intercept altitude (faf) when following the glideslope can happen during certain temperature conditions (an entirely different conversation). This has to do with the fact that those step-down altitudes (where they exist) are "indicated" altitudes. The glideslope is descending at a fixed angle (for example 3 degrees or so) and therefore its (the glideslope) "true" altitude always remains the same at any point regardless of temperature. By following the glideslope the "indicated" altitude at any point along the glideslope could (based on existing temperature) be different (e.g., lower) than a published minimum step-down altitude.

$\endgroup$
3
  • $\begingroup$ Thanks for your answer. My instructor is kind of a dive and drive kind of guy but I know that is now discouraged. That is why I believe he likes that method. One of the things I need to work on is being able to slow down the plane in a descent without my vertical speed going all over the place. I am just an inexperienced pilot trying to get better. $\endgroup$
    – DLH
    Aug 30 at 18:01
  • $\begingroup$ @DLH Slowing down in a descent was my biggest challenge when I started flying approaches. Get more aggressive at reducing power and use pitch only to stay on glide slope/path, rather than pitching for speed like you probably learned during primary training. $\endgroup$
    – StephenS
    Aug 31 at 1:49
  • $\begingroup$ This is the most reasonable answer. Strive the follow the GS but remain above the MEA for each stepdown fix. The glideslope only provides obstacle clearance from the precision FAF to the DA. It doesn't provide obstacle clearance for the stepdown... the MEA does that. $\endgroup$
    – wbeard52
    Aug 31 at 17:29
6
$\begingroup$

In the Center, when vectoring for an ILS, we will give you an altitude that will be UNDER the glide slope (but at or above our minimum vectoring altitude) for the localizer intercept vector. Your clearance to join will have a heading to fly, and altitude to maintain until joining the localizer. We do this to ensure you're not "chasing the glideslope" from above, and to preclude any possibility of intercepting a false glideslope.

Vectoring you to the localizer above the glideslope is considered an error.

Essentially, we do the same thing your instructor taught you.

$\endgroup$
2
  • 1
    $\begingroup$ I had a brain fart in my earlier comments. Yes, as you say, 5–9–1 says to vector aircraft to intercept final: "For a precision approach, at an altitude not above the glideslope/glidepath or below the minimum glideslope intercept altitude specified on the approach procedure chart." $\endgroup$
    – randomhead
    Aug 30 at 19:45
  • $\begingroup$ @randomhead -I thought you may have misspoke. $\endgroup$
    – atc_ceedee
    Aug 31 at 2:16

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.