Question about ILS

bc2209

bc2209

Well-Known Member
You are on glide slope and at minimums you go visual. You are in a stable descent to land and have the runway in sight.

However, you end up low and below the glide slope with the runway is still in sight and in a stabilized descent.

Must you maintain the glide slope the entire way down?

Is this something that would be a fail on a checkride?
 
Quite possibly. There is no reason not to follow the GS all the way down. Any flight above or below the GS is considered a deviation and should be corrected. In the aircraft I fly it's a good way to drag the gear through the approach lights if you deviate below and is not tolerated on checkrides. In fact, during an autoland deviating below the GS without immediate correction requires an immediate GA.
 
A300Capt said:
Quite possibly. There is no reason not to follow the GS all the way down. Any flight above or below the GS is considered a deviation and should be corrected. In the aircraft I fly it's a good way to drag the gear through the approach lights if you deviate below and is not tolerated on checkrides. In fact, during an autoland deviating below the GS without immediate correction requires an immediate GA.
Click to expand...
What about a glide slope that doesn't coincide with the VGSI? I would presume that when going visual you would use that.
 
DPApilot said:
What about a glide slope that doesn't coincide with the VGSI? I would presume that when going visual you would use that.
Click to expand...

Why would I disregard the very thing that got me to that point which is the electronic GS. My understanding is the GS is getting a reading from the aircraft antenna location on the aircraft whereas the VGSI is set up based on the pilot's eye height. This can be quite a difference in a very large jet, especially in close to the runway.

If I were flying an ILS and broke out at mins and saw the runway, I would continue to follow the ILS GS to the runway. If the aircraft was setup to autoland that's what it would do. If whatever I was doing for the last 5 miles was keeping me on a stable trajectory to the touchdown zone, why would I change it the last 200' or so?

I have seen many beautiful approaches (mostly in the sim) turn to crap as the student breaks out, goes completely visual, fixates on the approach lights and touchdown zone while completely ignoring the GS and flt director and dives for the runway while going below the GS. All the while becoming completely unstable and dangerously low in the last half mile.

On the other hand, If I were flying a non precision approach and broke out at mins or a visual approach at night without an ILS then the VGSI would be my primary means for obstacle clearance.
 
bc2209 said:
Is this something that would be a fail on a checkride?
Click to expand...

Here is what the ATP PTS says in the precision approach task:

16. Maintains localizer and glide slope within one-quarter-scale deflection of the indicators during the visual descent from DA/DH to a point over the runway where the glideslope must be abandoned to accomplish a normal landing.
Click to expand...

If I understand your question, you were asking about the segment between DA and touchdown. I read the PTS to say you can go below the glide slope after reaching the DA, but not more than an quarter scale. That is the only PTS that I found that speaks to that segment of the approach. Other PTS's give other allowable variances for the segment of the approach that comes before reaching DA. So, it depends on what check ride you are taking as to what is allowable.

One of the problems with check rides is that the examiners sometimes don't really know the standards. In the case of the ILS approach, the standard used to be one-quarter scale above and zero below the glide slope. I've even heard of a fellow who was busted on a ride because the examiner leaned over to look directly at the instrument and ruled that the applicant had gone below the glide slope although parallax made it look like he was right on the glide slope to the pilot. So, going back to your question of would it cause you to fail a check ride; who knows. I'd say probably not as long as it wasn't very far out, but you never know when you're going to draw the short straw and get the check pilot whose personal standards are out of line with what should be expected.
 
A friend failed a 121 sim check because of this. Got to mins, runway in sight, so he put it down short. They wanted glide slope to the piano keys. "Next."
 
Yeah a fellow student failed his IR today because he went below after going visual. I didn't ask specifics as he is pretty down about it but it will be interesting to hear how far below he actually got when got examiner pulled the plug.
 
gliderboy said:
A friend failed a 121 sim check because of this. Got to mins, runway in sight, so he put it down short. They wanted glide slope to the piano keys. "Next."
Click to expand...
That's not what the PTS says. I don't understand why people don't read the PTS before a checkride.
 
bc2209 said:
You are on glide slope and at minimums you go visual. You are in a stable descent to land and have the runway in sight.

However, you end up low and below the glide slope with the runway is still in sight and in a stabilized descent.

Must you maintain the glide slope the entire way down?

Is this something that would be a fail on a checkride?
Click to expand...

You need only enunciate the magic words, "Descending visually below glideslope."
Also, if they want monkeys who follow nice little lines around so as to get a cookie, then they should hire monkeys.
Fly the airplane. Don't hit nothin'. Don't do nothin' stupid.
//endrant
 
Here's a real life scenario to your question:

The old Quito, Ecuador airport was very challenging to fly into. If you were following the glideslope to touchdown, it would put you on the ground about 2800 to 3000 feet down the runway. Quito is about 9500' MSL. There is a hill about 3 miles from the end of runway 35 that requires you to be on the glideslope to clear. Company procedures at the time required you to monitor the radar altimeter and once it got to about 900 feet it would start increasing indicating you had crossed over the hill (terrain). Once the radar altimeter started back up, you could descend to one dot low on the glideslope to minimums which was 652' AGL. If, and when, you broke out you would be right where you wanted to be (the VASIs were the color they should be) to touch down in the first 1500 feet. We could accept a 15 kt tailwind on runway 35 since there was no approved approach to runway 17. As you can imagine, you really needed to get the airplane on the ground ASAP so touching down using the glideslope as the only reference would put you 3000 feet down the runway at near tire touchdown speed limits (Not good). I saw my share of airplanes off the end of runway 35, including an A340, that didn't use that technique. Granted, this is the exception, not the rule.

I can't see many good reasons to descend below a nice stable 3 degree glideslope during an approach. But, to answer your question....In my opinion, once you've acquired the runway visually at or below ILS minimums, you are free (legally) to deviate from the glideslope unless it puts the aircraft in some unsafe state. Is it wise? Probably not, Is it legal? I don't think you would bust a check ride on it but you better have a good explanation for your decision. What if you are parking down at the end of a 12,000 foot runway - I think it's legal to land long isn't it? That would certainly deviate from a glideslope, albeit high. What if you had an inbound emergency landing right behind you and you really needed to vacate the runway ASAP. I don't think it's unreasonable, when warranted, to land a little low (within reasonable limits) and get off a high-speed that you might not otherwise make.

If you do it, you better have the skill and wisdom to back up your decision. Just my 2 cents.
 
Crop Duster said:
You need only enunciate the magic words, "Descending visually below glideslope." ..................................{con't}//endrant
Click to expand...
THIS! I think if your "friend" had said something along the lines of, "I have the visual, descending to land" or as mentioned above this approach would not have been an issue. Much like a circle to land, you need to let the examiner know when you are leaving the MDA and beginning your descent for landing (otherwise he doesn't know if your landing or not holding altitude).

Also, in a crew environment, if you don't verbalize your intent, you leave the other pilot in the dark...not a good thing. The failure to communicate with your crew on this single approach would be reason enough for the bust. IMHO.

Not knowing the full story, my experience tells me that the evaluator might have seen weakness in other areas of the flight/manuvers and this was the icing.
 
cencal83406 said:
I don't think reading the PTS does much good for a 121 ride since the expectations are made pretty clear throughout training.
Click to expand...

Why wouldn't it be? On any 121/135 check ride you are held to the standards to what certificate you hold. I've had an ATP for a while now, and I just got a brand spankin new Type Rating YESTERDAY, and guess what one of the first things the examiners did? Broke out the ATP PTS and went over it with me so there would be no questions on what was expected on the type ride.
 
CaptBill said:
I can't see many good reasons to descend below a nice stable 3 degree glideslope during an approach. But, to answer your question....In my opinion, once you've acquired the runway visually at or below ILS minimums, you are free (legally) to deviate from the glideslope unless it puts the aircraft in some unsafe state.
Click to expand...

With a typical SoCal marine layer of 600' and 5 miles (or better) I go visual when I breakout and drop below the ILS every time. Never gave it a second thought until I read this thread.
 
bc2209 said:
You are on glide slope and at minimums you go visual. You are in a stable descent to land and have the runway in sight.

However, you end up low and below the glide slope with the runway is still in sight and in a stabilized descent.

Must you maintain the glide slope the entire way down?

Is this something that would be a fail on a checkride?
Click to expand...
You guys are wasting time citing the PTS. It's an FAR, and when you are within Class D airspace, the answer is "yes" for large aircraft or turbine-powered aircraft arriving at a runway served by an instrument approach with vertical guidance, and "yes" for all airplanes arriving a runway served by a VASI. See 14 CFR 91.129—Operations in Class D airspace.

(e) Minimum altitudes when operating to an airport in Class D airspace. (1) Unless required by the applicable distance-from-cloud criteria, each pilot operating a large or turbine-powered airplane must enter the traffic pattern at an altitude of at least 1,500 feet above the elevation of the airport and maintain at least 1,500 feet until further descent is required for a safe landing.

(2) Each pilot operating a large or turbine-powered airplane approaching to land on a runway served by an instrument approach procedure with vertical guidance, if the airplane is so equipped, must:

(i) Operate that airplane at an altitude at or above the glide path between the published final approach fix and the decision altitude (DA), or decision height (DH), as applicable; or

(ii) If compliance with the applicable distance-from-cloud criteria requires glide path interception closer in, operate that airplane at or above the glide path, between the point of interception of glide path and the DA or the DH.

(3) Each pilot operating an airplane approaching to land on a runway served by a visual approach slope indicator must maintain an altitude at or above the glide path until a lower altitude is necessary for a safe landing.
Click to expand...

Item (3) gives you relief for when it's necessary to land and safely stop. Ducking under the glideslope (visual or otherwise) in an airplane with a long body (i.e., a jet) is generally a no-no, as you might drag various bits of the airplane through the approach lights/etc. if you take it to an extreme.
 
skypilot6 said:
Why wouldn't it be? On any 121/135 check ride you are held to the standards to what certificate you hold. I've had an ATP for a while now, and I just got a brand spankin new Type Rating YESTERDAY, and guess what one of the first things the examiners did? Broke out the ATP PTS and went over it with me so there would be no questions on what was expected on the type ride.
Click to expand...

In my experience in the 121 world, the company expectations for maneuvers are published in the training manual and coincide with the PTS.

There are definitely operations where dipping below an electronic glideslope is ok. In a 121 jet, as @A300Capt said, I can't see a reason. The exception being as @Capt Bill pointed out for a specific procedure at a specific airport.
 
skypilot6 said:
Why wouldn't it be? On any 121/135 check ride you are held to the standards to what certificate you hold. I've had an ATP for a while now, and I just got a brand spankin new Type Rating YESTERDAY, and guess what one of the first things the examiners did? Broke out the ATP PTS and went over it with me so there would be no questions on what was expected on the type ride.
Click to expand...

Well sure, it's handy, but not required. I haven't seen an ATP PTS in our training department at all.

My point is mostly that, if you know your profiles and flows, and you are on day of checkride, there is no reason you should even be close to the "tolerances" of the ATP. (And as an aside, 90% of the ride is A/P on). 600 ft engage, per the profile, 80 feet disconnect on a precision per the profile, and at MDA on a non-precision, disconnect, per the profile. And at any other time the examiner asks, for example doing the steep turns, or a bit farther out on single engine approaches. But even then, you have a F/D up, per the profile.

If you feel better looking through the PTS as part of your prep, that's a great thing.

Read Polar's post above. He's spot on and more eloquent to boot. He is also in a 121 training department IIRC.
 
Last edited:
On my IR checkride I was told to fly it all the way down to the ground. That's what I did. In real life 121 I start duckin down after minimums (half dot, which is still within tolerances) in order to get into ground effect earlier, use less runway, and have greater likelihood of a smoother landing because of the shallower angle. (makes it easier to judge the flare)

I don't really see what's wrong with this but I'm open to critique.
 
You must log in or register to reply here.
Back
Top