Descent Below VASI on Approach

[Blackhawk]

Originally Posted by minitour

Close.

That's for entering the traffic pattern and for an instrument approach procedure with vertical guidance.

The applicable section is...

91.129(e)(3)

You just got to sections 1 and 2.

(e)(3) states...
(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.

No mention of large or turbine power.

-mini

Disregard all after...
However, just to clarify, it does NOT have to be instrument conditions. If there is an instrument approach procedure with vertical guidance, you must follow the vertical guidance to DH/DA.
This bit one crew I know of while the FAA was riding in the jumpseat. Crew dropped below VASI and glideslope They tried to argue that they were "at an altitude necessary for a safe landing"; FAA pulled out the section mentioned about descending below GS prior to DA/DH.

[minitour]

Originally Posted by ppragman

Do you do a runup before every takeoff when flying a piston engine airplane? If not you're complacent! And complacency kills!!!

What does the checklist say? Does it say "BEFORE TAKEOFF" and then list "run-up" or does it say "First Flight Items" and list "run-up"?

There's a big difference.

Why limit it to pistons? Shouldn't I be checking flaps before every flight? Rudder bias? Thrust attenuators? Why are they first flight items and not "before takeoff" items? Rudder bias is important to me on every flight. Why do I only rotary test stall warning prior to each leg and not the whole thing? Don't I want to make sure my fire warnings are going to go off every leg? How do I know they didn't fail on the landing?

Complacency is saying "oh I'm so comfy wit dis airport I cud land n make first turnoffz! Oh hai thatz be approach lights! Oh teh noez!"

There are other ways to speed up your turn and none of them include landing long or short so you can make a more convenient turn. There are times I'd love to do that, but it isn't fair to the people in the back or my wife at home expecting me to come back......with a job.

Originally Posted by Blackhawk

Disregard all after...

Huh?

However, just to clarify, it does NOT have to be instrument conditions. If there is an instrument approach procedure with vertical guidance, you must follow the vertical guidance to DH/DA.

Agree 100%. The reg doesn't specify conditions, just runway and vertical guidance. The reg does allow for lower pattern altitude if you have to for cloud clearances, but doesn't allow you to go below electronic GS to land on the numbers.

Poor choice of words on my part.

This bit one crew I know of while the FAA was riding in the jumpseat. Crew dropped below VASI and glideslope They tried to argue that they were "at an altitude necessary for a safe landing"; FAA pulled out the section mentioned about descending below GS prior to DA/DH.

Ouch.

-mini

[400A]

PPR

I'm not quite sure I understand what you are trying to say. My only stance is that I do what I feel is in the best interest of safety VS getting things done in a timely manner. The airplane I fly, I don't feel the reduction in safety (ie dipping low on the GS to touchdown before the 1000 foot markers, or landing long to make a taxi way, etc) is worth the trade off of a minute or two of taxi time.

Landing on contaminated runways is no different, in the airplane I fly. There are performance numbers for slick runways (be it ice, water, snow, dead penguins, etc), if the runway isn't comfortably long enough, I don't land. If I don't cross the threshold at 50 feet, power at idle and on speed, those performance numbers are out the window and I just became a test pilot. The people I fly around in back don't deserve that and my integrity doesn't allow it.

You may think that coming in low over the threshold shortens your landing distance, but unless you can eyeball and extend the arrival end of the runway "backwards" 1000 feet or so, cross that point at 50 feet and touchdown at or near the width stripes then you aren't shortnening your landing distance. Too shallow increases ground roll and too steep increases ground roll, relative to your computed numbers from the POH dependant on how the POH numbers were derived.

If you feel that in the aircraft you fly you can do these things safely, then by all means, I am the last person to tell someone else how to fly an airplane I don't fly, nor have ever flown. But don't put words in my mouth and accuse me of being only safe in theory on the internet, you don't get play with my integriy and reputation.

[minitour]

Originally Posted by 400A

Too shallow increases ground roll and too steep increases ground roll, relative to your computed numbers from the POH dependant on how the POH numbers were derived.

I'm starting to think that no one teaches this to primary students.

But don't put words in my mouth and accuse me of being only safe in theory on the internet, you don't get play with my integriy and reputation.

You're dangerous.

-mini

[400A]

Originally Posted by minitour

I'm starting to think that no one teaches this to primary students.


You're dangerous.

-mini

Your MOM!

[ppragman]

Originally Posted by minitour

I'm starting to think that no one teaches this to primary students.


You're dangerous.

-mini

It depends on how you do it, power on stall at the numbers with power quickly reduced to idle is better than a steeper power at idle approach in some airplanes. And yes, I've tested it in a couple of birds.

Touching down sooner is going to save you runway as opposed to touching down later if you keep the same "optimal" rate of descent, which varies for aircraft type and loading. I'm fairly good at eyeballing it in the Cherokee 6 now, and was sharp at it in the 207. It just takes practice.

[minitour]

Originally Posted by 400A

Your MOM!

...doesn't know who mah daddy is.

What's your point?

-mini

[Blackhawk]

Originally Posted by minitour

Huh?


-mini

Military phrase. Disregard everything I just said on the radio.

[minitour]

Originally Posted by Blackhawk

Military phrase. Disregard everything I just said on the radio.

You fancy military guys and your rock n roll...

-mini

[seagull]

Originally Posted by ghogue

I agree that the RC is subject to the AGC's interpretations. I guess my question in this case is what purpose is the RC if only the AGC can respond to questions such as these? I'm merely curious how it works. I would think that the CC would inform the RC's to cease responses like the one I posted if they had no authority to do so.

I just used that post to respond to several points being made, not in direct response to what you had written.

In any event, not trying to have any "tone" at all, just need to be emphatic that you cannot use any local (which includes the region) opinion of a regulatory interp. It is a very important point if you want to not get violated, so I am trying to make the point very strongly.

The RC can have any opinion they want. Their purpose is regulatory enforcement, not guidance.

[Roger, Roger]

Originally Posted by calcapt

Just asking the question: Why would you want to descend below the VASI? Do you need a rule to say that?

Flying a piston single or twin and you want to hit the threshold to make the first exit.

[minitour]

Originally Posted by Roger, Roger

Flying a piston single or twin and you want to hit the threshold to make the first exit.

...because that extra 45 seconds of taxi time is a pain in the neck.

-mini

[calcapt]

FO: Captain, You have descended below the VASI

CA: No worries mate, I want to make the first high speed
FO: I read on JC that calcapt said this wasn't a good idea
CA: calcapt? I hear he is all mouth and no trousers

FO: You might be right, let's do it your way

30 seconds later........

CA and FO: Damn, now that we have gotten our bat in a sticky wicket, we really should of listened to that calcapt bloke, he really knows his onions.....

[minitour]

Originally Posted by calcapt

1-800-BIG-RIGS

FWIW, I got my first shot at flying a Pulsating VASI tonight to a runway with an out of service Glideslope. What a neat (yet sensitive) contraption thar.

-mini

[dasleben]

Originally Posted by minitour

1-800-BIG-RIGS

FWIW, I got my first shot at flying a Pulsating VASI tonight to a runway with an out of service Glideslope. What a neat (yet sensitive) contraption thar.

-mini

We have one at the airport I'm based at. There's a fairly good amount of terrain, so it's actually set at a 3.5 degree descent. Very strange, that.

[Roger, Roger]

Originally Posted by minitour

...because that extra 45 seconds of taxi time is a pain in the neck.

-mini

Meh. One day I'll see the light and be as conservative as you. For now, I see nothing wrong with hitting the threshold, especially in a piston single like a 172.

[seagull]

Originally Posted by Roger, Roger

Meh. One day I'll see the light and be as conservative as you. For now, I see nothing wrong with hitting the threshold, especially in a piston single like a 172.

Until you hit that last moment downdraft or have your engine fail on short final when you needed a little power to make that threshold....

[Doug Taylor]

For the "duck under" VASI types, make sure you look at your FOM and see what it says about deviating from the GS or VASI.

[minitour]

Originally Posted by Roger, Roger

Meh. One day I'll see the light and be as conservative as you.

I'm far from conservative...just experienced enough to know that I don't need to save a minute by ducking under a glide slope.

Scared myself one too many times doing that as a CFI. Luckily, once was enough. The aiming points are there for a reason...aim for them.

-mini

[deadstick]

Originally Posted by ghogue

Mike,
VASI is not generic for the other systems. The generic term is VGSI (Visual Glideslope Indicator) which includes VASI, PAPI, Pulsating Systems, Tri-color Systems, and Alignment of Elements Systems. IOTW, a PAPI is not a type of VASI, it's a type of VGSI.

I know many use VASI in a generic sense, but in a letter from FAA Regional Counsel, they state that the term VASI in 91.175 (visual references for descent below DA/MDA), does not allow for substitution by other systems, to include PAPI.

Gary

I was just looking in the ol' OPSPECs, C053 I believe, and remembered this thread. In the part that copies 91.175, it lists "Visual glidepath indicator (such as VASI, PAPI)" instead of "The visual approach slope indicator." If anything, if it's good enough for 135 it should good enough for the fun-lovin' 91 crowd, right?

[minitour]

Originally Posted by deadstick

I was just looking in the ol' OPSPECs, C053 I believe, and remembered this thread. In the part that copies 91.175, it lists "Visual glidepath indicator (such as VASI, PAPI)" instead of "The visual approach slope indicator." If anything, if it's good enough for 135 it should good enough for the fun-lovin' 91 crowd, right?

I don't think that's necessarily true. How many part 91 pilots get to pick an airport for an alternate that's forecasting 400-1 weather at the ETA? You can under 135...assuming the airport meets the requirements.

-mini

[shdw]

Originally Posted by minitour

I'm starting to think that no one teaches this to primary students.

I don't get it, why would they? Ground roll is a function of kinetic energy which is directly related to airspeed. How much ones ground roll is has to do with their airspeed, not the descent angle chosen.

Originally Posted by blackhawk

you must follow the vertical guidance to DH/DA.

Just so others know, this was blackhawk's interpretation of regulation 91.129 (e)(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.

I agree with that interpretation. Once below the DH/DA of a typical precision system or any airport served by a visual guidance system that should be adequate to be safe to descend below, hopefully the FAA would agree.



Where to land? The numbers or the thousand foot markers, it seems this debate trickled over to this thread. I will speak only of GA aircraft in a quick analysis I would like to throw out here for others to examine.

A typical glide path is built on a 3 degree slope, this would be a glide ratio of approximately 19 and 1. With this glide slope you cross the 200 foot AGL point at a distance of 3816 feet. If one was aiming for the thousand foot markers they would be 2816 feet from the numbers.

Let's just throw in some actual glide ratios now, the C172 glides at 9 to 1 according to the POH, from readings I have seen people experiment getting numbers as high as 12 to 1. Each of these assume no flaps, and obviously aren't calculating glide ratio with full flaps power idle. I would guess with full flaps power idle it is closer to 6 to 1. So I did some calculations based on that.

Let us recall just a paragraph ago that if we aimed for the numbers we must be at least 200 feet or higher at 2816 feet from the runway to remain on or above glide slope. Here is a list of distances at an altitude of 200 feet for the glide ratios mentioned above:

12 to 1 results in 6.4 degrees and a distance of 2382 feet
9 to 1 results in 4.8 degrees and a distance of 1783 feet
6 to 1 results in 9.6 degrees and a distance of 1182 feet

The conclusion is with a C172 at least, an idle power approach at about 60/65 knots will result in these distances, each of which will keep you above the glide slope until you are at or below 200 feet if your aim point was the numbers. I didn't take the time to calculate when in fact you would dip below the glide path with these descent angles, obviously it would vary based on your actual glide angle. My guess would be at a glide angle of 5 degrees you wouldn't dip below till VASI until under 100 feet.

[400A]

Originally Posted by shdw

I don't get it, why would they? Ground roll is a function of kinetic energy which is directly related to airspeed. How much ones ground roll is has to do with their airspeed, not the descent angle chosen.

Negative ghost rider. Draw out an airplane crossing the threshold and it's flight path. The flight path would be about 3 degrees. Break that into horizontal and vertical components. Too shallow a descent and you have more horizontal component, too steep and you have too much vertical. Too shallow equates longer ground roll, ie more engergy to dissipate, too steep and you have to flare higher to arrest the descent rate and thus float more chewing up more runway before you can get the weight on the wheels so the brakes can stop you.

The point isn't to nitpick performance details or lay claim to being the best pilot ever. The point is, those numbers you get from your POH or EFB, or dispatch are the result of a very accurate and calculated way the airplane will be flown. Deviating from that and those numbers are useless.

Driving home the bigger point, the reason people are "dragging" the airplane in, or landing on the numbers is because they want increased landing performance, when in fact, they have no way of knowing if they are actually getting better performance (shorter landing distance) or if they are simply getting the illusion of that. I would think, that if one really understood what your landing numbers meant, and everything was legal, there would be no reason to be creative in your operation of the aircraft.

In a perfect world, we as pilots shouldn't have to be performance engineer specialists, the book says X, we need X + whatever. To get X you do A B and C with the airplane. The FAA and the Regs are very clear about what you can and can't do with performance and what you need (121/135). If landing shallow, or landing on the numbers, etc were proven and reliable techniques, we would have procedures for them.

As much as we, myself included, like to bag on the FAA for being a government run entity, there are some fairly smart people at the helm on this stuff and I think we all could do well to heed their wisdom and play by the rules to the best of our abilities.

[minitour]

Originally Posted by shdw

Just so others know, this was the interpretation of regulation 91.129 (e)(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.

I agree with that interpretation. Once below the DH/DA of a typical precision system or any airport served by a visual guidance system that should be adequate to be safe to descend below, hopefully the FAA would agree.

What do you mean hopefully the FAA would agree? If that was "the interpretation", then the FAA has spoken. Where is this interpretation?

-mini

[shdw]

Originally Posted by minitour

What do you mean hopefully the FAA would agree? If that was "the interpretation", then the FAA has spoken. Where is this interpretation?

-mini

Blackhawk said "follow vertical guidance to the DA/DH" while the FAA regulation says, "maintain an altitude at or above the glide path until a lower altitude is necessary for a safe landing." The FAA doesn't say anything about the DA/DH that I saw, is it listed somewhere else showing they agree?

Edit: Oh I am sorry I see the problem, I didn't say in the original post that it was blackhawks interpretation, my fault I changed that now.


400A: I am not really following you, ground roll doesn't depend on the flare. If you touch the wheels to the runway at 50 knots it will take less distance to stop than if you touch the wheels at 55. If you always touch at full stall (33 in a C172) than it wouldn't matter if you came in on a 1, 3 or 5 degree slope, as long as you got to stall speed before the wheels touched. What am I missing?