Vertical path non-precision approach safety?

z987k said:
I agree that a constant descent rate is better than dive and drive, although if it's going to be close I want some extra time at MDA to look around.
That said, your #3 is one of the more ridiculous things I've read on the internet today. How on earth are you going to hit anything if you're at or above MDA? You have an absolute minimum of 250ft of obstacle clearance, and possibly a whole lot more... depending on lots of things that terps explains. A non precision approach is not scud running.
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The whole point is creating an "ILS like" approach. You get down there, if you see it, great. If not, you go. "Taking a look" is what they are trying to avoid.

So you're saying that the risk at 600 feet AGL is the same as at 10,000 feet? Clearly the risk is higher when you are lower, even on an approach path. The longer you are at that lower altitude, the more you are exposed to that increased risk.

There are numerous ways that driving around at MDA is risky. For instance, if you level off and don't advance power, then you don't have much margin for a stall recovery. If you're instrumentation is off, you may be outside of the TERPS protected area, and near obstacles, etc.

I agree that it is generally an acceptable risk to be at MDA, but the idea that it is not risky at all is just not true. The airlines are all about acceptable risk, and minimizing the risks as much as practical. So if you can make a non-precision, which aren't as common as ILS procedures in airline flying, more like an ILS, it brings the risks down, which is why many have moved to that type of procedure.

It's really not easy to explain how airlines think about safety on a forum typing on an iPhone! It's not how most pilots think about safety, though most airlines are trying to educate their pilot groups about contemporary safety, and safety management.

Basically the safety = reducing risk to an acceptable level, and each airline decides for itself what risks they think are acceptable. Their procedures reflect those management decisions.

Clear as mud?
 
Approach stability. It's THE foundation that helps to ensure a safe approach outcome in a transport category aircraft. I never fully understood just how important it was until I actually flew one. Is it easy sure but when it goes down hill it does so in a hurry, much faster than in smaller aircraft which is why airlines require a missed approach when tight parameters are not met. Each airline has their own criteria that must be met and it's usually not all that different. At my airline the basics for IMC are that you must be configured by 1000', on speed within certain parameters, engines spooled, and within the lateral confines of the runway. The other little nugget thrown in there is that we are not to exceed a descent rate of 1000 FPM (unless situation requires it and it is briefed ahead of time). That last one tightens things up a bit.

That being said, the whole concept of a continuous descent approach, VNAV, whatever you want to call it is to aid in making a non precision approach as stable as possible. Can dive and drive be done safely? Absolutely but you that type of approach doesn't necessarily lead to a stabilized approach and arguably sets you up to be unstable (the whole dive idea you know!). In theory on a continuous descent approach you should arrive at your DDA at your VDP, see the runway, and land without having to make more than normal pitch or thrust changes. Therefore it's simple to deduce that the idea is that there's no safe reason to stick around at MDA/DDA past the VDP because no positive outcome can result.

As was stated earlier, it's about calculated risk. Frankly if these procedures, which are safer IMO for the type of aircraft I fly in the environment I fly in don't allow me to get into an airport because I "didn't stick around long enough to look around" then so be it. I'll divert. Buzzing around at MDA making big thrust changes while looking for a runway through low visibility. No thanks.
 
PhilosopherPilot said:
The whole point is creating an "ILS like" approach. You get down there, if you see it, great. If not, you go. "Taking a look" is what they are trying to avoid.

So you're saying that the risk at 600 feet AGL is the same as at 10,000 feet? Clearly the risk is higher when you are lower, even on an approach path. The longer you are at that lower altitude, the more you are exposed to that increased risk.

There are numerous ways that driving around at MDA is risky. For instance, if you level off and don't advance power, then you don't have much margin for a stall recovery. If you're instrumentation is off, you may be outside of the TERPS protected area, and near obstacles, etc.

I agree that it is generally an acceptable risk to be at MDA, but the idea that it is not risky at all is just not true. The airlines are all about acceptable risk, and minimizing the risks as much as practical. So if you can make a non-precision, which aren't as common as ILS procedures in airline flying, more like an ILS, it brings the risks down, which is why many have moved to that type of procedure.

It's really not easy to explain how airlines think about safety on a forum typing on an iPhone! It's not how most pilots think about safety, though most airlines are trying to educate their pilot groups about contemporary safety, and safety management.

Basically the safety = reducing risk to an acceptable level, and each airline decides for itself what risks they think are acceptable. Their procedures reflect those management decisions.

Clear as mud?
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It was the hitting at tower part that I took exception to. I was wondering how you would do that at/above MDA.

I agree with the constant descent approach. It's much more stable. But if the weather is truly crap, and it's a non-precision approach, I really do want more than 1 second to have a look, otherwise you're not getting in. Medium intensity lights, no runway markings, etc all take a bit more than a glance to say, yep I've got it. Then throw in the fact that I might be single pilot and don't have an extra set of eyes looking outside for lights and the runway...
 
z987k said:
It was the hitting at tower part that I took exception to. I was wondering how you would do that at/above MDA.

I agree with the constant descent approach. It's much more stable. But if the weather is truly crap, and it's a non-precision approach, I really do want more than 1 second to have a look, otherwise you're not getting in. Medium intensity lights, no runway markings, etc all take a bit more than a glance to say, yep I've got it. Then throw in the fact that I might be single pilot and don't have an extra set of eyes looking outside for lights and the runway...
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The goal isn't to get in, the goal is to be safe.
 
jtrain609 said:
The goal isn't to get in, the goal is to be safe.
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As the saying goes, if you truly wanted to be safe you'd never turn a wheel.

So, that's not really the goal.

The goal is for the company to make money, and the way it does that is by safely taking pax from point a to point b...and it requires both to be functional.
 
z987k said:
But if the weather is truly crap, and it's a non-precision approach, I really do want more than 1 second to have a look, otherwise you're not getting in. Medium intensity lights, no runway markings, etc all take a bit more than a glance to say, yep I've got it. Then throw in the fact that I might be single pilot and don't have an extra set of eyes looking outside for lights and the runway...
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If you're at a derived DA on path and you don't see the runway right away, you're not going to be making a very stabilized descent to the runway. At 140kts 400' above the ground, if you wait 5 seconds to start down you're already almost 1/4 mi further along. That's what the procedure is trying to avoid.

It's been eye-opening getting back into GA instrument flying--it's highlights how much more forgiving a difference 60 kts on a non-precision approach makes.
 
Hacker15e said:
As the saying goes, if you truly wanted to be safe you'd never turn a wheel.

So, that's not really the goal.

The goal is for the company to make money, and the way it does that is by safely taking pax from point a to point b...and it requires both to be functional.
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Sure it is, it's just not YOUR goal.

If the guys that put the weapons on your aircraft are unable to do so because of a policy that nobody agrees with prevents them from doing so, do you go out there and do it yourself? Of course not.

In the same vein, and as its been explained to me, the FAA is the one driving this boat and telling all part 121 airlines that dive and drive doesn't exist anymore, and that this is the new normal and that NO airline will be doing dive and drive anymore.

With all that in mind, my job is not to get the airplane to the expected destination at all costs. My job is to follow the company policies and procedures, and if those don't allow me to get into the expected destination, then I go somewhere else. I am not Superman. I cannot save the operation. All I can do is operate safely and within the rules that are handed to me. 99.9% of the time, the result is that we go where we're expecting to go. The chances of me going to an airport that doesn't have an ILS, where the only option is an RNAV approach with a DDA, where I can't get in, and where I COULD HAVE gotten in "if only we had that last 75 feet," is so small it almost isn't worth talking about. It's a hypothetical that's so far out in the realm of "things that almost never happen" that this discussion is academic.

So again, my job is not to get there at all costs. My job is to follow the guidelines laid out by the FAA and my employer. Those guidelines say that if we have to use a CANPA style approach, and that the extra 75 feet added to make a DDA prevents us from getting in, then we go somewhere else. What will most likely happen is that we'll gas up, and an hour later go shoot the approach and get in no problem. And that's IF we don't have the holding fuel to wait out the weather, which we'll probably have if we thought this was going to happen.

Also, the amount of altitude that you add to make a DDA depends on the airplane. For us, it's 75 feet, because that's what the engineers have told us we're likely to lose in a worst case scenario when transitioning from going down at about 700 FPM to going around. Thus, the DDA is designed so that you don't go through the floor of the MDA, as the -0 tolerance still applies.
 
Very interesting discussion, one of the better ones we've had on JC.
I will say this, in the corporate world the school houses don't have a clue about this stuff especially in the older certified jet aircraft that I've flown. I generally use VNAV whenever I can and if I do it in the sims they usually look at me like I'm over complicating things. "Just dive to MDA and you'll see the runway".
Just one of the MANY reasons I can't wait to get out of this segment. I've grown up past the I'm a better pilot because I can do it without any of these new fangled gizmos. Fact is the gizmos make it safer and those that don't want to learn it are either too stubborn or too stupid to learn a new method. Being a stick and rudder guy and having the ability manage automation shouldn't be a challenge for a professional.
 
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But the gizmo's can make it more dangerous as well.

What I learned from this thread:

A) What "VGSI and descent angles not coincident" really means.

B) Following the VNAV path down to it's 50 foot threshold crossing height from MDA (DDA) might not be safe if A above is a player. In other words, the approach only gets you to the MDA safely, after that, your VNAV path isn't guaranteed to keep you out of the weeds.

I wish somebody would post the full article the OP was talking about in the first post.

PS: I'm not knocking gizmos's. I love my autothrottles and my VNAV and all that. But complete understanding of what they do and are doing is really super important.
 
DE727UPS said:
But the gizmo's can make it more dangerous as well.

What I learned from this thread:

A) What "VGSI and descent angles not coincident" really means.

B) Following the VNAV path down to it's 50 foot threshold crossing height from MDA (DDA) might not be safe if A above is a player. In other words, the approach only gets you to the MDA safely, after that, your VNAV path isn't guaranteed to keep you out of the weeds.

I wish somebody would post the full article the OP was talking about in the first post.

PS: I'm not knocking gizmos's. I love my autothrottles and my VNAV and all that. But complete understanding of what they do and are doing is really super important.
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Where's the full article at?
 
jtrain609 said:
Sure it is, it's just not YOUR goal.
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That's all valid and interesting, but that's not at all what I was saying.

In Post 84, you say, "the goal is to be safe."

I replied that, if your goal was really to be safe, you would never leave the gate.

Thus, given the fact that you do leave the gate, by definition your goal is not to be safe...it is to move pax from point to point safely (which drives the entire conservative decisionmaking mindset behind this entire discussion).

Which is a very different objective than to simply "be safe".
 
Didn't read the whole thing but did anyone reference the Lear into the trees following the approach plate exactly.
 
jtrain609 said:
With all that in mind, my job is not to get the airplane to the expected destination at all costs. My job is to follow the company policies and procedures, and if those don't allow me to get into the expected destination, then I go somewhere else. I am not Superman. I cannot save the operation. All I can do is operate safely and within the rules that are handed to me. 99.9% of the time, the result is that we go where we're expecting to go. The chances of me going to an airport that doesn't have an ILS, where the only option is an RNAV approach with a DDA, where I can't get in, and where I COULD HAVE gotten in "if only we had that last 75 feet," is so small it almost isn't worth talking about. It's a hypothetical that's so far out in the realm of "things that almost never happen" that this discussion is academic.
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Uhm, no, it's not really that academic, but I guess you don't get out to San Francisco that much.

"NAV RWY 28L-28R ILS GP OTS ..."

It's not actually that unlikely (in fact, it caused a divert for me last week so I'm either quite unlucky or a complete hack), but I don't have the fancy equipment that the ERJ does. We're also not required to do CANPA, and we also don't have any vertical guidance when we do do CANPA.
 
My first and only rule is situation awareness in which the same non-precision approaches I mastered in a GA aircraft doesn't cut it in a heavy jet especially if a stable approach isn't possible I will not do it.
 
Plus, a lot of us are governed by the principle of the VDP. The CANPA approach pretty much gets you at your VNAV DA/DDA at your VDP so even though you're technically not at your MAP on some approaches, you'd be conducting a MAP at your VDP.

Before we'd "dive and drive" to the MDA, find the runway and then begin a normal 3:1 descent at the VDP. If we didn't see the runway, flying at MDA, reaching our VDP prior to our MAP, we'd be bugging out anyway.
 
Hacker15e said:
That's all valid and interesting, but that's not at all what I was saying.

In Post 84, you say, "the goal is to be safe."

I replied that, if your goal was really to be safe, you would never leave the gate.

Thus, given the fact that you do leave the gate, by definition your goal is not to be safe...it is to move pax from point to point safely (which drives the entire conservative decisionmaking mindset behind this entire discussion).

Which is a very different objective than to simply "be safe".
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Which is why safety = acceptable risk, not NO risk at all. A safe flight isn't a flight with zero risk. It is a flight where the risks are mitigated by procedure and proficiency to the lowest level possible.

Of course risks can't be completely mitigated (reduced to zero), and that left over "residual risk" is accepted.
 
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