Remember LP approaches? Last year we shed some light on these obscure but increasingly common instrument approaches, which are part LPV and part LNAV. At the time, this was mostly an academic conversation–nobody could actually fly an LP approach. But that’s about to change.
A whopping 80 foot reduction in minimums for an LP approach vs. LNAV, but at what cost?
As a quick review, LP approaches are basically the WAAS GPS equivalent of traditional localizer approaches–precise lateral navigation, but no glideslope. They are being set up at a number of airports where a full LPV approach simply isn’t possible, usually due to infrastructure or terrain issues. There are now 412 LP approaches in the FAA’s inventory, far less than the 3,000+ LPV approaches, but still a decent number.
To fly an LP approach, you need to have a WAAS GPS, like a Garmin GTN 750/650. If you have an older GNS 430W/530W, you just need to have software version 3.3 or higher. The problem has been that, even with the right equipment, the LP approaches were not in the Jeppesen NavData database that drives these modern GPSs. So you couldn’t fly them if you wanted to.
Recently, though, word has trickled out that LP approaches are finally hitting the Jeppesen database–perhaps as soon as the February 7 update. That means those 412 approaches will finally be flyable.
So what? Isn’t the addition of a bunch of new WAAS approaches a good thing? Not necessarily.
The problem is that LP approaches do not show an advisory glideslope. Remember that LNAV approaches (like LPs, a non-precision approach) create a mathematical glideslope that can be displayed on your GPS and HSI–annunciated as LNAV+V on most GPSs. This isn’t a real ILS-style glideslope, just a way to fly steady descents from the final approach fix (FAF) to the missed approach point (MAP). Nonetheless, this is a major help for pilots, eliminating the “dive and drive” method of flying an approach.
It’s gone with LP approaches.
Why would such a helpful tool be removed from a WAAS approach? The FAA was worried about pilots confusing LP and LPV approaches, and flying an LP advisory glideslope right down to the runway as if it were an LPV glideslope. So early guidance from the agency was that LP approaches could not have any type of glideslope indication. GPS manufacturers duly complied with this directive.
That beloved +V advisory glideslope is gone with an LP approach.
The benefit you get in exchange for this loss of glideslope display–lower approach minimums–is pretty insignificant. Take the state of Ohio: there are 16 total LP approaches in the state, with a median benefit of only 20 feet in lower MDAs. That’s impossible to even notice on the altimeter. The greatest reduction in MDA is only 140 feet and there are two cases where it’s 0 (the LP MDA is exactly the same as it was for an LNAV-only approach). In those cases, you’ll see no improvement in minimums but you’ll lose your advisory glideslope. That’s a bad trade.
Remember that you can’t choose which approach to fly–LP approaches are only set up when there is no LPV approach, so this isn’t just a fail-down mode for LPV. If you choose the RNAV Runway 22 approach at I69, for example, your GPS will fly the LP approach whether you want to or not. There’s no avoiding them with fancy button pushing.
The only good news is that the FAA seems to have recognized its error, and is now allowing avionics manufacturers to display an advisory glideslope on LP approaches. Advisory Circular 90-107 now says, “The avionics integration may include advisory vertical guidance during an LP approach.” Garmin says they are aware of this change, and are considering adding the LP + V feature. But it will probably be quite a while before this upgrade comes to your cockpit.
So for now, spend an extra minute briefing your next flight and look to see if there’s an LP approach. If so, don’t plan on seeing a glideslope. You’ll want to know that long before you hit activate and realize your trusty old LNAV approach has been replaced.
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To quote Dr. McCoy – “The bureaucratic mentality is the only constant in the universe!”
Only the FAA could take a system that was working and enhanced safety, break it so that it is now less safe and then say they recognize and understand the problem, but it will take months or years to fix it.
I have a quibble with the following statement from your article:
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Remember that LNAV approaches (like LPs, a non-precision approach) create a mathematical glideslope that can be displayed on your GPS and HSI–annunciated as LNAV+V on most GPSs. This isn’t a real ILS-style glideslope, just a way to fly steady descents from the final approach fix (FAF) to the missed approach point (MAP).
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The advisory glideslope available on most procedures with LNAV-only minimums should be followed only to the MDA, unless upon reaching the MDA, you can continue visually per 91.175. The advisory glideslope is designed to take you to a point about 1,000 down the runway, not just to the MAP.
Fair point, Bruce, but the intent of the +V is (at least to me) to avoid the dive and drive approach. There are some airports where following the +V glideslope religiously from MAP to runway will get you close to some trees. You might not hit them, but they look awfully close (which is probably why there’s no LPV in the first place).
My philosophy is to fly the +V to the MAP, but then ignore it. It’s a way to remind me that this is not a precision approach.
Good Morning John,
Do you really fly that advisory glide path to the MAP?
Possibly you meant to say you fly the advisory glide path to the MDA.
That is amost correct. You need to start the level off procedure far enough above the MDA to avoid going below. After you have leveled off, you can stay at the MDA until you reach the MAP where the missed approach procedure should be initiated.
Happy Skies,
Old Bob
Good clarification Old Bob–the advisory glideslope is only flown to the MDA, NOT the MAP.
Hi Bob
Until the FAA authorized us to use the MDA as a DA on the approaches when following FMS guidance (as noted in a ball note) we added 50′ to the MDA and referred to this new altitude as a “Derived Decision Altitude (DDA).” New GPS charts have eliminated this “ball note” nomenclature and now list a DA for LNAV/VNAV approaches.
OC
Good Evenng OC,
Obviously, I have missed the FMS provision that you describe (I have not f;own an FMS in the last twenty three plus years) But I think it is fair to say that All VNAV approaches have a DA or DH and all LNAV approaches publish an MDA. Any approach that has a DA or DH allows us to make the go/no go decision at the DA/DH, but when there is only an MDA, we must initiate the level off before reaching the MDA.
As you have described, I recommend that we use ten percent of the rate of descent for the time to initiate the leveling maneuver. For a five hundred foot rate of descent, your fifty foot figure works out well.
Is there some regulation published which will allow you to use a published MDA in the manner of a DA when you are using an FMS? That I have missed. Interesting.
Happy Skies,
Old Bob
Look at the LP MDA minimums at Telluride CO using the RNAV (GPS) Z RWY 9 approach… Compared to the other 3 approaches, this LP gets you significantly lower…
Wow. What a major improvement! While I do not consider myself any sort of expert on the nuances of X or Z approaches, it appears to me that the big difference is the rate of climb required to be able to use the Z approach.
Excellent use of variables.
Happy Skies,
Old Bob
Good Evening All,
There is at least one approach where following the Advisory Glide Path below the MDA will put you into the rocks. That is at N23, Sidney, NY, Rwy 7.
When the weather is well above the published minima, the advisory glide path does make for a very easy to fly stable approach.
No argument at all.
However, when executing a low visibility approach into a rich obstacle environment it is often an advantage to use the classic Dive and Drive. Admittedly, that approach requires more attention, planning, and technique, but it can result in a higher percentage of safely completed approaches. I do believe that the FAA will start to add the advisory glide path to what is allowed , but it does bring up the point that the advisory glide paths are NOT the same as flying an LPV or an ILS approach.
All flight below the MDA must be conducted so as to avoid obstacles that MAY be in the way of the approach. I like the advisory glide path being available, but I wish more people were aware of the potential for an obstacle being in the way of the approach to the airport. I have seen at leaston approach where the LP beats tha LNAV by over 80 feet. That can be an important eighty feet.
I am sure there are other places where the improvement will be even better. We are in the process of gettig an approach approved for our airport and, right now, it appears that we may get a one hundred footb lower ceiling minima using the LP than the LNAV.
Number one; do not sell the LP short and, number two; do not put as much reliance on the Advisory Glide Path as you put on an LPV glide path or an ILS glide slope.
Happy Skies,
Old Bob
Bob,
I have followed your sage advice for more years than either of us need to count. Your comment that planning and conducting a “dive and drive” approach into an obstacle rich environment might be safer than a constant rate approach flies in the face of accident statistics and common sense. No one is advocating following a glide slope/glide path/gradient path below minimums without adequate visual reference. Constant angle approaches are dramatically safer than dive and drive, and with a /V reference they are even better. Yes, if you follow the path on an LP approach below minimums it will take you closer to the obstacle that precludes the approach from becoming an LPV, (but still clearing it) This is why we only continue VISUALLY. Pilots are still in a much safer position, on a stabilized descent than trying to fly level at MDA, fully configured, while searching for the runway (which may now be blocked from view by the nose, and watching their timer.
OC
Good Evening OC,
I see that I have not explained myself adequately.
I do NOT contend that my method is safer than just using the advisory glide path and executing a miss if the required cues are not available uoon reaching the MDA.
It is my contention that with proper planning and execution a suitably safe arrival could be made by setting up for a steeper approach further along the approach path.
Our light airplanes, and every airliner I have flown for that matter, can safely make six degree approach paths to a safe landing providing adequate planning is used. Since we do not have an electronic glide path for the six degree approach, I like to calculate a VDP based on that six degree slope and I like to be flying all level and stabilized at a steady power that will comfortably maintain the safety of the MDA while I am getting close enough to the VDP to see the required cues before leaving the safety of the MDA.
It is not a choice between two ways of executing one approach, it is way of using a sane and safe procedure that IS inside the rules that exist to enable us to make a landing under conditions where the approach would be missed using the stable descent approach via the advisory glide path.
The classic example is an approach to five hundred and one where precisely those conditions are prevalent.
Coming down the Advisory Glide Path we will be at the MDA between one and a quarter and one and a half miles from the runway threshold. That would probably mean a missed approach as long as the visibility really is just one mile. A good safe missed approach, but, nevertheless, a miss!
We could level off at the MDA and fly level until we got to the six degree VDP where we should have a good view of the required cues, (About three quarters of a mile out), but why not set up for that eventuality long before the decision must be made?
When the weather is well above the minima, I would certainly ride down that very easy and comfortable advisory slope, but if the weather is at all marginal, I want to be ready to make that six degree approach and safely land at my destination. On top of that, if the circling minima is the same as the straight in miminima, being level at the MDA as I arrived near the MAP may allow me to see that a circle is a practical solution.
When the weather is really down at the published minima, I want every advantage to be on my side.
Make any sense at all?
Happy Skies,
Old Bob
The LP approach is a significant step back. Essentially what results practically is something like the old GPS overlay with lower minimums. The synthetic glide path was a tremendous safety enhancement and my system would fly it perfectly. No longer. What a mess. One step forward, two steps backward.
Good Afternoon Paul,
May I respectfully ask that you carefully look at this situation once more?
The reason we execute instrument approaches is to land safely at our destination.
If the obstacle environment is excellent and if we want to spend the money to install a full ILS, the approach to two hundred and a half is a piece of cake. Easy to fly and easy to execute the miss. However, if the airport is in an obstacle rich environment and the funds are not available to install an ILS, there are many non precision approaches that will allow safe IFR approaches to fairly low weather minima.
The classic Dive And Drive is more difficult to execute, but it often will let us land when the visibility is lower than we would need if we set up a precision style approach.
Different strokes and all that jazz.
I would hate it if the FAA chose to eliminate those nice non-precision approaches that serve us so well. If the ceiling is five hundred feet and the visibility is only one mile, a 3 degree precision approach would have us at five hundred feet between one and quarter to one and a half miles from the runway threshold.
Consequently, it would be a mandatory miss with the precision approach. If I have properly planned for a controlled descent on a six degree fight path via the Dive and Drive, the approach would be safe and efficient.
Why should I be penalized by such an approach no longer being provided? We have been safely executing such approaches for well over eighty years. If you do not care to use those approaches, that is fine with me, but I do NOT want to lose that capability.
Please be careful as to what you ask for.
The FAA has NOT taken a step backwards. They are accommodating those of us who are happy with the level flight segment non precision approach.
Happy Skies,
Old Bob
Bob,
I am afraid you are not seeing the the guy in the gorilla suit. Accident statistics make it clear that we have NOT been flying dive and drive approaches safely for the past 80 year. These approaches, as you point out, are more difficult and involve a significantly higher level of risk than the constant angle approach. It has been over 15 years since most major airlines determined that this increased level of risk and its potential consequences did not justify continuing to fly these (dive-and-drive) approaches.
Many of us conducting flight training are deeply concerned about accident rate in GA and are doing all we can to reduce that rate and save some of those lives that will be lost if we are not successful. It is simply a question of Risk Management. Constant angle approaches, especially with vertical guidance, are dramatically simpler and safer to fly.
I am sure with your skill and experience you are able to manage this added risk routinely. But, to many less adept pilots this additional risk has been fatal.
Let me ask you: If it were your family members riding in an aircraft with a another pilot flying a NP approach to minimums at night, which type of approach would you prefer be attempted?
OC
Good Morning OC,
I am afraid we must agree to not agree!
I do feel it is dangerous to attempt any type of approach if you have not been trained to do so and training in low visibility approaches has been sadly neglected for many years.
As to the safety record, I have not seen a serious study for the last ten to fifteen years, but the Mitre Corporation was tasked by the FAA to do such a study a few years ago. They found that Air Carriers had a better safety record using the precision approach, but that we GA pilots had a better record executing non precision approaches. It was noted that they were surprised at the results shown and postulated that it might be due to the very small numbers of light GA aircraft that were involved in the sample.
In reference to the air carriers, most ceased doing anything other than precision approaches around forty years ago. I flew the 737 from 1972 to 1974. It was the last airplane in which my airline used circling approaches and we dropped them while I was flying the airplane.
Now the important part.
We did not cease using circling and non precision approaches due to any safety problem. We quit using them because there was no need. All the airports we used had ILS approaches to multiple runways.
The reason we stopped using them was because we could save fifteen minutes of training time on each hood check. It was strictly the cost savings of less training time.
It is my contention that we instructors have NOT done a good job of training students in the intricacies of the non precision approach mainly because the airlines quit going to small minimally equipped airports.
I disagree with your thought that it is inherently dangerous, but I do agree that such approaches need extra training to be conducted safely.
I think we will agree that IFR flying does add to the safety of flight for most of us, but there are folks who do not fly IFR who have done so safely for many years.
I think it is easier to be safe if one is trained to fly on instruments and I do believe the Dive and Drive is safe IF we are properly trained.
The same is true of circling approaches. They can be safe, but additional training is required beyond that which just meets minimum standards.
We who regularly operate from small poorly marked airports can do so safely IF we get proper training and I think you will find that properly trained pilots DO have the safety record that Mitre found.
My first year as a DC-3 copilot shooting non precision approaches via the low frequency range convinced me that it can be done safely by a low time pilot if he is properly trained.
Happy Skies,
Old Bob
Oscar,
While it has been demonstrated that a non precision approach using a constant descent angle is a clear winner from a safety perspective for large Turbine aircraft, it has not been demonstrated for smaller piston aircraft. MITRE did a study and did not find that it improved accident rates for the latter category of aircraft, in fact the opposite was true although it was not statistically significant.
Also, note that not all airports and non precision approaches are created equal. There many such runways are that are simply not appropriate for a constant angle descent from the FAF to the threshold. A part 139 airport is not the same as a county airport without an approach light system in an obstacle challenged environment. Of course the airlines won’t be flying into these GA only airports.