383 Why Your RNAV Glide Path Won’t Capture—and How to Fix It + GA News
50:59 Share

Have you ever wondered why your autopilot sometimes refuses to capture the glide path on an RNAV approach? The problem usually isn't your avionics. It's how you're following the approach.

Today I'll explain the key differences between ILS and RNAV glide slopes and glide paths, and give you a simple formula that ensures your autopilot captures and follows a glide path every time. And in our update sections, we'll talk about two accidents, one involving a Honda jet that went off the end of a runway last month in Oregon, and a beach baron that ended up in a pond at my home airport.

Hello again and welcome to Aviation News Talk where we talk general aviation. My name is Max Trescott. I've been flying for 50 years. I'm the author of several books and the 2008 National Flight Instructor of the Year. And my mission is to help you become the safest possible pilot.

Last week in episode 382, we talked about settings that I recommend for the Garmin G1000, 3000, 5000, and Cirrus Perspective Avionics to boost your situation awareness and help you fly smarter. So if you didn't hear that episode, you may want to check it out at aviationnewstalk.com slash 382. And if you're new to the show, welcome. Glad you found us.

Now, if you would, in whatever app that you're using to listen to us, touch either the subscribe key or in the Spotify or Apple podcast app, the follow key so that next week's episode is downloaded for free. And see if you know any of these people who've signed up in the last month to support Aviation News Talk.

They include a new Patreon mega-supporter, Pamela Burgess, those are the folks who donate $50 a month, and other Patreon supporters including Jason Lyons, CB, Rich A. Looney, and Michael Keaveney. We've also had donations via PayPal from Jeffrey Vale, Daniel Reed, Stefan Balmer, and Guillermo Naranjo Alanis.

Thank you so much for your support. And if you've occasionally thought about supporting the show in the past, now would be a great time to do it. And if you sign up now, I'll read your name next week. Just head on out to aviationnewstalk.com slash support. Coming up in the news for the week of May 12th, 2025, ForeFlight integrates FAA weather cameras.

FAA lists some restrictions on experimental aircraft. And you won't believe how badly one Texas pilot handled a job rejection and what it cost him. All this and more when the news starts now.

From AOPA.org, ForeFlight integrates FAA weather cams. Since rolling out the technology in Alaska, the FAA has expanded weather camera coverage to include hundreds of locations across 24 states. At each location, a cluster of up to four cameras uploads images on a 10-minute cycle, allowing pilots to observe visibility and precip at any given location from anywhere in the world.

The FAA WeatherCam network, which was built out and continues to expand, can now be viewed within ForeFlight. A detailed briefing posted by ForeFlight walks users through the steps to enable the camera layer and begin viewing images within the app. The Weather Camera Map layer requires a ForeFlight Pro level description and is among many new features and updates planned or recently enabled. From FlyingMag.com, FAA lifts some restrictions on experimental aircraft.

FAA announced an immediate policy change that allows experienced pilots to operate multiple experimental aircraft with less documentation and procedures. Effective immediately, pilots who hold three Authorized Experimental Aircraft, or AEA, authorizations in high-performance piston aircraft can operate additional experimental aircraft by completing only aircraft-specific ground and flight training without the previously required practical test.

U.S. Representative Sam Graves from Missouri said,

The FAA has now streamlined this process and made it easier for experienced pilots to operate multiple types of aircraft without all the red tape. The change represents a major shift in how the FAA manages authorizations for experimental aircraft. Previously, pilots needed to submit formal applications and documentation to the FAA for each additional experimental aircraft they wanted to fly.

Under the new program, authorization will be provided through a simple logbook endorsement from the CFI who provided the training, rather than through formal FAA documentation. And also from FlyingMag.com, Secretary Duffy will allow air traffic controllers to work past age 56. Transportation Secretary Sean Duffy says he'll use his authority given to him by Congress to

to allow controllers to continue working past the current mandatory retirement age of 56. In an interview on NBC's Meet the Press, Duffy said that he has the power to issue exemptions to ATCs that permits them to continue working until they turn 61. A spokesperson for NATCA, the National Air Traffic Controllers Association, confirmed that Duffy does have that authority. The

The spokesman said, quote, that authority has been in law for decades. Through this process, air traffic controllers can apply for a waiver to continue working past age 56, and it does not change the mandatory retirement age of 56. From CNN.com, air traffic control hotline between Pentagon and Reagan National has been broken since 2022.

A hotline between air traffic controllers at Ronald Reagan Washington National Airport and the Pentagon intended to coordinate aircraft has not worked since March 2022, the FAA revealed in a congressional hearing on Wednesday. The FAA was not aware the direct line was broken until a May 1 incident where a helicopter circled the Pentagon and caused two flights to abort landings. Franklin McIntosh, the FAA's deputy chief operating officer, testified.

The airport was the site of the deadliest U.S. airline crash in more than a decade when an American Airlines original jet and an Army Black Hawk helicopter on a training mission collided on January 29th.

The unit flying the helicopter that circled the Pentagon was the same one involved in January's mid-air collision. Military flights to the Pentagon have been suspended since the incident and will not resume until the hotline is fixed, McIntosh said. The hotline is maintained by the Department of Defense and is one way for controllers to coordinate in addition to using regular landline telephones.

From GeneralAviationNews.com, pilot seriously injured when he forgets to remove wheel chocks. I'm guessing you can figure out what happened here. The pilot told investigators that after he started the Beach F-33A's engine at the airport in Tahlequah, Oklahoma, he realized that the wheel chocks were still in place on the nose landing gear tire. He set the parking brake and exited the airplane with the engine still running. As he removed the chocks, they inadvertently hit the propeller and pulled his arm into the propeller arc.

The pilot sustained a serious injury to his right arm. The airplane sustained minor damage to the propeller. Probable cause, the pilot's failure to remove the wheel chocks before engine start, which resulted in the inadvertent contact with the propeller while the engine was running. From avweb.com, overrun accident traced to pilot fatigue and other factors.

A confluence of errors and misfortune characterized the accident report from Transport Canada of a Boeing 737 operated by low-cost Canadian operator Flair Airlines.

There were no injuries among the 140 on board after the aircraft departed the runway on landing at Waterloo Airport on November 25, 2022. It started with the captain, who was the pilot flying, having accrued significant sleep debt over the week before the flight, which began late on November 24 as an overnight red-eye trip.

On landing, the captain was operating after nearly 18 hours of wake period at the end of a circadian low. Ceilings were reported as 600 feet above ground with minimum visibility. Complicating the following sequence of events, the left thrust reverser was inoperative and stowed in the locked position in accordance with the MEL.

At about 70 feet above the runway's surface, the captain intended to disconnect the autothrottle, but instead accidentally activated the takeoff go-around or TOGA control. According to Transport Canada, "...the left reverse thrust lever had been locked in the stowed position per the minimum equipment list."

When selecting the right reverse thrust lever following touchdown, the pilot removed his hand from the forward thrust levers, allowing the left one to advance undetected as commanded by the autothrottle. So the aircraft was configured with reverse thrust on one engine and takeoff power applied on the other.

The report concluded, when the captain applied maximum braking, there was 2,500 feet of runway remaining and the aircraft was traveling at a ground speed of 115 knots with no speed brakes, one engine at near maximum thrust, and the other engine nearing maximum reverse thrust. At this speed and in this configuration, there was insufficient runway remaining to stop the aircraft and it overran the end of the runway.

And finally, from FlyingMag.com, pilot sentenced over threat to kill prospective employer. A Texas man made several threats after failing his blood alcohol test and having his job offer rescinded.

The Texas pilot was sentenced after being charged with a criminal complaint after threatening to kill an employee at a charter company he applied to work for. According to a news release from the U.S. Department of Transportation's Office of the Inspector General, the pilot from Waco, Texas, was sentenced to one month in jail, 12 months of probation, and a $25 special assessment by a federal judge. The criminal complaint alleged that in February 2024,

The pilot interviewed for a chief pilot position with an unnamed company in Florida. He received a job offer from the company, but failed his blood alcohol screening, causing the offer to be rescinded in March. After being notified that he wouldn't get the job, he called and harassed an employee for about five days.

Months later, in June 2024, he called again and left several threatening voicemails. On July 2nd, he left another voice stating the following, I'm coming for you, expletive. You know what? I'm being evicted from my place residence because of your expletive and your actions. I'm going to come after you, you piece of expletive, and I'm going to knock on your door and I'm going to kill you. Okay, get it?

And there's more, but I think you get the general idea. The harassment and threats continued in several more voicemails until the victim reported them to the FAA and a local sheriff's office. And here's just a tip. Next time, just send a thank you note and skip the threats. Coming up next, a few of my updates, including information on two recent accidents. And then we'll talk about why sometimes your autopilot won't couple to an RNAV glide path. All right here in the Aviation News Talk podcast.

And now let's get to the good news. This comes from Patreon mega supporter Richard Eide. He writes, I passed my instrument checkride this week. Thank you so much for all of your great content and guest interviews. As always, it helped me to prepare and remain safe throughout. Keep up the good work. Well, Dick, thank you so much for your support and congratulations to you.

And now let's get to our video of the week. This comes from Garmin and it's about Autoland. The story in AvWeb says until now, Garmin's revolutionary Autoland system has only been available for turboprops and jets, but now it's available for the Cirrus SRG 7 Plus series.

So this video shows exactly how Autoland works, and Cirrus refers to that as their safe return technology. I had the pleasure of being at Garmin six years ago, the day they announced this, and was able to

interview some of the engineering staff that worked on it. It's really quite remarkable. Interestingly, a few years before that, I'd had a conversation with one of the co-founders at Cirrus, and he had mentioned that had they anticipated the interest in creating this technology, they probably would have come up with a steerable nose wheel. Cirrus, of course, has differential braking. There is no direct control over the nose wheel. Nonetheless, they figured out how to make it work

And to see this video and all of our videos of the week, head on out to aviationnewstalk.com slash video. And on that same page, you'll find links that you can use to become a supporter and start supporting the show. So when you go out to view the videos, look at the bottom of the page for the video links. And at the top of the page, you'll see four options listed for supporting the show. Again, that's aviationnewstalk.com slash video.

And you may know that this year, Lightspeed is giving away four Delta Zulu headsets to Aviation News Talk listeners, and the first winner has been selected. Congratulations to Chris Hui, who lives in Arizona. He spent 21 years in the Army and says that flying is his life. And

And if you have already signed up for the giveaway, guess what? You're automatically entered for that next drawing, which will be sometime in early July. And just a reminder, it's a top of the line Delta Zulu headset worth about $1,200. And so if you haven't signed up, go ahead and take a moment to do that because just like Chris, somebody has to win. So it's not too late. Head on out to aviationnewstalk.com slash giveaway and sign up for the Lightspeed headset giveaway. And of course, whenever you buy a Lightspeed headset,

Lightspeed will send a check to support Aviation News Talk, but only if you first go to the special link we've set up for you to get to their website. So when you buy, go first to aviationnewstalk.com slash lightspeed, which will take you to their website where you can make your purchase.

And here are a couple of quick listener emails. This comes from Daniel Reed. Max, really enjoyed your episode on best garment and Cirrus Perspective settings to fly smarter and safer. Although I have 300 plus hours in combined Cirrus Perspective, Perspective Plus, and Perspective Plus Touch avionics, I found your review invaluable. Well, thanks for that, Dan. And also thanks for your recent donation.

And Jason Thaggard writes,

I've never heard anyone advocate for TrackUp as well as you did, and I'm going to try to start using it. Thanks. That's great, Jason. And I totally get if you've been staring at a NorthUp radar screen for all these years, it would be tough to switch to TrackUp. One thought I have is that if you really find it too difficult to adjust to, go ahead and leave your main moving map in NorthUp.com.

But then when you really have to look at traffic, switch to the traffic page, which is heading up. And of course, that's where I think some of the greatest value comes from in terms of using heading up or track up. And now let's take a look at two recent accidents in which having a little extra speed on final was not a good thing. First up is a preliminary report that's just out for a HondaJet accident that occurred on April 7th at the North Bend, Oregon airport.

This was one of three HondaJet runway excursions that happened in just a six-day period. In this case, the jet went off the end of the runway and ended up in the water. I talked about that accident at the time and noted the aircraft was a little fast and that it landed on a wet runway. Just days after that crash, the HondaJet Owners and Pilots Association did interviews with a couple of publications. Here's in part what an article in AOPA Pilot Magazine said.

The Aviation Safety Network has recorded 35 incidents and accidents involving Honda jets since the groundbreaking aircraft was certified in December 2015, of which 29 of the 35 involved runway excursions. The owner group analyzed runway excursions in 2023 and concluded that some can be traced to techniques that pilots learned while training for their private pilot certificates in light piston trainers.

Many pilots were taught to increase approach speed during gusty conditions. In many aircraft, the side slip may safely be used to maintain runway alignment in the crosswind. Pilots generally seek to extend the flare for a soft touchdown and hold the nose wheel off the ground after the main wheels touch to maximize aerodynamic braking.

In a HondaJet, however, those are all techniques to avoid, said David DeCurtis, safety chair of the HondaJet Owners and Pilots Association. Quote, adding half the gust of V-Ref is absolutely the wrong thing to do in a HondaJet.

He said, adding that the aircraft was designed to handle adverse wind and weather conditions, short of wind shear, at its prescribed landing speed, so pilots must trust the techniques taught during type training and forget about trying to grease the landing. Quote, your target is VREF, period, end of story. Rather than adding a margin of safety with extra speed during gusty landings,

You're adding a margin of risk, DeCurtis said. To help other pilots get it right, the owner groups developed the HJOPA Proficient Pilot Program, which it plans to launch in May. The program emphasizes training and highlights the differences pilots can expect in flying the HondaJet. The program's launch will include its first instructional video focused on details of HondaJet's landing procedure, which DeCurtis previewed ahead of its official release.

Procedures that pilots might consider departures from the norm include minimizing the flare and seeking to plant the wheels firmly on the runway, generating up to 1.5 Gs on touchdown. This creates the prescribed full landing gear compression that DeCurta said is desirable because it maximizes friction between the tires and the pavement, thus maximizing directional control. Quote, "...friction is dramatically more efficient in directional control than your rudder," he said.

The forthcoming video also advises against using a side slip on approaching crosswind conditions, recommending instead a crab and kick technique to compensate for crosswind. DeCurtis suggests maintaining the crab all the way to touchdown, timing the runway input to align the nose with the centerline to the last possible instant. A side slip, banking into the wind with ailerons while countering the turn with opposite rudder, risks wingtip contact with the runway.

The prompt lowering of the nose wheel to the runway at touchdown, which Honda calls prompt derotation in its flight manual, is another departure from the way many pilots are accustomed to landing. Getting the nose wheel down quickly, though, increases the pilot's control on the ground. The goal when landing the HondaJet is a rapid and firm transition from flying to taxiing. It might help to think of an F-18 landing on an aircraft carrier with its gear struts absorbing the impact.

And now here's what the preliminary report says about that crash in Oregon. It says, as he approached the airport, the pilot configured the airplane for landing on the ILS Zulu approach to runway 5. He had flown this particular approach regularly because each Monday for the last year, he flew the same flight around the same time, transporting the operator's employees from St. George, Utah to North Bend, Oregon, returning each Friday.

The front right seat passenger, the son-in-law of the airplane's owner, was a student pilot nearing his certification, but he was not flying the airplane. The pilot detailed his pre-landing procedures, specifically describing how he determined VREF,

He stated that he entered relevant data into the airplane's FMS system, which included the following data blocks. Runway condition, wet. Weather information, 11 degrees C. Flap setting, full down. Runway selection, runway 5. Wind information, provided from the airport's AWOS. And the airplane's weight, which he recalled was around 9,000 pounds. The FMS then provided the required landing distance of approximately 4,200 feet, which he thought was well under the runway length.

The pilot recalled that on the day of the accident, the approach was normal, and there was a reported crosswind of nine knots. There was limited visibility due to darkness at that time of the morning, and he did not specifically observe standing water on the runway. But the pilot was aware of recent heavy rainfall. And here's a key point. The report says the airplane crossed the runway threshold around 117 to 118 knots, significantly

slightly above the VREF calculated speed of 113 knots, which he configured due to the crosswind. The airplane touched down on the runway surface at about 1,000 feet from the approach end, near 113 knots, consistent with his typical procedures. The pilot further stated that the initial braking felt normal, and he anticipated the airplane's deceleration rate would enable him to exit the runway at taxiway Bravo.

As the airplane continued the landing roll and was about halfway down the runway, the braking was seemingly ineffective, though there were no warnings or messages. The pilot and passenger then applied maximum brake pressure, but the airplane was not responding. Recognizing the inability to stop, and as the landing roll continued toward the localizer antenna at the end of the runway, the pilot maneuvered the airplane to the right to avoid the structure. The

The airplane traversed through grass and mud before descending an approximate 15-foot embankment into adjacent water. A review of ADS-B data showed that at 6.06 a.m., the airplane touched down on the runway near the aiming point markings. The airplane continued down the centerline, decelerating from a ground speed of about 128 knots to 125 knots, which was the last recorded hit.

Now, recall that the pilot calculated a landing distance of 4,200 feet and a VREF of 113 knots. Well, the NTSB came up with different numbers. According to the report, the airplane had been upgraded with HondaJet's supplement, quote, wet and contaminated runway performance. The logbooks indicated the software had been upgraded in the FMS to reflect the revised AFM. The definition containing the supplement for wet runway is then water depth on the runway of less than an eighth of an inch.

The VREF and landing distance required were calculated from the FMS based on the temperature of 11 degrees, the self-reported weight of 9,000 pounds, a wet runway, negligible tailwind and headwind, a runway slope gradient of 0.05%, and an airport altitude of 16 feet. The FMS provided a required landing distance of 5,910 feet and a VREF of 111 knots.

And by the way, it turns out that runway 5 has a length of 5,980 feet, just 70 feet longer than the required landing distance calculated by the NTSB. Now, the big question in my mind after reading this was, why did the pilot add a few knots for a crosswind? Do you increase your approach speed when there's a crosswind? And if so, why?

And what's the source of information you use that provides that guidance? I think most pilots are familiar with the FAA guidance to add half of the gust factor to your approach speed when the wind is gusting. So if the winds are reported as 20 knots gusting to 30, the gust factor is the difference between those numbers are 10 knots and you would add half that or five knots to your final approach speed.

But that has nothing to do with crosswinds. I never increase my speeds for crosswinds. And I started to search and see if I could find any guidance for doing what this pilot did, which was increase his speed because of a crosswind. All I could find was that some aircraft manufacturers do suggest a small addition for crosswinds in their POHs, typically two to five knots above normal approach speed in strong crosswinds.

But that is aircraft-specific advice, not a blanket FAA policy. And I should note that as far as I know, none of the POHs for airplanes I fly say to add a few knots for a crosswind, and I don't.

Now, I have read that some instructors suggest carrying two to five knots extra in strong crosswinds for what they call added controllability margin. And they stress this is a technique, not a rule. And I worry that sometimes the word technique is sometimes used to mean the way I like to do it, the way one of my instructors did it, even though it's not in the POH. So I would say be careful about doing things your instructor taught you that aren't outlined in the POH rules.

for the airplanes you fly. And don't just add a few extra knots to your final approach speed without a good documented reason for doing it. It's very easy for pilots to be undisciplined about their approach speed by adding a few knots for wind gusts, and then a few more for a crosswind, and then a few more for the wife and kids. But landing fast can be just as bad as flying too slow. So

Be disciplined about your final approach speed, know your target approach speed, and do whatever it takes to maintain that airspeed on final.

Now let's talk about another accident that has to do with excess speed on final. Now this happened quite some time ago, and I worked this up right around the time the Reagan National Midair Collision occurred, but we've had so many other stories in the news that I've postponed talking about this one until now. This involved a Baron G58, so a later model with a Garmin G1000 in it.

The aircraft was a November 586 Romeo Foxtrot and it sustained substantial damage following a runway overrun after landing at my home airport of Palo Alto, California. The two occupants on board were not injured. The aircraft was landing on runway 13 and ended up in a pond at the end of the runway. METARs before the accident were 180 at 5 knots, 3 mile visibility in drizzle, broken clouds at 1700 feet.

and shortly after the accident it was winds 2004 gusting to 15 knots four mile visibility drizzle and broken clouds at 1400 feet the aircraft ran off the end of the runway hitting a berm at about 39 knots and then plopped into a shallow pond at the end of the runway

The aircraft only sunk down to the bottom of the wing, so exiting the plane was probably fairly easy. Oddly, this accident is similar to the last fatal accident at our airport in a couple of ways, which I'll talk about in a moment. A look at FlightAware shows that many of the flights for this aircraft were from Camarillo Airport in Southern California,

and the registration is for a company in Oxnard near Camarillo. Just for reference, the Camarillo runway is 6,000 feet long, so perhaps most of the pilots experience

It was landing on runways longer than Palo Alto. Our runway is just shy of 2,500 feet long, so that's a big difference. Runway 31 is used almost all the time, I'd say at least 95% of the time, but this accident, like the fatal accident I mentioned, occurred on runway 13. We don't know the weather at the exact time of the accident as the tower failed to make a METAR measurement that hour, probably because they were focused on dealing with the accident.

so the winds did favor runway 13 with a right crosswind. On the day of the accident, the aircraft departed Camarillo IFR for a 50-minute flight to Medford Field in Tulare, which is in California's Central Valley. It remained there for eight minutes and then departed IFR for the one-hour and four-minute flight to Palo Alto. It made one 360-degree turn before starting the RNAV GPS 3-1 approach on

most likely to avoid a conflict with an aircraft on an instrument approach to the San Jose International Airport. When we have winter storms, the wind generally comes from the southeast, and when aircraft are being vectored to San Jose's runway 12L and right, they're usually vectored on a path that crosses the approach into Palo Alto, so we often have delays flying that approach during bad weather.

The RNAV-31 approach is the only approach to Palo Alto, so this aircraft would have been cleared to circle to land on runway 13.

The approach appears normal and the aircraft was instructed to circle north of the field, which is typical, putting it on a left downwind for runway 13. Traffic pattern altitude on that side of the airport over the bay is 800 feet MSL. A beam of the runway, the aircraft's altitude varied between 735 feet and 760 feet, so it was slightly low, but certainly within the plus and minus 100 feet that examiners look for on downwind during check rides.

And being the 1-3 numbers, the ground speed was 135 knots. That sounds fast, but the aircraft would have had a tailwind, which was probably higher than the wind speeds measured on the ground. So we don't really have an accurate indication of its airspeed on downwind. But the speed on downwind was not the issue. Generally, when I'm flying a traffic pattern, I start to descend when I'm being the numbers. But this aircraft was still at 735 feet on the base leg, so it didn't descend at all on the downwind.

Also, the aircraft turned so that its base leg was between 0.8 and 0.9 nautical miles from the runway. That might have worked if the aircraft had been descending on base, though I typically like to turn base closer to a mile and a half from the runway. So the aircraft was higher than usual and closer to the runway than usual. So you can probably imagine what came next. I took the flight data from adsbexchange.com and loaded it into flystow.net, and I'll tell you what I saw.

First, I want to thank Tom Turner for giving me the approach speed data for the G58 Baron. We've had Tom on the show here before. He publishes the Flying Lessons Weekly newsletter, which I highly recommend, and you can find it at thomaspturner.com, and I'll include a link to it in our show notes. So if you don't already get that newsletter, go ahead and sign up for it.

He said the approach speed for this aircraft was 95 knots indicated at maximum gross weight, and that speed could go all the way down to 81 knots at what he described as a ridiculously low weight. This aircraft had just two people on board and had flown for two hours.

So let's say the approach speed should be somewhere around 90 knots or perhaps slightly lower. Looking at the cockpit view, here's what I saw. The aircraft had slowed to 118 knots ground speed when it started to turn base. On the base turn, the aircraft climbed 50 feet, perhaps because flaps were added, and the speed immediately decreased to 90 knots, most likely due to the flaps, but all

also because it was now facing more into the wind. While in the base turn, the pilot apparently recognized that he was high as the descent rate reached 1,450 feet per minute as the pilot started turning onto final. As the pilot rolled onto final, the descent rate increased to 1,550 feet per minute, and the speed started to accelerate. At the beginning of the final, at 460 feet, the ground speed had increased to 110 knots.

Remember that approach speed should be somewhere around 90 knots, and this airplane had some headwind component, so it was over 20 knots fast. The top speed reached on final was 116 knots, or at least 26 knots fast. That occurred when the plane was at 290 feet and just a third of a mile from the threshold. At that point, the aircraft was still descending at 1,300 feet per minute.

Shortly after the threshold, the aircraft was still 25 feet in the air at 103 knots, or 13 knots over approach speed.

ADS-B data shows the aircraft at field elevation at a point about 500 feet down the runway, still doing 99 knots. 850 feet later, the aircraft was still at 85 knots, so it's likely that the aircraft was still in the air, and the ADS-B data just doesn't have enough resolution to distinguish between an aircraft on the ground and an aircraft that's floating at high speed in the flare. The

At this point, the aircraft was beyond the halfway point of the runway and would have had less than 1,200 feet remaining. The aircraft continued to decelerate slowly in the last data point before it left the runway, showed it still moving at 48 knots. At the end of the runway is a berm that I think is probably about 2.5 feet high. The aircraft would have hit that, probably losing its nose gear, and then immediately slid into the pond where it came to rest.

And the fatal accident that I mentioned occurred a couple of years earlier than that.

and involved a Mooney for a pilot who was not based at the field and didn't have much prior experience landing at Palo Alto. It was also with relatively low weather and some obstructions of visibility. He was told to enter a left-based runway 13 and had trouble spotting the runway. By the time he spotted it, he had crossed through the center line and had to correct back toward the runway. He too landed long about halfway down the runway.

I believe he tried to do a go around and unfortunately that didn't go well and he ended up in the pond. I don't think the final report is out yet for that crash. And I should mention that there's one other challenge with runway 13 and that is that there's a fairly high levee. I would guess it's at least six feet high at the end of the runway and often it has people walking along it observing the aircraft.

And so airplanes tend to pass pretty high over the levee and therefore they land long on runway 13. So that's just one of the challenges with landing from that direction. So I think the key thing to take away from these two accidents is know your target approach speed, maintain your target approach speed, and if you're unable to maintain it, then you should go around early.

Coming up next, our main topic about why sometimes the RNAV glide path won't capture and how you can fix that. All right here on the Aviation News Talk podcast. Have you ever flown an RNAV GPS approach and had trouble getting your autopilot to capture the glide path? Now this is a surprisingly common issue that I've seen a number of times when flying with pilots. So I wasn't too surprised recently to see a Facebook post in which the poster encountered this issue. Here's what he wrote.

Was test flying a 2019 Cirrus SR22T yesterday for a buddy thinking of buying and went to shoot an approach in VFR conditions back to his airport?

It had an RNAV LPV approach. I loaded the approach and went direct to the IAF at the altitude on the approach plate. Upon reaching the fix, I hit the approach button and it started navigating the approach course. I could see the glide slope above me and slowly coming down to where it would normally grab the glide slope. On the scoreboard, the GS was in white and would normally grab green and start descending on the approach with WASP. Instead,

Glide soap continued down below my altitude and I had to hand fly the approach in. I've shot this approach hundreds of times in my aircraft without this issue. After landing, we found the Garmin database has expired on the plane and needs updating. This is a G6 Perspective Plus. Has anyone experienced the same thing with expired database? So can you guess the issue that the poster was having and why his autopilot didn't capture the GPS glide path?

By the way, he's a little inaccurate in his recollection. He said that he saw GS and white on the scoreboard. Actually, he would have seen GP for glide path. And he talks about grabbing the glide slope, but with RNAV approaches, it's called the glide path. Anyway, as soon as I read the post, I knew what the issue was. But more interesting was reading the many comments that

and seeing that no one had correctly identified the issue. Instead, there was a random collection of guesses, none of which were relevant, which got me wondering, where do you get your information? Do you go to experts or rely on what people tell you in a Facebook post? And if your post receives 50 comments, how do you know which, if any of the comments are correct?

I posted a comment which said in part, it sounds like you're staying level at the IAF altitude and expected to capture the glide path at a much higher altitude than the glide path intercept altitude published for the final approach fix. That's not the proper way to fly an approach, though it will work for an ILS. However, that often won't work for an RNAV approach.

That elicited a comment from someone who was, ironically, 100% wrong when they wrote, it's 100% proper to intercept the GP slash GS further out with an ILS as long as you intercept from below, there's no risk of false glide slope. No issue ever doing it with magenta guidance.

First, you should not be intercepting an ILS glide slope or an RNAV GPS glide path at any altitude other than the published glide slope altitude. Yes, of course, you can often get away with doing it on an ILS, and that's what led this original poster to encounter his problem. He was apparently used to flying an ILS approach improperly and has been able to get away with doing that. So he used that same improper technique on an RNAV approach and wasn't able to get it to work.

Now in the FAR aim, aim 5-4-5B says in a note, quote, the ILS glide slope is intended to be intercepted at the published glide slope intercept altitude. So what this tells us in essence is to properly fly an ILS, you are supposed to fly all of the step downs until you reach the glide slope intercept altitude and then fly level until you intercept that glide slope at the glide slope intercept altitude.

Can you get away with intercepting an ILS at a higher altitude? Yes, you can often do that. Though the danger in flying an approach this way is that you could accidentally capture a false glide slope that's at a higher angle than the normal 3 degree glide slope.

You may recall that a year ago in episode 321, we talked about false glide slopes when talking about Air India Express Flight 812, which crashed in 2010 after the pilot, who was suffering from sleep inertia, captured a false glide slope and began descending along it at a high speed and with a high descent rate.

The aircraft, Boeing 737, was returning from Dubai to Mangalore, India. However, the cockpit voice recorder revealed that the captain had been asleep for a significant portion of the flight, awakening only shortly before the crash. Compounded by issues such as inadequate descent planning and reliance on visual cues due to radar unavailability, the crew found themselves on an unstabilized approach, ignoring multiple warnings and calls for a go-around from the first officer.

The aircraft ultimately overshot the runway, impacted various structures, and resulted in numerous fatalities. Investigation highlighted the captain's failure to discontinue the unstable approach as the primary cause, with contributory factors including sleep inertia and improper descent planning.

So, one issue with intercepting an ILS at a higher than published altitude is that you could capture a false glide slope, which is why you're supposed to intercept the glide slope at the published intercept altitude. If you do, it's impossible to capture a false glide slope at that altitude. So, you might be wondering why if you can often get away with flying an ILS incorrectly and capture the altitude at a higher than published altitude,

Why can't you get away with doing the same thing on an RNAV GPS approach? To answer that, first think about the differences between the glide slope of an ILS and the glide path to an RNAV approach. What's the big difference between the two? Yes, there are different frequencies involved, but not only are the frequencies different, but they're used in fundamentally different ways. Think about the ground infrastructure required for these two different types of approaches.

For an ILS, you have a localizer antenna and transmitter located at the far end of the runway. And you also have a glide slope antenna and transmitter located off to the side of the runway, about 750 feet beyond the runway threshold. Now think about the ground infrastructure required for an RNAV approach. Still thinking? Yeah, there isn't any, is there?

That's one of the beauties of creating an RNAV approach. They are relatively easy and inexpensive to implement because no additional equipment needs to be added to an airport to create an RNAV approach. Now, let's do a thought experiment and see how using sensitive measuring equipment we might be able to detect an ILS glide slope and an RNAV glide path.

The ILS glide slope is relatively easy to detect. If we have a receiver tuned to the glide slope transmitter frequency, we should be able to detect and measure that signal in a large area in front of the antenna. Now let's do the same thing for the glide path signal. If we tune a receiver to the GPS frequencies, can we detect and measure a glide path signal anywhere along the approach path to the airport?

Well, you might be able to detect GPS signals, but they're the same signals that have always been broadcast by GPS satellites. And the signals you detect, the same ones used by your GPS receiver, will be fundamentally the same along the approach path to the airport as they are pretty much anywhere else in the world. Which is to say that you won't be able to detect and measure a glide path signal anywhere along the approach path to the airport.

While an ILS glide slope signal is a physical radio beam that exists along a path to the airport, there is no such radio beam defining a GPS glide path to the airport. You can search for it all day long, but it does not exist. So what is an RNAV glide path if we cannot physically detect and measure it? Here's the answer.

It's essentially a figment of your GPS receiver's imagination and of your imagination as well. It does not physically exist. It's not real. So where does it come from and what is it? Now, a GPS receiver is really good at doing one thing, and that is using signals from satellites to precisely locate where in the sky or where on the earth it is located.

But the avionics box that contains a GPS receiver also contains a lot of computing power. Which is why these boxes are often called navigators, because they are more than just a GPS receiver. They are essentially computers that can compute paths that we can follow, either with a car or an airplane. And those paths that we're following, well, they aren't real. For an ILS, the localizer and glide slopes are real. They are radio signals that are transmitted to create specific paths for us to follow.

But the GPS paths computed by a navigator are just computations. They are a computer saying, here's the path you should follow. And that path it creates would never leave the navigator if you didn't have some type of display connected to your GPS receiver. And that data it creates that you're looking at never goes any farther than the display in your eyes and never leaves the confines of the airplane.

It's not much different than sitting at home and staring at a computer screen, which is what I'm doing right now. Any path created by your computer doesn't go anywhere. It's just displayed on your screen so that you can see it. And that's why I said an RNAV glide path is essentially a figment of your GPS receiver's imagination. It's not real. It's just a computation inside the box. So why can't our autopilot couple to a glide path just anywhere along where we think the glide path should be?

Well, because the computer glide path does not extend from infinity to beyond, as Buzz Lightyear might say. Yes, of course, theoretically, the firmware in your GPS navigator could be rewritten to create a glide path that extends for many miles out from an airport.

But that's not how the software designers set up the glide paths. Instead, they set them up so that they work only when you fly an approach properly or close to properly, as defined by AIM 5-4-5B, which we discussed earlier.

So as we've discussed, you can often get away with flying an ILS improperly. For example, you can often cross the IAF at the altitude published for that fix and remain at that altitude without descending. Then as you reach the glide slope, your autopilot will typically capture the glide slope, even though you may be thousands of feet above the published final approach fix glide slope intercept altitude. The Facebook poster I talked about tried that one flying an RNAV approach and didn't understand why it didn't work.

And now we know the reason it didn't work, which is that the commuter glide path doesn't exist that far away from the airport. Here's what you will see if you try to incorrectly fly the approach that way.

At some point, beyond the IAF, you'll see the glide path indicator, shaped like a diamond, at the top of the vertical deviation indicator. As you get closer to the airport, at some point that diamond will start to move down toward the center of the indicator. Normally for an RNAV approach, that diamond is colored solid magenta, but in this case it will be a hollow white diamond.

That white diamond shows you where the glide path would be if the autopilot were able to couple to it. But as long as it remains a hollow white diamond, your autopilot cannot couple to it. It doesn't matter whether the autopilot's been properly placed in the approach mode and that the white GP indicator is showing on your autopilot scoreboard indicating that the approach mode is armed. If you have a hollow white diamond, the autopilot cannot couple to the glide path.

You can, of course, disconnect the autopilot if you choose and hand fly the airplane to follow the white diamond down along, well, let's call it a faux glide path depicted by the white diamond.

By contrast, if you were to fly an RNAV GPS approach properly, which we've said is to descend it every step down until you're down at the published final approach fixed glide path intercept altitude, there will come a time when the glide path indication turns from a hollow white diamond to a solid magenta diamond, and at that point, the autopilot can couple to the glide path. While I've been aware of this behavior, there still have been times at the end of a long trip

When I've watched a pilot try to couple to a white diamond, then I too have been surprised when it didn't happen. Even though if I'd given it a little more thought, I would have remembered that it wouldn't capture. So this subtlety, a white diamond versus a solid magenta diamond, is easy to miss and forget, especially if you're a little fatigued at the end of a flight.

Even though I've been aware of this behavior, I could never find documentation that stated at what point along the approach an RNAV glide path indicator turns to a solid magenta diamond, and knowing that would be helpful for all of us. So after reading the Facebook post, curiosity got the better of me, and I resolved to find an answer to that question. So I drove to the airport and hopped into one of my club's AATDs for an hour to find the answer.

I flew four different RNAV approaches, including the one flown by the Facebook poster, and got consistent results for all four approaches. For each approach, I started at the IAF and descended it every step down. In other words, I flew the approaches properly.

Then, at the moment when the glide path diamond turned to solid magenta, I took a photo that captured the airplane's distance to the next fix on the approach. And it's good that I took a photo, because when I left the airport, I still hadn't figured out the answer to when the switch to magenta occurred. I had hypothesized that the transition would occur at some fixed distance past the intermediate fix, or perhaps at some fixed distance before the FAF, but that turned out not to be the case.

Unfortunately, I flew more than one approach as I picked up one subtlety that could have easily been missed. When I got home, I put together a spreadsheet for the four approaches that calculated the distance from the plane to each fix on the approach when the diamond changed colors. What I found was the diamond always changed to magenta while crossing the fix preceding the FAF.

Now, in most approaches, the fix before the Faf is the intermediate fixer If. But a number of approaches have more than one fix between the If and the Faf. And on those approaches, the switch does not occur at the If, but at the fix before the Faf. For example, one of the approaches I've flown for real and which I replicated in the simulator is the Oakland, California RNAV GPS Yankee 2.8 right approach.

The IF has NAGV, and there are three fixes between the IF NAGV and the FAF Kavsa. And the diamond turns magenta at Nixti, the fix before the final approach fix. So now that we understand the algorithm, we have a formula for flying an RNAV approach that you can use every time you fly so that the autopilot will reliably couple to and descend along the glide path. And here it is.

When flying an RNAV GPS approach, lie all of the step-downs available as you cross each fix. When you get to the fix before the FAAF, you want to be at the target altitude for crossing that fix. Then as you cross that fix, the diamond will turn magenta and it should be somewhat above you. In most cases, you won't need to make that last step down to the published final approach fix glide path intercept altitude. You could instead stay at the altitude published for the fix before the FAAF.

Then if you've properly pushed the APR key on your autopilot so that the approach mode is armed, as you intercept the glide path, the autopilot will couple to it and descend along it. Try this formula and see if it works for you. And remember that a GPS glide path can't couple to the autopilot until you cross the fix before the FAF. And knowing this can help eliminate at least one automation surprise when you fly.

And just a reminder that I love hearing from you and I read many of your emails on the show. If you'd like to send me a message, just go out to aviationnewstalk.com, click on contact at the top of the page. That's absolutely the best way to send me a message. And of course, I also want to thank everyone who supports the show in one of the following ways. We love it when you join the club and sign up at aviationnewstalk.com slash support to

To support the show financially, you can also do that at aviationnewstalk.com slash PayPal. We also love it when you leave a five-star review on whatever app that you're listening to us on now. And of course, if you're in the market for a headset, please consider buying a Lightspeed headset and using one of the links in our show notes, because if you use those links, they will donate to help support the show. So until next time, fly safely, have fun, and keep the blue side up. And remember that you can always go around. You can always go around.

coming down to your side baby sliding upside down you can all