GPS And ADS-B Problems Cause Cancelled Flights

Something strange has been going on in the friendly skies over the last day or so. Flights are being canceled. Aircraft are grounded. Passengers are understandably upset. The core of the issue is GPS and ADS-B systems. The ADS-B system depends on GPS data to function properly, but over this weekend a problem with the quality of the GPS data has disrupted normal ADS-B features on some planes, leading to the cancellations.

What is ADS-B and Why Is It Having Trouble?

Automatic Dependent Surveillance-Broadcast (ADS-B) is a communication system used in aircraft worldwide. Planes transmit location, speed, flight number, and other information on 1090 MHz. This data is picked up by ground stations and eventually displayed on air traffic controller screens. Aircraft also receive this data from each other as part of the Traffic Collision Avoidance System (TCAS).

ADS-B isn’t a complex or encrypted signal. In fact, anyone with a cheap RTL-SDR can receive the signal. Aviation buffs know how cool it is to see a map of all the aircraft flying above your house. Plenty of hackers have worked on these systems, and we’ve covered that here on Hackaday. In the USA, the FAA will effectively require all aircraft to carry ADS-B transponders by January 1st, 2020. So as you can imagine, most aircraft already have the systems installed.

The ADS-B system in a plane needs to get position data before it can transmit. These days, that data comes from a global satellite navigation system. In the USA, that means GPS. GPS is currently having some problems though. This is where Receiver autonomous integrity monitoring (RAIM) comes in. Safety-critical GPS systems (those in planes and ships) cross-check their current position. If GPS is sending degraded or incorrect data, it is sent to the FAA who displays it on their website. The non-precision approach current outage map is showing degraded service all over the US Eastern seaboard, as well as the North. The cause of this signal degradation is currently unknown.

What Hardware is Affected?

GPS isn’t down though — you can walk outside with your cell phone to verify that. However, it is degraded. How a plane’s GPS system reacts to that depends on the software built into the GPS receiver. If the system fails, the pilots will have to rely on older systems like VOR to navigate. But ADS-B will have even more problems. An aircraft ADS-B system needs position data to operate.  If you can’t transmit your position information, air traffic controllers need to rely on old fashioned radar to determine position. All of this adds up to a safety of flight problem, which means grounding the aircraft.

Digging through canceled flight lists, one can glean which aircraft are having issues. From the early reports, it seems like Bombardier CRJ 700 and 900 have problems. Folks on are speculating that any aircraft with Rockwell Collins flight management systems are having problems.

This is not a small issue, there are hundreds or thousands of canceled flights. The FAA set up a teleconference to assess the issue. Since then, the FAA has issued a blanket waiver to all affected flights. They can fly, but only up to 28,000 feet.

This is a developing story, and we’ll be keeping an eye on it. Seeing how the industry handles major problems is always educational, and there will be much to learn in the coming days.

A Bolt-On I2C Navigation Key For Your Next Project

We often talk about the advantages of modular hardware here at Hackaday; the ability to just order a few parts online, hook them up with some jumper wires, and move onto the software side of things is a monumental time saver when it comes to prototyping. So anytime we see a new module that’s going to save us time and aggravation down the road, we get a bit excited.

Today we present the very slick I2CNavKey developed by [Saimon], a turn-key interface solution for your builds that can’t quite get away with a couple toggle switches. It not only gives you a four-way directional pad with center button, but a rotary “wheel” like on the old iPods. All of which you can access easily and with a minimum of wiring thanks to the wonders of I2C.

But even that might be selling the module short. This isn’t just a couple of buttons on a breakout board, the I2CNavKey is powered by its own PIC16F18345 microcontroller and features three configurable GPIOs with PWM support (perfect for an RGB LED) plus 256 bytes of onboard EEPROM storage.

[Saimon] has released the entire project as open source hardware for your hacking pleasure, but you can also get them as ready-to-use modules on Tindie for $18 USD [Editor’s Note: Because of a typo we originally we left the 1 out of the price]. Whether you’re a paying customer or not, you get access to the project’s absolutely phenomenal documentation, including a nearly 30 page manual that contains everything you’d ever want to know about the I2CNavKey and how to integrate it into your project. If all hardware was documented with this level of dedication, the world would be a much nicer place for folks like us.

If you recognize the name, or perhaps the affinity for neat I2C-connected input devices, it’s probably because you’ve seen his very similar I2C rotary encoder on these pages previously, which was a finalist in our Open Hardware Design Challenge during the 2018 Hackaday Prize.

Simple Hand Tools Turn Brass And Steel Into An Amazing Astrolabe

There’s something enchanting about ancient tools and instruments. The idea that our forebears were able to fashion precision mechanisms with nothing but the simplest hand tools is fascinating. And watching someone recreate the feat, such as by building an astrolabe by hand, can be very appealing too.

The astrolabe is an ancient astronomical tool of incredible versatility, allowing the user to do everything from calculating when the sun will rise to predicting the positions of dozens of stars in the night sky. That it accomplishes all this with only a few moving parts makes it all the more fascinating. [Uri Tuchman] began the astrolabe build shown in the video below with only a few hand tools. He quickly had his fill of the manual fretsaw work, though, and whipped up a simple scroll saw powered by an old sewing machine foot treadle to speed up his work. The real treat though is the hand engraving, a skill that [Uri] has clearly mastered. We couldn’t help musing that a CNC router could do the same thing so much more quickly, but watching [Uri] do it was so much more satisfying. Everything about the build really makes a statement, from the contrasting brass and steel parts to the choice of complex Arabic script for the markings. [Uri] has another video that goes over astrolabe basics and his design process that’s well worth watching too.

While it’s nowhere near as complicated an instrument, this astrolabe puts us in the mood to watch the entire Clickspring clock build again. And [Chris] is working on his own ancient instrument build at the moment, recreating the Antikythera mechanism. We can’t wait to binge-watch that one too.

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How Etak Paved The Way To Personal Navigation

Our recent “Retrotechtacular” feature on an early 1970s dead-reckoning car navigation system stirred a memory of another pre-GPS solution for the question that had vexed the motoring public on road trips into unfamiliar areas for decades: “Where the heck are we?” In an age when the tattered remains of long-outdated paper roadmaps were often the best navigational aid a driver had, the dream of an in-dash scrolling map seemed like something Q would build for James Bond to destroy.

And yet, in the mid-1980s, just such a device was designed and made available to the public. Dubbed Etak, the system was simultaneously far ahead of its time and doomed to failure by the constellation of global positioning satellites being assembled overhead as it was being rolled out. Given the constraints it was operating under, Etak worked very well, and even managed to introduce some of the features of modern GPS that we take for granted, such as searching for services and businesses. Here’s a little bit about how the system came to be and how it worked.

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Retrotechtacular: Car Navigation Like It’s 1971

Anyone old enough to have driven before the GPS era probably wonders, as we do, how anyone ever found anything. Navigation back then meant outdated paper maps, long detours because of missed turns, and the far too frequent stops at dingy gas stations for the humiliation of asking for directions. It took forever sometimes, and though we got where we were going, it always seemed like there had to be a better way.

Indeed there was, but instead of waiting for the future and a constellation of satellites to guide the way, some clever folks in the early 1970s had a go at dead reckoning systems for car navigation. The video below shows one, called Cassette Navigation, in action. It consisted of a controller mounted under the dash and a modified cassette player. Special tapes, with spoken turn-by-turn instructions recorded for a specific route, were used. Each step was separated from the next by a tone, the length of which encoded the distance the car would cover before the next step needed to be played. The controller was hooked to the speedometer cable, and when the distance traveled corresponded to the tone length, the next instruction was played. There’s a long list of problems with this method, not least of which is no choice in road tunes while using it, but given the limitations at the time, it was pretty ingenious.

Dead reckoning is better than nothing, but it’s a far cry from GPS navigation. If you’re still baffled by how that cloud of satellites points you to the nearest Waffle House at 3:00 AM, check out our GPS primer for the details.

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Using Moiré Patterns To Guide Ships

Moiré screens for arrows
Moiré screens for arrows

[Tom Scott] ran across an interesting visual effect created with Moiré patterns and used for guiding ships but we’re sure it can be adapted for hacks somewhere. Without the aid of any motors or LED animation, the image changes as the user views it from different angles. When viewed straight on, the user sees vertical lines, but from the left they see a right-pointing arrow and from the right, they see a left-pointing arrow. It’s used with shipping to guide ships. For example, one use would be to guide them to the center point of a bridge. When the pilots see straight, vertical lines then they know where to steer the ship.

US patent 4,629,325, Leading mark indicator, explains how it works and how to make one. Two screens are separated from each other. The one in front is vertical but the one behind is split in two and angled. It’s this angle which creates the slants of the arrows when viewed from the left or right. We had to convince ourselves that we understood it correctly and a quick test with two combs showed that we did. See below for the test in action as well as for [Tom’s] video of the real-world shipping one.

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