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64

Most commercial aircraft transmit their GPS-based position twice per second. This is part of their Automatic Dependent Surveillance – Broadcast (ADS–B) broadcasts. The problem with providing world-wide receiver coverage for this system is that the frequency it uses only travels line via line of sight, so it won't travel past the horizon. Providing coverage ...


44

The speed indicator in the cockpit shows indicated airspeed. Indicated airspeed is usually different than GPS speed, due to wind and aerodynamic effects. GPS speed is your speed with respect to the ground. If you are standing on terra firma it reads 0. If it reads 100 knots you will be 100NM away from where you are now in one hour, so long as you keep ...


44

They're different usage cases, and have to be engineered differently. Three major points: A shark tag doesn't have to survive a 500mph impact (#7 on the list) with the ground, and a flight recorder has to be able to do so. It adds a lot of padding and weight, and limits the kind of battery that can be used. Sharks also don't dive to a depth much greater ...


36

theoretically? GPS IS receive only. There's no way to talk to the GPS satellite network except using the big antennas of the network owners (the US DoD) and the communications are no doubt heavily encrypted. Now, does that mean it's "safe" for aircraft electronics. Any receiving antenna does have an EM field around it, so if you believe the myth that those ...


36

The other answers seem to make a simple thing way too complicated. Yes there are DMEs or TACANs, that are sometimes used to get a ground speed, but it's only accurate if you're tracking exactly to or away from it. And it certainly wasn't used to calculate speed enroute unless one of your navaids was a VOR/DME or equivalent. Rather than using DME they'd be ...


34

If the GPS is unavailable, it will be quite an impact to the aviation industry. All airliners in-flight will experience degraded RNAV performance, but they would make it to the destination using VORs, DMEs and ILSs. For general aviation, things are not so lucky. The GPS display provides an excellent situation awareness in small aircrafts; without it, ...


27

It only takes 3 satellites for a GPS fix (4 if you want altitude). There are 32 satellites currently in orbit and at any given time you can most likely receive a signal from half a dozen of them at least. That being said the chances of them failing completely is almost 0%. But of course what if they did, well... There is always the Russian version of GPS ...


26

Well, most airlines do cross the ocean with GPS in today's world. That being said, most (if not all) transcontinental airliners, and many flying domestic routes as well, have what's called an inertial navigation system (a form of dead-reckoning where gyros and accelerometers are used to compute changes in position). The INS feeds into the flight management ...


24

The absolute minimum for a generalized vehicle that needs to know its position and attitude (orientation) in space is one per degree of freedom. This can be reduced if we have information about the natural modes of the system and their stability. For simplicity, let's assume a vehicle moving in 3 dimensions, that means a total of 6 DoF: 3 coordinates in ...


22

The device you are talking about is called a transponder. This is a device that listens for a signal (an interrogation) and responds with information about the airplane including an ATC assigned code, altitude information and additional aircraft info for certain equipment. There are 2 ways ATC watches airplanes: Primary Radar Secondary Surveillance Radar ...


22

"It depends". As others have mentioned, GPS is receive only. In theory at least, when everything is operating normally. In practice, some GPS units can fail in a way that causes them to become an unintentional radiator of energy. GPS signals are VERY weak, so it doesn't take much to jam them. However, this should be an exceptionally rare event, and ...


21

Airliners do generally have GPS receivers, but GPS doesn't give you the information that's needed in this case. In AF 447, the primary consequence of the blocked pitot tubes was that the flight envelope protection system couldn't do its job properly and therefore automatically disengaged together with the autopilot. The subsequent crash was caused by the ...


20

We were crossing the seas centuries before GPS, INS or really any other form of modern technology. All you need is a clock, a compass and a sextant. And some largely-forgotten skills, like how to do math without a smartphone.


19

A blind encoder is an altimeter that encodes pressure altitude and outputs it on a databus. They are "blind" in that they do not display data to the pilot. Most general aviation units use a parallel bus with Gillham encoding. More expensive units and air data computers use serial bus output, commonly ARINC 429. Historically, the blind encoder existed to ...


18

The following is, in respect of aircraft, speculation. However, I did spend a decade working on the GPS based tracking systems mentioned in the question, with particular emphasis on remote operations in rural Australia. We did trial the use of Iridium, so I will comment on that too. Firstly such systems do not report in real time, that is baloney put out by ...


18

With the proper knowledge of the aircraft systems almost anything can be turned off. That's what we do at the end of almost every flight day. Most of the communications systems can actually be turned off fairly easily, but the average person would not know how to do it. In airplanes like the 777, there are multiple ways that they communicate but all of ...


18

Here's a very simple graphic of what you could be seeing: (source: cadblog.net) And this is why we land into a headwind rather than the tailwind, since otherwise we would land at a faster speed and require more runway to stop. GPS measures ground speed, or absolute speed. The pitot tube on the aircraft will measure the speed relative to the airflow ...


18

As stated in the othe answers, GPS is the US Global Positioning System GNSS is an umbrella term that encompasses GPS as well as other nations' satellite systems that achieve essentially the same capability RNAV is the aircraft capability that allows you to navigate from point to point, defined by Latitude/Longitude and independent of any ground-based ...


17

There's one method that has been successfully used since long-distance flights became available - you took out your map, and tried to match it to features under your plane. This allowed you to correct your course and have an average ground speed information. Obviously, this doesn't work over the ocean - it's yet another reason why ocean flights have always ...


16

The main issue is that we can only get groundspeed from GPS data. Winds aloft aren't known exactly at a particular place, so they could be rather inaccurate -- certainly not enough to leave to the hands of the autopilot. The decision to use GPS data to verify airspeed would lie in the hands of the crew. Anyway, they were too preoccupied to go and check that ...


16

LPV, LNAV/VNAV, and Baro VNAV are considered to be an 'Approach with Vertical Guidance (APV)'. These types of approaches are differentiated from 'Precision' approaches (ILS, PAR, etc.) in the FAA AIM (Section 5-4-5, Paragraph 7): (b) Approach with Vertical Guidance (APV). An instrument approach based on a navigation system that is not required to meet the ...


16

Yes, the details are in FAA AC 90-108: 7. Usage of Suitable RNAV Systems. Subject to the operating requirements in this AC,operators may use a suitable RNAV system in the following ways. (1) Determine aircraft position relative to or distance from a VOR (see first note in subparagraph 7b), TACAN, NDB, compass locator (see second note in ...


15

GPS speed is already available to the crew, although not in an easy to see place. It isn't designed to cross-check other instruments because it is showing entirely different information. The winds are changing the actual speed of the airplane across the ground (which GPS shows) and altitude affects the air density (which changes the airspeed shown on the ...


15

In the days before GPS, we routinely crossed the oceans using inertial navigation systems. The system I was familiar with used 3 separate inertial systems (Carousel was the brand name). You could choose to navigate by any single one, but the most common way of using them was to have the autopilot "average" the positions. You could also choose to exclude any ...


15

It's probably possible with only the GPS receiver, but it wouldn't be easy and you might have to make some compromises on the airframe design to achieve the necessary passive stability. The traditional set of sensors for this kind of application are, roughly in order of priority: GPS 3-axis rate gyro 3-axis accelerometer 3-axis magnetometer pitot alpha ...


14

Yes, without a shadow of a doubt. Many airports now publish GNSS (Generic term for all types of satellite navigation) approaches, completly negating the need for those aids even during complex, critical phases such as approach and landing and take off and departure. Modern GNSS systems are capable of utilising synthetic VORs where even when doing something ...


14

The question you should be asking is rather, how did airliners navigate before the widespread adoption of satellite-based navigation systems such as civilian GPS? One can navigate by way of landmarks (as is typical in low-altitude VFR general aviation), but more typical in commercial aviation in the absence of GPS would probably be to navigate by either ...


13

The other answers about wind are true, but this isn't what you're seeing in your simulation. What you're actually seeing is the difference between true airspeed and indicated airspeed. True airspeed is the plane's actual speed through the air. With no wind, this is the same as the plane's speed across the ground. This is what your GPS displays. The ...


12

Shark tags work by only sending the logged data when the shark resurfaces. Between those it just stores the data in memory until it can send it. Sending underwater takes a lot of power otherwise.


12

In the USA, ADS-B requires a WAAS position source. A Garmin 530W can be used, but not a 530. Here's a full list of FAA certified equipment needed for ADS-B. I hope that helps.


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