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Questions tagged [gnss]

GNSS is a global satellite navigation system. GPS is the US GNSS.

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19
votes
5answers
8k views

Why is there a difference between GPS Speed and Indicator speed?

I just played with flight simulator and noticed that the GPS shows different speed from the speed indicator in the cockpit. Also, GPS speed is higher than the Indicator. Any Idea why?
40
votes
12answers
30k views

Why don't all commercial aircraft transmit GPS data in real time?

It seems strange that trucks and taxis can be set up to transmit GPS data in real time but aircraft cannot. Wouldn't this be a useful function and feasible to implement?
28
votes
6answers
16k views

Is it possible for a modern commercial airliner to stop being tracked without substantial mechanical failure?

I was speaking to someone about the MH370 incident, and they suggested that a hijacker could turn off the device that sends the plane's current position, resulting in the appearance of a catastrophic ...
37
votes
9answers
44k views

“Airplane mode” does not disable GPS… is it safe to use GPS in flight?

I noticed that even when my phone is in "airplane mode", I can still use the GPS. Theoretically a GPS receiver just receives data, so I guess it would not jam anything. On the contrary, on the ...
16
votes
3answers
6k views

Why isn't an LPV SBAS approach considered a precision approach according to ICAO?

According to ICAO's classification, LPV SBAS approach is in the APV group, because it doesn't meet some specifications for precision approaches. But what exactly does it not meet? Glossary: LPV: ...
18
votes
6answers
5k views

What will happen if satellite navigation fails?

My understanding is that aircraft use GPS systems for navigation (maybe not the only way to navigate). I would like to understand what would happen if the GPS system fails. Are there any other ...
28
votes
6answers
19k views

How do airliners cross the ocean without GPS?

How do airliners cross the ocean without GPS? Do they use dead-reckoning or are there navigation aids floating out there?
15
votes
2answers
6k views

Can GPS be used in lieu of DME for instrument approaches?

Instrument approach charts list the equipment required to fly them in their name. For this example let's say we have an ILS or LOC/DME 36R approach. This approach requires an ILS receiver for the ILS ...
5
votes
1answer
721 views

Why would a Mode-C transponder report a different altitude than an altimeter/GPS?

This is related to a small single-engined plane. On a recent flight, the controller kept telling me that I was 300 ft higher than it appeared on my altimeter and GPS (which were in sync). This was ...
24
votes
13answers
10k views

How did planes measure their speed relative to the ground before GPS?

How did planes measure their ground speed before GPS? If they used some sort of anemometer to measure speed, that would only measure the speed of the plane relative to the air through which it is ...
16
votes
4answers
16k views

Is LPV considered a precision approach?

WAAS LPV approaches can have decision altitudes as low as 200 AGL, the same as many Cat I ILS approaches. Previous opinions on the Internet have quoted the FAA as saying LPV is considered a non-...
13
votes
5answers
6k views

Which is more accurate for height measurement: GPS or barometer?

I am not a pilot and have come to this site to ask a question about the measurement of height. This is as a result of the comments made as a result of a question in the Physics Stack Exchange forum "...
11
votes
3answers
1k views

Could the GPS be used to aid the autopilot with speed?

In the AF447 incident, the autopilot system was offline due to the aircraft's pitot tubes being obstructed by ice particles. Since the physical condition of the plane in air is cold and risky, the ...
21
votes
6answers
4k views

What's the minimum number of sensors for a hobby GPS waypoint-following UAV?

I would like to develop my own guidance, navigation and control (GN&C) flight software on a Raspberry Pi, for a small hobby fixed-wing UAV. From a physical standpoint, what is the minimum set of ...
16
votes
3answers
31k views

What is the difference between GPS, GNSS and RNAV?

I would like to know the fundamental difference between GPS, GNSS and RNAV. How are they related each other? Are all/some of them synonyms?
8
votes
3answers
2k views

How is GPS RAIM availability calculated?

I recently had someone ask me if there was a GPS RAIM availability calculator available for the iPad. There isn't, but it got me thinking that I could write one. After doing some searching, I can't ...
7
votes
3answers
4k views

Why don't airliners have a navigation GPS as back up in case of a pitot tube malfunction? [duplicate]

Why don't airliners have a navigation GPS as "back up" in case of a pitot tube malfunction? Aeropero 603 and Air France 447 plus many other im sure, could have been saved if these aircrafts would have ...
6
votes
2answers
2k views

How to navigate an aircraft without GPS? [duplicate]

In case of loss of GPS: how can an aircraft not only be navigated but navigated so precisely that it can pinpoint its destination airport ? (case in point: Finland and Norway are telling airline ...
5
votes
1answer
405 views

Is there any reason to have ADS-B out that is not based on GPS?

The ADS-B system is only as accurate as the location data source it uses. In the US the 2020 ADS-B mandate requires that horizontal location data be from a GPS source with minimum performance ...
4
votes
1answer
1k views

Why does Boeing 737 use 2 Inertial Reference Systems (IRS) and GPS?

According to this website the Boeing 737 aircraft use 2 IRS and 2 GPS: IRS L & IRS R. Why? Apparently they are totally independent of each other. Could somebody explain a little bit why they need ...
3
votes
2answers
305 views

What did Fiji have to do when it incorporated GPS into its aviation system?

I'm reading the BBC's How Fiji changed the way we travel; The little Pacific island nation was the first to incorporate GPS into its aviation system – and in doing so forever changed the way we get ...
7
votes
1answer
599 views

What effect would an air-to-air GPS jamming system have?

I just noticed an interesting AIC: NOTIFICATION OF GPS JAMMING EXERCISE – HEBRIDES RANGES DURING PERIOD 21 JULY - 1 AUGUST 2014. PDF available on Eurocontrol (official) or Scribd (mirror). The ...
6
votes
2answers
1k views

How can I tell a GPS installation is acceptable for IFR use?

I am evaluating an aircraft for use under IFR. I want to know if the GPS that is installed is acceptable for use under IFR. I have access to the logbooks and documentation. I want to check: That ...
6
votes
3answers
7k views

What are the differences between a GPS coupled autopilot and a GPSS autopilot?

I'm trying to understand the differences here between an autopilot that is "coupled" into a GPS/NavCom like a Garmin 530W and what GPSS and altitude hold (like in an S-TEC 50 autopilot) have to do ...
5
votes
2answers
880 views

Can a GPS signal sent to a plane be spoofed?

Related to What effect would an air-to-air GPS jamming system have?, I'm wondering whether it is possible for a terrorist (or likewise, law enforcement) to manipulate GPS signals received by a jet, re-...
5
votes
2answers
506 views

Can I use my non-WAAS GPS receiver with ADS-B in the United States?

I have a older style Garmin 530. Can I use this GPS as the position source for an ADS-B installation?
4
votes
3answers
1k views

Exactly what kind of radios are prohibited for passengers inside an aircraft?

I know that passengers are asked to put their cell phones on flight mode. But some carriers allow use of WLAN on-board. So, what radios should passengers refrain from using? Also, if a person uses a ...
4
votes
1answer
193 views

Why might a moving map Android app consistently record altitude off by 120 feet?

I fly Cessna 172 and Cherokee Warrior both older models without a GPS. I have a very useful freeware navigation app on my android phone which is really good in every regard other than it always reads ...
3
votes
1answer
3k views

Is GLS (GBAS landing system) an RNAV approach?

PBN which is contrast to conventional navigation consists of RNAV and RNP. And I know that general RNAV approach of IAP has up to 4 minima such as LPV, LNAV, LNAV/VNAV, and LP. And I know that GLS ...
2
votes
1answer
743 views

Why do Computer Navigation Fixes still exist now that GPS waypoints can be used to define tracks?

A CNF is a point that defines a navigation track for a GPS, but why is it used when you there are GPS waypoints that are created to define a track?
2
votes
1answer
439 views

How do GLS avionics plot an entire accurate approach path?

I'm studying wireless navigation systems, especially GBAS. I have gone through some ICAO documents regarding GBAS. From what I have read, FAS data is included in Message Type 4. Closer examination of ...
2
votes
1answer
217 views

Why is there a provision of pressure setting in GPS?

Some of the GPS have a provision of setting barometric pressure (QNH/QFE). How does it work?
0
votes
2answers
983 views

How does GPS measure any plane's ground speed?

How does GPS measure an equipped airplane's ground speed assuming that the plane in question actually uses GPS as opposed to an inertial navigation system or other method? (This was originally part ...