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Questions tagged [gnss]

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

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In the rare event that the U.S. DOD shuts off the GPS, what's the alternative?

In the U.S., the Department of Defense along with other Federal Agencies of the Government operates & maintains the GPS. In the rarest of the events, if for any reason whatsoever, the Government ...
RaajTram's user avatar
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45 votes
12 answers
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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?
JoelFan's user avatar
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38 votes
9 answers
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"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 ...
Nicolas Raoul's user avatar
30 votes
6 answers
23k 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?
flyingfisch's user avatar
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28 votes
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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 ...
andrewb's user avatar
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13 answers
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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 ...
Pat's user avatar
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21 votes
3 answers
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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?
Francesco C's user avatar
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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 ...
Greg McNulty's user avatar
20 votes
6 answers
6k 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 ...
KurioZ7's user avatar
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19 votes
3 answers
22k views

What are satellite time, GPS time, and UTC time?

What is the difference between Satellite time, GPS time and UTC time? How are these calculated from one another?
Sourabh Jain's user avatar
18 votes
5 answers
11k 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?
Super Hornet's user avatar
18 votes
3 answers
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What makes flight recorders harder to find than tagged sharks?

It really bothers me that we can't find planes that weigh tons with black boxes (AFAIK) technology that's almost obsolete, on the other hand shark tags (AFAIK) work great for long time and we can ...
Marware's user avatar
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4 answers
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If a GPS displays the correct time, can I trust the calculated position?

Suppose I plan to reactivate an airplane that has been stored in a boneyard for a year or two, or at least power it up and turn on the avionics. Also suppose for the sake of the question that the GPS ...
Steve V.'s user avatar
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17 votes
3 answers
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Are NDBs and VORs dying as a navigational method?

I am new to aviation, so bear with me on this question: I have read in multiple places that the VOR/NDB navigational aids are dying out to GPS. Is this true? Are more modern aircraft being built with ...
Jon's user avatar
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17 votes
4 answers
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Can a pilot use their GPS/FMS to fly a VOR or NDB approach?

GPS is more accurate than a VOR or NDB signal. Can we use a GPS to fly a VOR or NDB approach from the initial approach fix through the missed approach and hold? I know there are two types of ...
wbeard52's user avatar
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4 answers
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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: ...
Jakub's user avatar
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2 answers
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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 ...
ryan1618's user avatar
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17 votes
4 answers
26k 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-...
newmanth's user avatar
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16 votes
6 answers
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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 "...
Farcher's user avatar
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15 votes
6 answers
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Why don't planes (mostly airliners) primarily use GPS for navigation?

For the four airliners that I use in Microsoft Flight Simulator (A320neo, A319, A310-300, and 747-8I), I always have to align IRS and set up RAD NAV on the MCDU. Why can't we just use GPS? On the 747, ...
DaCuteRaccoon's user avatar
15 votes
4 answers
5k views

Do airlines use GPS for critical purposes? If so, why?

It is being reported that airlines in Finland have noticed interference with their GPS signals near Russia. This is causing them to be unable to land at at least one airport: Lithuanian airline ...
User65535's user avatar
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13 votes
5 answers
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What is the geoid undulation used for in aviation?

In addition of the altitude found on aerodrome information, the French AIP also mentions the value of the geoid undulation:: AIP for Lyon - Saint Exupéry (LFLL) Geoid undulation is also found in ...
mins's user avatar
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12 votes
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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 ...
Cray Kao's user avatar
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3 answers
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LPV/LP approach (RNAV with WAAS): What is actually the "channel number"?

Curious about the answer to this question: How may I verify WAAS channel number on G1000?, I just found that SBAS/WAAS use in aviation seems to be poorly explained. In particular the WAAS "channel ...
mins's user avatar
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11 votes
1 answer
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How do I tell a Garmin 430 not to exit a hold?

Let's say that we're directly west of CATLI and have been cleared direct CATLI for the RNAV approach. We load the approach into ...
Steve V.'s user avatar
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10 votes
2 answers
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Why is training regarding the loss of RAIM given so much more emphasis than training regarding the loss of SBAS?

I've noticed a lack of subject matter on the loss of SBAS as compared to RAIM. In the ACS there is mention of RNP, SBAS (WAAS), and RAIM, which are all related, but the available content for RAIM and ...
Ryan Mortensen's user avatar
10 votes
3 answers
18k 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 ...
Pugz's user avatar
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10 votes
1 answer
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How do aviation GPS navigation systems report GPS accuracy?

While looking over a tutorial on how to operate the Garmin GNS430, I couldn't find any info on how the device would report a degraded or low accuracy signal. What are the accuracy requirements for ...
Geoffrey Gallaway's user avatar
10 votes
1 answer
2k views

Does altimeter setting affect the vertical guidance in a LPV approach?

I had assumed during a WAAS approach when the GPS is in LPV mode, both lateral guidance and vertical guidance are generated from GPS/WAAS signals and the pitot-static system should have no effect on ...
CrepuscularV's user avatar
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10 votes
1 answer
807 views

How does an FMS shift after losing all external navaids?

It's not uncommon for polar flights to lose GPS signal (ionosphere issues due to the high latitudes). But it is not a concern because the typical IRS drift is 650 meters for every hour of flight, and ...
user avatar
9 votes
5 answers
522 views

Do GPS coordinates of a fixed point in space ever change?

As I understand, GNSS uses the WGS84 model of the earth to pin-point points in 3D space. However, once the GPS coordinates of a point in space have been determined (say a GPS waypoint), do it's ...
PapaMike99's user avatar
9 votes
1 answer
446 views

Do GPS systems in modern avionics mitigate against spoofing attacks?

There exist a number of different techniques [PDF] to mitigate (or at least detect) GPS spoofing, but the most effective techniques require access to the military-only M-code [PDF]. However, there was ...
forest's user avatar
  • 236
9 votes
1 answer
2k views

When should I start turning in this circling approach?

I've been practicing circling approaches in Homestead General Aviation Airport in Homestead, Florida (X51). I performed the RNAV (GPS) RWY 10 approach with circling minimums. My questions are: a) ...
Charles's user avatar
  • 151
8 votes
2 answers
1k 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-...
Danny Beckett's user avatar
8 votes
2 answers
10k views

What is the benefit of having baro-VNAV in addition to a WAAS GPS?

On Cirrus' 2015 aircraft page, they advertise Baro-VNAV capability in the new model. Having never done an LNAV/VNAV GPS approach (only LNAV or LPV), I'm wondering: when would I actually use it, if I ...
Mike's user avatar
  • 452
8 votes
1 answer
828 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 ...
Danny Beckett's user avatar
8 votes
3 answers
3k 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 ...
Lnafziger's user avatar
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8 votes
1 answer
169 views

Due to the corrective calculations being ground-based, does the reliability of WAAS degrade with increases in altitude?

Since the WAAS system utilizes stations at known, fixed locations on the ground to make determinations for positional correction, is there a loss in the precision or validity of that correction with ...
Ryan Mortensen's user avatar
8 votes
2 answers
830 views

Is a "GPS required" ILS (or other navaid-based) approach considered a "GPS approach" for alternate planning's sake when TSO-C129/196 gear is in use?

If you have TSO-C129/TSO-C196 GPS gear (vs TSO-C145/146 WAAS/SBAS gear), you either have to have a non-GPS approach at your destination, or a non-GPS approach at your alternate. If your choices are ...
UnrecognizedFallingObject's user avatar
7 votes
3 answers
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 ...
Pierre Fortin's user avatar
7 votes
1 answer
2k views

How does drone reliance on GPS make it 'semi-stealthy'?

I saw this on CNN today. For months, US intelligence and military personnel in Iraq have been raising alarms about the risk to American forces from these newer, more sophisticated Iranian-made drones....
Cascabel_StandWithUkraine_'s user avatar
7 votes
2 answers
4k views

What is a blind encoder?

As I'm studying, I found that GPS has to have 5 satellites or 4 satellites with "blind encoders" to use RAIM. What is a blind encoder and what is its purpose?
Mun Park's user avatar
  • 497
7 votes
2 answers
5k 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 ...
summerrain's user avatar
  • 3,434
7 votes
2 answers
13k views

Can I use an expired IFR-certified GPS with an out of date database in lieu of DME?

I know I should update the database in my GPS, but nevertheless I'm wondering if i can use an expired IFR-certified GPS with an out-of-date database in lieu of DME
rbp's user avatar
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7 votes
2 answers
6k views

Why RNAV SIDs and STARs are RNAV 1 instead of RNP 1?

I am studying for my CFII check-ride and I was wondering to know why SIDs and STARs are not RNP 1 but RNAV 1? Let's start with the following two definitions RNP - Required Navigation Performance: It's ...
Ivan Parra's user avatar
7 votes
1 answer
6k views

Why are there GPS MOCAs?

The Pilot Controller Glossary (and other places) define MOCAs as: MINIMUM OBSTRUCTION CLEARANCE ALTITUDE (MOCA)− The lowest published altitude in effect between radio fixes on VOR airways, off-...
JScarry's user avatar
  • 7,464
7 votes
1 answer
2k views

What US airports have approaches with LAAS?

LAAS (Local Area Augmentation System) is a ground-based GPS augmentation system, intended to be placed at airports to get position accuracy down to around 3m (~10ft) from WAAS's 10m. I've read that ...
egid's user avatar
  • 23.3k
7 votes
1 answer
443 views

If a SID chart says "GPS... required", can the plane use a different GNSS?

This US/FAA standard instrument departure says "Note: GPS or DME/DME/IRU required." If the aircraft could tune into a different GNSS like GLONASS, could the pilot still legally fly the departure ...
slantalpha's user avatar
  • 4,203
7 votes
1 answer
332 views

How can I check that the GPS receiver is sending data to the transponder?

I fly an ultralight aircraft. The GPS is a puck-type device from which the TX line runs to the mode-s transponder. The transponder does not readily show if it is receiving position data. The data is ...
Srini's user avatar
  • 73
7 votes
1 answer
269 views

Is there any plan to create GPS approaches to water areas for seaplanes?

Is anyone working on differential GPS approaches for seaplanes? They are a largely ignored resource with great capabilities for certain remote places
Guyfacey's user avatar