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Questions tagged [gnss]

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

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49
votes
5answers
11k views

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 ...
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?
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 ...
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?
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 ...
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 ...
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 ...
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?
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 ...
17
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3answers
3k views

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 ...
17
votes
3answers
2k views

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 ...
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?
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-...
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: ...
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 ...
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 "...
13
votes
3answers
3k views

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 ...
12
votes
1answer
2k views

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 ...
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 ...
10
votes
1answer
547 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 ...
9
votes
2answers
7k views

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 ...
9
votes
1answer
675 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) ...
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 ...
8
votes
1answer
775 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 ...
8
votes
1answer
1k views

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 ...
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 ...
7
votes
2answers
2k 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?
7
votes
1answer
2k views

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 ...
7
votes
1answer
866 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 ...
7
votes
2answers
6k 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 ...
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 ...
7
votes
1answer
220 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 ...
7
votes
1answer
252 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 ...
7
votes
1answer
246 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
7
votes
1answer
488 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 ...
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 ...
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 ...
6
votes
2answers
1k views

How can I keep the data on a KLN89b GPS up to date?

I'm looking at a Mooney M20C with a pretty dated panel, but it's airworthy and could be a great opportunity to build some retrac time. The KLN89b GPS is IFR Certified, but is positively ancient. ...
5
votes
2answers
505 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?
5
votes
1answer
464 views

What are the considerations for coding the GPS before engine start without external power?

Suppose I would need 10-15 minutes to fully configure my G1000 on a C172 ahead of a flight, with the flight plan, my personal view settings, etc., and prefer to do that before starting the engine. My ...
5
votes
2answers
4k 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
5
votes
1answer
2k 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-...
5
votes
1answer
200 views

What does “zero offset between two waypoints” mean in ICAO Doc 4444?

My question is with reference to the GNSS based separation specified in ICAO Doc 4444. Could someone explain the significance/meaning of the condition "zero offset between two waypoints" criteria? if ...
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
1answer
343 views

Why is there a GPS/RNAV waypoint co-located with a VOR?

There is an RNAV waypoint named STYCK co-located at what appears to be the exact location of the LOA VOR (coordinates match precisely as well). Why would the creation of a waypoint be necessary if IFR ...
5
votes
1answer
714 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 ...
5
votes
1answer
404 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 ...
5
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 ...
5
votes
2answers
268 views

Is the Bendix/King KMD-550 airplane icon always oriented to the north?

I have a 2001 Cessna 182T with King avionics. The KMD-550 moving map display correctly shows "track up" but the little airplane icon is always pointed to the north. How can I set this so that it ...
5
votes
2answers
690 views

Can the iPad use GPS data from a Garmin aera 660?

Can the iPad use GPS data from a Garmin aera 660 portable GPS unit? I assume this would happen via Bluetooth, if it's possible. I would like the more accurate WAAS data from the Garmin for use with ...