Questions tagged [gnss]

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

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9 votes
5 answers
475 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 ...
0 votes
1 answer
125 views

Passenger GNSS lock during ascent and descent

When flying on commercial flights for the past several years I've used GNSS on my smartphone to track my location for fun. The signal strength in the cabin isn't ideal, but it's generally good enough ...
0 votes
1 answer
82 views

Difference between accuracy, integrity, availability, continuity, and functionality

My understanding is that accuracy is how close my estimated position is to my actual position at a certain point in time. I don't really understand how integrity is different from accuracy. Continuity ...
1 vote
1 answer
104 views

How to update the navigation database on a Garmin GPS 165 TSO?

What is the update process for updating GPS 165 TSO. The updates are available on shop.jeppesen however, how to transfer them to this GPS ??
1 vote
1 answer
207 views

Approach miniumum when I lost WAAS during approach

I have a GPS receiver with WAAS. During an LPV approach, I received an LOI message That means I only lost WAAS, not RAIM. Did I just need to change minimum to LNAV and continue the approach?
0 votes
1 answer
125 views

IFR plan only with GPS

I'm right before CFII checkride I understand that if it is without WAAS, I need navigational equipment other than GPS because I can flight plan based on GPS either destination or alternate. However, ...
1 vote
1 answer
82 views

Data for mapping a past flight?

Is there a website that shows past flight tracks of a few days back? tells how to use FlightAware to see a past flight on a map.  But is there any public source of times/coordinates for past flights? ...
2 votes
2 answers
429 views

Is the GPS ground track true or magnetic?

This question arises from the Garmin GPS units (eg. GNS530 or GTN750), but the term ground track appears in a general context of GPS units so my question is also general. Is the ground track (TRK in ...
15 votes
6 answers
8k views

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, ...
6 votes
2 answers
3k 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 ...
19 votes
3 answers
21k 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?
5 votes
2 answers
2k views

How is TSO C145 equipment different from TSO C146 equipment?

From the AIM1-1-18 c1) C145 - "Airborne Navigation Sensors Using the GPS Augmented by the Wide Area Augmentation System" C146 - "Stand-Alone Airborne Navigation Equipment Using the ...
5 votes
2 answers
792 views

What is the difference between SBAS and SBAS PA mode on my FMS?

We have a Collins FMS, and in the GNSS control page it tells you what mode it is operating in. In the instance that I checked it, it said "SBAS PA". The flight manual said that it can ...
18 votes
4 answers
6k views

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 ...
1 vote
0 answers
49 views

RAIM Checks when using GNSS in lieu of DME for distance information

I understand that a RAIM has to be checked on the ground as part of preflight, as well as before the commencement of an RNAV/RNP approach. What I am unable to find information on online, is whether a ...
4 votes
1 answer
815 views

GNSS approaches: Why does LNAV minima even exist? Wouldn't all aircraft fly to LNAV/VNAV or LPV minimums?

I am new to instrument flying and am trying to wrap my head around the different types of GNSS approach minimums. I am having an issue understanding why LNAV minimums exist. My understanding is, if ...
4 votes
1 answer
292 views

What does it mean for a GPS PRN to be unserviceable?

There is a current NOTAM: !GPS 02/035 GPS Navigation PRN 28 unserviceable Feb 21, 2023 2020Z to May 31, 2023 2359Z What exactly does it mean for a GPS PRN to be unserviceable, and what significance ...
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 ...
0 votes
1 answer
106 views

Does Garmin G300 GPS use true heading or magnetic?

Does Garmin G300 GPS use true heading or magnetic? Sorry couldn't find this information anywhere else.
2 votes
1 answer
536 views

Does EASA allow using a portable GPS for RNAV capability?

Assume an older IFR-certified aircraft with the classical equipment, that is two VOR/ILS receivers with plain CDIs, ADF and DME, but no GPS. It can be flown IFR, but many routes can't be used, because ...
5 votes
3 answers
2k views

Why should the optimum position of GPS Antenna be close to aircraft's CG?

In CAE OAA Book11-Radio Navigation Chapter-18 Page-318, under GPS Error, "The optimum position for the antenna is on top of the fuselage close to the aircraft's centre of gravity". In the ...
6 votes
1 answer
272 views

How to reduce the volume of the GTN750 traffic warning beep?

We've got a GTN 750 with ADS-B IN and OUT. When we encounter traffic it emits a high pitched pulsing beep. It cannot be muted by any means - say you are on final and there's an aircraft holding short ...
0 votes
3 answers
3k views

What do ENR,TERM and APR mean in the HSI? Also how may I call this part on the HSI?

How should I answer when my instructor asks me what it means during the flight? I searched but couldn't find a definitive answer.
8 votes
1 answer
438 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 ...
1 vote
0 answers
269 views

Along Track Distance ATD

ATD (Along-Track Distance) is used by ATC for certain types of (rare) NON-Radar Separation. I am training as an Air Traffic Controller in the USA. I have been told the only way to know if an aircraft ...
0 votes
4 answers
280 views

Are there (ideas for) GNSS based attitude indicators?

With upcoming GNSS systems that have better accuracy than GPS, could there be an GNSS based attitude indicator? Does maybe one already exist? I could imagine having 4 sensors (front, aft, left ...
17 votes
4 answers
13k 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: ...
17 votes
4 answers
17k 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 ...
11 votes
3 answers
4k 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 ...
3 votes
1 answer
5k views

How to track a flight that I am flying in using the GPS antenna in my mobile phone (without internet)?

I am in India. I booked my first flight ticket a few weeks ago and am very interested in identifying locations as well as geographical and human structures that I will see. I have downloaded many GB's ...
5 votes
1 answer
590 views

What does a DME indicator do in HOLD or RNAV mode?

I found this DME indicator on the Cessna 210. Its mode switch has four positions - NAV1, NAV2, RNAV and HOLD. NAV1 and 2 are clear - it uses the NAV1 and 2 freq respectively. I'm wondering what the ...
16 votes
6 answers
11k 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 "...
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 ...
0 votes
1 answer
2k views

Can single engine/smaller aircraft turn off ADS-B?

I was just looking at the adsbexchange website, and was wondering if it was possible for smaller, private aircraft to turn off their ADS-B? I was wondering this because id figure that maybe not ...
2 votes
1 answer
400 views

Do the regulations allow DME from an expired IFR-certified GPS with an out of date database to be used for this ILS approach under an IFR plan?

Since we cannot fly an RNAV approach with out of date GPS database, the approach in question is KCRE ILS 23. Whether it was asking for V2F or the full approach starting from ASHES (which is 18.5 DME ...
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
5 votes
2 answers
1k 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 ...
3 votes
1 answer
1k views

Is a non-WAAS Garmin 530 certified for an LNAV/VNAV approach?

I may not understand all the details of what I'm asking but trying to wrap my head around it. I am aware that before WAAS, some GPS aircraft were equipped to get vertical guidance by a Barocorrected ...
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....
5 votes
1 answer
896 views

Why do some GPS receivers suppress RAIM integrity warnings after you pass the FAF?

RAIM performs an integrity check 2NM from the FAF. If RAIM is lost before the FAF, one should execute the missed approach. However, if RAIM is lost after passing the FAF, some GPS receivers will ...
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?
6 votes
2 answers
1k views

Does the altitude or attitude of an aircraft affect GPS accuracy?

Of course we are assuming an effective signal is being received. I live near Idaho Falls, Idaho with a field elev of 5300ft. If I shoot an approach will GPS be more or less accurate then landing at ...
7 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-...
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?
1 vote
1 answer
311 views

Why are SBAS-equipped planes exempt from the preflight prediction check?

My question stems from this other question: Why is training regarding the loss of RAIM given so much more emphasis than training regarding the loss of SBAS? Two answers say losing RAIM puts a question ...
10 votes
2 answers
4k views

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 ...
6 votes
2 answers
1k views

Why weren't SA-On GPS units updated to become SA-Aware?

SA = Selective Availability (gps.gov) SA-On and SA-Aware are widely used in current air transport aircraft (...) GPS that behave as if SA is still active (SA-On) GPS that behave as if SA has been ...
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 ...
0 votes
3 answers
574 views

What kind of airspeed does a (3D) GPS measure?

Assuming a GPS receiver is advanced enough to compute 3D position/velocity with reasonable accuracy, it can indicate not only the aircraft's ground speed (which ignores altitude changes), but ...
0 votes
1 answer
284 views

Is it possible to export NMEA data from a Garmin GDL-39 to a custom Android App?

Hi I was wondering if it's possible to receive NMEA data from a Garmin GDL 39 on an Android device (preferred over Bluetooth) as I can't find any information out there on it.