GTN750 and Instrument Work

bartmc said:
You are aware that the military takes GPS out from time to time? you're also aware that I've had a GPS failure in flight and got a subsequent software patch out of Garmin after reporting it? You are aware that the GPS signal is very low power and can easily be jammed?
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The moron has no idea.

I have completely lost GPS many times. Twice due to the military.




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Ron Levy said:
I don't often say anything negative about anyone publicly, but your posts are almost invariably inaccurate, misleading, or flat-out contrary to either the FAR's or the laws of physics. Your very limited experience as a newly-rated pilot operating Light Sport Aircraft is just not sufficient for the subjects on which you post. You really need to stop posting until you learn a lot more, because you waste a lot of my time posting corrections to your erroneous information (and I feel compelled to do that in case someone who doesn't know better reads what you write and maybe gets hurt).

BTW, your car GPS isn't operating in flight, doesn't require the same level of confidence, and yes, I have lost the satellite signal while driving more than once. anyway. It's just not 100% reliable in an airplane -- really.
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Big +1, but so much of what he says is so incomprehensibly ludicrous that I still suspect he's a clever troll who gets a rise out of wasting the energy of those such as yourself.
 
RoscoeT said:
Big +1, but so much of what he says is so incomprehensibly ludicrous that I still suspect he's a clever troll who gets a rise out of wasting the energy of those such as yourself.
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The thought had crossed my mind. Perhaps it's crossed the MC's minds, too.
 
CTLSi said:
Again, when was the last time you lost GPS in your car? Unless your receiver dies, you won't see that. There are two levels of redundancy in a system that provides you with six sats at all times (you only really need 4) than you need to do fixes in 3D space.

And there is a whole new gen of sats about to be deployed to replace the older system that will be even more robust, and provide even more reliability.

The GPS system will not go down, and unless Obama manages to allow Russia to get close enough to jam the system, it wont be going down. But if Russia does get that close, flying and driving your toys using GPS will be the least of your worries.

One other thing. While you are busy wasting fuel and time pinging between VORs, I am flying a straight line to my waypoints, strung together in a straight line to my destination.

Read the link I provided. It gives a hint just how reliant we are on GPS.
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Welp....Whatever makes you feel warm and fuzzy at night. Just know that you couldn't be more wrong on this subject and there are quite a few people in this thread who have quite a bit more experience than you that have given specific examples of times we have lost GPS reception while flying along. Also, in the example I gave, I was on an IFR flight plan at night in high terrain in a normally asperated 182, so following the airway really wasn't a choice, it was required for safe operation of the aircraft (as in, not hitting stuff): GPS or not. You may be reliant on GPS, but as much as I love GPS, I am not (nothing at my current job has it) and there are many others out there who safely fly from point a to point b sans GPS each and every day.
 
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jesse said:
lol, I've lost gps integrity to the point to where a GPS driven approach wasn't an option on a handful of occasions. I've lost complete GPS coverage for extended periods of time to where even enroute navigation wasn't possible a few times.

Those that say GPS always works and are willing to trust their life on that don't understand how frail it can be and obviously don't fly enough hours in the system otherwise they would see the failures themselves.
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There are multiple point of failure available in the GPS system, some even before it gets to your antenna, the scariest of which give you an offset with no other indication of something going wrong. That's what the whole TSO-146 stuff addresses and why you need it to shoot lower approaches.
 
CTLSi said:
Again, when was the last time you lost GPS in your car? Unless your receiver dies, you won't see that. There are two levels of redundancy in a system that provides you with six sats at all times (you only really need 4) than you need to do fixes in 3D space.

And there is a whole new gen of sats about to be deployed to replace the older system that will be even more robust, and provide even more reliability.

The GPS system will not go down, and unless Obama manages to allow Russia to get close enough to jam the system, it wont be going down. But if Russia does get that close, flying and driving your toys using GPS will be the least of your worries.

One other thing. While you are busy wasting fuel and time pinging between VORs, I am flying a straight line to my waypoints, strung together in a straight line to my destination.

Read the link I provided. It gives a hint just how reliant we are on GPS.
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I lose GPS signal once to twice a month on average on boats. Heavy weather is often accompanied by unreliable signals.
 
Henning said:
There are multiple point of failure available in the GPS system, some even before it gets to your antenna, the scariest of which give you an offset with no other indication of something going wrong.
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Can you describe a GPS system failure which would give you and "offset" beyond the system accuracy limits for IFR operation but not give you any indication of the failure (i.e., no RAIM or INTEG lights) even on a c129 non-WAAS system?
 
Ron Levy said:
Can you describe a GPS system failure which would give you and "offset" beyond the system accuracy limits for IFR operation but not give you any indication of the failure (i.e., no RAIM or INTEG lights) even on a c129 non-WAAS system?
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Not sure what causes it, I have been told a timing error, but on multiple occasions on the ICW (around Norfolk on the Elizabeth River through Portsmouth GPS is notorious for failing) or wherever I'm in confined waters and can notice, all of a sudden I jump from the middle of the channel to some distance inshore and will stay that way sometimes for a while with an offset, the unit perfectly happy with that result. I have also seen my altitude readout with +/- several hundred feet. RAIM does catch this stuff, but not every GPS system has it is my point, and the issue behind RAIM and other integrity monitoring stuff in the TSOs and why you can't use non TSO equipment for IFR requirements.
 
Henning said:
Not sure what causes it, I have been told a timing error, but on multiple occasions on the ICW (around Norfolk on the Elizabeth River through Portsmouth GPS is notorious for failing) or wherever I'm in confined waters and can notice, all of a sudden I jump from the middle of the channel to some distance inshore and will stay that way sometimes for a while with an offset, the unit perfectly happy with that result. I have also seen my altitude readout with +/- several hundred feet. RAIM does catch this stuff, but not every GPS system has it is my point, and the issue behind RAIM and other integrity monitoring stuff in the TSOs and why you can't use non TSO equipment for IFR requirements.
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I've seen that in my car's onboard GPS.
 
Jaybird180 said:
I've seen that in my car's onboard GPS.
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It's also the basis of the price difference, all that integrity monitoring stuff. Not saying it costs the difference, just what makes it so they can demand the price.
 
Henning said:
Not sure what causes it, I have been told a timing error, but on multiple occasions on the ICW (around Norfolk on the Elizabeth River through Portsmouth GPS is notorious for failing) or wherever I'm in confined waters and can notice, all of a sudden I jump from the middle of the channel to some distance inshore and will stay that way sometimes for a while with an offset, the unit perfectly happy with that result. I have also seen my altitude readout with +/- several hundred feet. RAIM does catch this stuff, but not every GPS system has it is my point, and the issue behind RAIM and other integrity monitoring stuff in the TSOs and why you can't use non TSO equipment for IFR requirements.
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Every TSO'd aviation GPS has RAIM. Every single one. What happens with your car or boat GPS isn't the issue here.
 
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Ron Levy said:
Every TSO'd aviation GPS has RAIM. Every single one. What happens with your car or boat GPS isn't the issue here.
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Except that RAIM doesn't fix anything it just tells you something is jacked. So you're still hosed in that scenario.
 
Ron Levy said:
Every TSO'd aviation GPS has RAIM. Every single one. What happens with your car or boat GPS isn't the issue here.
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:sigh: Ron, when the RAIM finds issue with the GPS signal, what happens on a TSO box, does it correct for the error, or does it quit providing navigation?
 
jesse said:
Except that RAIM doesn't fix anything it just tells you something is jacked. So you're still hosed in that scenario.
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At least you know not to follow it into a big rock, which is my point in response to Henning's comment suggesting there could be failures without any warning flags.
 
Henning said:
:sigh: Ron, when the RAIM finds issue with the GPS signal, what happens on a TSO box, does it correct for the error, or does it quit providing navigation?
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It flashes big warnings which tell you to use something else for navigation.
 
Henning said:
:sigh: Ron, when the RAIM finds issue with the GPS signal, what happens on a TSO box, does it correct for the error, or does it quit providing navigation?
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AIM 1-1-18 discusses what RAIM does and the messages and functionality available under various scenarios. The main thing it does is to predict, based on your flight plan, whether signal loss should occur based on aircraft and satellite predicted positions vs time. One of the TSOs does this automatically and the other the pilot must run a RAIM prediction manually as I understand it. The GTN 750 does RAIM automatically but also has a manual RAIM prediction tool the pilot can use.

AIM 1-1-18

3. Receiver Autonomous Integrity Monitoring (RAIM). When GNSS equipment is not using integrity information from WAAS or LAAS, the GPS navigation receiver using RAIM provides GPS signal integrity monitoring. RAIM is necessary since delays of up to two hours can occur before an erroneous satellite transmission can be detected and corrected by the satellite control segment. The RAIM function is also referred to as fault detection. Another capability, fault exclusion, refers to the ability of the receiver to exclude a failed satellite from the position solution and is provided by some GPS receivers and by WAAS receivers.

4. The GPS receiver verifies the integrity (usability) of the signals received from the GPS constellation through receiver autonomous integrity monitoring (RAIM) to determine if a satellite is providing corrupted information. At least one satellite, in addition to those required for navigation, must be in view for the receiver to perform the RAIM function; thus, RAIM needs a minimum of 5 satellites in view, or 4 satellites and a barometric altimeter (baro-aiding) to detect an integrity anomaly. [Baro-aiding satisfies the RAIM requirement in lieu of a fifth satellite.] For receivers capable of doing so, RAIM needs 6 satellites in view (or 5 satellites with baro-aiding) to isolate the corrupt satellite signal and remove it from the navigation solution. Baro-aiding is a method of augmenting the GPS integrity solution by using a nonsatellite input source. GPS derived altitude should not be relied upon to determine aircraft altitude since the vertical error can be quite large and no integrity is provided. To ensure that baro-aiding is available, the current altimeter setting must be entered into the receiver as described in the operating manual.

5. RAIM messages vary somewhat between receivers; however, generally there are two types. One type indicates that there are not enough satellites available to provide RAIM integrity monitoring and another type indicates that the RAIM integrity monitor has detected a potential error that exceeds the limit for the current phase of flight. Without RAIM capability, the pilot has no assurance of the accuracy of the GPS position.
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Ron Levy said:
At least you know not to follow it into a big rock, which is my point in response to Henning's comment suggesting there could be failures without any warning flags.
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I said no such thing. You always read more into things than exists. I said that the GPS signal can provide such errors which is true. Aviation equipment quits providing navigation at that point.
 
RotorAndWing said:
On the Airbus it will alert you that GPS has degraded.
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What does the FMS do with that info? What about the display? Does it switch to an alternate guidance or just switch to a 'dumb mode' autopilot holding heading and speed?
 
Henning said:
What does the FMS do with that info? What about the display? Does it switch to an alternate guidance or just switch to a 'dumb mode' autopilot holding heading and speed?
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The GTN 750 manual discusses this. It goes into "Dead Reckoning" mode:

1.10 Dead Reckoning
[FONT=Berkeley Book,Berkeley Book][FONT=Berkeley Book,Berkeley Book]Dead reckoning is a feature that enables the GTN to provide limited navigation using the last known position and speed after a loss of GPS navigation while on an active flight plan. [/FONT]
[/FONT][FONT=Frutiger 47LightCn,Frutiger 47LightCn][FONT=Frutiger 47LightCn,Frutiger 47LightCn]CAUTION: [/FONT][/FONT][FONT=Frutiger 57Cn,Frutiger 57Cn][FONT=Frutiger 57Cn,Frutiger 57Cn]Navigation using dead reckoning is only an estimate and should not be used as the sole means of navigation. Use other means of navigation, if possible. [/FONT]
[/FONT][FONT=Berkeley Book,Berkeley Book][FONT=Berkeley Book,Berkeley Book]Dead reckoning becomes active after a loss of GPS position while navigating using an active flight plan and the flight phase is either En Route (ENR) or Oceanic (OCN). [/FONT]
[FONT=Berkeley Book,Berkeley Book]"DR" will be overlayed on the ownship icon. The To/From flag is removed from the CDI. The Dead Reckoning annunciator (DR) appears on the lower left side of the map display and will replace ENR or OCN when a GPS position is unavailable and the unit is in Dead Reckoning mode. All external outputs dependent on GPS position are flagged. [/FONT]
[FONT=Berkeley Book,Berkeley Book]Terrain will be noted as not available and new terrain advisory pop-ups will not occur. Traffic and StormScope information will not be shown on the Map page, but will continue to be available on their own dedicated pages. XM weather will still be available on the Map page. [/FONT]
[FONT=Berkeley Book,Berkeley Book]Dead Reckoning mode will continue until GPS position is restored, when GPS navigation is restored Dead Reckoning mode is exited. The DR annunciations will be removed and GPS information will be used to compute navigation related information for the current flight phase. [/FONT]
[FONT=Berkeley Book,Berkeley Book]Dead Reckoning is only allowed in En Route and Oceanic phases of flight. If the unit is in a Terminal or Approach phase of flight when Dead Reckoning takes place, "No GPS Position" will be displayed on the map pages and all navigation data will be dashed. If you are operating in Dead Reckoning mode and a transition to Terminal or Approach phases of flight would occur from the projected Dead Reckoning position, Dead Reckoning mode will be discontinued. "No GPS Position" will be displayed on the map pages and all navigation data will be dashed. [/FONT]
[/FONT]
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Since the navigation signal is flagged, the autopilot should disconnect.
 
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Henning said:
I said no such thing. You always read more into things than exists. I said that the GPS signal can provide such errors which is true. Aviation equipment quits providing navigation at that point.
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You said "RAIM does catch this stuff, but not every GPS system has it is my point." My point is every certified aviation GPS has it, so what your car or boat GPS did is irrelevant to the discussion.
 
Ron Levy said:
You said "RAIM does catch this stuff, but not every GPS system has it is my point." My point is every certified aviation GPS has it, so what your car or boat GPS did is irrelevant to the discussion.
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Correct statement. All TSO C129 and C146 receivers have RAIM - just not necessarily automatic with WAAS capability. With TSO C129 boxes (non-WAAS) the pilot has to verify RAIM manually before IFR flight that relies on that box for sole RNAV guidance, etc.
 
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Henning said:
What does the FMS do with that info? What about the display? Does it switch to an alternate guidance or just switch to a 'dumb mode' autopilot holding heading and speed?
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When GPS primary is lost, the ″GPS PRIMARY LOST″ message is displayed on ND and PFD.

Each FMGC receives a position from each of the three IRSs, and computes a mean-weighted average called the “MIX IRS” position.


Each FMGC computes its own aircraft position (called the "FM position") from a MIX IRS position and
a computed radio position, or a GPS position.
The FMGS selects the most accurate position, considering the estimated accuracy and integrity of
each positioning equipment.
GPS/INERTIAL is the basic navigation mode, provided GPS data is valid and successfully tested.
Otherwise, navaids plus inertial or inertial only are used. (Refer to DSC-22_20-20-10 Navigation
Modes).
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FOR RNAV(GNSS) APPROACHES
RAIM and AIME are available worldwide, if 24 GPS satellites or more are operative.
If the number of GPS satellites is 23 or less, check RAIM/AIME availability using the approved version of the Honeywell / Litton ground-based prediction software.
RAIM availability may be checked using the PREDICTIVE GPS MCDU page
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ERRONEOUS GPS PREDICTIONS
The following procedure must be followed whenever a GPS RAIM availability Check is necessary.
If the predictive GPS status appears at the different times (ETA -15 min, -10 min, -5 min, 0 min,
+5 min, +10 min, +15 min) as for example N, N, N, Y, N, N, N, the displayed N may be spurious.
To determine the GPS availability at ETA -15:
‐ Enter the destination in the WPT field [3L],
‐ Enter, the ETA -15 value in the ETA field [3R] on the MCDU PREDICTIVE GPS page and check
that a “Y” is displayed at the ETA time.
Repeat this last action as necessary for each different times: -10, -5, 0, +5, +10, +15.
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You guys are entertaining as well as informative. Thank you. Someone mentioned earlier in the thread about jamming the signal. I have lost GPS signal two times in the 21 months I have owned the GTN.

Ironically both times, the RAIM prediction indicated no problems and I lost the signal on GPS approaches to the same airport and to the same runway. I have not lost the GPS signal on any other of the dozens of approaches I have flown with the GTN to any of the other airports I have flown.

How easy is it to jam?
 
I wonder if future navigators will receive not only GPS, but also Galileo and Glonass, which are the European and Russian variants of GPS.

Having some redundancy and error checking in a plane sounds like a good thing.

I'd guess it would make you less vulnerable to jamming, which doesn't require a powerful transmitter.
 
NoHeat said:
I wonder if future navigators will receive not only GPS, but also Galileo and Glonass, which are the European and Russian variants of GPS.

Having some redundancy and error checking in a plane sounds like a good thing.

I'd guess it would make you less vulnerable to jamming, which doesn't require a powerful transmitter.
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Garmin's portable Bluetooth GPS for use with the iPad uses Glonass signals. Not sure on their certified gear.
 
The internal GPS on the newest iPad / iPhone uses GLONASS as well.

Interesting story - was cruising along IFR over California one day when every GPS receiver on the plane stopped working.

After much troubleshooting, the problem turned out to be the Garmin external antenna that was driving our GNS480. Apparently, there is a somewhat known, intermittent issue where the antenna circuit board starts to de-laminate. When that happens it actually JAMS the GPS frequency enough to bring down all other GPS receivers in the aircraft.

At the time, my iPad was paired with a Delorme inReach that was feeding GPS position. Of course, it died as well when this happened. However, after I unpaired it, the iPad was the _only_ working GPS in the plane - I believe this is because it was using GLONASS.

(Once I powered down the 480, all GPS receivers came back online)

Replacing the antenna fixed the issue.
 
petrolero said:
Correct statement. All TSO C129 and C146 receivers have RAIM - just not necessarily automatic with WAAS capability. With TSO C129 boxes (non-WAAS) the pilot has to verify RAIM manually before IFR flight that relies on that box for sole RNAV guidance, etc.
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When operating in a SBAS enviroment, a RAIM check isn't required on a TSO 146 box, according to Garmin.
 
Ron Levy said:
You said "RAIM does catch this stuff, but not every GPS system has it is my point." My point is every certified aviation GPS has it, so what your car or boat GPS did is irrelevant to the discussion.
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Do you understand that not every GPS receiver is a certified unit and that we were discussing GPS in general and its 'inability to fail' not Aviation GPS units?:dunno: Read for context Ron, the subject of GPS failure extends far beyond the receiver units and a RAIM 'failure' is as much of a loss of GPS navigation as any other possibility. The context was GPS doesn't fail, the offset signal is a failure of the system that will leave your TSO GPS set in a mode that will not provide you navigational guidance.
 
NoHeat said:
I wonder if future navigators will receive not only GPS, but also Galileo and Glonass, which are the European and Russian variants of GPS.

Having some redundancy and error checking in a plane sounds like a good thing.

I'd guess it would make you less vulnerable to jamming, which doesn't require a powerful transmitter.
Click to expand...

The multi satellite system boxes already exist outside the aviation realm.
 
dans2992 said:
The internal GPS on the newest iPad / iPhone uses GLONASS as well.

Interesting story - was cruising along IFR over California one day when every GPS receiver on the plane stopped working.

After much troubleshooting, the problem turned out to be the Garmin external antenna that was driving our GNS480. Apparently, there is a somewhat known, intermittent issue where the antenna circuit board starts to de-laminate. When that happens it actually JAMS the GPS frequency enough to bring down all other GPS receivers in the aircraft.

At the time, my iPad was paired with a Delorme inReach that was feeding GPS position. Of course, it died as well when this happened. However, after I unpaired it, the iPad was the _only_ working GPS in the plane - I believe this is because it was using GLONASS.

(Once I powered down the 480, all GPS receivers came back online)

Replacing the antenna fixed the issue.
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The Cellular and Wireless section in this link shows that the newer iPhones use both GPS and GLONASS which is good to know for redundancy sake.

https://www.apple.com/iphone/compare/
 
BillTIZ said:
It's a rental. The owner replaced a dying KLN89B with the 750 that he got at discount. The local radio shop needed to sell/install xx systems per year to keep his Garmin contract. He got a great discount at the end of the contract year.
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Which plane is this in?
 
I did my instrument training using a GTN 750 so it's all I know. However, at home I have a simulator along with Reality XP Garmin 530W setup and used it extensively during my training. I found the 530 to be quite capable and wouldn't have any problems using it if I found myself in an aircraft equipped with it.

But to reiterate BTIZ's original post, having a 750 is sort of cheating.
 
the400kid said:
I did my instrument training using a GTN 750 so it's all I know. However, at home I have a simulator along with Reality XP Garmin 530W setup and used it extensively during my training. I found the 530 to be quite capable and wouldn't have any problems using it if I found myself in an aircraft equipped with it.

But to reiterate BTIZ's original post, having a 750 is sort of cheating.
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Spoiled:D
 
KSCessnaDriver said:
When operating in a SBAS enviroment, a RAIM check isn't required on a TSO 146 box, according to Garmin.
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True. A manual RAIM check isn't required. But that's because the system is continuously monitoring integrity in a TSO 146 box when in WAAS coverage. In that sense, RAIM is being checked continuously and automatically.
 
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