Ipad compatible bluetooth GPS which has an external antenna socket and external pwr input?

Discussion in 'Global Navigation Satellite Systems' started by Peter, Nov 6, 2011.

  1. Peter

    Peter Guest

    This is for an aviation app.

    The Ipad GPS is crap. Great on the ground (wifi/GSM fix assistance)
    but loses fix readily in the air.

    Apple have stupidly made the i-devices incompatible with all normal
    serial NMEA GPSs. There are I think two BT GPSs which work with it but
    neither has the external inputs.

    A good GPS is doubly important because the IOS API does not pass the
    constellation data to the application. All it gives you is a computed
    value for the accuracy of the fix. Good for locating the nearest McD
    Peter, Nov 6, 2011
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  2. Peter

    Alan Browne Guest

    My main frustration with the iPhone is also the very starved GPS
    interface. I'd love to see more of what's going on with the receiver
    and sats status. Moreso in the iPhone 4S (which I don't have) that also
    uses GLONASS.

    For airborne use I'd get a dedicated aviation receiver - though I can
    understand the seductive appeal of the iPad for such with its gorgeous
    larger screen. Maybe the solution is in a non-Apple tablet?

    I'll be ordering the etrex 30 soon. It uses both GPS and GLONASS. (Not
    an aviation receiver).

    As to your last statement, the iPhone GPS doesn't need to be that good.
    It's assisted. The correlators are driven "lazily" to save power. My
    tests of its tracks against a WAAS GPS recorder show (in controlled,
    open sky areas with good ground truths) 2 - 5 m on the WAAS GPS receiver
    and 15 - 20 m on the iPhone 4.

    For VFRing around, the later is sufficient, actually - though not sure
    how much coverage you would get in some areas.
    Alan Browne, Nov 6, 2011
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  3. Peter

    Peter Guest

    The Samsung Galaxy 10" tablet is the main competitor. Very similar to
    the Ipad, slightly less slick finger gesture implementation but
    actually fine for the job. Runs Android.

    And Oziexplorer exists for Android right now.
    20m is fine for enroute IFR too.

    It's just that the GPS has problems keeping a fix once it has got one
    - something which is quite unusual in the GPS business.
    Peter, Nov 6, 2011
  4. Peter

    Alan Browne Guest

    A handheld is not a certified receiver, not a certified navigation
    system. To whit I've had a GPS go haywire due to interference from the
    radio in my car (wild position and velocity error. Turn off the car
    radio and all was well).
    Not really. Spend time in a leafy forest with steep hills and gullies
    and it's quite common. That is to say loss of fix or wild errors due to
    multipath and/or aggressive tracking attempts (attempting to fix with
    low SNR [which many low end receivers attempt]).
    Alan Browne, Nov 6, 2011
  5. Peter

    miso Guest

    You have to wonder is the speed of the aircraft effects the ability of
    the GPS to maintain lock.

    These smartphones and tablets are Swiss army knives, or is Leatherman a
    more familiar term these days. They do nothing very well, but do a lot
    of stuff. If I want to take a photograph and I care about quality, I use
    something called a camera. The smartphone camera is great when you have
    nothing else, but seriously it isn't a camera. If I need a maps with
    tracking, I use a GPS, not my phone.

    Anything analog is compromised by design. You have cost constraints,
    power constraints, size constraints, etc. Nothing analog is perfect.
    When you design a GPS as a GPS, you are not constrained with having to
    live with a phone in the box too. A GPS in a phone or tablet can't steal
    too much power, especially in a phone with captive battery. (I hope
    there doesn't come a day when all phones go captive battery just to save
    money. The near field sensor on the back of some phones has made the
    door a very expensive item.]

    I'm amazed the FAA approved the ipad for sectionals. Hopefully good
    pilots have a paper backup. I used to carry USGS maps as backup when I
    first started using GPS navigation in the big empty. I still carry a
    backup GPS. While Garmin is the brand to buy for a lot of reasons, it
    doesn't have the greatest reliability record. In the last decade, they
    have been pretty good, but I know a few people that had their Garmin's
    fail in the field in the 90s, especially in cold weather.

    Incidentally, the Etrex series has had some switch issues. It isn't my
    Garmin of choice. I don't line the buttons on the side. I think that
    form factor is more likely to get damaged. Also that joy stick can be
    trouble. However it is a big price increase to get the GPS MAp 62, so I
    understand why the etrex line exists. I'd be more inclined to buy a used
    GPS Map 60 series, which is what I use now.

    I see the GPS 62 has a three axis compass. The GPS 60 compass is just
    terrible. My solution is to carry a real lensatic compass. I have never
    used the barometer either. I'd have to review the old models. but I
    think I got the sensor version because it was the only one that took
    microSD cards.

    If you could tolerate touch screen devices (I hate them), the units
    without keys would be a better choice than the Etrex. I bet a touch
    screen device is a little better in real life waterproofing since it has
    fewer points of entry.
    miso, Nov 7, 2011
  6. Peter

    macpacheco Guest

    If you never read this:
    Then you really shouldn't mess with non certified GPS in IFR. If
    you've read, then you're en enlightened person...
    My usual ramble follows, the real point is made already... Big fan...
    John Deakin rules. Learned a ton of stuff you'll never dream of
    learning from instructors (mostly about aircraft piston engines).

    Also if you never tried an Anywhere Map device, you really should.
    Their stuff is sooo much cheaper and leaps and bounds better than
    Garmin (and traditional competition). They don't force you to buy a
    new system just to upgrade the software. I used their software 10+
    years ago on an Compaq iPaq with an external USB GPS sensor, it worked
    perfectly. I flew a few "emergency simulation" approaches (with a
    safety pilot) using their solution instead of an ILS receiver, with
    better results than what you'll get from your typical run of the mill
    ILS receiver on old aircraft. Soo much easier to intercept the
    localizer with precision, and that was before WAAS (I was in Florida
    back then).

    For enroute and terminal the real issue is just keeping a lock on the
    signals, having an up to date database and navigation software that
    doesn't calculate things wrong. Even 100 meter error isn't an issue.
    RNP 0.3 is 550 meters, RNP 0.1 is 185 meters (currently RNP 0.3 is the
    tightest RNP standard used outside of approaches) ! You need to have a
    huge IONO storm with very few satellites without WAAS to be outside an
    RNP 0.1 track (vast majority of airliners today can't do better than
    RNP 0.3). Anyhow if you don't have a certified IFR receiver, radar
    control will assume your navigating that long direct leg via dead
    reckoning + VOR fixes, where errors of many nautical miles are the

    Bottom line is we should be able to use a decent handheld SBAS enabled
    GPS for enroute and terminal operations. But the FAA certification
    police will never allow it, due to their usual paranoia. Perhaps a
    simplified certification procedure. One can wish.

    Just having your current wind compensated ground track at all times is
    a huge workload reducing advantage. That alone pays for having a VFR
    GPS onboard.

    Marcelo Pacheco
    macpacheco, Nov 7, 2011
  7. Peter

    Peter Guest

    I am sure that is the case, and this is a very common problem in the
    GPS world. I have one GPS here (Fujitsu LOOX 60N) which can take an
    hour to lock if you are driving *when* it is switched on. I also have
    a satellite phone here (Thuraya 7100) which will *never* lock in an
    aircraft; I have a preflight checklist item to turn it on ;) And
    without a GPS fix the phone does nowt... All Thuraya phones have the
    same shitty GPS (except possibly the latest XT one which I have not
    I don't think they "approved" them as such. In the USA, and in Europe,
    there has never been any law controlling *portable* equipment (other
    than RF transmitting equipment), and there has never been any law
    mandating the carriage of a specific type of paper chart. So an
    "approval" of the Ipad is a non-event.

    What is new is approving it to replace paper charts for public
    transport (AOC) operations. But despite the news hype from Apple and
    the airlines concerned, no detail has come out AFAIK of what exactly
    is being approved. Using the Ipad to store and display Jepp plates, if
    you carry a set in a box somewhere, is a non-event. I don't believe
    any airline is using an Ipad as the sole device for carrying that kind
    of data. Look at the recent debacle where IOS 5.0.0 was going to
    silently delete some app data, if new data was downloaded onto the
    device. For starters, I would expect any AOC approval to contain a ban
    on the use of the Ipad for casual multimedia/email by the pilots (like
    downloading a 2GB p0rno movie when in the hotel ;)). It is airline
    property after all.
    Peter, Nov 7, 2011
  8. Peter

    macpacheco Guest

    That's news to me. I never seen a GPS receiver that will lock in
    Cessnas (120kts) or airliners (400kts).
    I have used Garmin and iPaqs (with Anywheremap software) for about a
    hundred of hours with total success as PIC.
    Of course trying to operate a GPS receiver using an airliner window
    makes for a challenging time keeping a lock on a lot of GPS
    satellites, but I've never seen the software lockup the receiver.

    That's an indication that GPS equipment is an excellent paper weight.
    Using any tablet/laptop for viewing approaches or maps requires as
    much certification as using a camera to document a flight. The only
    applicable FARs only require that the PIC makes sure the electronic
    equipment doesn't cause interference with navigation instruments,
    except for airline flights where you have to respect operational specs
    each airline imposes on their pilots.

    The FARs require specific certification if you intend to use the
    equipment as a primary navigation source. There's a fairly acceptable
    exemption if the equipment will be used only to increase situational
    awareness (handheld GPS), then its just the same as using a tablet/
    laptop to view approaches.

    As long as the equipment is not permanently installed on the aircraft,
    inspectors can't make any fuss out of using handheld GPS receivers/
    tablets/laptops, for moving maps, following approaches, or anything
    that isn't a primary navigation instrument.

    The sad part is you can't file an instrument flight plan using a
    handheld GPS like you had an non approach IFR GPS receiver, in
    practice, as long as you do frequent cross checks, you can use a
    handheld GPS for IFR flying for flying long direct legs. Chances are
    the VOR receiver you will use to cross check will be less reliable
    long term than the handheld GPS.

    For a complete discussion on the subject: http://www.avweb.com/news/pelican/182076-1.html

    Marcelo Pacheco
    macpacheco, Nov 7, 2011
  9. Peter

    Mike Coon Guest

    Both the Loox N500 devices taht I have owned have been very variable on
    getting initial fix, whether walking, driving or stationary. Using
    "QuickGPS" to download an ephemeris (I gather) via internet seems to make
    little difference either.

    Years ago I found that my ancient Garmin GPS-II+ could get a fix in an
    airliner more readily if I used its ability to set the altitude manually to
    35,000 feet (or whatever the captain announced) first. But the screen now
    shows too few pixels to be any use!

    Mike Coon, Nov 7, 2011
  10. Peter

    Alan Browne Guest

    GPS maintain lock on each satellite in large part by the Doppler shift
    due to the difference in velocity from the receiver v. the GPS
    satellite. When a GPS is standing still on the ground it still has a
    large velocity component with respect to the satellite.

    So whether airborne or "still" on the ground, a GPS receiver is always
    "moving" with respect to the satellites.

    IOW, it doesn't matter.
    Alan Browne, Nov 7, 2011
  11. Peter

    Ed M. Guest

    Aviation users are rapidly adopting iPads in the cockpit -- not for
    its GPS, but for a lot of other attributes.


    "February 19, 2011
    Executive Jet has earned official authorization from the FAA to use
    the Jeppesen Mobile TC App for iPad as a sole reference for electronic
    charts and as a direct replacement of paper aeronautical charts in the
    cockpit. . . . For now, the FAA's approval for the Jeppesen app on the
    iPad is for Executive Jet, and only Executive Jet. Jeppesen hopes
    that's just the beginning and, according to Jeppesen, many carriers
    may feel the same way.

    .. . . Still, some question the prudence of eliminating paper charts as
    a backup in the cockpit. For that, Executive Jet offers redundancy --
    each cockpit carries two pilots and two iPads."


    "May 31, 2011
    Alaska Airlines is now giving iPads to all of its pilots to replace 25
    pounds of flight manuals."

    American Airlines pilots union has a story in their August magazine
    about flight tests of iPad. The whole file is about 2 MB. The iPad
    story is on pgs. 8-11.


    "In June, LAX B777 pilots began in-flight evaluations of Apple iPads
    with electronic terminal charts and digital flight manuals.

    .. . . The lightweight iPad is secured to the forward chart holder
    using NASA-designed Velcro, to the left of the captain and to the
    right of the first officer.

    .. . . Immediately it was apparent that we were dealing with something
    that was going to be a game-changer in the cockpit. The ability to
    zoom in to different parts of the airport quickly and accurately is
    far superior to our old way of doing things. There was absolutely no
    glare on the screen and it was as bright or dim as you wanted the
    display to be.

    The iPad was excellent for use en route. There was no more fishing for
    alternates in your 1,500-page Far East
    book that you may or may not have the correct page for. Try that at
    night in the weather. It makes a review of places like Cold Bay,
    Alaska and Petropavlovsk, Russia much easier and at your fingertips.

    .. . . Approaching Tokyo Narita, we had a good review of all the pages.
    By then, we figured out how to use favorites and set up all of the
    pages we would need in order, from the arrival to the gate. To get
    from one page to another, all you have to do is “swish” your finger
    across the page. This is another huge benefit over paper.

    .. . . There are a few things I can’t say for sure about the iPad
    because I can only imagine them. First, the reduction of a 40-pound
    kit bag down to a one-pound iPad has got to be the single biggest
    benefit to us.

    .. . . I can honestly say that using the iPad in all phases of flight
    with a Class B application is a significant safety enhancement. The
    ability to look up material very quickly gives you more time to look
    outside and fly the airplane.

    Flying at night, the iPad is far superior to a paper chart due to its
    back-lighting. On the ground, there is definitely less “heads down.”
    Finally, all the information is in one place, not in two or three
    charts scattered all over the cockpit."

    An FAA notice from May 2011:


    A few Jepessen pages on the topic:


    Ed M., Nov 7, 2011
  12. Peter

    Peter Guest

    Do you have a reference for that?

    I think you mean to say: if the equipment is panel mounted.
    Peter, Nov 7, 2011
  13. Peter

    Alan Browne Guest

    You cannot, in any way use a handheld for IFR navigation.

    As to panel mounts, they can be certified for IFR (appropriate TSO(s))
    or not. If certified and if the installation is certified for that
    aircraft (STC (type or specific to the tail number)), then it may be
    used as primary means (but possibly in conjunction with VOR/DME/ADF for
    approaches - again wrt to TSO (see TSO-129/145/146) its cert level).

    It's a complex area - but a handheld is definitely not going to be an
    IFR nav system.
    Alan Browne, Nov 7, 2011
  14. Peter

    Peter Guest

    Reference please.
    May not be sensible, but it's not illegal in Part 91 ops. No reg says
    what equipment is to be used for enroute nav.
    Peter, Nov 7, 2011
  15. Peter

    macpacheco Guest

    Right, but when you're under radar control, flying a long direct leg,
    the primary navigation source you'll use is your DG, Altimeter. The
    handheld is just an online flight computer.

    Have you read http://www.avweb.com/news/pelican/182076-1.html

    John Deakin, a 35000 hour pilot with over ten thousand hours as an
    airline capitain makes the case in an entirely convincing way for me.
    Perhaps you can read the article and post your disagreements about it
    here, then we can really discuss it in an open minded way.

    But anyways, here I go again:

    Sure enough you really shouldn't shoot a GNSS approach in actual IFR
    weather without an IFR certified GPS/SBAS receiver with adequate
    certification for the approach, but for enroute / terminal ops, as
    long as you file /A or /U, you can request direct legs and fly them
    with handhelds. Just like you can request a 500 mile direct leg and
    fly it using dead reckoning + VOR cross checks, an assinine FAA
    inspector might tell you that you can't do that cause you don't have
    certified RNAV equipment to calculate that route, but there's no reg
    that require that RNAV equipment to fly a long direct leg. Remember
    that the #2 pencil you wrote your clearance with, the piece of paper
    you wrote it on, timer, ruler, flight calculator, all that stuff is
    not FAA certified ! As long as you don't crash or put others in danger
    by using your handheld IFR, ARTCC doesn't (and shouldn't) care.

    Of course if you ask an FAA inspector, he'll say otherwise, but then
    we won't be able to quote rules that specifically forbid it.

    If you don't have a modern IFR certified SBAS receiver onboard, not
    using a handheld that is stupid ! The workload reduction that the
    handheld brings is enourmous (specially if its a moving map), and of
    course, it really should have an up to date database. And even if you
    do have a great IFR certified SBAS receiver on board, that handheld
    can save your life if you get an electric failure that causes that
    certified receiver to go down in actual.

    Not everything that is officially approved is smart, and not
    everything not officially approved is dumb. This topic falls under the
    latter side.

    There are tons of extra safety features on handhelds that don't make
    it into certified units due to the prohibitive cost of certified unit
    software development.

    Marcelo Pacheco
    macpacheco, Nov 8, 2011
  16. Peter

    Alan Browne Guest

    The regs don't say what's prohibited.

    Google away. Begin with the FAR's and look specifically at TSOs 129,
    145 and 146. That'll get you going on what's _required_ for IFR using GPS.
    The regs state what equipment (appropriately certified) _can_ be (as
    opposed to must be) used when in compliance with the appropriate TSO's
    and installed per original aircraft type cert and/or STC's (type or
    specific to a given airplane).

    Minimum equipment lists specify the minimum _required_ equipment for IFR
    flight including what limitations there will be for given equipment. If
    your plane has only ADF and VOR, then you certainly can do enroute, but
    are limited to non-precision approaches.

    So you can use a handheld if you desire, but certainly not as sole means
    for IFR in any portion of the flight.
    Alan Browne, Nov 8, 2011
  17. Peter

    macpacheco Guest

    That's right, the handheld isn't sole means (and will never be), and
    that's what the TSOs are about ! There's air traffic radar, VOR, DG
    and of course your Compass. I would never be dependent on the handheld
    so that if it fails the safety of my flight can never be in jeopardy.
    Just like I would never carry electronic only maps on a single
    Minimum equipment lists for voice and navigation radios include only:
    "Two-way radio communications system and navigational equipment
    appropriate to the ground facilities to be used."
    You're not trying to make the handheld fit the regs. If you do, you'll
    find that its not forbidden.
    You can consider it a help for situational awareness. Looking at it
    more often than the DG doesn't make it your primary instrument, keep
    up that crosscheck.

    I make three extra points:
    1 - The handheld is more reliable than any mechanical gyro onboard an
    old aircraft (DG, AI, TC).

    2 - The total risk of the handheld failing (including signal issues)
    is lower than most other critical instruments onboard, and its failure
    mode will be very obvious, different from all the complex knowledge
    necessary to cope with a tumbling/dying/blocked Turn Coordinator,
    Directional Gyro, Attitude Indicator or Airspeed indicator. An VOR and
    NDB don't have RAIM ! Both can fail and still appear ok for the pilot.

    3 - The workload reduction from using the handheld is far more
    important than technicalities of the FAA. It actually frees up your
    time to keep yourself minutes ahead of the aircraft, instead of
    seconds. The FAA will never admit to that ! Not having to bracket
    courses on a VOR or ILS approaches (with the GPS, you know your exact
    ground track and the lateral deviation in meters, so intercepting a
    course can be done in 1% of the time the old fashioned way takes)
    Even when flying that ILS, VOR or NDB approach, using the GPS just
    to tell your current ground track and lateral deviation from the
    approach course (cross checking with the other instruments) is
    priceless. The real risk is it can make you lazy, and forget the hard
    way to do it. It actually makes an NDB approach safe, while without a
    handheld, I consider all NDB approaches forbidden for myself in IMC.

    Of course some will never accept that utilization as a possibility. I

    As John Deakin says:
    The number one rule of flying is "Don't hit nuthin'." (Next is "Don't
    do nuthin' stupid.") Alas, if people would only follow those two rules
    we could get rid of the FAA and most of the FARs.

    Is it really that stupid or risky using a handheld ? Does the FAA regs
    actually add to safety as long as you're a smart, minimally competent
    pilot ? The TSOs are very important to use that SBAS/COM/NAV approach
    certified receiver alone, without backups. And of course, flying a LPV
    approach (without an ILS or VOR on the same course) with a handheld in
    IMC is 100% stupid. But if there's an ILS and you're using the
    handheld to speed up course interception and fine tune your heading to
    keep the localizer precisely centered, than that's a good thing.

    Marcelo Pacheco
    macpacheco, Nov 9, 2011
  18. Peter

    Alan Browne Guest

    A handheld cannot give you aircraft heading, only track. As such it is
    not an ideal means for orienting the aircraft. One could look at an
    error, say 4° of track and then apply that to the current heading to
    make a correction. This is poor-cousin technique.
    The failure of a handheld GPS is little different, and when it fails it
    fails totally. If my attitude indicator fails, it rolls over, but the
    T&B and heading indicator continue to indicate properly (even with a
    winding down gyro due to a vacuum failure the heading indicator will be
    pretty good v. the attitude indicator).

    That is the essence of partial panel training. There is no "partial
    panel" for a handheld GPS.
    OTOH, a handheld gives both VFR and IFR pilots overconfidence that can
    lead them to disaster (as it did a high school friend of mine, who later
    in life, an engineer, IFR-rated pilot flew his Cessna-150 into a very
    tall radio transmission tower on a VFR flight in near IMC conditions.
    He died. Took over a week to recover his body from the tower. The
    tower owner sued his estate leaving his wife and kids pretty much
    nothing. I assume that he was using his GPS and that was a major
    contributor to the accident: over confidence. [Gilbert was a very sharp
    engineer and no blushing flower wrt his abilities. That got him killed

    With vaccuum driven heading NDB approaches can be a lottery (as check
    pilot for my father I let him do 3 NDB approaches in a row w/o him
    remembering to reset his heading. He wasn't too pleased with that
    session at C-182 rental rates).

    With a slaved or AHRS driven heading, there is no reason to avoid an NDB
    approach in IMC - that's what the high DH is for.
    The three basic rules of aviation are actually:
    -aviate (don't hit nutin, don't do nutin stoopid)

    In that order. Always.
    No. However there are the rules which must be obeyed. Nobody will get
    in trouble for using a handheld, as long as he has and uses the other
    required nav instruments and charts on board. Once you go "sole means"
    with a handheld you are not only illegal - but raising the risk.
    Debatable. A handheld does not fit into the instrument scan very well.
    If it is yoke mounted or 'velcroed' to the top of the dash, then possibly.
    Alan Browne, Nov 9, 2011
  19. Peter

    Peter Guest

    No GPS can give you the heading.

    Heading comes from a slaved compass system, normally.
    Nothing to do with GPS. He hit the tower because he was too low :)
    AHRS doesn't give you a heading.
    There is no such reg.
    A GPS is not in the "scan" as such.

    In all phases of flight, one flies a HEADING. A GPS may be used to
    make adjustments to the HEADING.
    Peter, Nov 10, 2011
  20. Peter

    macpacheco Guest

    I guess you're talking panel mounted here, correct ? I though we were
    talking handhelds. Can you mention one handheld that can receive an
    external slaved compass information ? Built in compass are worthless
    due to the difficulty of mounting the GPS with good enough alignment
    with the aircraft.
    That's right, there has even been crashes of airliners with full EFIS
    systems due to lack of situational awareness and with the pilot flying
    being behind the aircraft (I recall an American Airlines Boeing
    crashing into a mountain in Colombia or Peru about 25 years ago, ATC
    forgetting about the aircraft was a major factor as well). There's no
    replacement for an active mind validating all information available
    (cross checking everything). I'm sorry for your loss Alan, but I don't
    accept blaming any instrument (certified or not) as the cause of the
    crash. Overconfidence is a mental trait, not an instrument problem.

    Altitude is a great friend of mine. I have a paranoia over flying low.
    I always want to cruise at least 3000 ft above the MEF, even when the
    winds are disadvantageous. Primary concern is loosing an engine but
    avoiding granite is also a great thing. I like to cruise at 10000ft or
    higher, even on air breathing pistons.
    Yes it does. AHRS stands for: attitude heading reference system.
    It provides attitude, yaw and heading information. It needs to be
    aligned at startup, and it will suffer from some level of drift,
    however most solid state AHRS, have drift rates almost two orders of
    magnitude less pneumatic gyros. And don't suffer from progressive
    failures like typical gyros. And it can be slaved to a compass for
    automatic realignment of the heading information.
    The regs are pretty clear about that:

    Sole means - take for instance a Garmin G1000. It will replace all
    steam gauges on an instrument panel, with one on board you technically
    need no backup instruments (it has AHRS, air data computer, SBAS/VOR/
    COM/transponder, reads the engine probes). You can fly around in the
    soup, and shoot SBAS and ground instrument approaches, without all
    those older instruments. Its a medium cost EFIS system that has almost
    everything you can ask for on a small aircraft.

    Primary means - Like sole means, but you need to have backup
    instruments. Applies to older GPS (non SBAS) receivers which could be
    used only for GPS/LNAV approaches, but you need to have enough
    instruments so that if the GPS signal has insufficient geometry (for
    RAIM check), you can revert to a full set of backup instruments
    (including non GPS radios), and fly a non GPS approach for landing.
    Peter, actually using a non certified instrument as sole means or
    primary means clearly violate the regs for IFR.
    But using it in constant cross check with you DG/Compass/Turn
    Coordinator, VOR/NDB, and using it as a cross check to your altimeter
    is a great thing. What you really shouldn't do (its both dumb and
    illegal) is for instance using only the GPS track, and forgetting
    about the DG/Compass, and not using some kind of frequent cross
    checking between the GPS and VOR (plus visual references if possible).
    But if you activelly cross check with the other instruments then its
    neither sole means or primary means.

    I don't know what kind of nice aircraft you guys might fly, but I
    never made it past those analog DGs which are fairly small and
    impossible to accurately read a heading down to a single degree. For
    me those are worse than any handheld (except for following radar
    vectors), when you're not under vectoring or following a visual
    reference, you want to fly a ground track, the heading is the means to
    try to approximate that ground track, however the GPS eliminates all
    that bracketing work, and you can fly a given ground track,
    crosschecking the track with the DG and Compass.

    What I do and advocate doing is safer than flying without any GPS at
    all, but of course I would much rather have any SBAS capable GNSS
    panel mount (as long as its LPV certified).
    macpacheco, Nov 10, 2011
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