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I've read a couple of times that "own-ship position display" is not authorized for use on Class 1 or 2 EFBs (by the FAA), and that both the FAA and EASA are cautioning against that feature's use on EFBs in general. Own-ship position is an aircraft's GPS position displayed against georeferenced charts and diagrams.

Obviously the use of a portable device - iPad or otherwise - should not be enough for primary navigation, but what safety concerns do the authorities have with own-ship display?

Specific accident reports or official citations would be great.

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    $\begingroup$ Can you clarify exactly what "own-ship position display" actually means? I can guess, but I've never heard the term before and a link to a definition would be great. $\endgroup$ – Pondlife Jan 11 '14 at 21:34
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    $\begingroup$ @Pondlife I'm actually having a really hard time finding a legit definition. I'll update the question when I've got something; in the meantime, it's basically georeferencing the aircraft's position onto a chart. $\endgroup$ – egid Jan 11 '14 at 21:39
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Display of ownship's position has a very strong effect on the mental model that the pilot has of it's navigation. When the EFB displayed position is wrong, the change that the pilot will detect that by comparing to other instruments or outside visual are very limited. This is a safety concern.

To have the EFB approved to display ownship's position, the most straightforward way would have been to certify it under TSO C129a "Airborne Supplemental Navigation Equipment using the Global Positioning System (GPS)" TSO-C129a has now been superseded by TSO-C196 which has slightly different requirements.

Often class I or class II EFB will have a GPS receiver that technically could be used as the source of ownship's position. The GPS receivers chips used in are not designed and certified against the "Minimum Operational Performance Standards for Airborne Supplemental Navigation Equipment Using Global Positioning System (GPS)” (RTCA document DO-208), which is a requirement of TSO-C129a or "Minimum Operational Performance Standards for Global Positioning System/Aircraft Base Augmentation System" (RTCA document DO-316) which is a requirement for TSO-C196.

The major technical difference between simple commercially available GPS chips and aviation grade GPS chips is that the latter include a Receiver Autonomous Integrity Monitoring (RAIM) function which does Fault Detection (and Exclusion).

If a GPS satellite would drift out of it's orbit or GPS data gets corrupted in the receiver, an ordinary GPS chip would most likely display a position error, while an aviation GPS chip would either indicate a failure state (fault detection) or still display the correct position (fault exclusion). This protects the pilot from being mislead by a map shift.

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    $\begingroup$ Also, in a portable device without an external mounted antenna, it is much more likely to have part of the available satellites unavailable (blocked by part of the airframe) which makes it much more likely to have a position error. $\endgroup$ – Lnafziger Jan 12 '14 at 13:34
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    $\begingroup$ Do you know of any examples where a pilot's inaccurate EFB caused an accident or incident? Or do you think that the FAA is speculating? $\endgroup$ – egid Jan 12 '14 at 17:36
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    $\begingroup$ I don't know of any particular GPS/EFB accident or incident from the top of my head, but the problem with potential misleading GPS position is real. Although there is a healthy portion "better safe than sorry" involved in certification, the FAA is certainly not speculating here. $\endgroup$ – DeltaLima Jan 12 '14 at 19:20
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    $\begingroup$ This is part of why I always have Foreflight's "position accuracy" element turned on. If it starts indicating less than 5 meter accuracy you probably don't want to trust it. (That indication itself isn't perfect - certainly not enough to rely on as a primary position source - but it's better than nothing...) $\endgroup$ – voretaq7 Jan 23 '14 at 18:47
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I can't speak for EASA, but as far as the FAA the short version (from AC 120-76B) is that In-flight depiction of own-ship position is classified as a major safety effect and cannot be formally authorized for use on a Class 1 or Class 2 EFB.

So basically the only kind of EFB that the FAA wants displaying own-ship position in flight is a Class 3 system (basically a permanently-installed piece of hardware that's gone through all the certification and testing requirements of any other piece of installed navigation equipment, like for example your panel-mount GPS or an approved MFD like a Garmin GMX 200).

As far as I can find the FAA hasn't given an official reason for this (I went on quite a hunt), but I suspect it is out of an overabundance of caution: Class 3 EFBs are subject to strict design and change controls (like any other TSO'd avionics hardware), whereas iDevices, android tables, laptops, and their internal/plug-in/wireless GPS receivers are not.

The FAA has no way of ensuring that changes (like say a Stratus firmware update or an iOS update) won't adversely affect the accuracy of own-ship position display, nor can they guarantee that the EFB software will correctly detect GPS errors and disable own-ship position display. They would prefer you not have the display at all than rely on possibly inaccurate information and wind up flying through airspace you shouldn't be in (or worse, flying into an obstruction) because you were trusting your EFB's position display.


A tiny bit of light at the end of the rainbow, at least for us light General Aviation piston folks:
AC 120-76B is specifically aimed at part 121, 125, 135, 91F, and 91K operators (i.e. "Not light GA").
The rest of us Part 91 folks are supposed to look at AC 91-78 (which talks about EFBs and removal of paper from the cockpit), and that Advisory Circular is blissfully silent on the subject of own-ship position.

That seems to imply that you can strap your iPad to your Cessna's yoke and turn on own-ship position display and not incur the wrath of the FAA - an interpretation you can find others on the internet agreeing with - though it should certainly not be considered a navigational reference (merely "an aid to situational awareness").

It's also worth noting that if you don't display own-ship position data there's nothing that says you can't use it -- e.g. by turning off the little airplane graphic but still centering your map based on your GPS information. I know ForeFlight has this capability.

Standard Disclaimer:
I'm not a lawyer and I don't work for the FAA. My interpretation of regulations is worth exactly nothing.

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