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0 pointsizacus2y ago0 comments

Err, yeah - the airliners still mostly use INS for their navigation (with corrections, either manual or automatic, depending on equipment and age), but ADS-B indeed needs to report its location from a GNSS "High-integrity position source". So scratch the INS part.

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lxgr2y ago

Pure INS should be pretty rare these days, no?

I believe it's now usually a combination of multiple sources (e.g. ground-based navaids like VORs and DMEs, GNSSs/GPS, and INS to reject most spoofed signals or in case everything else fails).

izacusOP2y ago

Not sure what do you mean with "pure" INS. Primary INS is still standard - as in, all the navigation is driven primarily from INS system outputs.

But, as it always was, it is regularly corrected with GNSS or navaid corrections. As far as I know most airliners still don't automatically enter corrections for INS and require manual input (basically retyping of GNSS data from a screen into a keypad) to put human into the loop which can verify if GNSS is being spoofed. The pilots can alternatively do the correction using VOR/DME navaids or even their eyes if they feel like it.

As far as I know, it's becoming much more common to have INS with ability to automatically correct drift from GNSS in smaller planes (and I'm sure that will make it to airliners sooner than later).

MadnessASAP2y ago

You're both right, the aircraft position as reported to aircrew, displayed on maps, and fed to the flight director (the autopilots outermost loop) is a blended INS/GPS solution. The opensource drone projects Ardupilot and PX4 have a lot of info and implementations of this actually.

However the autopilots inner loop and Flight Direction Indicator (artificial horizon) are going to be driven almost entirely by INS. This is because GPS positions can't update fast enough, are noisy, and don't provide velocity, acceleration, or orientation (outside of even slower position integration). Also those systems are not particularly involved in where the aircraft is, rather they care about where it is going.

I haven't looked into what the requirements of ADSB position information is, I don't suspect that they mandate GNSS but they may mandate a degree of accuracy. From an ATC perspective within crowded airspaces ADSB would be augmented by primary surveillance radar to prevent mishaps, spoofing, and errors.

For what it's worth my day job is aircraft avionics, navigation equipment is pretty much daily for me.

Ps. Hi HN, Reddit refugee and my first post here.

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