Peter wrote:
Well, INS by itself is completely useless; it needs an update to get it started. About all an inertial nav system can do without that is finding true north, which I believe most can do within some minutes.
Well, in the current climate (of GPS jamming and worse spoofing), of course the IRU (“INS”) is updated on the ground (in Honeywell case of G650 by GPSs) and continuously until de-selecting reference units (GPS, “hybrid”, dme/dme, vor/dme). The “INSs” are very useful, as you describe yourself, for as long their position data is not invalidated by GPS spoofing input data, hence why we de-select them in know spoofing area.
As soon as you reach, from a, oceanic crossing, land fall and ground based navigation stations, the “INSs” will be updated and shortly after archive an EPU level sufficient (or not) to meet RNP for the type of Enroute and Terminal planned.
Nice 
Thanks for posting these.
Of course an INS which is constantly being updated by DME/DME and/or GPS could be accurate enough for a while after the update stops.
Well, INS by itself is completely useless; it needs an update to get it started. About all an inertial nav system can do without that is finding true north, which I believe most can do within some minutes.
Airliner grade INS is a few NM out after crossing the Atlantic (w/o GPS) which is about 2500nm, and I personally saw that in a 747 cockpit pre-9/11, so should be just fine for flying an IAP, having got a fix some minutes before. But somebody decided otherwise…
Peter wrote:
Not a Lear; sorry. A $60M GulfstreamSo you are doing it with DME/DME corrections.
INS not good enough for this?
You got it! ;-)
The “INS” aka IRS→IRU will, as mentioned, maintain high precision for some time after de-selecting the GPSs (keyword “de-selecting” as opposed to getting “spoofed” BEFORE de-selecting them and thus updating the “INS” position with false position data (from the spoofed GPSs)).
Yes, DME/DME, VOR/DME will be used to update the “INS” and maintain a lower level (eventually) of RNP capability (sufficient for the eg. Newcastle International Terminal Arrival (according to the charts details “dme/dme”).
Airborne_Again wrote:
INS alone. Of course an INS which is constantly being updated by DME/DME and/or GPS could be accurate enough for a while after the update stops.
Yes, in the case of the EGNT STAR the GPSs are removed from the equation (IRU position data input) before the initiation of the STAR.
Not sure if it has any interest, but attached are some photos of my latest spoofing experience North of Turkey last week. You can see the GPS 1 is completely without data flicking on/off with a spoofed “far off” from the correct FMS (IRU) position. GPS 2 is a similar status.
Further, the first signs of spoofing in this cockpit (and likely other similar Honeywell equipped cockpits) is the blue CAS msg. ATC ADS-B Transmitter Fail.. Quick action to de-select the GPSs and the 3 “hybrid” IRUs will assure/maintain correct IRU/FMS position data (having isolated the GPSs and “hybrid” position data).
Recovering the GPS position data, say 30-90 minutes later has proven to not always be as simple as one would think. In fact, on multiple occasions now, my GPS 1 has never recovered until after a full power down on the ground.
Peter wrote:
INS not good enough for this?
INS alone. Of course an INS which is constantly being updated by DME/DME and/or GPS could be accurate enough for a while after the update stops.
Good job they are not running a modern war!
Yes, I know there are missiles using INS with crazy accuracy, but the flight time of the missile is short and that’s anyway not what you find in a typical aircraft because there is no need.
Not a Lear; sorry. A $60M Gulfstream
So you are doing it with DME/DME corrections.
INS not good enough for this? Well EASA/Eurocontrol know everything 
Good job they are not running a modern war!
Not the weekend, and not my plane either. But I did my French IR renewal, and an FAA IPC while I was at it, in the Happy Birthday SR22 (F-HBDY). Five approaches, four at Avignon and one at Cannes. Only two are necessary, but practice never hurts.
Meanwhile my engine is back at the shop at Cuers and will hopefully get reinstalled over the next couple of weeks.
Video of last two weeks flying around in DA42. ENGM-LSZG-LELL-LEIB-LSZH-LFMD-LESL-LFMV-LSZG-LFMV-LESL-LESB
Peter wrote:
How are you supposed to fly them, unless you have INS?
The 3 IRUs we have are normally updated via the 2 GPSs. When de-selecting the GPSs the “hybrid” mode of the IRUs become the next most accurate position sensor, initially as good as GPS. So you maintain a relatively high EPU (Estimated Precision) that will almost certainly maintain the RNP (Required Navigation Performance) for the duration of an arrival and approach to landing. If the “hybrid” IRUs are de-selected (or downgraded) the IRUs will look for the next level down, DME/DME, received from available ground sources (ILS/VOR/DME) as the position source. Basically you´re just flying good old RNAV based on ground stations (ILS/VOR/DME) with an EPU within the RNP for the Terminal Arrival procedure, but in the case of Newcastle International not the Arrival Transitions.
Peter wrote:
That plane looks like a Lear, but even so…
Lol. I´m too old and bored to care about aircraft size, speed etc. bates ;-)
Airborne_Again wrote:
That class of aircraft would have DME/DME RNAV, or? Anyway, INS is not precise enough for RNAV/RNP 1.
Yes, of course updates can be made from DME/DME as well.
Peter wrote:
How are you supposed to fly them, unless you have INS?
That class of aircraft would have DME/DME RNAV, or? Anyway, INS is not precise enough for RNAV/RNP 1.
How are you supposed to fly them, unless you have INS?
That plane looks like a Lear, but even so…
… no personal posts, so that’ll be it 🤣
