OK I see, well I can't imagine trying to navigate around the FSX world without a GPS so I'll have to use the default FSX model then. It's an instrument you can pop up through the menu tab or shift 1 for my system. Its a shame that something more similar to the real Bendinx King unit couldn't be modelled for the PMDG verision of JS4100 , but I would imagine it's a limitation of FSX.Thanks for the responseJim V

If the a/c is fitted with FMS it navigates using inertial navigation, only using GPS as a means of updating.You should never use GPS as a primary means of navigation. In UK/European airspace it is forbidden to be used as such. To be used only as a means of confirmation of position.Try flying a model like the VC10 or Concorde which are both fitted with INS as are many other models in the sim. The CIVA INS gauge is one of the finest gauges you will ever see.vololiberista

If the a/c is fitted with FMS it navigates using inertial navigation, only using GPS as a means of updating.You should never use GPS as a primary means of navigation.

Uh...The J41 uses the integrated GPS receiver to provide position data to the FMS. When RAIM is available, which in the CONUS is better than 99% of the time, GPS is the sole contributor to the FMS composite position. When RAIM isn't available, or when the GPS is deferred, the system reverts to using DME/DME, VOR/DME, or single DME depending on what navaids are available in the vicinity. The fact that the airplane uses an FMS doesn't necessarily imply that an inertial solution is available. In the J41 (and in the CRJ as well), without a valid input from one of the sources listed above, the box will only provide a valid position for 30 seconds using last known PPOS and current AHRS data. This is known as Dead Reckoning (DR) mode. After 30 seconds, position data is no longer valid and the FMS is effectively lost until a valid input is regained.

Uh...The J41 uses the integrated GPS receiver to provide position data to the FMS. When RAIM is available, which in the CONUS is better than 99% of the time, GPS is the sole contributor to the FMS composite position. When RAIM isn't available, or when the GPS is deferred, the system reverts to using DME/DME, VOR/DME, or single DME depending on what navaids are available in the vicinity. The fact that the airplane uses an FMS doesn't necessarily imply that an inertial solution is available. In the J41 (and in the CRJ as well), without a valid input from one of the sources listed above, the box will only provide a valid position for 30 seconds using last known PPOS and current AHRS data. This is known as Dead Reckoning (DR) mode. After 30 seconds, position data is no longer valid and the FMS is effectively lost until a valid input is regained.

That doesn't seem all that reliable I have to say!! Airbus and many others use a form of INS as the principle guidance in the manner I have described.vololiberista

The J41 is also a little turbo prop, not a jetliner. Jetliners yes have inertial positioning, but will the FMS will always use what it thinks is the best position, so when an aircraft is equipped with GPS, it will mostlikely use that, if the plane has no GPS, it will probably use the DME/DME, as INS, IRS drift over time. Thus, why you need both IRS and DME/DME to fly a RNAV approach, for if you only went with inertial navigation, you could be dangerously off course.

. for if you only went with inertial navigation, you could be dangerously off course.

Not so!! As long as I have a map I can fly a fix and update the INS and that would be accurate enough to fly across the Atlantic! I don't even need a radio beacon just a paper map.vololiberista

And which fix are you going to find over the atlantic..?Anyway, this is not the topic. The way the J41's FMC works has been described now in detail..

Not so!! As long as I have a map I can fly a fix and update the INS and that would be accurate enough to fly across the Atlantic! I don't even need a radio beacon just a paper map.vololiberista

And then you would no longer be flying with just inertia. And accuracy on flying over the Atlantic compared to the accuracy required to fly an instrument arrival/approach are very different things. When flying purely Inertial Nav only over large bodies of water, certain things are usually done, like using true headings as opposed to magnetic, along with the various other position checks and oceanic updates with controllers. When the plane has GPS, odds are when you finally get a signal from the VOR on the other side of the pond, you will have little course correction required. Inertial only, you will find the change to be far more dramatic.

And then you would no longer be flying with just inertia. And accuracy on flying over the Atlantic compared to the accuracy required to fly an instrument arrival/approach are very different things. When flying purely Inertial Nav only over large bodies of water, certain things are usually done, like using true headings as opposed to magnetic, along with the various other position checks and oceanic updates with controllers. When the plane has GPS, odds are when you finally get a signal from the VOR on the other side of the pond, you will have little course correction required. Inertial only, you will find the change to be far more dramatic.

The VC10 and Trident were both fitted with two Delco Carousel INS units which coupled to the autopilot brought autoland to the aviation industry. In my mind that is accurate enough!!vololiberista

The VC10 and Trident were both fitted with two Delco Carousel INS units which coupled to the autopilot brought autoland to the aviation industry. In my mind that is accurate enough!!vololiberista

Autoland in the VC10 and Trident is based on tracking an ILS localizer and glideslope signal along with other inputs (radio altimeter)

The VC10 and Trident were both fitted with two Delco Carousel INS units which coupled to the autopilot brought autoland to the aviation industry. In my mind that is accurate enough!!vololiberista

KAL007 used INS and is the main reason that INS is no longer considered sufficient. But as has been mentioned, this is (was) a thread about the JS41 FMS which does not use INS.

Autoland in the VC10 and Trident is based on tracking an ILS localizer and glideslope signal along with other inputs (radio altimeter)

Are you sure the Tridents had INS fitted? I didn't think they were long range enough. I know both had a Smith's Autoland but that was done via the ILS signal, not the inertial systems.