Problems keeping to LNAV flightpath in RNAV approach with E195

[LecLightning56]

I have just been experimenting with RNAV approaches with the E195 in P3D v4. In particular, I have been using a challenging approach, the RNAV to runway 02 at Kathmandu (VNKT). The initial stages of the RNAV course, by way of a STAR arrival, appear to have been conducted faultless. However, in the latter stages, the aircraft seems to have extreme problems following the LNAV course and executes a series of rather rapid S-turns in order to attempt to regain the correct track. This is worsened a few miles out from the runway itself, whereupon the aircraft still has serious problems maintaining a controlled flightpath laterally (still under FMS control and autopilot, NAV and VNAV selected and operative), rendering manual take-over to land safely when one might have hoped that, particularly with low visibility, the aircraft should have followed a more accurate profile.

Has anyone had any experience of RNAV approaches and have you experienced similar issues? 

[LecLightning56]

Tried this again, this time with FMS-managed speed, and the aircraft just is not capable of keeping to the correct track between successive waypoints.

I shall throw down the gauntlet to anybody who believes that they can fly a satisfactory automated RNAV approach to runway 02 at Kathmandu with, e.g. E195, all the way to minimums (which you might have to do in poor visibility), without the issues that I have experienced.

One thing that does occur which is odd with the E195, is that a pronounced freeze occurs in P3D v4 (and P3D v3) just before a deviation in the flightplan occurs which is identified by a bearing which starts with a highlighted 'L' symbol in the FMC (e.g. L344 degrees with the L highlighted, presumably meaning a left turn to 344 degrees).

Anyway, I have thrown down the gauntlet for anybody to prove that this RNAV approach (runway 02 to Kathmandu) is possible fully automated with the E195 to minimums (other unnamed products are successful, particularly the smaller more agile twin jets). If you are successful with the E-jets on this RNAV approach, then a video to show how it is done may be of interest.

[FeelThere_Vic]

Have you tried an RNAV approach at any other airport?

[LecLightning56]

I admit that I have not tried an RNAV approach at another airport, but this does not detract from the fact that the RNAV 02 at Kathmandu is possible with accuracy in P3D v4 using an A320, Boeing 737 and Boeing 757. I believe that the Embraer E-Jets are in a category rather lighter than A320 and should be equally as capable of reproducing similar results to the aircraft quoted. It is this consideration which is being contested here and I shall only be satisfied if somebody can provide evidence that the Feelthere aircraft is up to the job for this procedure. If the real-world aircraft is capable of this approach without special modification, the Feelthere model should also be similarly compliant and as a user of the Feelthere model I don't expect to pick and choose an approach procedure at another airport specifically to match the peculiarities of the model itself which have no regard for real-world operations. It is good that the Feelthere aircraft has an RNAV capability but disappointing that one's enjoyment of this facility could be compromised by other issues which are only encountered by trial and error.

My challenge still stands and I await with interest for any user-feedback or from Feelthere themselves which demonstrate compliance for the specified procedure at Kathmandu.

[LecLightning56]

I have now put the E195 through its paces on the Zurich (LSZH) RNAV 14 approach in P3D v4. RNAV seems to work well initially on this approach (the final part is a 12nm straight-in approach on runway heading to RW14), but things go wrong on the final 3.5nm to the runway threshold under LNAV/VNAV control. Before minimums are called (200 feet above threshold), the aircraft drops below the VNAV path suddenly but if left alone climbs slightly later to get back on the vertical profile (again under full LNAV/VNAV control). This does not seem normal behaviour compared with other experiences and disconcerting if the weather is marginal and subject to a decision at minimums. Finally, once autopilot is disengaged, the aircraft has an unusual tendency to track to the left of the runway centreline under conditions of nil wind. Again this tendency seems rather abnormal (what is the driving force for this?).

Please explain whether or not my experiences are not untypical, or if the E195 shouild be more capable of a more accurate flightpath with respect to the VNAV profile defined in the FMS.