Database Coding and FMS Behaviour for VPT (prescribed visual flight track) procedures
 

There are some offset non-precision approaches that require a prescribed visually flown flight track from tha MAPt/Minimum to the runway, Nice being a prominent example.

I'd be keen to know how different FMS/databases handle this when the approach is flown using the FMS.

With a database coded like most other approaches, i.e. a missed approach following after the MAPt, "my" Honeywell FMS will sequence from the MAPt to the runway if no missed approach is performed, thereby giving an immediate turn command after the (fly-over) MAPt where continued straight flight would be required (until intercepting the runway centerline).

Now I do fully understand that the visual part should not be flown using FMS guidance but this requires a "split second" disengage of the FMS (as it should not be disengaged before the MAPt to allow flying the MisAP with FMS guidance if there's no contact but cannot be disenganged after the MAPt without entering a turn toward the runway).

IMHO it could also be corrected by entering a "heading" / "vectors" type leg after the MAPt or leaving a discontinuity that will result in the A/C maintaining the last track/heading which our database provider seems to consider against the rules.

A quick web search didn't leave me with any clues about coding standards for situations like this.

Any input on existing coding standards or simply practice on various A/C would be helpful.

Thanks!

VPT procedures and database coding don't go together well. I would suggest that Jeppesen or Lido whoever codes the database for Honeywell have deliberately left that out to avoid crews trying to fly it using any reference to the FMS.


HDG and ALT modes are they way to go. Its an older style procedure and should be flown with more basic autopilot mode selections. Not everything can be RNAV based.

The Jeppsesen coding I have seen causes the procedure to suspend at the MAPt, whether it be the runway or 4 miles prior to the runway (KTVL as an example). If the pilot intends to land he still has the final approach course available during suspend. It it is an offset course, he has to manually align the airplane with the runway. That's why offset final approach courses intercept the runway center line extended several thousand feet prior to the AER.

ARINC 424 coding requires a terminator at the end of each segment. Depending on the procedure, the coding reflects the LTP/FTP, TCH, MAP, RW, etc. to provide the required information such as GPA. It isnt really how the individual databases handle it, it is about how the procedure was coded.
In the coding for this discussion, something like this may be coded:

http://i68.tinypic.com/s5d9as.jpg
or

http://i63.tinypic.com/znoevd.jpg

or
http://i65.tinypic.com/6putd2.jpg

AF: if I understood correctly what you ask for, I am afraid it is beyond the basic logic of the device.

Some pictures before we continue

https://s19.postimg.org/u45zlfnjj/nice04_a1.jpg

https://s19.postimg.org/3khzx1cdr/nice04_a2.jpg
courtesy of Lufthansa FlightNAV, Zurich who I hope do not object much.

After seeing the first plate, try this coding example:

http://i64.tinypic.com/2ynmbeq.jpg

Note: All of these examples are from ARINC 424

Could you suggest coding for G/A with immediate right turn after MAPt (as in Nice) whilst retaining the RWY THR WPT? I think that's what AF looks for but is impossible.

As to my understanding, the FMS logic does not activate the missed approach unless the TOGA button is pressed OR the missed approach is activated on the CDU.

As this approach requires a level turn for the go-around, the latter would be used.

IMHO that means unless the missed approach is activated, the sequencing continues after the MAPt, sequencing to the landing runway by default.

So I suppose it should be possible to enter a "heading", "track" or even discontinuity leg after the MAPt that would result in the A/C continuing straight ahead (or at least not "jerking" towards the runway) when doing nothing at the MAPt.

I am not trying to fly the VPT using the FMS, just keeping the FMS from turning where it shouldn't turn.

Best to look up Visual RNAV. Visual RNAV and Visual RNAV RNP were trialled at Nice, I believe Air France is currently flight testing with ProSky. JetBlue uses RNAV Visual into JFK.

http://i67.tinypic.com/15etyzs.jpg

You want the actual coding?

Sure. Would be interested to see how that is coded.

Me too. /reply not too short now/

hahaha...you guys are funny! Even if I could, you know how much that code costs/worth!

If one can't fly the VPT into Nice, you shouldn't be in the front of a plane.

GF

GF, that's uncalled for. :=

Simple question, if the FMS produces reasonable results for RNAV VIS in TLV, why not in NCE? Understanding my FMS helps me not be a slave to it. Besides, something tells me that OP has rather significant experience in INN ...

FD, there is RNAV VIS to many airports, but currently, AFAIK, it is all custom procedures that specific airlines have paid for.

As shown by the plates, there is RNAV VIS in the works for NCE.

If you want to understand the FMS, it would be a good read to review the ARINC 424 coding manual. There are nuances between the different manufacturers, but they are all pretty close. ARINC 424-17 (older)

You want actual coding for exactly what APT/RWY/APP?

TLV: This can be a confusing procedure, (especially the Jepp plate (GPA?) even though the waypoints are shown as flyby, the pilot must make sure to flyby the waypoints, not begin the turn at the waypoints.

http://i68.tinypic.com/hueydi.jpghttp://i63.tinypic.com/28i5gts.jpg

Flying an RNAV Visual is really flying two simultaneous approaches; an Instrument Approach and a Visual Approach. You must navigate via FMS to maintain the published track to touchdown while, at the same time, flying a visual approach which requires keeping sight of the terrain, airport and/or preceding aircraft.
Important to remember that these procedures are usually not coincident with the PAPI.

I am indeed able to fly that VPT even without any FMS at all but still find it annoying and less than optimum use of equipment that the FMS commands a turn when no turn is required because the interaction between the database and the assumptions the FMS designers made clash with reality for offset approaches.

I do know about ARINC 424 leg types but some FMS manufacturers are less generous than others in giving away the abilities of their kit in those manuals usually handed to pilots...

As posted it's of course possible to disengage the AP before the MAPt to avoid the jerk at the MAPt, and 99,9% of cases one will be visual well before the MAPt given the weather Nice is blessed with.

It's more a matter of elegance than ability.