RNP AR Nav Accuracy during Arc turns

[GustavoLaPasta]

Hello everyone,

i've recently flown the RNP Y RW30 (AR) Approach into TLV - LLBG.

Unfortunately the aircraft did not follow the ARC after the BG112 waypoint and instead turned immediately with a bank angle of 30deg resulting into an exceedance of the maximum Xtrack Error for the approch leading to an unsuccessful approach. (SEE Attached Images)

I don't know if there is a fix to this issue, maybe Hardy can help us out.
thanks to anyone who will look at this.

Regards

Gustavo

[Hardy Heinlin]

Hello, sorry, I can't help if it's in the database.


|-|ardy

[GustavoLaPasta]

Thank you anyway Hardy

[Hardy Heinlin]

I haven't checked the database yet, but I found out that I might be able to clear that problem by modifying PSX. The reason the FMC x-track error in the above case is on the right-hand side while it actually is left is because PSX detects the RF turn direction by comparing the outbound course with the next inbound course, in other words, if a turn is greater than 180° (as in the above case), PSX inverts the x-track error.

I had implemented this method because turn directions are sometimes incorrectly coded in the databases (L and R letters swapped). I think I'll add another safety filter ...


|-|ardy



Problem solved now in PSX 10.142 (upload in September).

[GustavoLaPasta]

Very good Hardy, thanks for your efforts!

[Avi]

Thanks

[Hardy Heinlin]

PSX update 10.142 is now available:

https://aerowinx.com/board/index.php?topic=4191.0


|-|ardy

[Avi]

Thanks Hardy,

It flies it now very nicely.

Cheers,

[richjb]

I haven't checked the database yet, but I found out that I might be able to clear that problem by modifying PSX. The reason the FMC x-track error in the above case is on the right-hand side while it actually is left is because PSX detects the RF turn direction by comparing the outbound course with the next inbound course, in other words, if a turn is greater than 180° (as in the above case), PSX inverts the x-track error.

I had implemented this method because turn directions are sometimes incorrectly coded in the databases (L and R letters swapped). I think I'll add another safety filter ...


|-|ardy



Problem solved now in PSX 10.142 (upload in September).

The error in coding actually happens in the real world.  It is one reason why RNP AR approaches are subject to a database review and validation, i.e., the "Golden Database" before an operator allows that approach to be used in RNP AR APCH operations.  It is a very time consuming and expensive requirement, and one reason why RNP AR APCH has not moved into general aviation/business aviation.  It is also why were are looking to alternatives to RNP AR APCH, namely Advanced RNP or A-RNP.

Rich Boll
Wichita, KS

[DougSnow]

For FAA operators, each procedure (if it wasn't designed by the FAA) has to be specifically approved by a Sim Validation by a least one operator of large transport category equipment.  For example, I asked our Ops people to get approval for the RNP-AR to Runway 13 at FSIA, since we use the airport as an ETOPS alternate.

The Sr Mgr of Flight Training on one of our fleets used to work at a company and he designed -AR approaches around the world, so he is an expert in all things -AR. When they piled into the 777 SIM to test the procedure (we got the data from our FMS provider), that -AR procedure didn't pass what the FAA would require and approve.  He reported his findings to FAA, and offered to the host nation's procedure designers on slight modifications to the procedure so it could be usable - and approved by the FAA.

[Jeroen Hoppenbrouwers]

Just to add some more real-world experiences with the FAA. Contrary to popular belief  ( :-) ) they are not here to make your life difficult. If you have a reasonable request, especially technically, they will go to great lengths to see whether the request can be made to fit into the regulations. Regulations are usually written in blood so bending them is not done, but working with you to find a way through them is common.

Example: we had to complete an STC on an Airbus A330 that happened to be done in Xiamen, China. We had been preparing it all, aircraft unseen, for about 6 months and then COVID19 broke loose. Normally we would spend a few weeks in the aircraft to measure it all up and to do prechecks before FAA inspection, but all this was now not possible, including the FAA inspection.

We proposed to execute the complete STC (drilling holes, pulling wires, installing boxes, testing everything, inspecting the wires, demonstrating the correct functioning, etc.) remotely, by competent (Chinese local) people on the aircraft in association with remote (video link) FAA and company engineering people. Given the circumstances the FAA agreed to give it a try. I designed, constructed and shipped special test equipment to Xiamen to pre-test a few things without drilling holes, which gave valuable details on how not to do things for real. With those results in hand I fixed some typical A330 naggings and then the hole drilling started and the installation was completed. All remotely.

Last week we received the STC   \o/

Maybe this wasn't the last one we ever did remotely!


Hoppie

[DougSnow]

And for our FSIA issue, since no one else under FAR 121 had asked for the airport before, the FAA head inspector over the C384 (RNP-AR) OpSpec and our pilot who used to design AR approaches were able to speak to each other, so he knew what the FAA would require in the Sim test as far as test conditions required (Max ISA Dev, Min ISA Dev, 30 Kt X-Winds, Mx Landing weight and so on). Instead of the FAA flying the approach in OKC (the OKC Sim base was closed due to the bug), we flew it in our 777 sim here in Memphis. 

Our recent FAA proving run to get some new Oceanic Ops Approvals, in the "table top" inspection we did that via Zoom with the FAA in their offices and us in our conference room as our control center is still locked down, but there was still a Fed on the Jumpseat (well they were going to Hawaii).  So the FAA is getting somewhat comfortable in being creative.