Originally Posted by
ABUSMAN
Wow~I'm speechless to see your tremendous knowledge. Many thanks.
Too many information to take in, so firstly let me summarize it.
1. ADS-B data can be either picked up by ATC on the ground or by Satellite which are fed to a contracted subscribers(ATC, or Flight Radar24 etc.). The first case requires antennas and processors etc. to display targets while the second case only requires processors to assemble data obtained from data provider such as Aireon.
2. ATC only care about what's written on the filed flight plan. If it is a LAT/LONG coordinate, it is LAT/LONG not ARINC424. However ATC do receive ARINC424 standard notation in reality which they are well aware of.
Okay!
To clarify my previous question, let's take an example in the second last page of NAT OPS Bulletin2018_003(Rev01).
Filed route contains a waypoint 5230N02000W.
FMS can only display this waypoint as N52W020 due to its capability(Max 7 digit)
1. In this case, when ATC picks up FMS route, Half degree is missing. So my understanding is that to avoid this confusion it's better to use a special format that ARINC424 use which includes letter 'H' to represent a half coordinate. I stand here to be corrected.
2. Ultimate question (Reason why I started this thread)
If a filed route contains a waypoint 5200N02030W, FMS can only display this waypoint as N52W020. Again, this is not representing a real coordinate. Unfortunately there's no special format to represent Longitude half degree coordinat in the ARINC424 standard. Pilot always crosscheck the waypoint coordinate to see if the filed coordinate is correctly inserted into this waypoint. However there's no way that ATC can check whether this waypoint is correctly representing a filed coordinate by only looking at the name of the waypoint.
I hope my question is better described this time. Again, any comments are highly welcomed.
From your summary, I agree with your first point #1. Your first point#2 I agree with part of - what I don’t agree with is that ATC are aware of arinc424. Yes, we know it exists, but our systems are all different and generally don’t support it. We want what was filed in the FPL (either lat/long or 5LNC identifier)
the standards and guidance are described within bulletins for each respective airspace. Whilst that’s confusing and a lot of work, the general guidance can be found within ICAO Doc10037 (Global Operational Data Link (GOLD) Manual). An OUT OF DATE copy can be found at
https://www.skybrary.aero/sites/defa...34.pdf#page114. Chapter 4 deals with flight crew procedures and the relevant paragraph may be 4.4.6 which deals with CPDLC reporting procedures.
Within NAT HLA the big units automate the use of UM137 (Confirm Assigned Route) messages and expect to receive your DM40 by way of response. The ground atm systems compare what’s received with the safe trajectory stored within the ground system and alert the controller if they don’t match. Controllers use these alerts to prevent Gross Navigation Errors (and intentions), in effect preventing safety risk events.
The reference here I think answers your question ( I had to do a bit of digging to find the reference) which essentially means that 424 is used on board to accommodate database and display screen size constraints, but it permits full access to coordinates. When dealing with ATC, they want to know these coordinates and aren’t interested or can’t accept ‘424 - flight deck shorthand’ in communication.
HTH