FMS coding

28.10.2004

Submission:

When coding procedures into database and decoding one needs to know whether a fix is "fly-by" or "fly-over" but sometimes it is not clear. For example the SID RIMIT 6A (Sliac LZSL), is the Locator F a fly-over waypoint?

SID BERVA 6A (Bratislava LZIB). The fix, where course is changed from 042 to 357 (R-357 JAN). Is it fly-by or fly-over? SID BERVA 8B (Bratislava LZIB), is VOR/DME JAN a fly-by waypoint?

Is it possible to identify type of fix (by/over) or does it depend on state rules or airline's rules?


Pavel Lebedev - RUSSIAN FEDERATION

Answer or Commentary:

(I.W.

I did not design these SIDs so like you I have no idea about the rational behind them. All the same I can see that they would be difficult to code into the FMS system. In fact these are standard SIDs not RNAV so they should be flown manually. However let us look at them individually, firstly the BERVA 6A.

Looking at the chart it looks like the position I have marked with an arrow is a fly over way point. However one should check the text associated with the SID. This states:


BERVA 6A - Climb on RWY HDG, at 900 ft/ 247 m MSL turn right to HDG 110°, intercept track 042° (bearing from NDB OKR 042°), intercept R-357 VOR JAN to BERVA.


The important part is "HDG 110°, intercept track 042" and does not give a fix to fly over. So in this case I would consider it a fly by waypoint.

Next the BERVA 8B

Once again the SID text needs to be closely studied.

BERVA 8B - Climb on RWY HDG to TP (3.7 NM/6.9 km DME OKR, 3.3 NM/6.2 km DME OB), turn left to track 039° to NDB OB, intercept R-246 VOR JAN (track 066°) to VOR JAN, intercept R-357 VOR JAN to BERVA.

In both instances OB NDB and JAN VOR the SID text does not say "after passing......intercept", it says "to track 039° to ... intercept". So in this case I would consider both as fly by waypoints.


Finally to the Rimit 6A
RIMIT 6A - Straight ahead; at 2600 ft/792 m MSL, but the latest at 16.2/30.0 DME SLC, turn right to L "F", turn right track 307° to RIMIT.

This one is even more difficult to code, even after consulting the text. However this SID suggests that the locator "F" is a fly over way point, as the text of the SID says "turn right..." not "intercept..."

This whole question brings up the point that as procedure designers we must take FMS coding into account as even standard procedures (i.e. to be flown manually) are often coded into an FMS system. I think that care must be taken by procedure designers that the text of any procedure (SID or approach) is unambiguous to the data base coders who may not know the rational behind the design of a procedure.)