FMS entry into racetrack

[PENKO]

The title says it all. Ususally one would enter a racetrack reversal procedure as if entering a hold. But our FMS isprogrammed to bypass all that and go straight to some self defined waypoint as I'm sure most of us have seen. So for instance instead of performing an offset entry, the aircraft flies straight to the outbound leg. Now I don't have a problem with that, but where is it written that this is an acceptable approach procedure? Mind you, I'm not talking about an RNAV approach, just the way the FMS treats a standard conventional racetrack.

Looking forward to your answers!

[Capt Claret]

Haven't used the hold function all that often, usually only in the sim but it's always done the sector entry that was dictated by the entry track to the holding fix (B717).

[rudderrudderrat]

Hi Penko,

In the old days we only had a stop watch and an RMI needle to navigate. Hence we had to overfly the holding facility to confirm our "starting" point. We had 3 approved entry procedures which guaranteed we'd remain within the protected holding area.

With modern FMS, we don't need to overfly the facility - we can just navigate to a point on the holding procedure (contained within the FMS approved programming).

[ant1]

I've noticed myself if that it doesn't do offset (parallel) entries. Instead it does a teardrop. I have wondered myself if that was theoretically acceptable.

[DFC]

Have a look at ICAO DOC 8168. There is a section that deals specifically with this.

When the hold is not based at a navaid i.e. it is at a VOR/DME fix etc there are very specific rules about making entries to the hold that are not exactly the same as the Sector 1,2,3 manoeuvres we use at a beacon.

Most if the info from the DOC is reproduced in the ATC section of the Jepps.

[Old Smokey]

PENKO,

I'm not going to mention the maker's name (litigation and all that), but there is one currently used FMS for wwhich there is a CURRENT warning that the FMS MAY make the incorrect entry.

If you want to PM me, we can discuss it, but your use of the term FMS (as opposed to FMC) got my interest, the 'rogue' system is an FMS.

Regards,

Old Smokey

[411A]

Instead it does a teardrop. I have wondered myself if that was theoretically acceptable.
The ATC folks that I have spoken with, say....perfectly OK with them.
If they're happy, I'm happy.

[ant1]

DFC, I looked at the DOC, particulary the table depicting all the different entry flavours and it gave me a headache.

I'll take 411A approach: if they are happy, I'm happy.

Nonetheless, revisiting 8168 was not a waste of time: it reminded me that an offset entry is actually a teardrop and not a parallel as I wrote above.

So I should have written: the FMC goes for a teardrop (offset) when IMHO it should do a parallel. As I just said, not that I care that much, just out of curiosity.

[aterpster]

411A:

The ATC folks that I have spoken with, say....perfectly OK with them.
If they're happy, I'm happy.

ATC is not the approving authority for such matters. Ask them a question like that and usually they will say, "Fine by us." That changes nothing.

[411A]

"Fine by us." That changes nothing.

And, you know this, how?
The holding maneuvering airspace is far larger than what you might expect.
In actual fact, it matters little how you enter, and FAA guys agree.

[aterpster]

411A:

I am quite familiar with FAA holding pattern crieria. I work with it all the time. There are 31 different templates to fit well over 100 combinations of speed, distance from facility, and altitude.

The FAA folks I work with are the TERPs criteria designers. To assure containment the recommended entries become critical in certain circumstances when jet aircraft elect to hold at maximum authorized speeds.

There is some margin for entry selection, generally within 5 degrees. So, when an FMS selects a teardrop instead of a parallel it is within the margin.

I've been to more than one meeting in OKC, which were about all this stuff. I don't recall having seen you there. :)

Controllers don't know squat about holding pattern protected airspace, just as they don't know about CTL airspace, or any other segment of an IAP. However, their airspace managers do and it's them who make sure holding patterns and other IAP airspace doesn't overlap conflicting airspace, etc. Controllers work the traffic and hopefully follow established procedures.

[LLLK]

Aterpster I'm with you all the way - in my experience ATC know a lot about ATC and not that much else.

I think that automated holding is a very grey area - there is no recognised industry standard for FMS/FMC to fly conventional holding/racetrack or RNAV holding (other than PANS-OPS) and different manufacturers have made different design decisions.

There is a standard for RNP holding but that requires so much airspace to protect it that no-one uses it. I think some of the newer boxes actually follow the RNP holding concept but how they ensure that they are inside the conventional/RNAV protected area is not clear.
:hmm:

[STBYRUD]

Hmm, Ive had a Smiths dual FMC unit (on a 737NG) incorrectly select a teardrop entry today from a position with more than 20° offset from the 'reciprocal inbound'... Inbound course 060, on radial 085 inbound towards the station - right turns.... To be honest I cannot remember that I've ever seen the thing to a paralell entry...

[411A]

To be honest I cannot remember that I've ever seen the thing to a paralell entry...
They normally don't, simply because it is normally not programmed into the specific unit.
A parallel entry places the airplane on the non-holding side of the fix, so...in order to make all normal holding entries the same, the tear-drop procedure is used.
Many (all) stand alone GPS navigators used on business jets do the same.

Now lets see...in talking to many TRACON and ARTCC controllers (and supervisors) I have never ever had any of them complain about a tear-drop holding entry procedure.

So, if they're happy, I'm happy....pedantic Eurolanders and malcontent Terps conference attendees, notwithstanding.:eek:

[aterpster]

LLLK:

I think that automated holding is a very grey area - there is no recognised industry standard for FMS/FMC to fly conventional holding/racetrack or RNAV holding (other than PANS-OPS) and different manufacturers have made different design decisions.

The ARINC boys developed holding standards for FMS platforms a long time ago. Alas, these non-pilots failed to really understand the FAA or ICAO specifications for holding.

[deefer dog]

aterpster:

I enter at the fix at the appropriate speed for my level. My choices are TEARDROP, REVERSE or even DIRECT. I pick the FASTEST to suit MY needs, in the hope that my approach will be expedited, as long as I remain on the holding side.

Am I busting any regs according to the FAA or ICAO that ARINC boys didn't understand?

Many thanks, Deefer


The FAA folks I work with are the TERPs criteria designers.


Do they coordinate in any way with the folks who write the regs?

[ant1]

411A A parallel entry places the airplane on the non-holding side of the fix, so...

Well, that's the way we all learned it, isn't it? But the way "our boxes" do the teardrops -when they should be doing parallels- is by turning before the station/fix instead of overflying it and going into the non holding side. This non standard "fly by" philosophy could also be implemented to the parallel entry thus not putting the aircraft in the non-holding side.

The only explanation to the teardrop over parallel choice I can come up with is the following:

At the end of the teardrop you have more room before passing the station/fix after the reversal has been completed.