ATS a la mode

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Rotten Apple #1
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ATS a la mode

Post by Rotten Apple #1 »

Well, Dang Me if'n I learnt somethin' new bout that fancy cruise control on the NG.

Supposing one is on a visual approach, at a thousand feet above aerodrome height, the Flight Directors (FDs) are cycled and the missed approach altitude set in the MCP (as per SOPs).

I have known since initial training that cycling the FDs would remove the lateral and vertical FD bars, and place the Autothrottle System in either:

ARM, or MCP speed.

If the vertical mode was initially Level Change, the autothrottle goes to ARM. If the vertical mode was Vertical Speed, the AT goes to MCP SPEED.

What if the vertical mode was VNAV at time of FD cycling (such as on a RNP approach or Non Precision Approach with vertical guidance)? The ATS is initially in FMC SPEED. What does it go to post-cycling? ARM, MCP SPEED, or FMC SPEED?
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Rotten Apple #1
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Re: ATS a la mode

Post by Rotten Apple #1 »

Well darn it, it goes to ARM. It surprised an F/O and myself a few weeks back on approach into PVR when it did so. Perhaps I knew it at some time but forgot. Anyway, not a big deal. BTW, pressing the SPEED button on the MCP places the ATS into MCP SPEED, if that's your happy place.

That's all. I'm going back to being grumpy about something. Anything. The last four days of having fun on my pairing has me drained.
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CCR
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Re: ATS a la mode

Post by CCR »

So...outside of the academic interest, and unless I'm missing something from the FOM, why would one recycle the FD's on a VNAV (RNP or NON-RNP) approach? I flew the PVR VOR DME 2 22 approach the other night and for interest sake flew it to the 770 minimums to see what the spatial orientation looked like. At 1000' the MA was set and then at 770' I disconnected and flew onto the center line utilizing the PDI for vertical guidance versus diving for the PAPI. I don't believe there is a provision at this point to cycle the FD's. Insight? :rolleyes:
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jjj
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Re: ATS a la mode

Post by jjj »

Don't feel like pulling out the book so I'm prepared to be incorrect on this one but:

For non-vnav non-precision approaches the pitch mode "shall" be v/s,

and the FD's shall be cycled at the appropriate time.

MCP SPD is obviously most desirable in most cases and flying with bogus FD info in front of you is not desirable.

CCR, I do not argue that your VOR aproach was unsafe, but I do not believe it was by the book.


Cheers all!


jjj
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CCR
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Re: ATS a la mode

Post by CCR »

As far as I know, the VOR DME TWO 22 approach meets the criteria to conduct a Non-RNP Non-precision VNAV approach. Maybe I'm talking about apples while JD is talking about oranges. JD?
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Ryan Coke2
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Re: ATS a la mode

Post by Ryan Coke2 »

Triple J, you are talking about non-vnav approach, ccr was doing a non-rnp w/vnav path guidance approach.

And yes CCR, what you did was correct, no need to cycle the FD's. And I would agree, I don't know why JD ended up doing this while in VNAV other than having too much fun on his pairing.

Another note though; be weary of the coding of the database for an approach when in VNAV--if it does not have the runway threshold coded in you may get vnav trying to fly the missed when you were planning to continue and land, or you may also get the autothrottles going to arm (as JD described) if there is a disco after the missed approach point.
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Rotten Apple #1
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Re: ATS a la mode

Post by Rotten Apple #1 »

Guilty of 'lengthy-internet-forum-post-by-blackberry' disorder (Plus bailing to catch recip. jumpseat on Jazz trip home. Thank you Captain and crew!!) I think it is apples and oranges as CCR said.

Anyway, the set-up: Daytime VMC trip onto 22 at PVR. Absolutely right, VNAV could have been used for the whole approach. This day in question, traffic ahead (arriving from south-eastern side of approach) slowed considerably, and it was necessary for us to manoeuver over to the left significantly to join the extended runway centerline behind him. As the VOR DME 2 RWY22 track inbound to the airport is offset from the centerline (is it 9 degrees?), it was necessary to disregard the FD lateral guidance. Rule number 7 of EFIS flying is to clear PFD of junky information that is not to be followed precisely.

Hence the cycling of the FDs, on this, a visual approach, as cleared by PVR ATC. In truth, maybe we could have bled the speed earlier and not crept up on guy in front of us so quickly. Can't recall the gradient path for the constant angle approach, but I recall it's higher than 3, no?

The setup for the post was misleading. Just thought it interesting that the cycling ended up sending ATS to ARM. As I said, I may have known this at one time during six years on the machine, but as it is the norm to disengage autopilot but keep the FDs on for the entire approach, one would normally have seen FMC SPEED the whole way down, and then have disengaged the AutoThrottles prior to touchdown.
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Last edited by Rotten Apple #1 on Mon Apr 06, 2009 7:08 pm, edited 2 times in total.
jjj
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Re: ATS a la mode

Post by jjj »

Check,

Did not realize that the approach met the criteria for VNAV.

By the book - love it!


jjj
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CCR
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Re: ATS a la mode

Post by CCR »

Can I complicate the matter?

Thought about it and then chatted with Ian F. No real SOP for this as it is a "one off". Either way doesn't seem to be an issue as long as you are aware of the modes you will see. Thanks JD for opening this discussion. Next time I'm there will try the opposite way and see how I like it.


The coded GP is 3.55. PAPI is 3.0
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