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ILS sidestep procedure...

Started by cagarini, Fri, 11 Jun 2021 00:14

cagarini

On a given 747 FCOM there's this page:


When the PNF selects both FDs Off, then On, an the AP Off, does the A/T not require re-engagement, and will the FMA show SPD|BLANK|BLANK or all blank ?

Thx

Jeroen Hoppenbrouwers


Will

#2
I can't speak to the 747, but we used to do this maneuver frequently into KSTL, my old home base. There used to be LDA approaches to 30L and 12R; the LDA was significantly offset from the runway but parallel to it. You'd intercept the LDA and fly it as a non-precision approach, but as long as you respected the MDA, you could tune the ILS in the second NAV radio for glideslope guidance and treat it as a precision approach. By MDA you'd receive clearance to land, at which time you'd de-select the LDA frequency, tune the ILS frequency, bank to intercept the final approach course while staying on the glideslope, and then finish on an actual ILS. The transition used to happen somewhere between 1000' and 500' AGL, which was as close to barnstorming as it got.
Will /Chicago /USA

cagarini

#3
Thx for your posts.

Yep AT mode stays !


Hardy Heinlin

The A/P will be off for just three seconds or so.

Nevertheless, perhaps they just forgot to mention the A/T disconnection. That would make sense because after the "Disconnect" part they wrote "Re-engage the autopilot and autothrottle".

United744

I don't see the point of disconnecting the AT system?

Hardy Heinlin

On the 744 you shouldn't keep the A/T engaged in SPD mode when the A/P is disengaged. Human pitch corrections are followed by the A/T's airspeed corrections and thus additional pitch variations, leading to human overcompensations into the other pitch direction and continuous oscillations on the pitch axis. The A/P provides a finer pitch control.

United744

I stand corrected. I thought AT with manual flight was permissible. I can certainly see the pitch coupling problem.

Jeroen Hoppenbrouwers

I suppose that the three-seconds-without-A/P would theoretically not require the A/T to be disconnected as well, but that to maintain routine and in the case the A/P would not reconnect or whatever, it is preferred to always go both, period?


Hoppie

dhob

Boeing automation policy is if the autopilot is off, then the auto-throttles are off. However, our company policy allows auto-throttles to remain engaged during approach. Auto-throttles are turned off no later than 100 feet. Actually works well.

Further, the NGFMC has an OPC option that if enabled will automatically retard throttle for flare. This is different than the autoland auto-throttle function of FLARE. This allows for a manual landing with the auto-throttles engaged through touchdown. This option is currently not enabled on our fleet, but many operators use this feature on the 777 or 787.

Another way of accomplishing the ILS side-step without turning off the A/P is to select TOGA while holding the thrust levers, then immediately select V/S mode. The V/S opens to the current airplane VVI which will continue the descent. Select HDG SEL, set the heading for intercept and enter the new ILS into the FMC, and select INTC CRS at 6R. Arm the APP switch. The NGFMC will automatically sequence to the next waypoint.

Britjet

Dhob,
I agree that your procedure will work in most situations, but you may find that you will get an "ILS INHIBIT' message when you try to select another ILS. Switching off both the AP and FDs stops this from happening and allows ILS selection.
Peter

Hardy Heinlin

But he first selects TOGA, then V/S ...

|-|ardy

Britjet

Ah, yes..does this remove the inhibit? I can't remember...:-(

Hardy Heinlin

Yes, it removes the ILS inhibit. It just keeps the multichannel A/Ps and automatic rudder control engaged until a different mode is selected; maybe you were thinking of that ...


|-|ardy

dhob

When TOGA is selected, the glide slope and localizer are no longer captured, thus ILS tuning is no longer inhibited. The FMAs change to TOGA, as such if LAND 2 or LAND 3 was annunciated, it changes to CMD, and the multiple autopilots revert back to one. A priori the rudder is no longer controlled by the autopilots.

Hardy Heinlin

Quote from: dhob on Sat, 17 Jul 2021 07:32
A priori the rudder is no longer controlled by the autopilots.

"A priori" ... "no longer"?

I understand the phrase "a priori" -- but not in the context of the quoted sentence.

I've learned that even the single CMD keeps controlling the rudder when TOGA pitch and roll modes were engaged during autoland operation. In asymmetric thrust conditions (E/O), the pilot has to be prepared to manually kick the rudder in the moment when the ALT mode engages at MCP ALT capture. Is that different in your airline? Do you kick the rudder even in CAT III conditions in the moment when pressing TOGA at 23 feet RA during an E/O autoland?

dhob

No, I should been more clear. The autopilots will continue to control the rudder until either the pitch or roll mode is changed. As discussed, as soon as HDG SEL is selected, the rudder control is no longer. A priori or "it follows", poor use of the phrase.