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B737NG_Pilot
15th May 2013, 12:08
There are certain B737NG Aircraft, with AFDS deselected, and A/T in the ARM Mode the A/T Retards at 27FT, irrespective of the type of Approach being conducted. There is nothing in the FCOM or FCTM, that explains this behaviour.

.. Thanks

BOAC
15th May 2013, 14:29
I think all 737. 'ARM' can make for an interesting approach in the (rare) event the approach is flown at Vref+5 and then back to Vref-5 in the flare, especially at F40..

SR-22
15th May 2013, 15:59
Why would you keep the A/T armed during a manual landing? That contradicts how Boeing says it should be done

BOAC
15th May 2013, 16:11
Well, I wouldn't but some might.:)

ant1
15th May 2013, 22:16
I'm writing from memory here and if I recall correctly it's 27ft or 24ft depending if it's single or dual channel.

On long runways I've waited, out of curiosity, to see them go into RETARD mode and many times this has not happened (-800).

This SPEED OFF method, which after some incidents is now discouraged by Boeing, is supposed to give you underspeed protection (Alpha floor as it appears in the 737 manuals and no, tonight I'm not quoting the exact volume and page). I have tried it on the sim on an ILS, you don't get Vref protection, no selected speed protection either, the A/T Alpha floor will engage the A/T in SPEED mode approaching stall speed. The trim wheel will insist on grabbing your attention for what seems an eternity before the Alpha floor gets any chance to do it's job.

You can read about this feature on the never ending Turkish/AMS thread

Off to sleep

Papa_Golf
15th May 2013, 22:31
I have a question similar to the one posted in this topic.

What might happens if during a single channel approach someone do not disengage the AP. Would the aircraft continues to fly the vertical profile until it crashes onto the runway? Would it instead disengages or revert to basic CWS modes?

Did not find anything about it in the FCOM2.

ImbracableCrunk
16th May 2013, 00:43
The plane will autoland single-channel. (That according to the last few sim instructors I've had.) No 400' bias trim, but it'll still flare.

Don Bobbio
17th May 2013, 21:52
It won't flare. You don't get "flare armed" in single channel. Only in dual channel you will get it. In single channel it will just follow the glideslope untill it meets the concrete with existing vertical speed.
Regards

ImbracableCrunk
17th May 2013, 22:19
Don Bobbio:

It won't flare. You don't get "flare armed" in single channel. Only in dual channel you will get it. In single channel it will just follow the glideslope untill it meets the concrete with existing vertical speed.


Are you basing at on the fact that you don't get a FLARE ARMED, etc? That's true, of course, but as the instructors explained the flare logic is still in the approach mode, annunciated or no.

I have no first-hand knowledge since when I'm in the sim I'm not testing A/P modes, but that's what they told me.

BOAC
18th May 2013, 08:05
There is an ancient thread somewhere about 's/channel and flare'. I never got to prove or disprove it, sim or cockpit.

Don Bobbio
18th May 2013, 08:47
Imbracablecrunk,

The fcom is quite clear about it. Flare and touchdown capability is not available in single channel.
If flare is not armed it cannot engage.

Just recently, a crew in my company wanted to set up for an autoland but they pushed button's in the wrong order and they didn't properly check fma's. They didn't get a 'flare' armed indication and made a rough landing.

Best to try it in the sim sometime. Only takes a few minutes.

ant1
18th May 2013, 10:22
As we all know the GS "flares" at a certain height above the RWY (coincidentally around 50ft?, can't remember any more). Maybe that's why you get some kind of flare single channel. Wouldn't do it on the real thing but why not try it in the sim next time you go for a ride?

despegue
18th May 2013, 10:48
No.
The aircraft will NOT flare on a Single channel ILS autoland.
Only the comparison of the dual channel autopilot will provoke an arming of the flaring mode, an accurate backtrim ( used in the flare mode by the dual channel autopilot by the way) and a flare mode activation.

galdian
18th May 2013, 11:12
SR-22

NO - not quite right regards Boeings statement (unless the FCTM has been seriously re-worded in the last year or so).

Boeing do not NORMALLY recommend....however where the Training Department are capable and the line pilots are capable and the concept has been demonstrated....then Boeing are happy for the procedure to be used.

Manual operation? Regardless of whether disconnected or speed deselected (ie armed) assuming a normal approach or operation the PF has to MANUALLY move the thrust lever, so flying with A/T disconnected is...manual and with speed deselected (ie armed) is...manual.

Benefits? Should you be distracted and your airspeed decreases in ARM mode the system will (politely) firstly suggest you're an idiot and allow you to correct things before proving you're an idiot and applying power; when disconnected you go straight through to proving you're an idiot courtesy of stickshaker.
Not to mention the immediate application of power in a GoAround (assuming TOGA is pressed).

Any idea the number of GoArounds that are f**ked up in one way or another?
Having power immediately applied and trending the aircraft AWAY from the ground not the worst thing for safety IMHO.

Finally a question (and apologies if my understanding is incorrect).
I believe the A/T on B777 and B767 can be "turned off" however Alpha Floor protection always remains and cannot be removed by the pilots.

Why is Alpha Floor protection good safety for 777/767 passengers but 737 passengers only deserve a stickshaker, stall and VERY hard (probably off airport) return to earth?

Cheers.

galdian
18th May 2013, 11:19
Separate Topic regards Single Channel approach with A/T ARM, maybe obvious but:
- as above ARM mode is a manual operation UNLESS speed decreases towards a stall;
- 2 seconds after touchdown A/T will disconnect (as per dual channel ops).

Cheers.

Cough
18th May 2013, 12:27
Going back to the s/ch autoland...

I can only talk classics - On a dual channel autoland with the trim bias coming in, the control column goes from a forward position to quite an aft one (of course not helped by the pitch power couple when the A/T retards the thrust levers.) This is quite a lot of control authority that the system needs in order to achieve a satisfactory autoland.

Single channel, without the trim bias I don't see how a reliable autoland is achieved. I have heard there is a limited attempt at a flare which I would have used in dire straits, but I guess this is limited by the control authority of the autopilot...

How much of this is relevant to the NG I dunno!

SR-22
18th May 2013, 13:16
From the latest Boeing 737NG FCTM:

Autothrottle Use

Autothrottle use is recommended during takeoff and climb in either automatic or
manual flight. During all other phases of flight, autothrottle use is recommended
only when the autopilot is engaged in CMD.
During engine out operations, Boeing recommends disconnecting the autothrottle
and keeping the throttle of the inoperative engine in the CLOSE position. This
helps the crew recognize the inoperative engine and reduces the number of
unanticipated thrust changes.
Note: The autothrottle logic on some airplanes allows the autothrottle to be
physically engaged during engine out operations.

Autothrottle ARM Mode

The autothrottle ARM mode is normally not recommended because its function
can be confusing. The primary feature the autothrottle ARM mode provides is
minimum speed protection in the event the airplane slows to minimum maneuver
speed. Other features normally associated with the autothrottle, such as gust
protection, are not provided. The autothrottle ARM mode should not be used with
Non-Normal Checklists. Some malfunctions that affect maneuver speeds cause
the autothrottle to maintain a speed above approach speed.




And:

The autothrottles should be disconnected when the autopilot is disengaged.

BOAC
18th May 2013, 13:58
As I posted at the start, anyone who actually flies 'recommended' approach speeds will find that there are (on the 73 Classic anyway), weights at which Vref F40+5 triggers the so-called 'alpha-floor' in ARM. However, given that this condition (accurate speeds) is very rare, it normally goes unnoticed.

I once sat next to my Fleet Manager as he flared 'high' in ARM and in came the A/T. It was a graceful flypast of the landing zone.:)

galdian
18th May 2013, 23:54
SR-22

Thanks for C&P, and there it is:

"Authrottle ARM mode

The autothrottle ARM mode is NORMALLY (again, NORMALLY) not recommended..."

Refer to my previous as to when Boeing WILL accept its use.

BOAC - we had a lot of guys come off heavies, in the SIM they were allowed to flare high (50'), speed deteriorated....and the autothrottle cut in.

THE SYSTEM OPERATED AS IT SHOULD FFS!!...it was the numnuts in the left seat and the Instructors seat who were dysfunctional and should have been M.E L'D :}

Cheers.

SR-22
20th May 2013, 18:33
Well I guess you can always play around with words.. but I think it states pretty clearly, "normally" or not, but main magic words here are "NOT recommended" and Boeing would not have put it there for no reason.

Denti
20th May 2013, 20:53
Alas, boeing is quite happy to change that advise quoted above if they are happy with additional training on the 737 that covers the AT arm mode. They even issue a different FCOM in that case that says about AT use:

To simplify thrust setting procedures, autothrottle use is recommended during takeoff and climb in either automatic or manual flight. During all other phases of flight, autothrottle use, other than in the ARM mode, is recommended (if serviceable) only when the autopilot is engaged.

The autothrottle ARM mode feature provides minimum speed protection in the event the airplane slows to minimum maneuvering speed.

ssangyongs
21st May 2013, 01:37
Approach (APP) Mode Single A/P

A single A/P ILS approach can be executed by engaging only one A/P in CMD after pushing the APP mode select switch. Single A/P approach operation is the same as dual, with the following exceptions:

• full automatic flare and touchdown capability is not available.FLARE is not annunciated and stabilizer trim bias is not applied

• A/P status of SINGLE CH is annunciated for the entire approach after localizer capture

• an A/P go–around is not available.

So what does it mean by 'full automatic flare and touchdown capability'? if OK465 that aircraft will still land smoothly (possible without flare?)

galdian
21st May 2013, 10:46
SR-22

Well "play around with words or not" I have used ARM mode for 24 years and it has never "bitten me", has given me good advice on occasion - as well as assisting with positive thrust during Go Arounds/Missed Approaches.

I DO find it strange that any airline would not strive to understand the increased SAFETY associated with ARM mode, in effect making a positive decision to operate with LESS safety than is available.

"...Yes M'lord, XXXX Airlines decided the Management/Training Department/Line Pilots were too lazy or too stupid to understand the "ARM" system so it was better to ignore it, albeit with a reduction in safety."

M'lord: "And prey tell how you convinced your passengers that operating with less safety was a plus for them??" :p

Just having a bit of fun :ok: although in the big picture ARM mode is good **** and enhances/improves safety, EOFS!

Cheers

markoaviator
14th Feb 2020, 09:46
Flare is possible in single channel autopilot,not like dual-channel with stabilizer trim nose up but aircraft will make flare and landing.
And it is proven to me and shoven in real FFS by the instructor and said just in case of life saving (with one engine and or no more fuel with low visibility