B737NG A/T Retard in ARM Mode
 

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

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..

Why would you keep the A/T armed during a manual landing? That contradicts how Boeing says it should be done

Well, I wouldn't but some might.:)

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

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.

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.

B737NG A/T Retard in ARM Mode
 

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

Don Bobbio:

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.

There is an ancient thread somewhere about 's/channel and flare'. I never got to prove or disprove it, sim or cockpit.

B737NG A/T Retard in ARM Mode
 

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.

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?

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.

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.

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.

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!

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.

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.:)

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.

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.