Auto throttle ARM Mode 737CL-NG

[rudderrudderrat]

Hi BOAC,

It may be as c100 driver points out. Our manuals were written by the company, based on Lockheed's original. I can remember the term "Alpha Floor" from the manual, but the aircraft only displayed "ALPHA" in the speed window.

It was autothrust adding power to prevent the speed from dropping further - more like AirBus VLS - not as AB does with full TOGA during ALPHA FLOOR. We usually left autothrust in for the approach (belt & braces to prevent flying less than VREF), and disengaged it before the flare.

Potential Tail Strikes (pitch > 10degs) were usually caused by flying too slowly just before the flare, leaving no room to pitch up for the landing.

[de facto]

Quote:'For the B737 the auto-throttle will increase thrust to maintain its minimum speed (the books say approx 1.3 v/s) however what the book does not say is that if the MCP altitude is above current altitude that is true however if below the current altitude then the thrust will close and the elevator will pitch down to minimum speed. Min Speed reversion is an MCP SPD mode.'

c100 driver:
Very interesting thank you so much for this info.You say this info is from an official source?I am very very interested.
You are saying that if Missed approach altitude is set at 5000 feet(and you fly at 6000feet),with A/P OFF and A/T in ARM mode,approaching 1.3vs of your minimum speed for flaps setting, the thrust will close and elevator will pitch down (inducing a nose up?)aggravating the low speed condition??

Company used the ARM mode when landing flaps were selected and app speed set.
I always did turn OFF the A/T during visuals,manual flying at high altitudes..so i guess this the reason i never experienced it.

What i dont get is why Boeing accpets this alpha floor thing in my Fcom if it is wrong.

Concerning the VREF,isn't it based on 1.23VSO plus a 5% safety/regulations margin which adds up to 1.3VS?

Please correct me as what i write is NOT correct as i have no documents to confirm it.

Cosmic RAY,yes if you are flying close to vref on approach or close to the amber band on the speed tape,the aircraft will be flying with 'on the back side of the drag curve?'and you will need much more thrust to get back to the appropriate approach speed.It happened to me last flight on a 900s,around 63T,i was vref plus 2 and needed to use 70% N1 to get a very slow increase in speed,when normally N1 of 60% would maintain the speed...you do feel like flying a c15 during slow flight,pitch for speed and power/thrust for altitude....

Thanks.

[Denti]

I have 3 times seen a high flare manoeuvre and A/T 'kick in' - it can, Denti. It can be hilarious to watch. I watched a fleet manager try to perform a low fly-by. Try it in the sim sometime.

Yup, if you flare way too high that can happen. If any autothrust mode other than GA is or becomes active when below approximately 27' RA (indicated) it will go into RETARD, as was discovered by the THY crew amongst many others.

We never had any issue with it to be honest and no tailstrike due to it, in fact the tail strike risk on the 737 fleet is much lower than on the airbus fleet and highest during take-off using incorrect rotation rates.

[c100driver]

You are saying that if Missed approach altitude is set at 5000 feet(and you fly at 6000feet),with A/P OFF and A/T in ARM mode,approaching 1.3vs of your minimum speed for flaps setting, the thrust will close and elevator will pitch down (inducing a nose up?)aggravating the low speed condition??

Almost correct, the F/D will pitch nose down with the A/P off and the A/T will retard to ARM. If the A/P was engaged the aircraft will go for a LVL CHG descent in MCP SPD

[RobinR200]

Maybe there are differences in wording on the NG. I fly the classics (300&500) and alpha floor protection is mentioned in the manuals.
AFS=A/T+AFDS.
When A/T performs minimum speed reversion its called minimum speed reversion.
When AFDS performs it, itīs called Alpha Floor protection because of the blinking A in the MCP speed display.

Alpha floor being equal to minimum speed when A/T is OFF.
Alpha floor being 5kts below minimum speed when A/T is in ARM (otherwise both could intervene at the same time).

[c100driver]

Hi RobinR200,

I am quoting the CL series not the NG. This is one of the problems with generic discussion and specific aircaft. Boeing does not have a standard aircaft and different customer aircaft can be almost a new type. The same is true of the manuals, and they are written with different build specifications in mind.

There are three sets of Manuals.

1. Boeing Master generic
2. Boeing Master customised for Airline Operator build specification
3. Airline Operator pilot manuals

Number three is written from 1 and 2 but is the property of the airline, and it will probably have the airline name in the header. This version is edited by airline fleet management for the use of crew operating aircraft belonging to the airline.

Boeing don't control what is written in those manuals. What is written in those manuals may not be striclty correct (usually changed for clarity or readability) or the same as 1 or 2 version manuals.

I would have a guess that you are reading from a company manual and not Boeing masters as I have never seen a master that mentions Alpha Floor on a Classic. If you are quoting from a master I would be very interested in the build spec of the aircraft it is written for.

[B777Heavy]

Kenya....A/P off and A/T off

[RobinR200]

C100 you are quite right. The company name is in the header in my manuals.
Thx for clarification!

Itīs nowhere written in our manuals, but in our day to day operation thereīs a general rule: manual flight = manual throttle. Itīs up to the pilot to leave the A/T in ARM or OFF. Because of the protection modes everyone is leaving it in ARM. Iīve never seen anybody putting it into OFF.
The only cases when we select it OFF is during events like TCAS, EGPWS or Stall recovery.

[latetonite]

For those guys clicking everything off for landing, do not forget to add a tad of thrust in case of a G/A. "TOGA" just gives you a FD in G/A mode.