Autothrottle ARM B737

[Allan]

Are you allowed to use the ARM function of the autothrottle during manual flight? Boeing does not recommend this, but I do believe that it's good to have the minimum speed protection. What are your thoughts?

[Wizofoz]

I've flown 737's for four different operators.

At Ansett it was SOP to "De-select" speed to leave the AT in ARM for min speed protection (Some choose to call it Alpha floor- it isn't!).

Boeing came out against this as they felt the possibility of uncommanded throttle activitey near the ground increased the risk of tail strike, and the other operators I've flown for have an "All in or all out" automation policy.

I personally liked having the AT in HOLD mode, but Boeing is the final arbiter.

Incidentally, another AN SOP was to fly manually, but leave the AT in MCP SPEED mode. It maintained the bug speed, then went into RETARD at 26ft RA.

[batty]

Can cause problems in the roundout when burning off the Vref + whatever component back to Vref since it could then kick in with the alpha/min speed protection and give you go around thrust just when you dont need it, totaly destabilizing you at the wrong moment....

[Shaka Zulu]

I use the ARM function of the AutoThrottle to fill out my Engine Trend Monitoring booklet without loosing low speed protection.
Especially helpful if sudden turb is encountered!
Cant think of any other operation that would validate the use of it

[LEM]

Boeing came out against this
Intersting, Wizofoz (I personally use the ARM trick...).

Could you tell us the source of this info?

[80/20]

The Boeing FCTM has this statement that the autothrottle ARM mode is normally not recommended because its function can be confusing.
Some features normally associated with the autothrottle, such as gust protection, are not provided during ARM mode.
One example how it can be confusing is when you sometimes get speed reversions on an approach - where the speed bug might “jumps” back up to a higher speed even when you are on target speed.
Many pilots use ARM and this is not prohibited.

[HSWL]

The way I see it is that Boeing designed the 737 and wrote the book based on exhaustive testing by their very experienced test pilots. Boeing generally don't put in a "not recommended" into the FCTM without very good reason. If the auto-throttle is MEL inoperative you can still operate the aircraft which in turn means it is safe to fly with the autothrottle turned off.. Best advice I can offer is to stick to the Boeing recommendation.

[Bumblebee]

I don't know about anybody else.....but i'm holding onto the thrust levers as i'm starting the flare...and if the speed protection is overly sensitive (as it is on some aircraft) and the A/T drops from arm in to MCP Speed when i'm at 20' i'm not going to let it move the thrust levers forwards..!

I think the benefit of having A/T go-around available is an advantage. Otherwise our SOPs mandate a Full energy G/A with manual thrust. Try doing that at Amsterdam with a level off of 1500'.....and think of the workload you potentially create for yourself and your colleague in the other seat. :}

[LEM]

It's always good to start an intersting discussion on this forum :ok:

Yes, the FCTM (page 1.30) states that the ARM mode can be confusing.
Actually, it protects you once, then you have to deselect again the speed mode once activated, or disengage completely the AT.

The go around feature is an advantage.

Below 27 ft the AT should command retard anyways...

[blackmail]

hello every one,

manual flight is just that. ... manual, autopilot disengaged, autothrottle off, flightdirector on/off is your choice. a good trick is to let the autothrottle stabilise on the targetspeed selected on the speedbug so you have already found the average thrustleversettings before selecting a/t off. i find it very useful to fly fuelflows as this is a good representation of the required thrust: fuelflow=thrust x tsfc.
tsfc=thrust specific fuel consumption expressed in kg/hour/kgf or lb/hr/lbf.

as for protections, you have your pilot non flying doing the monitoring of your flying abilities & hopefully he will speak up if you scew it up & even better take action if you really do not heed his advice( case of first officer =pnf).

[alexban]

Hy LEM,nice to hear from you

Actually,Boeing says in the FCTM (1.42 oct31/2003) that a/t use is recommended during takeoff and climb in either automatic or manual flight.During all other phases of flight,a/t use is recommended ONLY when the autopilot is engaged.

This is for a good reason. Although the ARM mode provides the minimum speed protection,usage of a/t arm mode in manual flight can have its down sides during landing,as batty said.
We don't use it ,but we had some pilots doing contracts for short periods at companies that insist on using the arm feature.
The a/t kicked in in a few instances,very close to the ground,almost during flare,not very funny. It can cause a tailstrike very easilly.
My guess,better full manual or full auto.Mr B knows why it doesn't "recommends" mixage.The system was not designed for that.Not like the bus has.
Brgds
Alex

[LEM]

Yeah.... you're probably right.............

I've never had any trouble using ARM, but I'll probably reconsider its use....



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