Authrottle usage 737-700
 

We are still in the "learning" stage of automation at my carrier, so wondering about a limitation that recently came out from flight ops. We are only allowed to use authrottles in the descent/approach if the autopilot is on. Once autopilot is disconnected off, we must also disconnect autothrottles. Flight Ops mgt. claims this is a "Boeing recommendation".

What does every other airline do? Thoughts?

The Boeing Flight Crew Training Manual has this recommendation.
"Autothrottle use is recommended during takeoff and climb in either manual or automatic flight. During all other phases of flight, autothrottle use is recommened only when the autopilot is engaged in CMD".
My company does not mandate this and allows use of autothrottle down to 50 feet on approach even when manually flown.
Hope it helps.

I believe most carrieres stick by the "all on / all off" philosophy.

The only exception being some operators using the A/T ARM mode as a "sorta-alpha-floor-protection-even-though-it's really-speed-floor-protection" during the manual stages of approach.

Advantage 1 - hit the TOGA button and you have the GA thrust setting available (where you may not get full whack but enables 1500-2500 fpm ROC). If in manual - well, you can't really have an SOP that says anything but "hit the target N1", and especially when light, things start happening very quickly! Flew with an operator with this policy, and out of 3 go-arounds from manual approaches, I had to take over 2 of'em :{

Advantage 2 - you can bug and fly Vref +5 without extra wind increment (IIRC! - not on the 73 for a year now :p), since the A/T is still engaged and will correct any underspeed.

Draw-back - if you float the aircraft and don't have your hand on the throttle, it may start adding N1 to keep target speed as you coast 2 feet above the runway.

Throw your SMS at it and see which comes out top ;)

That's blind reliance on automation for you...they forget how to fly the aeroplane.

Actually, nope. It will go into retard flare mode at 27ft but not add thrust in that stage of the landing process. We do use this method from the classics on and it worked well so far, however you have to know how it behaves if you come close to the lower speed limit and on capturing altitudes, otherwise you will be caught by surprise. Oh, and we still do add the wind additives for manual thrust and even that way in gusty weather the low speed protection will sometimes engage as it isn't apparently triggered only by going below bug speed but by trend as well.

Besides, if you are flying in ARM-mode not having your hand on the thrust levers is not really good airmanship anyway as it is basicly manual thrust except for low speed protection.

Denti, I stand corrected! It will of course go to RETARD @ 27 ft RA - see how much you forget when you don't fly the thing for 18 months? :}

In other words - Advantage 2, drawback 0 at half-time :ok:

This Boeing recommendation wouldn't in any way be related to the incident with the Turkish 737 at Schipol earlier this year would it?

Manual flying with the A/T engaged is a weird thing to do, try it.

@Dual ground, nope, that recommendation is much older. Besides, they were in automatic flight with autothrust on (until they stalled), in complete compliance with this boeing recommendation.

As the B737's autothrottle is basically a piece of crap, flying manually with the Autothrottle engaged will cause confusion, unstable conditions and ultimately an unsafe situation in gusty conditions. Don't do it.

I recommend to do the following in gusty conditions: autothrottle OFF, with or without autopilot engaged.

To amplify Denti's point about knowing "how it behaves if you come close to the lower speed limit", I know the days of flying correct speeds on finals are fading, but it was once the thing to do and it was by no means unknown to have the A/T rather unhelpfully 'cut-in' during a landing. There are some weights for a 737 where, particularly at F40, Vref+5 is actually just below or equal to 1.3Vs, at which the A/T mode described operates. The nett result of that is that an ACCURATELY flown Vref+5, and the start of a flare just a tad above 27'RA, and off we go:) Hours of fun and much entertainment for PNF........

Someone did it...gusty wind...low speed...throttles kick off...and BOOM....talilstrike!!!!!

FB

Really? Talestrike is something we havent seen in a long time on our boeing fleet, and FOQA doesnt show any trend in that direction (though we do fly in AT ARM), however on the airbus fleet there is a bad trend towards high talestrike rist at the moment, not on the 321 cause everyone is carefull, but on the 320 and 319.

It seems happened years ago to a crew not very experienced with the 800.
Anyway, it's not hard to believe that a sudden blast 2 feet from the runway can lead a nasty chat with the chief pilot:}:E.

Recently in UK, gusty condition around 40knots, one crew lightly scratched the engine nacelle...it would seem impossible...but it's not.

FB

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This is why the Autothrottle should never be engaged when flying manually. It wasn't the cause of this accident but it certainly made things worse. My company also follows Boeings "all off or all on" philosophy. I've read many opinions here about flying with A/T in arm mode and also feel this is a mistake. It's not an Airbus, I feel like Airbus philosophy is creeping into our Boeing procedures, calling ever damn FMA annunciation for example. As has been pointed out it is not an Alpha floor protection, it is appropriate when using LVL CHG in a descent as a speed protection but not close to the ground on approach. As pointed out, someone should have their hands on the throttles for that.

Our airline also used to use the "arm method" but after two incidents that the A/T being in armed was a partial cause we reverted to Boeing of "all on or all off" and have never had a problem since.

At an informal meeting with some Boeing Company pilots I asked about the "arm mode" on approach and they insisted that the FCTM statment should be followed and that it was placed there following investigations from a number of incidence reports.