Boeing 737 Autothrottle System

[woofer]

Going through the 'Boeing 737 Operations Manual', I gather that the autothrottle can be used for a manually flown precision or non-precision approach down to landing. Are there any Boeing 737 pilots who use the auothrottle for most manually flown approaches, and if so, is it an approved standard operating procedure with your company.

[Earthmover]

For us, manual flight = manual thrust unless you are operating to a thrust target - such as Take off, initial climb or Go-Around. If we are manually flying to a speed target, the autothrottle is disconnected. The reason is the large pitch couple associated with thrust changes. I believe most 737 operators adopt this technique - and I've been told that Boeing instructors teach it.

[rr892igw]

In our company A/T use is recommanded even in manual flight.All the way to touch down with auto retard.However if to much hunting by A/T is better to DESELECT MCP speed mode leaving A/T in ARM mode which keeps alpha protection active just in case speed drops below target or gust or windsheer.

[Earthmover]

rr892igw, absolutely - we do the same, but slightly different philosophy in that we always leave AT in ARM on final if flying the approach manually - it's the best of both worlds, since you don't have destabilising thrust/pitch inputs, but the protections are there as you say. BA do the same I think, but I know at least one other large operator who doesn't.

It's amazing how many ways there are to skin the same cat!

(edited after detecting that I had written complete garbage on my first try!)

[FlapsOne]

Auto-retard in manual flight.......get real guys!!!!!!!!!

[Slasher]

Our mob (or should I say the mob I worked for till recentley) had a policy of landing the 737 with AT deselected (ARM). However I found years ago its a good idea to keep MCP SPD in all the way down during a non-precision (NDB or VOR) app at night when nature is hurling huge buckets of water in your face and all you have are fuzzy lights ahead (and no CL or TDZ lighting) and the light of an odd angry lightning bolt to guide you.

In wx like this I used to keep the thing in. Stick to vertical profile as best you can. The AT will do a reasonable job of taking care of speed at a critical time when just trying to keep the bloodey aeroplane straight along the extended centreline in varying strong xwind takes precedance. Just as the AT retards, flare slightley and bobs your uncle. Gives you an idea where the hell the ground is too.

In good wx most pilots deselect SPEED mode at about 1000 ft. This still leaves in all your speed-protection sh!t. Only the Quake kids keep the AT in MCP SPD mode all the way to the deck till RETARD so Ive noticed.

[rr892igw]

I had the privilege to fly A330 and B777 as and FO before taking command on the B737,I guess that's the culture we inherited in this company.we are very use to flying manual with A/T to touch down.It is REAL to fly manual with auto retard,Flap One!:p

p/s: Its even better to have RA auto callout in sh*tty wx.(no visual height perception required)

[FlapsOne]

Then you are not flying manually then!

Do you ever fly an approach in the 737 with the autopilot engaged and manual throttle?

[QAVION]

I was under the impression that the thrust idle command came from the APFD system on all Boeings? Without the APFD active, the thrust mode will remain in "SPD" (i.e the thrust levers will remain above idle... and you won't have Autospeedbrakes, Reversers or Autobrakes on touchdown).

Rgds.
Q.

[Track]

From the 737 FCTM: "To simplify thrust setting proceduers, AT use is recommended during T/O and CLB in either automatic or manual flight. During all other phases of flight AT use is recommended only when the autpilot is engaged."

I guess this is why we disconnect AT but I have to admit never to have flown with AT engaged during manual flight. I recall something about PIT due to AT engaged in manual flight? Anyway, I think the ARM technique on approach sounds useful during GA.

[PILOST]

Flaps one, yes we do.

The MEL allows an a/c to be dispatched with A/T inop.So if you're doing multiple sectors on a loooooooog day you will use the a/pilot. :rolleyes: Yes, even on approach.We are trained for that.....that's why we get the big bucks! :D

Again, this is all left to the operator & how they train the crew.

:cool:
PILOST

[FlapsOne]

Yes of course if it's broken. That's why you can continue on a cat3 if the A/T fails. That wasn't my point.

You woudn't do it as a matter of routine though, surely!

[PILOST]

To answer Woofer's question, yes there are some operators that require the A/T to be used even in manual flying (when available).Mine is one of them.This procedure is approved by Boeing.

As eloquently put by Slasher in his earlier posting, the need to have the A/T operational throughout the flight regime especially on approach is a matter of safety & common sense, not to mention saving our butts! :D Our theatre of operations require us to fly in unpredictable tropical weather & making non precision approaches is part of our staple diet.Hence the need to have all available options ,automation & redundancies working for us & not against.

A pilot who is worth his or her salt would be profficient to handle all aspects of the a/c flying characteristics with & without system failure or failures.So having the A/T working with us is a wise option.As for the argument of throttle hunting & trim changes, that is easily addressed by selecting the ARM mode for the A/T.Again respective operators will have their views on this but like I said ours has been thought throughly before the proverbial "pen unto paper".

Flaps one, all our pilots are checked to fly at 'pure manual' mode but why do you leave yourself exposed to the 'elements'?It is a matter of policy & it's just that.

Safe Flying all
:cool:

[Eckhard]

I watched some-one (retired 744 skipper) fail an airline Sim assessment in the 733 'cos he left the A/T in whilst manually flying. The speed was +/- 10-15kts and the altitude +/- 300ft. It was painful to watch him struggling with a not very helpful (management) co-pilot. When it was my turn, I took the A/T out and passed!

O.K. it was only a sim but I certainly think it destabilises you slightly unless it is in a thrust mode, as noted previously.

We teach the same on the 744, by the way.

Qavion, the 733/734 A/T will retard automatically at 27ft RA (from memory), even on a manually flown approach.

A merry Xmas to all my readers! (O.K. my reader!)

[QAVION]

"Qavion, the 733/734 A/T will retard automatically at 27ft RA (from memory), even on a manually flown approach."

Thanks (again), Eckhard...
After some extra reading, I see that there is an "OR" logic gate in the A/T idle command.

The throttle on the 733/734 will retard 0.8 seconds after Autopilot flare (with A/P engaged) OR....

".... at 27 feet radio altitude if the Autothrottle is in speed mode and the flaps are greater than 12.5 units."

Cheers.
Q.

[loewe]

In my company:

Auto flight: At least one A/p in CMD and A/T on
Manual flight: Other than above configuration

The recommended procedure is to use A/T for all type of approaches.

We just have to pay attention at 27 feet RA, that A/T will retard, sometimes we have to guard the throttle so it will not retard to soon/fast.

The advantage to use A/T during manual approach is we don't have to increase FAS in gusty condition, because A/T through airspeed and acceleration sensing, it will correct wind and gust.
The FAS will remain in VRef + 5.

[LEM]

Good point, loewe.

However I have always found quite scary to trust the autothrottle Vref+5 in gusty winds.

It simply doesn't work as advertised, and one continually has to "help" waking up the trottle an inch up.

:suspect:

[Flight Detent]

Hi Guys,
Correct 'Loewe',
the A/T will correct for speed and acceleration variances, quite well!

Cheers:cool:

[Few Cloudy]

On the MD-80 where the thrust line is on the drag line the ATs is a great help on a manually flown approach right down to and after touch down.

On the DC9 it was a no no because there was no retard and once you landed the thrust levers would advance to try to keep the approach speed!

On the B-300 and up, where the thrust line is below the drag line, so you get a marked pitch couple with every thrust change, you can usually get a more stable approach by using manual thrust. There may be times when the ATs can be of assistance (we all know what a poor job of landing the AP makes in a crosswind situation so the combination of Ats on and AP off can make sense) but you must keep your hand on the thrust to get the feed back and anticipate the pitch couple.

I was glad of the Ats a few times at a low ceiling approach in LTN with a crosswind out of autoland limits. You can always override them but are a good aid.

I think the answer is that it is a matter for consideration and that reactions like "you aren't flying manually then" and other mores have no place in the discussion.

Now - what do you do on the A 320 with a fixed thrust lever position?

[alf5071h]

Do not forget that most aircraft have different AT control laws, in more modern aircraft these are quite complex, yet generally they are all designed for the primary roles; take off mode, cruise (climb / descent), and precision approach.

In addition to the differences in aircraft characteristics, each AT will also behave differently for each flight mode. When using AT without the autopilot, most ATs may not operate as you expect / require for a manual approach. Those ATs that I have flown all tended to destabilise the aircraft, making the approach pitch control just a little more sensitive, which in turn makes the speed oscillate.

Above all else, do not try to help or over-ride an automatic system, sooner rather than later it will bite back – in a big way. If you do not like the performance of an automatic system, then disengage it and take over manually. Treat autos like co-pilots if you don’t like what they are doing take over … if you don’t like what the Captain is doing … speak up.

“An autopilot is like a co-pilot, but never learns”.
“A co pilot is like an autopilot, but makes mistakes”. (Sorry co-pilots, you make mistakes in order to learn, and then you become Captains ... to make mistakes).

[BLE]

Boeing recommends AT use only when the autopilot is engaged.

The autothrottle ARM mode is normally not recommended because its function can be confusing. The primary feature the ARM mode provides is minimum speed protection in the event the airplane slows to minimum manuevering 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 manuevering speeds cause the autothrottle to maintain a speed above approach speed.

When using the autothrottle during autoland, position command speed to VREF +5 knots. Sufficient wind and gust protection is available with the autothrottle engaged because the AT is designed to adjust thrust rapidly when the airspeed drops below command speed while reducing slowly when the airspeed exceeds command speed. In turbulence, the result is that average thrust is higher than necessary to maintain command speed. This results in an average speed exceeding command speed.

During sporty landing conditions, my experience is that the most skilled aviators, without exception, prefer to disconnect the Boeing 737 "hunt-o-matic" autothrottle system.

No wonder it is the only autoflight system Boeing will allow to be inoperative for a Cat III autoland.

Bottom line: You squat to pee, you autothrottle to land;)

[BOAC]

I'm sure this has been covered on PPrune before, but if you work out Vref+5 and 1.3 Vstall at various weights (737) at Flap 40 in particular, there are certain combinations where the 'ARM' mode will keep on 'cutting in' if you fly ACCURATE speeds. It is a pain and I am (in a non-MCP way :D ), with BLE here.

[Hudson]

Amazing isn't it. Boeing spend thousands of dollars on testing a system and then publish a recommendation based upon the research into all the pros and cons and then operators think they know better. Why is it that Boeing advice is thrown aside ?

[Captain Stable]

Hudson, you need to remember that Manufacturers don't operate the aircraft day in, day out Operators will probably have several types (and several variants) on their fleets and need to have fleet commonality of SOP's and operating methods Operators are subject not only to the manufacturers' recommendations but also their local (national) regulatory authorities etc.

[HSWL]

From carefully reading all the replies - especially those where it seems obvious that use of the 737 A/T in Arm mode rather than off, is not recommended by the manufacturer - maybe Hudson has a good point after all, about sticking with Boeing.