Autothrottle curiosity

[Shermann 4]

Hi Guys, I have a simple question tha tis actually a curiosity, till now like for boing instruction i disconnect the AT as soon as i disconnect the AP. Now the stupid question i have in mind is if the 737 can land ith autothrottle on and ap off like the 777 or not. The stupid question comes from the accident of turkish airline in EHAM. While the pilots were setting the plane to land for a radio altimeter error the plane started to retard the throttles. This push in my mind thhe idea that the plane thought to be close to the runway so he lowered the speed. Now my question is if the 737 NGX can land with ap  off and AT on. Anyway why in the case of turkish the plane retarded the throttles? It was in autoland mode? and in autoland the throttles are retarded by the pilot or by the plane?

 

Thanks for the answer to this confusing question.

[pedrotrindade 335]

Now my question is if the 737 NGX can land with ap  off and AT on

 

Don't know if it is the correct procedure but i'm used to do it with no problems.

[ckaratr 4]

In Turkish Airlines accident; They tried to execute CAT III ils landing as i know. Radio altimeter measured -4 feet which means aircraft about to land / landed, over 1000 feet That's why auto throttle system retarded throttles.

 

I use a/t on without problem..

[Shermann 4]

so with AT on the plane retard the throttles? 

[pcubine 143]

so with AT on the plane retard the throttles? 

 

Yes. Until 2 seconds after touchdown.

[willywonka 36]

In the NG, Boeing recommends that if you're flying manually outside of thrust referenced phases (takeoff, thrust ref climbs, descends), you should disconnect the autothrottle! AP off = AT off.

​

According to the Boeing 737-NG Flight Crew Training Manual (FCTM), autothrottle use was recommended during takeoff and climb in either automatic or manual flight. During all other phases of flight, autothrottle use was recommended, "only when the autopilot is engaged." [source] (why is it filed under About>Employment section of the NTSB?)

 

​If I remember correctly, this is the opposite of the 777. 

​

​But as for if the plane can fly and land with AP off and AT on: yes, absolutely.

[fstulm 4]

Hello all,

 

No airplane retards automatically, throttles have to be retarded manualy, Airbuses included. At that point the AT steps out of the picture and that is a mandatory safety thing.

 

In low vis approaches even if fully coupled, it is the crew that decides upon minimums if they land or not. Should they continue to go on with the landing, a GA is still not out of the picture even if they have touched the runway. NOW, if at that point AT would have spooled down the engines the GA can be a disaster.

 

On landing, no AT robot can take the decision to spool down or GA, only a human, and it should stay that way.

 

Ionut (John) G, Micu

[scandinavian13 5,192]

No airplane retards automatically, throttles have to be retarded manualy, Airbuses included. At that point the AT steps out of the picture and that is a mandatory safety thing.

 

[...]

 

On landing, no AT robot can take the decision to spool down or GA, only a human, and it should stay that way.

 

That's certainly interesting, given how aircraft actually operate. What experience do you have to be making these statements?

 

The 737 has an AT mode called "RETARD." It specifically retards the thrust to idle. An Airbus uses a different methodology, though, where the pilot must physically move the thrust lever out of the detent.

[Spin737 102]

 Now my question is if the 737 NGX can land with ap  off and AT on. Anyway why in the case of turkish the plane retarded the throttles? It was in autoland mode? and in autoland the throttles are retarded by the pilot or by the plane?

 

Thanks for the answer to this confusing question.

 

Yes, the plane will retard the throttles in an autoland. Some airlines fly with the A/T in ARM mode where the A/T will provide a "back-up" for speed protection and still others fly with the A/T on even when flying manually.

 

Normal autoland: At 27feet the throttle get a RETARD command and will close by themselves.

[fstulm 4]

Hello all,

 

Kyle, my apologies, I was thinking too much about the non moving throttles on Airbus. I realized I made a mistake after I made the post but I did not get the chance to correct it.

 

I made quite a few autolands with the Queen and yes, Boeing does retard, it's just the reversers that have to be deployed manually and speed brakes put down manually also.

 

Regards,

Ionut (John) G. Micu

[scandinavian13 5,192]

I made quite a few autolands with the Queen and yes, Boeing does retard, it's just the reversers that have to be deployed manually and speed brakes put down manually also.

 

Yep. No worries. Sorry if I was overly blunt, but simmers are impressionable since they don't usually have actual experience, so they can soak up what people say like a sponge, even if it's incorrect.

[Xiter 0]

More information here guys. This concerns when the autothrottle is engaged without the autopilot during landing.

 

http://www.avsim.com/topic/345686-when-to-disconnect-auto-throttle-before-landing/page-4#entry3243307

 

Best regards,

Hans Hjorth

[cbrdriver 0]

I've actually forgotten to turn it off before (I blame my kids).

It did not retard, but forced me into a go around, as it fought to maintain the MCP set speed.

Not turning it off during approach, or before, IMO adds one more thing to think about during an already tense moment (again, in my opinion)

[JoeDiamond 67]

It did not retard, but forced me into a go around, as it fought to maintain the MCP set speed.

 

Thats a sim thing, the real airplane won't do that.

[Xiter 0]

As I said in the thread I linked to earlier, the sim requires that the APP mode is active for the autothrottle to retard at 27ft.

 

So there is a workaround to the problem. Hopefully that issue will be fixed in the next upgrade.

 

Best regards

Hans Hjorth