Fair notice to everyone: Replies are tending towards more 'heat than light.' Please, take a deep breath and choose your words very carefully going forward.

(...) choose your words very carefully going forward.

 

 

Does anyone know when SP1 for Asiana's pilot training programs will be released?   :P

Not any time soon. A lot of work still needs to be done :biggrin:

Just to add information, Then engines operate like said at Approach idle which is indeed higher than the ground idle to facilitate the GA thrust. The GE90 engines are certified to go fro FLT idle to GA in around 8 seconds, CFM engined do it in around 6 as said. As for the "The report clearly shows how slow the 777's engines behaved with the EEC magic in the background" They behaved normally?

Just to add information, Then engines operate like said at Approach idle which is indeed higher than the ground idle to facilitate the GA thrust. The GE90 engines are certified to go fro FLT idle to GA in around 8 seconds, CFM engined do it in around 6 as said. As for the "The report clearly shows how slow the 777's engines behaved with the EEC magic in the background" They behaved normally?

 

Yes they behaved perfectly normal from idle. They spooled up slowly.

 

Regards

Sorry FLEX i'm a little confused to what your saying, i don't mean to sound an idiot, maybe i'm missing something. As far as the report says the throttles were at idle until 100 AGL? Are you just saying that the 8 seconds it takes to spool up is slow in general? Or spooled up slow as in, they malfunctioned? As im aware the engines were working correctly?

Sorry FLEX i'm a little confused to what your saying, i don't mean to sound an idiot, maybe i'm missing something. As far as the report says the throttles were at idle until 100 AGL? Are you just saying that the 8 seconds it takes to spool up is slow in general? Or spooled up slow as in, they malfunctioned? As im aware the engines were working correctly?

 

Hehe no worries ;) Perhaps I am not being clear! The engines behaved perfectly normal. Normal however with EEC/FADEC equipped aircraft is still very slow, this is why an additional safety net (Stable approach criteria) is put in place.

 

Regards 

Ah yes! i understand now :) To be honest they are actually not bad for response time, some engines do it in under 8, and for such a big engine thats good! I think the FADEC does a good job myself! Totally agree on the safety net!

Ah yes! i understand now :) To be honest they are actually not bad for response time, some engines do it in under 8, and for such a big engine thats good! I think the FADEC does a good job myself! Totally agree on the safety net!

Fadec or no, jet engines inherently take time to spool up. So no way do you want them at idle at 100ft agl unless the landing is absolutely cast iron safe. A spool up time of 8 seconds would be right for the type of engine on the 777. The front fan is very large and heavy so it takes time to get it going fast enough to do any useful work. Remember that nowadays most of the thrust is generated by the front fan.

 

In comparison have a look at the RR Conway. This was the first bypass jet. The bypass ratio was very small in comparison to modern jets. The front LP compressor was still very large though. Until the development of the RB211 engine type they were the most powerful sub-sonic jet engines.

Having said that when the engines were at full tilt the eflux went supersonic. Watch this video and listen to the supersonic roar when the throttles are at maximum.

 

Even so you would not let the engines run down to idle low on approach. In an emergency they are your margin of safety.

 

https://www.youtube.com/watch?v=qBpUNx8CqiM

I'm beginning to think that the FADEC stuff doesn't increase engine responsiveness in the approach phase, but dampens thrust variations at higher altitudes (mainly in cruise). Damping then is removed for approaches.

 

Is that about what it's like?

I'm beginning to think that the FADEC stuff doesn't increase engine responsiveness in the approach phase, but dampens thrust variations at higher altitudes (mainly in cruise). Damping then is removed for approaches.

 

Is that about what it's like?

 

Hi Oliver, since you mention FADEC I will assume you are talking about Airbus.  You have modulated idle with flaps up & approach idle with config 1 selected.  Approach idle merely provides a higher idle setting to increase response time.

 

I am on my phone so unable to post a diagram, basically if you look at the thrust response curve you will see that the majority of time to spool is from the low end of the curve.

 

Will see if I can post the chart when I get home.

Thank you Rob, your reference already has helped me along:

 

http://www.pprune.org/tech-log/373290-nw-a320-tailstrike-den-possible-w-o-2.html

 

Approach idle, in the example depicted in the diagram, decreases response time by about 2 sec (25%). It's just the "high idle" thingy vs. the usual "low idle" condition.

 

FADEC or EEC, the same principle seems to apply. (As far as approach idle is concerned.)

Thank you Rob, your reference already has helped me along:

 

http://www.pprune.org/tech-log/373290-nw-a320-tailstrike-den-possible-w-o-2.html

 

Approach idle, in the example depicted in the diagram, decreases response time by about 2 sec (25%). It's just the "high idle" thingy vs. the usual "low idle" condition.

 

FADEC or EEC, the same principle seems to apply. (As far as approach idle is concerned.)

You can see even from that graph that nothing much happens at all until after 80%.

 

So if you are descending at the normal rate about 700fpm and you firewall the throttles at 100ft you might just get away with it if the ground underneath is completely flat with no obstacles. Otherwise splat!

So the moral in the story is as it has always been. Don't let the engines go down to idle thrust close to the ground.

 

Practise this in the sim - Do a few approaches making sure that you are at Vat+5 or Vat+15 depending on crosswinds as you cross screen height (35ft). Fly each approach so that your throttle setting is correct reducing to to idle on a subsequent approach and see how heavily you land. If you do it higher than screen height then in all probabilty you won't make the rwy. The only way to meet the Vat speeds with idle thrust is to have a too high rate of descent. Which cannot be recovered from close to the ground.

If the a/c systems make a mistake they rely on the crew to get the a/c out of the mess. If the crew set up the a/c systems incorrectly then sh-one-t in sh-one-t out as they say!

 

Hey Robin,

 

First thing, what is the name of the  777 operators you are talking about? slightly worrying that any any airline would ban flight crew from using Boeing's and every other 777' operators method of flying a NPA.  Of course hand flying is encouraged when 'Workload permits'  slightly hard to believe what you are saying so I would like to ask around about this.

 

upload pic

 

Did you read your own graphic carefully?

 

What Asiana crew did:

 

* Approx. 7 nm from touchdown, they used VS mode to *DESCEND* WHILST THE ALTITUDE WAS SET ABOVE THE AIRCRAFT ALTITUDE. Read that again.

 

In your diagram:

 

* "Set MDA(H)"

* At approx. "300 ft above MDA(H) set altitude to go-around altitude"

* At MDA(H) "intercept landing profile and disconnect the autopilot".

 

Even Boeing do not have you descending in VS mode with the altitude set ABOVE the aircraft!

 

777 or not - the procedure is the same. Not sure what the aircraft type has to do with it. Personally I recycle the GA altitude AFTER AP disconnect, but that is because of altitude capture.

 

Another FYI - some autopilots will altitude capture as you bring the altitude selector through the aircraft altitude, in order to prevent you descending (or climbing) away from the altitude preset. It forces you to consciously re-engage the mode and cause the aircraft to fly away from the preset altitude if that is what you want to do. I must say I was surprised when the 777 AFCS apparently let the altitude selector go through the aircraft altitude without capturing it/going to ALT HOLD mode.

 

Best regards,

Robin.

Dear Robin :)  was telling myself not to reply to either you or Kevin because I don't want to get this thread locked.

 

You have no idea what you are talking about. You are surprised at the behavior of the AFCS because you have no idea how the mode was designed. It worked correctly according to Boeing logic in V/S & Airbus logic in V/S is exactly the same in this respect.

 

I really can't be bothered to explain things to you guy's anymore... The diagram posted clearly shows that you have to descend in V/S with the MCP window above present altitude.  

 

Anyway Oliver gave me an idea, read the discussions below, a 3 second search saves me having to go around in circles with some of you guys....   :Rolling Eyes:

 

http://www.pprune.org/archive/index.php/t-386496.html