757/777 dynamicsa

[ghiom 2]

Hi allI made a flw flights recently with both AC. They are quite good actually.a) The 777 is almost perfect. it lacks some FMS features like the intercept, for example. The main problem is that at flaps 5, on Glideslope, A/P cannot maintain speed with autothrottle. It is like the AC is sliding. You have to drop the gears and lower the flaps to catch up the MCP approach speed. It makes approach difficult to fly.Also, I wish a 777-200 could be made. I wonder why PSS chose to design a 18hr-range aircraft. Who would like to spend this much time in front of a PC. Or who's got time?Will a patch be made to correct the remaining little issues?:( as already said in this forum, the 757 has a lot of potential to become very very good. Please guys at PSS, make the best you can to enhance the dynamics and the A/P. VNAV is unrealistic (very steep climbs at 5knots below the target speed). I am not sure CLB1 and CLB2 are correctly modelled.When dou you expect to have the list of the features being worked on?c) Is it possible to have a detailed explanation of the parameters on the app_control_coeffs.dat file? At least, users could tweak and report enhancements if any? I believe much of the A/P behaviour resides in this file, doesn'it?Good luck for the final product.You have my support.RegardsGhiom Viguie

[ghiom 2]

Am I the only one to have the problem mentioned in a)??Thanks for sharing your experience.Ghiom

[FOD 23]

GhiomWhy are you using 5 flap on the glideslope and what speed are you trying to hold?John Rooum

[ghiom 2]

I am using Flaps 5 when capturing the GS from a high altitude from ground (3000+ ft). There, the speed is the min for Flaps 5 depending on the weight, as marked on the tape.As soon as the G/S is capture, AC starts to descend at ~1000 V/S but the speed increases up to above clean configuratoon limit. There are two ways of recovering the requires speed:1) lower the gears (not advisable at 3000ft, usually rather at OM)2) use the speedbrakes (not advised as well)3) lower flaps (not the purpose of flaps)4) combine all aboveThe 757 does not have this problem.Thank you

[Triple7 1]

Hello,> 1) lower the gears (not advisable at 3000ft, usually rather at OM)You may use the gear at 3000ft.2) use the speedbrakes (not advised as well)You may use the speedbrakes on the ILS3) lower flaps (not the purpose of flaps)You may use the flaps at 3000ft4) combine all aboveThe correct approach.It should be as follows:Flap 5 should be selected prior to localiser interception.Select gear down and Flap 20 when the glide path is active, speed may then be reduced to Flap 20 recommended manoeuvring speed.It is permissible to use Flap 15 during the flight approach to enable a speed to be flown which is less than the Flap 5 manoeuvring speed, but is above the Flap 15/20 manoeuvring speed.At glide path interception select landing flap, normally Flap 30; select VREF+5 kts. Extension of Flap 30 at speeds in excess of VREF30+ 20 may cause flap load relief activation and excessive thrust changes. No additional wind correction is required to the final approach speed if the autothrottle is being used. When established on the glideslope, preset the missed approach altitude in the altitude window of the MCP.

[FOD 23]

Ghiom,I am not a 777 pilot but the only reason I can see for this kind of approach is if you have had a flap failure. I believe that the 777 is inherently "slippery" and speed will be difficult to control in this situation [high approach speed leads to higher than normal rod to maintain the glideslope etc etc ...] But if forced into this, there would be nothing wrong in using spoilers to control the speed prior to lowering the gear.However, the basic airmanship of any ILS is to set up a stabilised approach in terms of configuration, speed, heading and rod as soon as possible in order to minimise configuration changes in the final stages of the approach. This gives the best chance of a good transfer from instruments to visual etc. So, even if ATC requires an approach to intercept the glideslope at 3000 ft [and I wished delay lowering the gear], I would plan to intercept the glide at a lower, more controllable, speed with more flap selected.However, an interesting challenge and I guess that we need someone with 777 experience to comment on whether such an approach is SOP.RegardsJohn Rooum

[FOD 23]

Triple7,I guess out replies crossed. Both the same idea but I wonder why he tried it in the first place?John Rooum

[ghiom 2]

Thanks for your advices.I shall follow them, although being at Vref+5 at G/S intercept at 3000ft with lengthen the approach time which I don't like! or rather I cannot afford since time is very precious to me for flying -:)!Thanks again

[Triple7 1]

Correct!However you still need to configure the aircraft correctly.What kind of speed are you trying to fly down the ILS?A more common approach would be to do 160kts till 4D with flaps 15/20 and gear down.Start slowing down at 5/4D and flaps 30.Maybe if you explain a normal approach with every action you take we can look into it for you?