Auto throttle and mcp problem

[Jan Pemöller]

Yes but NEW is that this even happens when you have switched OFF the AT!

[bravolima]

Hello Jan,

during descent you switch off A/T? Is it a normal procedure?, I doubt. What I learned from a professional Airliner recently, and that is why I use more often LVL CHG during descent is, MCP calculates the rate of descent in LVL CHG mode very properly and you don´t have to deal with speed brakes. There are several ways to do a descent:

1.) Speed and V/S (needs frequent use of speedbrakes, professionals don´t like it very much, stress to the fuselage....) below FL100 it is appropriate
2.) Target Alt MCP/LVL CHG best way to come down from cruise in my opinion. Don´t forget to reduce speed approx. 20NM bevor T/C to .70 ( ~300 ktn)
3.) Target Alt in FMC and Speed (if you give more speed, rate of descent increase...)

I suppose if you change the procedure 1.) or 3.) to 2.) MCP calculates the rate of descent and as a result it adds thrust to increase your rate of descent.

my english is not as good as required, but play around with this three procedures and keep an eye on the N1 and you will find out, what I´m talking about. And don´t mix them up.....In any case A/T should be on. Don´t know any SOP which recommends switching off A/T. As far as I see that´s why PM assumes A/T is on în your case and applies thrust.
I think PM behaves normal.

regards

Bernhard (LSZH)

[RGroebl]

Tested LVCH this evening with newest MCP Build 438. At my sim the issue is not occured. I tested with A/T on. So in the moment LVCH function is correct.

Regards
Roland

[Jan Pemöller]

Thanks Roland ... I will try after holidays!

@ Bernhard: You have absolutely right. It was only a test with the "AT" off ... But properly should be: When "AT" is turned off - nothing should automatically power up the engines, or?!

Thanks
Jan

[767300]

Has anyone had problems with the CPflight MCP and the PM mcp. I am still getting a flashing AT light and strange number displays on the IAS window.

James

[Tony]

Hi James,


Flashing " 8 " in IAS window means OVERSPEED, according to Paolo from CPFlight.
Im interested to known if you have other " indications ".

Kind regards
Tony

[767300]

Thanks for that Tony, but it appears the auto throttle is overspeeding, On the take of roll I advance the throttles to N1 set from FMC. I engage N1 on the MCP, at Vr I rotate and follow pitch guidance from the AFDS, but the aircraft seems to shoot the selected climb speed on the FMC. I have the initial altitude restriction set aswell so selecting LVLCHG should set my rate of climb and thus be indicated on the flight director. I am retracting flaps on schedule.

James

[767300]

I am thinking my problem is the PM mcp..

[767300]

The AT light starts to flash for AT disco, this happens without any input from me.

JJ

[767300]

Hi just an update, its got to the stage were I cant perform any form of autoland. I did a test flight based on CATII mins, I started the approach in HGD select with VORLOC armed. ILS was tuned on both NAV radios and intercepted the ILS nicely, I waited for the GS indicator to come to the center position, pressed APP with one AP armed. The plane started to follow the ILS down and as it did I reduced spped on the MCP and lowering the flaps on schedule. Got to 138KTS at flaps 30 and all is well. The moment I lowered the gear the AT light started flashing and the AT was now disingaged. I had to manualy add power to maintain VREF 30,disconected the AP and landed manually.

I repeated the the flight but this time I didnt add power after the AT kicked out, instead I toggeled the switch and the AT rearmed but it didnt recover the GS and infact got quiet low before the power came back on to bring the speed back to where it should be. So I am stuck with visual approachs. I am not overspeeding the flaps as the system was stable until the gear was lowered. The same goes for take off. The moment I raise the gear the AT disconnects. I have checked that there is no cross mapping of switches so I am a loss as to what is happining.

James