Hello folks,

 

i have a prob with the landing speed @ MLAW or lower. The i should have around 137-140 KIAS but if i slow down the bird i will get a stick shacker. Gross weoght is  200t remaining fuel is 18t.

If i reduce the weight further the there is no change in low speed band. As im familiar with real world jets normally the Vstall changes with config and weight (of course attitude as well)

 

Any ideas welcome.

 

Thank you very much.

 

Michael Jahn

Hi Michael, I am trying to understand your problem description but I draw a blank with meaning of MLAW. Do you mean max landing weight (492,000 lbs)?

 

Are you trying to use an approach speed lower than the FMS generated Vref? Or, is your complaint Vref does not seem affected by gross weight?

Hi Michael, I am trying to understand your problem description but I draw a blank with meaning of MLAW. Do you mean max landing weight (492,000 lbs)?

 

Are you trying to use an approach speed lower than the FMS generated Vref? Or, is your complaint Vref does not seem affected by gross weight?

 

Hi Dan,

 

yes exactly i mean the max landing weight or lower. Im a bit confused that no matter what landing weight i use there is no change in the minimum speed at which i can fly. When fully configured -gear down flaps 30- i cant go as low as 160 KIAS. The stick shaker activates @ 140KIAS (barber pole starts @140 KIAS btw). Few weeks ago i had a quick spin in a B772 F full flight sim Vapp/Vref was 137 KIAS fully configured. 

 

Im still in the early stages of B777 flying. Im just trying to fly it raw data. The FMS usage is no problem for me (was rated on CRJ and now on E190)

I think this may have something to do with Vmcg and or other minimum control speeds due to the issues in an engine-out situation in terms of keeping directional authority on the rudder.

Well, the Vref will change with weight as with any other aircraft. Table is in the FCOMv1 pg PI.10.2; as for Vmcg the speeds (max thrust) are in another table I've seen elsewhere and they are much lower than Vref speeds as one would hope.  I think what you are experiencing is due to not setting Vref in the FMS thus the FBW is acting blind.... I think, not sure but this aircraft is not intended to be flow "raw data" which I think you mean no FMS.

I don’t think Vmca is the issue in this specific case, but the Vref for the 77L and F are indeed floored as a buffer to minimum control airspeed. This is to provide an additional safety margin for a single engine go around. If you look at the Vref charts that’s why there’s a decrease in Vref at higher pressure altitudes for weights lower than 200t.

Michael, you may want to double check that you entered a valid ZFW value, and you’re not doing anything silly like using lbs. on an airframe configured in Kg.

Vref for MGLW should be about 165 KIAS.

 

By keeping the AOA at 3 o'clock it really doesn't matter what the A/S is.  The AOA is a much better indicator of the correct A/S when landing than the IAS.   

First of all many thanks guys for your help. It is much appreciated! Looks like the T7 is a different bird than the E190. 

 

Well, the Vref will change with weight as with any other aircraft. Table is in the FCOMv1 pg PI.10.2; as for Vmcg the speeds (max thrust) are in another table I've seen elsewhere and they are much lower than Vref speeds as one would hope.  I think what you are experiencing is due to not setting Vref in the FMS thus the FBW is acting blind.... I think, not sure but this aircraft is not intended to be flow "raw data" which I think you mean no FMS.

 

G´day Dan,

 

yes i know that the Vref is changing with weight and that is what confuses me. I will set a valid Vref to have a look if there is any change in the PFD. So you say that the low speed band (and the stick shaker activation) in the PFD depends on a valid Vref in the FMS? So what happens if one has an complete FMS failure?:(

 

I don’t think Vmca is the issue in this specific case, but the Vref for the 77L and F are indeed floored as a buffer to minimum control airspeed. This is to provide an additional safety margin for a single engine go around. If you look at the Vref charts that’s why there’s a decrease in Vref at higher pressure altitudes for weights lower than 200t.

Michael, you may want to double check that you entered a valid ZFW value, and you’re not doing anything silly like using lbs. on an airframe configured in Kg.

 

Hi Brian,

 

i didnt change the ZFW in the FMS as i loaded the standard PMDG B777. I changed the fuel in the FSAction menu in the FMS. I set the FMS to kg. Which Vref charts do you mean? The PMDG manuals? 

 

Vref for MGLW should be about 165 KIAS.

 

By keeping the AOA at 3 o'clock it really doesn't matter what the A/S is.  The AOA is a much better indicator of the correct A/S when landing than the IAS.   

 

Hello Wilhelm,

 

i had a LAW of around 200t the tables say 137 KIAS then i changed the LAW to 180t i should fly a bit lower speed than 137 KIAS same goes for a nearly empty B777 state. In all three case i was stalling at 140 KIAS according to PFD low speed band and stick shaker. 

 

I will go ahead and give your suggestions a go and report back. I still have a phone joker a friend of mine is Cpt on the B772F. If all goes wrong he have to check the actual aircraft

I have never seen any REF speeds lower than 137kt in the 777. I thought this was due to the Vmca / Vmcg issues. That goes for both takeoff and landing REF speeds. Perhaps Kyle or another PMDG person could expand and or correct that?

 

EDIT: I have driven my car to about this speed, and hence, it is, in my opinion, still too low for a 200ton airliner! :wink:

 

PS - Don't tell anyone please.

According the the VREF table on pg PI.10.2, they will drop below 137 KIAS with F30 and GW < 200 kg. However, with a reasonably profitable payload and typical long range fuel reserves the lowest I see in use is 137 kts.

 

 

 

So you say that the low speed band (and the stick shaker activation) in the PFD depends on a valid Vref in the FMS? So what happens if one has an complete FMS failure?

 

I was just guessing, so I started looking in the documents (highly recommended for you too) and found that gross weight only comes from the FMC and again just guessing but maybe this partly explains your observation.  QRH 11.1 covers dual FMC failures, and also touched on by FCOM 11.32.6.

 

The stick shaker is not a stall, but just a warning that stall is coming and its time to pay attention. My suspicion is that it's activated at 140 KIAS because GW is not set by the FMC, I haven't found the reference for this in the documents yet.

 

More to the point, I believe, is why you would want to fly this aircraft without the FMC?  Usually it is because the unfamiliarity of it.. make sure you fly the tutorial flight even if you are a high time E190 pilot. It will be worth your time.

Hi guys,

 

i got it. I didnt prepare the aircraft properly. I took it out for a pattern but entered all required data. I was able to get the Vref=137 KIAS. So my problem has been solved and i have more understanding in the T7.

 

Many thanks for your help