Clean below green dot speed - 733

[SR71]

I'm interested to know whether, when the SOP suggested min clean speed, is below green dot speed, do your companies suggest/require adjusting the SOP?

Min clean speeds are obviously weight dependent, so in this case, is the suggestion that, even if below the weight at which an increased min clean speed should be used, one should work to those increased speeds anyway?

Yesterday @ 51.6T on APP, green dot speed was > 210kts.

Our SOP only advises use of 220kts above 53.07T....

:confused:

[SR71]

Am I the only one who isn't sure they've got the big picture with respect to "green dot" speed?

I realize there may be some confusion in my mind about the speed in question.

In our Tech manual this speed is known as the:

"Flaps Up Manoeuvering Speed"

I've heard this described in the past to be equivalent to Min Clean speed with flaps up.

However, further on in the Tech Manual the definition is given as:

"...an output of the SWC computed for the actual gross weight in question by the FMC. It represents best airspeed (climb or driftdown) for an aircraft in the clean configuration."

To me, this sounds like V_md i.e., where the (L/D) is maximum, and the speed I want to aim for, say, in the event of a double engine failure in order to maximize my glide range.

However, I am not clear whether or not it is actually more like "Best Range Speed", typically 20kts more than V_md, and where the ratio of (V/D) is a maximum and would therefore be the speed you get when you enter a CI = 0.

If this is true, in the case of a double engine failure I want to aim at a somewhat lower speed than green dot speed to achieve V_md.

The Smiths FMC Guide indicates (as one might expect) that the FMC TGT SPD on the ENG OUT CLB page is the speed for max (L/D) and is typically 20 kts above Minimum Manoeuvering Speed.

So whats up? Whats the definitive answer to the following questions:

1) Is green dot speed V_md or Best Range Speed, ~=1.3*V_md?
2) In the event of a double engine failure, I want V_md. May I compute this as ~=(FMC TGT SPD on the ENG OUT CLB page ) - 20kts? This would mean V_md for the 737 is ~=190-200kts....
3) Is there any correlation between "green dot" speed as Minimum Clean speed and Best Range Speed, ~=1.3*V_md?

I believe the reference to "green dot" speed as Minimum Clean speed is, technically at least, erroneous.

[OPEN DES]

hi SR71
I am sure that green dot is Vmd (max angle, max glide). its the maneuvering speed in clean config, used to go max angle, for drift down in case of terrain and in case of engine failure. minimum clean speed is a bit lower. in the airbus its called VLS. lowest selectable speed. i guess you re flying the 73 right? I would say you can go down to the start of the amber tape to achieve min clean speed, which equates to stickshaker at 1.3G right? However I would suggest to be a bit conservative, especially due to WX. Below green dot you ll be on the backside of the dragcurve so take care. I think its best not to go below green dot when clean. When ATC asks for minimum clean speed, I would go for green dot all the time.
Hope this makes sense

S.

[OSCAR YANKEE]

Maybe this is why Boeing never certified the Speed Tape on the Classic.
(I have allways wondered why......)
Rgds.

[Hudson]

Oscar Yankee. Could you elaborate on that please? If Boeing "never certified" the speed tape on the B737 Classics how come it was on all the Classics I used to fly?

[OSCAR YANKEE]

Yes.
My company operates the -500 classic, and -700NG (which I personally refer to as FG, but thats an different story.)
During training on the -500 we were advised to fly the certified min. block speeds 210 kts, 190 kts, 180 kts etc, for the various flap settings (Clean, 1, 5, etc) and add 10 kts if the GW was above 53 tonnes. (220, 200, 190 etc.) We were specifically advised not to rely on the green dot on the speed tape, for min. clean speed cause this was not certified by Boeing - block speeds were. Mind you I just tried to look it up, and the book only says that the green dot speed is "...the best airspeed (climb or driftdown) for an airplane in the clean configuration." Now whether the defined min. clean speed, has larger margins than the green dot speed I do not know.
The -700 speed tape apparently is a lot more advanced, since it precisely calculates min. speeds all the time, and shows them on the tape........

Rgds.

[SR71]

Interesting....

I've come to the following conclusions:

Green Dot Speed = V_md (Clean Config)

Min Clean Speed = Min Manoeuvre Speed (Top of the yellow bar on the speed tape)

[Obviously a function of weight, CG location & MNVR MARGIN variable on the PERF FACTORS page - I believe the default value is 1.3g? Your company's assessment of the necessary safety margin can thus be ascertained by their view on what this setting should be.]

I concur with OSCAR YANKEE regards flap retraction schedule in the sense that I've never been told to fly anything other than the standard speeds which vary depending on whether you're below or above 53T.

I can't ever recall, having cleaned up, seeing a case where the top of the yellow bar is > 210kts? In this case (if indeed it is possible) the question that begs an answer is obvious...

But the "green dot speed" is a red herring and it would appear confusion about what it denotes is widespread, presumably because of what it is known as: "Flaps Up Manoeuveriung Speed".

To my mind, in the event of an ENG OUT, if terrain clearance is an issue, I will aim for "green dot speed" as it represents (L/D)_max for the clean configuration. This assures me of the minimum possible "glide" angle.

If on the other hand, range is an issue, I will fly the speeds the FMC spits out with the CI=0 i.e., Best Range Speed. Alternatively, one might choose to fly the LRC speeds - slightly less efficient. (I believe that having reached the ENG OUT MAX ALT at the ENG OUT driftdown TGT SPD, it may take half an hour to accelerate to LRC!)

If neither is an issue, perhaps because obvious diverts are numerous, the debate about the importance of what speed to fly at reduces proportionally.

Please correct me if I'm wrong.

:ok:

[FE Hoppy]

Hi,
I'm not familiar with the 73 but on the EMB170 we have a green dot that is 1.3vs1g. This was going to be flap selection speed but is a little too active i.e. it changes too much in gusts and manouveres(sp) so we have gone to canned speeds. If you want to find best lift over drag look for diriftdown speeds in the aom/afm. If these agree with your green dot then there you have it. The problem you have with a non accurate definition of an indication is something that really should be addressed as this kind of thing can lead to problems.

regards,