Turbulence speed 737NG
 

Hi guys
The recommended procedure is 280 knots or 0.76 for Climb and descent only,for cruise it says Turb N1,but i had a discussion with my capt the other day about it who said 0.76 is used at any stage rzgardless of climb and descent.My question is Turb N1 equivalent to 0.76?what of your toughts on this?

The best plan is to try and ensure you sit half-way between the low and high-speed buffet margins on the display to give maximum room for speed changes. A fixed Mach will never work well..

BOAC is right. I bug the speed in the middle of the amber bands and let the speed do it's own thing within reason. The bugged speed works out around M0.77 at altitude and then the actual speed varies between 0.75-0.80 depending on the amount of and severity of the turbulence. Of course if it gets rough and the A/T starts chasing the speed too much, just disconnect the A/T and set the Turb N1:ok:

280/.76 means use the one which is smaller at the time of use.
in cruise , when u fly 280/.76 without engine anti-ice , the Turb N1 is around it .

We've done this one before.

The AFM clearly states 280/M.76 is the target for severe turbulent air penetration.

The Performance Inflight table is called "Flight With Airspeed Unreliable/Turbulent Air Penetration" because it's the same numbers.

My degree doesn't say "Aerodynamic Engineer," so I tend to follow what Boeing says.

Seems like a normal range for these types of airplanes...

A320 is 275/o.76


And like ImbracableCrunk said good to do what the book says but a good idea to find out what she says (:


Two reasons why these speeds are selected

1. It's the idea design speed and giving adequate buffer from high speed /low speed buffet...

2. There's an adequate margin from Vd as its a guru mantra to never go below the recommended speed and small increase is always preferable.

N1 limit,

I don't know who you fly for but my company's FCOM supp procedures is confusing on this point. You get used to poorly written manuals, by the way. The FCOM states 'approximately 0.76/280' for severe turbulence penetration but then shows a table which states that these speeds are for the climb and cruise only. They advise turbulence N1 for the cruise.

In my humble opinion the tables are correct and the prose is wrong. I say that merely because it would be common sense that your turbulence N1 and therefore Mach is effected by many factors, all of which I presume (I haven't checked because I have to cook supper now) are included in the PI section of the QRH. To have a blanket speed to be used in the cruise at all levels and weights seems a little odd to me.

Personally, I have only once experienced severe turbulence and the notion of setting any particular speed or N1 was laughable when you could barely make out the instruments. However, in moderate turbulence I think it is logical (though I appreciate my logic is often flawed) to set a speed that gives you a safe margin between stall and overspeed.

I think your Captain is misguided.

IFR 101
 

In the climb and descent, you are at a fixed power (Max Climb Thrust or Idle Thrust) so you pitch for airspeed. In level flight, you pitch for level flight and set the Target N1 for airspeed. Rather than make you guess the power setting, they give you one (and hope you can set it).

Boeing gives you a target airspeed for all phases. The tables in Performance Inflight have .76/280 listed for Climb, Cruise and Descent above 10,000'.

Boeing also adds in the FCTM, "Turbulent air penetration speeds provide high/low margins in severe turbulent air." They further say, ". . . do not allow the airspeed to decrease and remain below the turbulent air penetration speed because stall/buffet margin is reduced." Note they don't have the same warning here about being above. I'd guess that's why the target speed is closer to the top than the bottom of the limits.

So, for all who like to ride wherever the middle is, you're not following the FCTM as you're "remaining below" the target speed.

Hey folks
On the performance inflight table (airspeed unreliable/turbulence penetration) section you have climb 280/0.76 flaps up,cruise 280/0.76 flaps up,descent 280/0.76 flaps up tables,as per the FCOM 1 it further says 280/0.76 speed is only used as turbulence speed for the climb and descent for cruise use N1 turb,but the table for cruise says 280/0.76 for cruise with flaps up,can anybody try and clarify it to me?

I tried to address this in my last post: the table gives you .76/280.

The jet doesn't magically have a different number it needs in cruise as opposed to climb and descent - it's all the same. It's how you get to it that matters. Fixed power = variable attitude or fixed attitude = variable power. Easy. (Maybe not in severe turbulence, but the theory is good.) :)