SEA nw DC10
Topic Author
Posts: 471
Joined: Fri Oct 22, 1999 3:03 am

Question About Take Off...

Fri Oct 22, 1999 5:55 am

I have noticed this during take off evertime I fly on any type of jet. You're sitting there, the brakes are on, the captian releases the breaks and the engines start to rev up. Instead of a continuous "revving up", it feels like he puts them to 50% for like 6 seconds, then applies full throttle. Why is that? Why not just take right off to full power right off the bat? Thanks!!

Posts: 3612
Joined: Mon May 31, 1999 4:44 am

RE: Question About Take Off...

Fri Oct 22, 1999 6:08 am

I think it would be to violent and stressing for the engine to be accelerated from 0 to 100% suddenly.
During that 6 seconds, pilots check if all indicators such as oil pressures and others are ok, and just after this they increase to full power.

I'm sure you'll get better answers because I'm not a pilot.

Luis, Faro, Portugal

RE: Question About Take Off...

Fri Oct 22, 1999 6:15 am

Here is my understanding of this - feel free to correct any innaccuracies...

In my powerplants class, my professor told us that this is called "standing up the throttles," and that it is done to make sure that the engines are all turning at the same speed before applying full power. I don't know exactly what the purpose of this is, but someone in here probably does.
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Joined: Wed Oct 06, 1999 10:48 am

RE: Question About Take Off...

Fri Oct 22, 1999 6:23 am

Here's my answer.

First of all, the reason he hits the breaks...

1.) You are taxying at about 15 to 20 knots, just swiveling onto the runway and trying to line up would be suicide.

2.) To improve cornering, the slower you go, the easier it is to change direction.

3.) To slow the plane down when it's on the runway to avoid using up too much runway (it's needed for takeoff)

The reason about the throttles:

1.) "Standing the throttles": The pilot puts the engines up to 50% power, uses that thrust rating to check the RPM responce on the engines.

2.) A little push to help it finish out its turn to line up on the field.


The pilot increases throttles to fullpower when he's lined up on the field. He still holds the breaks down while he checks RPM, EGT, EPR, and ITT. Once everything checks out, he lets the breaks go and taxies.

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Joined: Tue Jun 15, 1999 11:29 am

RE: Question About Take Off...

Fri Oct 22, 1999 6:52 am

As others have said, once throttles are pushed up (partially) engine indications (N-2, N-2, EGT, Fuel Flow, etc.) are checked to assure each indiividual engine is within limits, and that both engines are actually matching each other's performace. Just beacuse both throttles are pushed to the same physical position doesn't necessarily mean the engines will react identically, and it occurs for a variety of reasons. There is a certain amount of throttle "split" allowable. Were both throttles pushed up to max right away, an asymetrical thrust situation could occur at a high power setting, and the aircraft could veer off to one side of the runway before the throttles could be retarded. I hate it when that happens!
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
Posts: 220
Joined: Sun Jul 18, 1999 4:42 pm

A Few Of You Got Peices Of It... :)

Fri Oct 22, 1999 9:10 am

Let's start from the beginning here. A pilot is not, in anyway, required to stop on in position on the runway prior to takeoff. This can be requested by the pilot if he has any concerns about wake turbulence (violent wingtip vorticies) from an aircraft that had just departed. The standard wait is 2 minutes. Either that, or, ATC will instruct for you to hold for traffic seperation and/or the wake turbulence I just talked about.

Now for takeoff. During a normal takeoff, PF will announce "Takeoff" and release the brakes, and thrust levers are advanced from idle to to 50% N1 (1.1 EPR). From there, the PNF will check that both N1 fans are rotating at the same speed. Once complete the PNF will call "Stabalized" and the PF will advanced the thrust levers at around 40 knots, to the takeoff thrust setting, whatever it may be. The pilot will maintain directional control, on the runway, by using the rudders (the two pedals at the feet of the pilot and co-pilot). Upon reaching 80 knots. PNF will check the EGT guages and make sure that the takeoff N1 for each engine has been reached. If there is a 1% difference between the two engines (or three, four...) it needs to be added to the log after the flight. PNF will announce "100 Knots" at the appropriate time. When the takeoff desicion speed (V1 or Vee One), the PNF will call "V1" and soon after "Rotate". The nose is then pitched to around 12 degrees (depending on your aircraft) and ladies and gentlemen you are airborne.

After that, PNF calls positive climb and PF calls Gear Up, yadda yadda yadda you're at your destination in no time  

Sorry if you were just wondering about the takeoff thrust I got a bit carried away  

Take care!

Posts: 1962
Joined: Tue May 18, 1999 8:32 am

Just Curious...

Fri Oct 22, 1999 9:32 am

Isn't there a point at about 70 knots or so when one pilot says "airspeed alive" to indicate that the rudder has become effective and that the pitot tube is functioning properly? Then isn't there supposed to be a point at which "crosscheck" is stated to confirm that both pilots' airspeed gauges concur? Are there many different versions of take-off procedures? Just curious.
An optimist robs himself of the joy of being pleasantly surprised
Posts: 220
Joined: Sun Jul 18, 1999 4:42 pm

For 'Hmm...'

Fri Oct 22, 1999 10:02 am

Yes you're correct, however, it is not really a part of the takeoff checklist on the types I am framiliar with. The rudder has a very slight affect on direction at 40 knots when takeoff power has been set.

You don't really notice that you are off the runway-centerline until you really get moving, anyhow (unless you've got a crosswind, which requires early rudder application anyway) if you've done a good job of lining up your tin-can.

Once pilots fly for a while, and get the hang of everything, it's all natural  

My cessna doesn't have a long enough takeoff roll to be worried about going off the side of the runway, so for now I just need to watch out for birds and such hehe.

Take Care,

RE: For 'Hmm...'

Fri Oct 22, 1999 10:11 am

That is a FS thing. The reason we say our airspeed is alive as if the airspeed indicator is not working flying will become very dangerous and you should abort you take off!!
About cross check only pilot is flying the airplane so the other one is always checking what he/she is doing.
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Joined: Tue May 18, 1999 6:40 am

RE: Question About Take Off...

Fri Oct 22, 1999 1:44 pm

The real reason the throttles are "stood up" prior to setting TO thrust is to ensure the engine interstage bleed valves have closed. In the 727 it is called the 1.4 EPR check. If the valve is closed the engine indications will be as follows...

EPR 1.4
N1 74%
N2 84 %
EGT 400c
Fuel Flow 4000 ppm

If the bleed valve fails to close the engine will compresser stall which means an abort.

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