AmericanAirFan
Topic Author
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Airline Takeoff Procedure?

Sun Jan 08, 2006 11:26 am

Today I was at AUS plane spotting and I saw a Delta Airlines 737-200 taking off on a 9,000 ft runway for a long time he had the throttle low until he had used 1,000 ft of the runway and then went full throttle. The plane cleared the end of the runway with about 500ft before it could have overran the runway being catastrophic. My friend told me they should have aborted takeoff and tried taking off from the beginning of the runway. His dad is a pilot he told me the reason the pilots do don't go full throttle is to detect any problems and make sure the engines read the same on thrust. Can anyone give me "Technical" information of exactly what goes on in the cockpit with the engines on takeoff? Also what would have been the proper thing to do in this situation?

-AmericanAirFan
"American 1881 Cleared For Takeoff One Seven Left"
 
727EMflyer
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RE: Airline Takeoff Procedure?

Sun Jan 08, 2006 12:05 pm

First, I doubt anything was really wrong. Sounds like they were going for a de-rated take-off, but somehow the calculations weren't quite right. Derated take-off's save fuel and wear on the engines by using all the availble runway instead of all the available fuel.

Appologies if something here isn't entirely accurate, but here is how this private pilot understands the big-boys. There are a couple of go/no-go checks the pilots of large aircraft use. You are thinking of the N1 checkpoint off hand. That usually takes only a few seconds to verify as the engines spool up. You will hear it as the brief pause in engine acceleration at the start of the T/O run. If that fails I doubt a pilot would wait a thousand feet to see if it fixes itself. The main one, which will tell a pilot if he needs to abort or not, is the V1 speed. Basically this speed must be reached by a certain distance down the runway to ensure the aircraft will become airbore in the event of 1 engine failure and that there is enough stopping distance to abort if need be. If V1 isn't met at by the specified distance: 1. something is probably already wrong, 2. the plane will likely over-run the runway if something else goes wrong, and 3. the take-off will be aborted. Conversely if something goes wrong after V1, you take off and deal with it in the air. I would guess in the T/O you witnessed the pilots recognized they wouldn't make V1 using their de-rate so they switched to a full power take off. After going full power they obviously met V1 or else they wouldn't have made it into the air!
 
bri2k1
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RE: Airline Takeoff Procedure?

Sun Jan 08, 2006 12:54 pm

The V1 speed is not something you try to reach in a certain distance. It's the speed above which stopping on the remaining runway would not be safely possible, and so unless there is a serious doubt about the airplane's ability to fly, you are going flying no matter what happens after V1 is reached. On a contaminted (icy) runway, V1 may occur very early in the takeoff run. If a reduced thrust takeoff is used, the actual takeoff thrust is used to calculate V1, not necessarily the maximum available thrust.

There are a lot of variables here. It is true that turbofan engines don't go from idle to full bore on the takeoff run. Normal procedure is usually to let the engines stabliize at an intermediate power setting, such as 45% N1, and if everything looks good, accelerate them to takeoff thrust. Under some conditions, especially if there were calm winds or a slight tailwind, such as could occur if the winds were variable at the time, it is conceivable that 1,000 feet of runway could have been used. Jet engines take time to spool up, and even if full takeoff thrust had been commanded prior to the 1,000 foot mark, it may have taken the engines until then to spool all the way.

If there was a headwind, and you were in front of the plane, the wind would have increased the time the sound from the engines took to reach you, and the engines may have been spooled long before you heard them. Also, without being in the cockpit, you really can't be sure if "full throttle" was used, or some other thrust setting.

One thing is sure though. It's highly unlikely you saw anything wrong. The winds at AUS currently are 200 at 13, and if it was a 9,000 foot runway, it's likely the plane you saw was departing to the North on runway 35R. Where were you spotting from that you could determine there was only 500 feet of runway left? A 737 is between 102.5 and 138.2 feet long! If you were anywhere near the terminal, at the departure end of runway 35R, the 737 would have been at V2 speed, probably at least 140 knots. Subtracting a few knots for the headwind component, and converting, the 737 would have been traveling around 220 feet per second. A 120-foot-long plane going 220 feet per second can play tricks on your eyes. The bottom line is, I doubt seriously that anything was wrong, and you just saw a normal takeoff.
Position and hold
 
EMBQA
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RE: Airline Takeoff Procedure?

Sun Jan 08, 2006 1:59 pm

Quoting AmericanAirFan (Thread starter):
His dad is a pilot he told me the reason the pilots do don't go full throttle is to detect any problems and make sure the engines read the same on thrust

Some what true. With some large high by-pass engines you don't go full throttle is one action as it will over torque the engine and fan blades.
"It's not the size of the dog in the fight, but the size of the fight in the dog"
 
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zeke
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RE: Airline Takeoff Procedure?

Sun Jan 08, 2006 2:31 pm

Quoting AmericanAirFan (Thread starter):
Can anyone give me "Technical" information of exactly what goes on in the cockpit with the engines on takeoff? Also what would have been the proper thing to do in this situation?

Normally given either a clearance to enter the runway and hold, or to takeoff, if cleared for takeoff, and not runway limited as it seems in this case normal to do a rolling takeoff.

The longer the aeroplane, the more straight you want to be before one increases the thrust levers to a predefined N1 or EPR, once lined up advanced the thrust levers and check to see the engine parameters are "stable" to the predefined level, while the aircraft is still rolling smoothly advance the thrust levers to takeoff thrust either manually or using the autothrottle (depending on what your flying).

If anything changes during takeoff, or since the takeoff performance was calculated and briefed, like notified of a slight windshear from a previous aircraft, wind changes to a tail wind, temperature, QNH, runway condition, load, birds etc, would not be uncommon to advance the thrust levers further to get maximum thrust from the engines rather than a derated takeoff.

Lots is considered for this critical phase of flight, nothing is left to chance.
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HAWK21M
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RE: Airline Takeoff Procedure?

Sun Jan 08, 2006 10:23 pm

Quoting AmericanAirFan (Thread starter):
for a long time he had the throttle low until he had used 1,000 ft of the runway and then went full throttle.

Presume you noticed the Sound difference or Momentum.

Quoting Bri2k1 (Reply 2):
On a contaminted (icy) runway, V1 may occur very early in the takeoff run. If a reduced thrust takeoff is used, the actual takeoff thrust is used to calculate V1, not necessarily the maximum available thrust.

Isn't N1 RPM used as backup reference on EPR Equipped Engines.
regdsMEL
I may not win often, but I damn well never lose!!! ;)
 
bri2k1
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RE: Airline Takeoff Procedure?

Sun Jan 08, 2006 10:56 pm

Quoting HAWK21M (Reply 5):
Isn't N1 RPM used as backup reference on EPR Equipped Engines.

Not for what you're quoting me on. Some engine management systems display N1 RPM as the primary indication of power being generated, some display only Engine Pressure Ratio (EPR), and some can display both. They're just measurements of how much power the engine is generating though, and have nothing to do with V1 speed.
Position and hold
 
A3204eva
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RE: Airline Takeoff Procedure?

Sun Jan 08, 2006 11:13 pm

(sorry haven't read entire thread, not got time atm!)

On T/O the pilot flying advances the throttles to around 50% N1 and once they stabalise at around 50, the throttles are then advanced to full power (which is whatever the FLEX is [depending on conditions, weight etc.])

V1 is the point on no return, as there's now not enough rwy to stop in time. So the pilot takes his hands off the thottles completely

Vr is the point of rotation.

V2 (isn't called out unless there's an emg) is the minimum safe speed to climb (especially used in an engine failure at V1)
"They have lady pilots......... they're not that good, but they have 'em"
 
Tristarsteve
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RE: Airline Takeoff Procedure?

Sun Jan 08, 2006 11:37 pm

In our airline, when take off is announced one pilot will stand the throttles vertical. If there are no runway length problems the brakes will be off and the aircraft will start to move. When the engines are stabilised at this setting, they will then press the TOGA switches on the throttles to allow the autothrottle to set the take off thrust. This will usually be well down from take off power. The autothrottle will now lock the throttles at this setting and they will stay there until they are reset to the climb setting.

In the winter, especially with freezing fog, the engines will be run up to 70% N1 with the brakes on and held there for about 30secs. This is to centrifuge any ice of the fanblades that has built up in the taxi.
 
CosmicCruiser
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RE: Airline Takeoff Procedure?

Sun Jan 08, 2006 11:46 pm

I don't think I would try to make this more complicted than it is. ZEKE probably had the best points. It just could be they may have rolled a little farther before getting t/o thrust set which ,though not a good habit to have, probably wasn't a big deal. Depending on your accel/stop dist. wasted runway could bite you in the butt one day especially in a heavier wgt. jet.

Technique will vary with diff airlines and each type of jet. One cannot say there is one definite procedure. As a comparison, on our MD-11s we push the throttles to the 10 o'clock position of N1(70-80%) (GEs use N1 and the P & W use EPR) and when they stablize we engage the A/T and t/o thrust is set. It doesn't take very many feet to do this. On the DC-10 even after t/o thrust is set the S/O will make small adjustments even though the A/T are engaged. Both jets MUST have t/o thrust set by 80kts. There is no more adjustments after this except for an emerg. With FADEC and "fly by wire" Thrust Control Modle in the MD-11 it's never a problem as the thrust is set quickly and accurately. On the DC-10 the A/T stop once the first throttle reaches the desired N1 therefore the S/O must "tweak" the others up. In a light jet 80 kts comes quickly and the S/O may not have them perfectly set.
 
AmericanAirFan
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RE: Airline Takeoff Procedure?

Mon Jan 09, 2006 4:01 am

Quoting Bri2k1 (Reply 2):
The winds at AUS currently are 200 at 13, and if it was a 9,000 foot runway, it's likely the plane you saw was departing to the North on runway 35R. Where were you spotting from that you could determine there was only 500 feet of runway left? A 737 is between 102.5 and 138.2 feet long! If you were anywhere near the terminal, at the departure end of runway 35R, the 737 would have been at V2 speed, probably at least 140 knots. Subtracting a few knots for the headwind component, and converting, the 737 would have been traveling around 220 feet per second. A 120-foot-long plane going 220 feet per second can play tricks on your eyes. The bottom line is, I doubt seriously that anything was wrong, and you just saw a normal takeoff.

I was on the end of the runway where he taxied into position and started takeoff which is runway 17L  Wink and there are big signs on the side of the runway marking every thousand feet of the runway and when I saw him lift off he was past the last marker 1 and a half mile down the runway away from me. Here is a picture to assure you that he started takeoff on 17L and not 35R.

http://img290.imageshack.us/img290/7135/p10100077wb.jpg

And if you see right under the nose that is the 8,000ft left marker. Also I am aware about sound and I was standing right beside him so I do know when the engine is not at full and when it is.

Thanks for the great information guys it's very interesting.

-AmericanAirFan
"American 1881 Cleared For Takeoff One Seven Left"
 
SlamClick
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RE: Airline Takeoff Procedure?

Mon Jan 09, 2006 4:04 am

Anyone familiar with AUS know if there is (a) a displaced threshold and (b) a local procedure of not going to takeoff power until reaching that point?

I ask because SFO has such a thing on 01L (and probably 01R too, just don't remember)

That is a primary departure runway and it is normal there for planes to turn the corner at the end, then roll up to the Takeoff Power Point before going TOGA. Some might taxi up there with more than idle power Smile Some have been suspected of taxiing up to that point at higher than usual taxi speed. Smile Your takeoff performance was predicated on being at a standing start at that point, and going to takeoff power in the normal manner from there.

So this local procedure would produce the effect you saw, if it is used at AUS.

By the way, as has been stated in a hundred previous threads the ability to reject the takeoff in the remaining runway is only one of several factors that can determine V1 and on a very long runway at low density altitudes and with lightly loaded or good-performing airplanes there is often more than enough runway to stop after V1 but we don't because taking off is safer in routine emergencies. (is that an oxymoron?)
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
AmericanAirFan
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RE: Airline Takeoff Procedure?

Mon Jan 09, 2006 4:23 am

Quoting SlamClick (Reply 11):
Anyone familiar with AUS know if there is (a) a displaced threshold and (b) a local procedure of not going to takeoff power until reaching that point?

Not that I'm aware of I got a screenshot of google earth I hope this clears things up a little bit.

http://img203.imageshack.us/img203/9596/blahhh0vt.jpg

The first place labeled '1' is where some planes taxi into position and start to takeoff. Most hold at the number '2' position labeled. The screenshot what my viewpoint was and where the 8,000ft left marker is. I've seen small business jets go full throttle with out really going to a an N1 of 50% to check the engines.
"American 1881 Cleared For Takeoff One Seven Left"

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