Boeing727
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...Single Engine Taxi...

Fri Jul 11, 2008 4:11 am

I fly in and out of IAH every time I go to work and have always wondered why none of the international airlines (Lufthansa, KLM, British Airways or Emirates) taxi single engine (B777) or dual engine (B747)...??? There must be a reason, especially with the Europeans...???

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as739x
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RE: ...Single Engine Taxi...

Fri Jul 11, 2008 4:19 am

Very tough on the nose gear


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LASoctoberB6
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RE: ...Single Engine Taxi...

Fri Jul 11, 2008 4:29 am



Quoting AS739X (Reply 1):
Very tough on the nose gear

Is it really? Why so?
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SFO2SVO
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RE: ...Single Engine Taxi...

Fri Jul 11, 2008 4:41 am



Quoting AS739X (Reply 1):
Very tough on the nose gear

I thought that was the reason Virgin America discontinued experiments with towing 747s all the way to runway - not sure how it applies to single engine taxi.
A pure guess - they want to make sure both/all 4 engines start successfully while still at the gate.
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PITrules
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RE: ...Single Engine Taxi...

Fri Jul 11, 2008 4:42 am

Widebody aircraft at heavy weights being taxied with a single engine require a good bit of thrust to get rolling and to make turns into the operating engine. This causes a yawing force (the airplane wants to turn away from the operating engine), which can only be counteracted by the nose wheel.

In addition, the heavier the aircraft, the more thrust required to start rolling. Jet blast might become a factor.

Some large aircraft have a limitation prohibiting single engine taxi at heavy weights.
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luisca
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RE: ...Single Engine Taxi...

Fri Jul 11, 2008 4:55 am

I personally experienced a 3 hour delay at ATL on DL once because engine 1 started perfectly, we taxied and then they could not get engine 2 started on a 757. Now we were boxed in in a way that made it difficult to get back to the gate and we also held back all aircraft behind us for a good 45 minutes.

But from an environmental point of view I agree with 1 or 2 engine taxis. It felt like such a waste once at LHR being stuck waiting for a gate for 30 minutes with all 4 engines on a 747 idling, I don't think it would be a problem at that point to shut off 2, we only had about 1000 feet of taxiing left.
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NZ1
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RE: ...Single Engine Taxi...

Fri Jul 11, 2008 6:33 am

NZ have started shutting 1 or 2 engines down on landing, and taxiing in to the terminal. Its not done before takeoff in case there is an engine fault. Wouldn't look good if you had just started up prior to lining up when you found there was a problem.


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DocLightning
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RE: ...Single Engine Taxi...

Fri Jul 11, 2008 6:59 am

I just flew on VX and we taxied about halfway to the runway before the captain turned on the #2 engine.
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DL WIDGET HEAD
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RE: ...Single Engine Taxi...

Fri Jul 11, 2008 7:11 am



Quoting AS739X (Reply 1):
Very tough on the nose gear



Quoting PITrules (Reply 4):
Widebody aircraft at heavy weights being taxied with a single engine require a good bit of thrust to get rolling and to make turns into the operating engine. This causes a yawing force (the airplane wants to turn away from the operating engine), which can only be counteracted by the nose wheel.

Rubbish.

DL has been using the single engine taxi procedure for many, many years. After millions of aircraft movements, no problems have resulted by this procedure and no undue stress has ensued on the nose gear principally because of a wonderful little invention called a steering wheel. Perhaps the Europeans will soon adopt this procedure on their twins owing to oils upward mobility.
 
CosmicCruiser
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RE: ...Single Engine Taxi...

Fri Jul 11, 2008 11:57 am

We've started using a 2-eng taxi (MD-11) both in and out but we shutdown #2 so there's no assymetrical loads.
 
airbuster
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RE: ...Single Engine Taxi...

Fri Jul 11, 2008 3:06 pm

KLM's policy AFAIK is to shut down an engine after landing, this is however SCD.
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HAWK21M
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RE: ...Single Engine Taxi...

Fri Jul 11, 2008 5:32 pm



Quoting Airbuster (Reply 10):

KLM's policy AFAIK is to shut down an engine after landing, this is however SCD.

What about twins if there is a turn on the side of the inboard engine enroute to the gate.
regds
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tdscanuck
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RE: ...Single Engine Taxi...

Sat Jul 12, 2008 12:40 am



Quoting DL Widget Head (Reply 8):
DL has been using the single engine taxi procedure for many, many years. After millions of aircraft movements, no problems have resulted by this procedure

Few problems...not "no problems."

Tom.
 
lowrider
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RE: ...Single Engine Taxi...

Sat Jul 12, 2008 12:50 am



Quoting PITrules (Reply 4):
In addition, the heavier the aircraft, the more thrust required to start rolling. Jet blast might become a factor.

It does. On the 74 we almost always taxi out on all 4 due to the high breakaway thrust required. It can be quite destructive, as Top Gear and Mythbusters have shown. We also have a fuel sampling requirement to satisfy before takeoff. After landing however, we can almost always taxi comfortably on 3, and often on 2, after a cool down period.
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CosmicCruiser
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RE: ...Single Engine Taxi...

Sat Jul 12, 2008 2:08 am



Quoting Lowrider (Reply 13):
On the 74 we almost always taxi out on all 4 due to the high breakaway thrust required.

Just the other day I started all 3, MD-11, because of a heavy weight and congested ramp but once on the long way to the runway I shutdown #2, taxied 12 min to the runway and restarted #2.
 
AA737-823
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RE: ...Single Engine Taxi...

Sun Jul 13, 2008 11:25 am

It is mechanically complex to taxi a 747 on two engines.
First off, it must be the outboard engines that stay running- they do the brakes... kinda important.
Secondly, if shut down both 2 and 3, then you must run the ADP to provide more hydraulic power.
JAL will often taxi with #3 shutdown after landing, but will only shutdown both #2 and 3 if they expect a real traffic jam on the way to the gate.

As far as other carriers, I can't speculate.
 
VTBDflyer
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RE: ...Single Engine Taxi...

Sun Jul 13, 2008 11:40 am



Quoting AA737-823 (Reply 15):
It is mechanically complex to taxi a 747 on two engines.
First off, it must be the outboard engines that stay running- they do the brakes... kinda important.
Secondly, if shut down both 2 and 3, then you must run the ADP to provide more hydraulic power.
JAL will often taxi with #3 shutdown after landing, but will only shutdown both #2 and 3 if they expect a real traffic jam on the way to the gate.

As far as other carriers, I can't speculate.

On my TG flight the other day (TR coming soon), we shut down the #3 engine (747-400) on taxi in. It was just a quick taxi and it was shut down about a minute after landing and runway turn off.

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CX Flyboy
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RE: ...Single Engine Taxi...

Sun Jul 13, 2008 12:29 pm

On the 777 on a single engine only a little bit of tiller is required to keep straight....no more than you would be applying on a day where there is a 20kt wind trying to blow your tail into wind anyway. It is no big deal at all, but having said that it is not something we do (Although our SOPs allow it).
 
lowrider
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RE: ...Single Engine Taxi...

Sun Jul 13, 2008 7:06 pm



Quoting AA737-823 (Reply 15):
First off, it must be the outboard engines that stay running- they do the brakes... kinda important.
Secondly, if shut down both 2 and 3, then you must run the ADP to provide more hydraulic power.

That is how we do it. Although the only reason to keep #2 hydraulics going is so you have reserve braking. The on ground demands on #2 and #3 are so low there is no issue using the ADP. With less idle thrust at lighter weights, we are better able to control the taxi speed with the throttles, which results in lower brake temps, always a concern with the steel binders.
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A342
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RE: ...Single Engine Taxi...

Sun Jul 13, 2008 8:00 pm



Quoting CosmicCruiser (Reply 9):
We've started using a 2-eng taxi (MD-11) both in and out but we shutdown #2 so there's no assymetrical loads.

Can you do a taxi on #2 alone? Being placed that high, jet blast shouldn't be that much of an issue (at least that's what I assume), and there's no asymetrical thrust.
Exceptions confirm the rule.
 
CosmicCruiser
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RE: ...Single Engine Taxi...

Sun Jul 13, 2008 9:46 pm



Quoting A342 (Reply 19):
Can you do a taxi on #2 alone? Being placed that high, jet blast shouldn't be that much of an issue (at least that's what I assume

We all practiced it in the sim at various weights and it isn't a problem unless you're heavy and in a congested ramp. We always stay below 40% N1 for norm ops.
Believe it or not the No.2 eng has the biggest jet blast footprint because it's actually tilted up in front so does present a real problem for jet blast.
here's a quote from the CFM:

The #1 and #3 engines are subject to FOD ingestion
and create a jet blast hazard at power settings greater
than 40% N1.
The #2 engine subjects the area to a longer jet blast
damage footprint at power settings greater than 40%
N1.
 
twal1011727
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RE: ...Single Engine Taxi...

Tue Jul 15, 2008 10:22 pm



Quoting NZ1 (Reply 6):
Wouldn't look good if you had just started up prior to lining up when you found there was a problem.

Take the very good with the rarely occasional bad and it adds up.

Quoting Airbuster (Reply 10):
this is however SCD

TWA also had "SCD"....a long time ago I asked my dad what this was and he said it was the
most important acronym in the flight manual.

SCD - Subject Captains Discretion

KD
 
A342
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RE: ...Single Engine Taxi...

Wed Jul 16, 2008 4:46 pm



Quoting TWAL1011727 (Reply 21):
TWA also had "SCD"....a long time ago I asked my dad what this was and he said it was the
most important acronym in the flight manual.

SCD - Subject Captains Discretion

Hogwash. It means Side Cargo Door, of course.  Wink
Exceptions confirm the rule.
 
JAGflyer
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RE: ...Single Engine Taxi...

Thu Jul 17, 2008 3:14 pm

I regularly see Dash 8s using only 1 prop. Sometimes the other one is spinning slowly or not at all.
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777wt
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RE: ...Single Engine Taxi...

Thu Jul 17, 2008 4:26 pm



Quoting Boeing727 (Thread starter):
why none of the international airlines (Lufthansa, KLM, British Airways or Emirates) taxi single engine (B777)

Not approved nor recomended by Boeing due to the way the hyd system is set up with the brakes on the 777.
 
EssentialPowr
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RE: ...Single Engine Taxi...

Thu Jul 17, 2008 10:19 pm



Quoting PITrules (Reply 4):
This causes a yawing force (the airplane wants to turn away from the operating engine), which can only be counteracted by the nose wheel.

The nose gear is certainly robust enough on an airliner for single engine or asymetrice taxis, as thousands are done every day. Nose gear tires do show increased wear over symmetric power taxi configurations, as that is how the above forces are resisted.
 
LimaNiner
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RE: ...Single Engine Taxi...

Fri Jul 18, 2008 5:00 am

I wonder if it wouldn't make sense to have a "double-wide" taxiway/"staging area", where planes taxi from the gate to the staging area, then shut down all engines except the APU. When that flight's slot is about 5 minutes out, ATC radios the crew to "get ready". The crew fires up the engines, taxis out when called upon, and goes.

In the common case, all engines fire up flawlessly, the plane taxis out, and takes off without a hitch.

In the rare case where there are problems getting all engines to go, there is no holdup for the rest of the flights waiting in line "behind" this one -- because they're not physically behind the plane with the failure...
 
CosmicCruiser
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RE: ...Single Engine Taxi...

Fri Jul 18, 2008 1:18 pm



Quoting LimaNiner (Reply 26):
When that flight's slot is about 5 minutes out, ATC radios the crew to "get ready". The crew fires up the engines, taxis out when called upon, and goes.

With the exception of your "double wide" taxiways that for the most part happens anyway. If you can't just stay at the gate, as we do, you push, taxi 100 yards, stop and shutdown. If seen it many times. The best option is just don't taxi if the gate isn't needed. Another problem with being at the runway with only APU powr is the configuration of the jet and subsequent checklist. Our policy, and I would guess most airlines would similiar, prohibits configuring the jet and running the Before T/O chklist untill ALL engines are started. That's going to take several minutes and you certainly don't want to be rushing or feel pressured to "get it done".
 
hercppmx
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RE: ...Single Engine Taxi...

Sat Jul 26, 2008 2:21 pm



Quoting JAGflyer (Reply 23):
Sometimes the other one is spinning slowly or not at all.

It could be possible that its taxing on one engine and the other engine is simply "windmilling"
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hypersonic
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RE: ...Single Engine Taxi...

Sun Jul 27, 2008 8:33 am



Quoting CX flyboy (Reply 17):

Given that this is a standard practice? Would you 'alternate' which engine you shut down, so as to ensure an even number of running hours overall?
I'd imagine if it was always engine 2# for example that was shut down & 1# always did the taxiing, The engine would accumulate far more running hours unfairly.
Cheers
 
theginge
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RE: ...Single Engine Taxi...

Sun Jul 27, 2008 10:22 am

BA on their A320's shut down one engine on taxi in and also on the 747-400 normally shut down the number 3 after landing. Not sure about the rest of the fleet.
 
airbuster
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RE: ...Single Engine Taxi...

Sun Jul 27, 2008 12:13 pm



Quoting A342 (Reply 19):
Can you do a taxi on #2 alone? Being placed that high, jet blast shouldn't be that much of an issue (at least that's what I assume), and there's no asymetrical thrust.

The #2 engine on the MD11 is slightly angled with the rear downwards and thus the jet blast will also be angled downwards. Actually increasing the chance of jet blast.

But i suppose it is possible to taxi single engine, the asymetrical thrust generated upon and engine 1 or 3 failure with the md11 does not decrease the performance of the aircraft more than if engine #2 were to fail. Another interesting point is that the MD11 is approved to do 2 engine take offs for ferry flights....

that's all i can remember from my md11 days....
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