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apodino
Topic Author
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Single Engine Taxis Overrated?

Sat Sep 29, 2007 11:50 am

I bring this up because of a discussion at my carrier, which does not utilize single engine taxi procedures. Management was questioned as to why we do not do single engine taxis. Some of the key points that were raised in response.

They did a test run of Single Engine Taxi procedures at ORD for a while. The results showed that our CRJ's actually burn more fuel on a single engine taxi than we do with both engines on. Part of this is the fact that with both engines running, idle thrust is sufficient, but with only one engine, now you have to really crank the engine to get the plane moving, which burns more fuel.

Because of the added strain on the one engine during an S/E taxi, there is a far greater chance of more frequent overhauls and problems with said engine, which add a lot to the MX costs. Additionally, since you are running the engine at a higher thrust setting, the intake air goes in at a faster rate and more powerfully, which on the ground is dangerous because it increases the risk of FOD damage (Hence the reason Powerbacks are not done much anymore).

Even though we do not operate any Boeing planes, I read a document from Boeing about single engine taxis. Boeing strongly discourages the use of the procedure and does not recommend that carriers use the procedure because it creates more problems than it solves.


So my question is, are airlines really gaining much at all by running the procedure, or did they rush into this in panic mode looking for any ways to save fuel and money that looked good on paper? And do airlines actually have data to support these procedure?
 
HT
Posts: 5864
Joined: Sat May 07, 2005 6:20 am

RE: Single Engine Taxis Overrated?

Sat Sep 29, 2007 11:56 am

How about moving this question to "Tech/Ops" ? Might be better off there ?! (Haven't hit "Suggest deletion" though ...).
-HT
Carpe diem ! Life is too short to waste your time ! Keep in mind, that today is the first day of the rest of your life !
 
flyf15
Posts: 6633
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RE: Single Engine Taxis Overrated?

Sat Sep 29, 2007 12:01 pm

I'd say the fuel burn issue could go either way. When I taxi the CRJ single engine, I still usually use idle thrust. Sure, you don't go all that fast but at least you don't have to ride the brakes... saves brake wear and can keep the BTMS's from getting high on hot summer days during taxi out. You're only supposed to taxi at a "brisk walk" anyways...

I feel single engine taxi is appropriate in two situations... during taxi in and during expected long taxi-out. For normal taxi-outs, I don't like it because it overloads the FO when they really should be looking outside instead. If we're going to be #40 in line for takeoff, I will most definitely go single engine. Also, even if your engine wear does go up on the operating engine, it is going to comparatively go down on the other engine.

All in all, for day-to-day ops, my view is that it doesnt really matter much either way.
 
phxplanes
Posts: 381
Joined: Sun Feb 27, 2005 9:24 am

RE: Single Engine Taxis Overrated?

Sat Sep 29, 2007 3:56 pm

Quoting Flyf15 (Reply 2):
If we're going to be #40 in line for takeoff, I will most definitely go single engine.

I'm not flying commercial airliners but I would agree with that. It its just a quick taxi and maybe 5 planes ahead of you, two engines probably is best but when you are going to be sitting in line there is no point in having two engines run.
Just my thoughts
 
scarebus03
Posts: 231
Joined: Sat Apr 30, 2005 3:14 pm

RE: Single Engine Taxis Overrated?

Sun Sep 30, 2007 2:46 am

The biggest problem with single engine taxi on transport aircraft happens when cooldown/heatup times are not respected. If you start an engine 3 minutes before going to takeoff power you will overstress the combustion section and turbines. Although it will not become evident until you are performing unscheduled engine removals thousands of hours before they're due accross your whole fleet. The same can be said about landing, applying reverse thrust then immediately shutting down one engine for the taxi in.

If your company has implemented this practice and doesn´t monitor the cooldown/heatup cycle of the engines before takeoff or after landing, any advantage to fuelsaving will be lost ten fold to maintenance,

Brgds
SB03
No faults found......................
 
tdscanuck
Posts: 8573
Joined: Wed Jan 11, 2006 7:25 am

RE: Single Engine Taxis Overrated?

Sun Sep 30, 2007 2:52 pm

Quoting Apodino (Thread starter):
Because of the added strain on the one engine during an S/E taxi, there is a far greater chance of more frequent overhauls and problems with said engine, which add a lot to the MX costs.

This doesn't really make sense unless you're running the engine up above cruise N1 during taxi...taxi thrust should never be so high that it's putting any significant strain on the engine.

Quoting Apodino (Thread starter):
Additionally, since you are running the engine at a higher thrust setting, the intake air goes in at a faster rate and more powerfully, which on the ground is dangerous because it increases the risk of FOD damage (Hence the reason Powerbacks are not done much anymore).

With tail-mounted engines, as on a CRJ, the risk of FOD damage goes down a lot. Powerbacks are a no-no because the T/R's blow anything on the ground forward and up in front of the engine inlets, which isn't the same as running the engines in normal configuration.

Quoting Apodino (Thread starter):
Boeing strongly discourages the use of the procedure and does not recommend that carriers use the procedure because it creates more problems than it solves.

Absolutely true.

Tom.
 
AAR90
Posts: 3140
Joined: Fri Jan 21, 2000 11:51 am

RE: Single Engine Taxis Overrated?

Mon Oct 01, 2007 2:04 am

Quoting Apodino (Thread starter):
So my question is, are airlines really gaining much at all by running the procedure, or did they rush into this in panic mode looking for any ways to save fuel and money that looked good on paper? And do airlines actually have data to support these procedure?

AA savings are beyond $100M per year --and that was last year. This year AA is hoping for an additional $35M.

Quoting Apodino (Thread starter):
Boeing strongly discourages the use of the procedure and does not recommend that carriers use the procedure because it creates more problems than it solves.

If you were Boeing (or any manufacturer) wouldn't your recommendation be the same? Afterall, you (the manufacturer) are not paying the fuel bills.
*NO CARRIER* -- A Naval Aviator's worst nightmare!
 
2H4
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RE: Single Engine Taxis Overrated?

Mon Oct 01, 2007 9:37 am

Do any aircraft models exhibit accelerated and/or noticeable wear on the nosewheel tire and/or bearings from asymmetric thrust during single-engine taxi ops?

2H4

Intentionally Left Blank
 
ConcordeBoy
Posts: 16852
Joined: Thu Feb 01, 2001 8:04 am

RE: Single Engine Taxis Overrated?

Mon Oct 01, 2007 12:18 pm

Quoting Flyf15 (Reply 2):
You're only supposed to taxi at a "brisk walk" anyways...

Hmph... our airport has jocularly threatened "speed bumps" upon a certain blue&orange carrier due to their breakneck taxiing

Quoting Scarebus03 (Reply 4):
The biggest problem with single engine taxi on transport aircraft happens when cooldown/heatup times are not respected.

IINM, didn't AA (and/or UA) have a serious problem with that, concerning the #2 on their D10s, back in the day?
Faire du ciel le plus bel endroit de la terre c'est impossible sans Concorde!
 
Max Q
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RE: Single Engine Taxis Overrated?

Sat Oct 06, 2007 8:36 am

Well I agree with you Apodino.

After years of telling us it was not kosher, management started telling us to try SE taxi on the 75 and 767.

I will not do it, as most of my peers agree, the extra power required after stopping and / or stresses on the airframe resulting make the whole idea a waste of time and fuel.
The best contribution to safety is a competent Pilot.


GGg
 
User avatar
777wt
Posts: 828
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RE: Single Engine Taxis Overrated?

Sat Oct 06, 2007 3:02 pm

Quoting ConcordeBoy (Reply 8):
IINM, didn't AA (and/or UA) have a serious problem with that, concerning the #2 on their D10s, back in the day?

That was Delta...they'd taxi on #1 and $3 on a DC-10 and fire up #2 when they get close to the runway...it has caused oil pressure problems in which they found out not enough time was given to allow the engine to warm up and has damaged the main bearings.

Single Engine taxi is not allowed on the 777 per Boeing...due to the hyd system for the brakes are powered by both of the engines.
 
metroliner
Posts: 846
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RE: Single Engine Taxis Overrated?

Sat Oct 06, 2007 3:02 pm

Quoting 2H4 (Reply 7):
Do any aircraft models exhibit accelerated and/or noticeable wear on the nosewheel tire and/or bearings from asymmetric thrust during single-engine taxi ops?

presumably they'd alternate the engine they used each taxi, though i can see how that also might increase wear and tear on the nosewheel...
Set the controls for the heart of the Sun
 
tdscanuck
Posts: 8573
Joined: Wed Jan 11, 2006 7:25 am

RE: Single Engine Taxis Overrated?

Sat Oct 06, 2007 7:02 pm

Quoting Metroliner (Reply 11):

presumably they'd alternate the engine they used each taxi, though i can see how that also might increase wear and tear on the nosewheel...

All of the single engine taxi's I've seen use the same engine each time.

Tom.
 
FlyUSCG
Posts: 520
Joined: Sat Jun 03, 2006 5:29 pm

RE: Single Engine Taxis Overrated?

Sun Oct 07, 2007 12:51 am

Quoting 2H4 (Reply 7):
Do any aircraft models exhibit accelerated and/or noticeable wear on the nosewheel tire and/or bearings from asymmetric thrust during single-engine taxi ops

We're not allowed to single-engine taxi on our Dash-8-100's at Piedmont for this exact reason. Our mechanics were finding cracks in the strut of the nose wheel so they stopped single engine-taxiing. However our -300's are still permitted to do it, although the majority of my captains either don't do it or only do it on the taxi in. Maintenance is currently putting a mod on the nose gear on the -100's to take care of it. And of POM mentions several times that when able, single-engine taxiing is mandatory. Now granted this is on a dash, so I don't what a turbo-prop requires for warm-up and cool-down etc...
Go Trojans! Fight On!
 
N353SK
Posts: 1021
Joined: Thu Jun 08, 2006 5:08 am

RE: Single Engine Taxis Overrated?

Sun Oct 07, 2007 8:14 pm

Quoting FlyUSCG (Reply 13):
However our -300's are still permitted to do it

Does the longer fuselage adequately disperse the stress or are there different reasons for allowing it on the -300?
 
2H4
Posts: 7960
Joined: Tue Oct 19, 2004 11:11 pm

RE: Single Engine Taxis Overrated?

Sun Oct 07, 2007 11:17 pm

Quoting N353SK (Reply 14):
Does the longer fuselage adequately disperse the stress or are there different reasons for allowing it on the -300?

Well, logically, the shorter fuselage on the -100s would give the engine more of an arm, resulting in a larger force applied to the nosewheel.

Conversely, the greater length of the -300s fuselage reduces the engine's leverage, and thus, reduces the amount of force applied to the nosewheel.

2H4

Intentionally Left Blank
 
pilotpip
Posts: 2844
Joined: Fri Sep 19, 2003 3:26 pm

RE: Single Engine Taxis Overrated?

Mon Oct 08, 2007 12:12 am

We'll single engine taxi when conditions permit. The ERJ is burning about 400pph per side at ground idle and there's enough power that we don't need much breakaway thrust to get rolling. Because of engine limitations we'll fire up both when we need extra time. This time of the year that only applies to the first flight of the day but as it gets colder we'll have to do it more.
DMI
 
FlyUSCG
Posts: 520
Joined: Sat Jun 03, 2006 5:29 pm

RE: Single Engine Taxis Overrated?

Wed Oct 10, 2007 1:04 pm

Quoting N353SK (Reply 14):
Does the longer fuselage adequately disperse the stress or are there different reasons for allowing it on the -300?

I forgot to mention it in my original post, but most of us think the only reason there is a problem is becuase of the *cough* "quality" *cough* rampers we have in PHL. I don't fly there much but apparently they can be pretty rough on the aircraft up there. And it's mostly -100's up there. So basically, no one is blaming it on the aircraft (plus it's a somewhat new change to our procedures).
Go Trojans! Fight On!
 
BWilliams
Posts: 152
Joined: Sun Sep 16, 2007 9:41 pm

RE: Single Engine Taxis Overrated?

Wed Oct 10, 2007 1:15 pm

Interestingly, I was listening to the JFK delivery/ground feed from liveatc.net, and the delivery controller was telling the a/c to keep one engine on for taxi, since ground was backed up with dozens of planes and 150 minute delay.

I realize that this was to save fuel,but del was telling them to keep one running for taxi before sending them over to gnd. Can the controllers technically do this, or was this just one of those things that JFK does to keep thingd running smoothly? (And yes, - do realize that pilots have that allpowerful "unable" if company prohibits it)
Regards, Brad Williams
 
loggat
Posts: 437
Joined: Sat Feb 12, 2000 11:34 am

RE: Single Engine Taxis Overrated?

Wed Oct 10, 2007 1:39 pm

He was probably telling them that they shoud plan their fuel load with that in mind. If you are going to have to taxi for an extra hour, it would be a good idea to load an extra 500 pounds of fuel or so.
There are 3 types of people in this world, those that can count, and those that can't.
 
pilotboi
Posts: 711
Joined: Thu Sep 06, 2007 8:16 am

RE: Single Engine Taxis Overrated?

Wed Oct 10, 2007 3:48 pm

Quoting Bwilliams (Reply 18):
Can the controllers technically do this, or was this just one of those things that JFK does to keep thingd running smoothly?

I think this is used more often when the delays are so long that aircraft will be waiting on the taxiways for a long period of time. And usually the pilots would want to shut down both engines. But ATC asks them to keep at least one on so that if everyone moves up a little bit, or they need to move one aircraft around to somewhere else, or even clear them for takeoff, then they can do it immediatly, instead of having to wait for the aircraft to startup. I think it's more of a "don't turn off all your engines" instead of a "you must turn off one of your engines"

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