n88kb
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UA Single Engine Taxi

Sat Apr 09, 2011 5:51 am

Hi there,

Way back in Oct 2005, I did a few flights with United and on two occasions (A320 IAD to LAS and a 733 SAN to SFO) we taxied on one engine from pushback to the runway. Is this still a common practice with UA and any other airlines for that matter? I know the reason is to conserve fuel and engine life and have never experienced this in Australia or Europe.

Cheers,
N88KB
 
Maverick623
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RE: UA Single Engine Taxi

Sat Apr 09, 2011 6:43 pm

Quoting n88kb (Thread starter):
Is this still a common practice with UA and any other airlines for that matter?

Yes. Most airlines in the US now use single-engine taxi as SOP.
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B6JFKH81
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RE: UA Single Engine Taxi

Sat Apr 09, 2011 7:18 pm

Quoting Maverick623 (Reply 1):
Yes. Most airlines in the US now use single-engine taxi as SOP.

Absolutely, especially at airports with longer taxi-out/in times. Sometimes though if you are expecting a very short taxi time after pushback, the second engine will get cranking right after the first one.
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MIAspotter
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RE: UA Single Engine Taxi

Sat Apr 09, 2011 10:07 pm

Quoting n88kb (Thread starter):
never experienced this in Australia or Europe.

I have experienced single engine taxi on Air France here in Europe...

MIAspotter
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CWAFlyer
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RE: UA Single Engine Taxi

Sun Apr 10, 2011 2:53 am

Many airlines do this with the exception of the first flight of day since some specific checks have to be done.
 
n88kb
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RE: UA Single Engine Taxi

Sun Apr 10, 2011 6:57 am

Thanks for the info.

Another question, Is single-engine taxi done always on the same engine eg No1? Or are the engines alternated, so on one leg No1 is used and the next No2 to even out the hours on the engines.

Cheers,
N88kb
 
Maverick623
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RE: UA Single Engine Taxi

Mon Apr 11, 2011 2:56 am

Quoting n88kb (Reply 5):
Is single-engine taxi done always on the same engine eg No1?

Normally, they are done on the same engine. Airbus planes, for example, use No1 (I don't remember which systems they power off the top of my head). The older 737s like to spool up #2 first, because it powers the A/C system (among others).

Quoting n88kb (Reply 5):
Or are the engines alternated, so on one leg No1 is used and the next No2 to even out the hours on the engines.

Short answer: Engine hours/cycles have nothing to do with single-engine taxis.
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AA737-823
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RE: UA Single Engine Taxi

Mon Apr 11, 2011 5:43 am

Quoting Maverick623 (Reply 6):
The older 737s like to spool up #2 first, because it powers the A/C system (among others).

That is completely false.

I'm a 737-200 and -NG mechanic; you can run any pneumatic system from any source. Normally, the #1 engine runs the #1 pack, and the #2 engine runs the #2 pack. But any combination of that setup is possible.
The APU only supplies bleed air to the left half of the pneumatic system, but that's easily changed by the flick of the "Isolation Valve" switch, which allows left air and right air to mingle.

Also, if you meant Alternating Current (instead of my previously assumed Air Conditioning) by "A/C," that's also false. Each engine has an IDG, and can power the majority of the essential systems. Besides, on single-engine taxi, you're typically running the APU for electric and bleed anyhow... unless you're planning a cross-bleed start from the other engine, in which case you've wasted your time, because you'll burn off all the fuel you saved by spooling up that engine to crank 40psi out of the high stage bleed.

To the original question, yes, LOTS of carriers do this. I first encountered it, personally, on a bankrupt TWA. But since then, I often see it done on Continental, ExpressJet, and others.
I don't mind it, from a mechanic's point of view, so long as adequate warm-up time is provided to the latter engine. Especially on JT-8's.
 
Got2fly
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RE: UA Single Engine Taxi

Mon Apr 11, 2011 4:09 pm

Subject to aircraft and airport limitations our airline encourages single engine taxi for departure and after arrival. It is estimated that it saves in excess of £1 million a year!

As Maverick623 mentioned on the Airbus we use engine number 1 for single engine taxi for the green hydraulic system.
 
Maverick623
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RE: UA Single Engine Taxi

Mon Apr 11, 2011 7:11 pm

Quoting AA737-823 (Reply 7):

That is completely false.

Then I've had several -300 pilots lie to me.

Anyways, a serious question, why do they prefer #2 on the start?
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longhauler
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RE: UA Single Engine Taxi

Mon Apr 11, 2011 8:04 pm

Quoting n88kb (Reply 5):
Another question, Is single-engine taxi done always on the same engine eg No1?
Quoting Maverick623 (Reply 6):
Airbus planes, for example, use No1 (I don't remember which systems they power off the top of my head).

A320 series aircraft when taxiing on one engine will taxi on Eng 1 as stated. This is basically for hydraulics.

Eng 1 powers the Green hydraulic system, and the Blue system is powered automatically on first engine start, and the Yellow system will be powered by an electric pump which is put ON for single engine taxi (normally it is engine driven by Eng 2). The PTU will not power up, as it does not become armed until the second engine start.

We have been told that running one engine and the APU, will burn 4Kgs a minute less fuel than running both engines. With approximately 500 A320 series departures a day (at AC), it can add up.

[Edited 2011-04-11 13:15:32]
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contrails15
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RE: UA Single Engine Taxi

Wed Apr 13, 2011 9:40 pm

We, (Jetblue) started to do one engine taxi's about 6 or 7 years ago system wide. Reason being, it saves you a ton of fuel. With going on the save fuel theme, we then installed GPU units on all jet bridges system wide so the APU dosen't have to run. After landing as well, the #2 to cut. Of course there are cases where both will be running coming into the gate and on occasion they ask if there clear to start the #2 upon pushback. I've seen the #'s of one engine taxi. It saves the airline lots of money.
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n88kb
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RE: UA Single Engine Taxi

Thu Apr 14, 2011 10:47 am

Thanks for the info Folks! Something further, How much more thrust setting is needed on a single engine taxi compared to two? I know it differs from aircraft to aircraft but say for example a 738?
 
bj87
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RE: UA Single Engine Taxi

Thu Apr 14, 2011 11:34 am

This is a common procedure these days. I had a single engine taxi on an Embraer Brasillia once. Also, British Midland used to shut down one engine of their F100s after landing.

Quoting n88kb (Reply 12):
I know it differs from aircraft to aircraft but say for example a 738?

I guess it would require quite a lot of power to get moving but once rolling it is probably about 30 percent more than normal. (but that is just a laments guess)

Things can really get interesting if you need to go around a tight left hand turn with only the left engine running. So I would think this isn't standard procedure on every plane, I can see an A320 or maybe an A330-200 do this but a B777-300 no way. On smaller aircraft with tail mounted engines it has been SOP for years for as far as I know. It saves thousands on engine maintenance.
 
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akiss20
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RE: UA Single Engine Taxi

Thu Apr 14, 2011 1:50 pm

Do 4 engine aircraft do a 2 engine taxi equivalent? If so, I am assuming it would be the inboard 2 to reduce FOD risk?
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n88kb
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RE: UA Single Engine Taxi

Thu Apr 14, 2011 5:10 pm

Quoting bj87 (Reply 13):
I guess it would require quite a lot of power to get moving but once rolling it is probably about 30 percent more than normal. (but that is just a laments guess)

So FSX is realisitic!   
 
EGGD
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RE: UA Single Engine Taxi

Thu Apr 14, 2011 5:27 pm

Quoting Maverick623 (Reply 9):
Anyways, a serious question, why do they prefer #2 on the start?

Presumably because #2 is on the opposite side of the aircraft to the boarding doors and therefore in some circumstances is safer to start earlier than #1. There are many reasons though, probably dependent on company SOP's, individual aircraft characteristics etc.
 
BoeingGuy
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RE: UA Single Engine Taxi

Thu Apr 14, 2011 8:44 pm

Quoting AKiss20 (Reply 14):
Do 4 engine aircraft do a 2 engine taxi equivalent? If so, I am assuming it would be the inboard 2 to reduce FOD risk?



Some customers taxi the 747 with two engines shutdown. It can be done with either the inboards or outboards from a technical standpoint, but likely the inboards shutdown as you state.

Quoting Maverick623 (Reply 6):
Normally, they are done on the same engine. Airbus planes, for example, use No1 (I don't remember which systems they power off the top of my head). The older 737s like to spool up #2 first, because it powers the A/C system (among others).



Boeing guidance is that you can taxi with either engine shutdown, but you should consider issues such as which direction the airplane will be predominantly turning during taxi (so you have the outboard engine being the one running).
 
canoecarrier
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RE: UA Single Engine Taxi

Thu Apr 14, 2011 9:23 pm

Quoting EGGD (Reply 16):
Presumably because #2 is on the opposite side of the aircraft to the boarding doors and therefore in some circumstances is safer to start earlier than #1.

If you have to deplane in an emergency that would make sense. Single engine taxi could add up to real cost savings as some others have said. I can think of several times I've flown out of JFK where we sat in line for takeoff in the early evening rush for over an hour or more.
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413X3
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RE: UA Single Engine Taxi

Thu Apr 14, 2011 9:34 pm

Isn't it true you harm the engine if you do not have it running for a few minutes before you push it to takeoff thrust?
 
contrails15
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RE: UA Single Engine Taxi

Thu Apr 14, 2011 10:34 pm

While pushing out #1 is started first. If you have to do an airstart and I"m speaking only about 2 engine wing fitted aircraft, the #2 is started do to ground having to go in front of the #1 to disconnect the air start hose and air conditioner hose from the aircraft.
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Maverick623
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RE: UA Single Engine Taxi

Thu Apr 14, 2011 11:59 pm

Quoting EGGD (Reply 16):
Presumably because #2 is on the opposite side of the aircraft to the boarding doors and therefore in some circumstances is safer to start earlier than #1.

Nope. We start #1 on Airbus and all air starts regardless of aircraft type or position.

Quoting EGGD (Reply 16):
There are many reasons though, probably dependent on company SOP's, individual aircraft characteristics etc.

There can be no other reason than individual aircraft characteristics. It doesn't matter which way the turn is, or where the jetway is, it's always #1 on Airbus and #2 on Boeing 737s.

Quoting contrails15 (Reply 20):
If you have to do an airstart and I"m speaking only about 2 engine wing fitted aircraft, the #2 is started do to ground having to go in front of the #1 to disconnect the air start hose and air conditioner hose from the aircraft.

A couple of years ago we standardized air starts to always start the #1 engine.
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B6JFKH81
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RE: UA Single Engine Taxi

Fri Apr 15, 2011 12:11 am

Quoting Maverick623 (Reply 21):
A couple of years ago we standardized air starts to always start the #1 engine.

That's what I was thinking but didn't want to make an idiot out of myself by saying it if I was wrong. Especially when we were having the ESC issue for the E190 APUs and most flights were getting a blow starts, I always remember the #1 getting cranked, not the #2.
"If you do not learn from history, you are doomed to repeat it"
 
pilotpip
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RE: UA Single Engine Taxi

Fri Apr 15, 2011 12:11 am

Quoting 413X3 (Reply 19):
Isn't it true you harm the engine if you do not have it running for a few minutes before you push it to takeoff thrust?

Most engines have a required run time before advancing to T/O thrust. In the case of the CF-34 on the 170/175 it's 2 minutes. This is something you have to take into account when doing a single engine taxi. To give you an idea, we usually start the #2 when we're about 4th in line if there are no heavies or 757s ahead of us.

Quoting n88kb (Reply 12):
Thanks for the info Folks! Something further, How much more thrust setting is needed on a single engine taxi compared to two? I know it differs from aircraft to aircraft but say for example a 738?

Can't speak for the 737, but for the ERJ-170 (that's what it says on the type) the aircraft will taxi just fine at idle on two engines. Breakaway thrust on single engine taxis for the most part is around 40% N1. That's maybe 1/4 thrust above idle. Basicallly, you bump the thrust up for maybe 30 seconds to 1 minute, then you let 70,000lbs of inertia do the rest. There are exeptions to this of course. A great example is DEN where if we use 8, or the other east runways we have a pretty good hill to climb to leave the ramp area. We try our best to get a taxi clearance while we're still rolling otherwise we might need to start the second engine before we are capable of moving forward without using excessive thrust.
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contrails15
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RE: UA Single Engine Taxi

Fri Apr 15, 2011 11:53 am

Quoting B6JFKH81 (Reply 22):
That's what I was thinking but didn't want to make an idiot out of myself by saying it if I was wrong. Especially when we were having the ESC issue for the E190 APUs and most flights were getting a blow starts, I always remember the #1 getting cranked, not the #2.

#2 always with an airstart. I do 2 to 3 airstarts a week and its always been like this here. Can't speak for other alirlnes.
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longhauler
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RE: UA Single Engine Taxi

Fri Apr 15, 2011 12:49 pm

Quoting contrails15 (Reply 24):
#2 always with an airstart. I do 2 to 3 airstarts a week and its always been like this here. Can't speak for other alirlnes.

I guess this is an individual airline SOP call. Both the E190 and the A320 have HP external air inlets in the lower centre of the fuselage. This would allow the air cart to be parked on either side, and the opposite engine started.
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contrails15
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RE: UA Single Engine Taxi

Fri Apr 15, 2011 9:33 pm

Quoting longhauler (Reply 25):
I guess this is an individual airline SOP call. Both the E190 and the A320 have HP external air inlets in the lower centre of the fuselage. This would allow the air cart to be parked on either side, and the opposite engine started.

Like you said, its centered under the plane so you can come at it from either side. I'm guessing because the air conditioner hose comes from the unit which is under the jetbridge, and we're told to keep that on until after the air start is done so you have to come from the left side of the plane. With that, it makes sense to start the #2. I'm always taking the air conditioner hose off before any, only cause its a pain to put back and i just want to get it out of the way.

I think your right though, its an individual airline thing. Policy is policy and I do as I'm told like a good little ramp rat.
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Maverick623
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RE: UA Single Engine Taxi

Sun Apr 17, 2011 3:21 am

Quoting contrails15 (Reply 26):

I think your right though, its an individual airline thing. Policy is policy and I do as I'm told like a good little ramp rat.

  
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