9V-SPJ
Topic Author
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Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 6:00 am

Hi everyone
I recently flew delta about 4x - ATL-JFK, JFK-CVG, CVG-ATL and most recently ATL-LAX. I noticed that on every single flight, the crew taxi on one engine, and when they near the departure runway, the second engine is started up. Same happens right after landing, one engine is shut down while the other is used to taxi with. Is this a fuel saving move? When did they start this practice? Also, I flew home to LA on DL603, a B762, and I noticed that while taxing on one engine, the crew had to use a significant amount of power to keep us moving. Is he saving fuel in the long run?
Just found this to be a bit odd.

9V-SPJ
 
WesternA318
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 6:02 am

Probably trying to save some gallons for the trip home, lol.
Check out my blog at fl310travel.blogspot.com!
 
ngr
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 6:05 am

I noticed the same thing when I flew on Delta over Thanksgiving. I flew BHM-ATL-CAE and CAE-ATL-BHM on MD-88s and 737-200s, and on 3 of the 4 flights we taxied on 1 engine. I wondered the same thing about fuel saving, because when until the 2nd engine was started, the pilot used a lot more thrust than I am accumstomed to. I flew on Delta in August and they taxied on both engines for all flights.
 
Azul320
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 6:06 am

Excuse me, while I kiss the sky
 
Go3Team
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 6:10 am

I wonder if that DL LGA fuel emergency a few weeks ago is related to this.
Yay Pudding!
 
LH423
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 6:10 am

I noticed this as well on my last AA flight, BOS-FLL. I didn't even notice until we were getting to the end of the take-off queue and then I heard the other engine start up. I thought that it was awfully quiet considering we were sitting in row 28 on an MD-80.

LH423
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n506cr
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 6:18 am

Azul320

great article! thanks for sharing!  Big thumbs up

.:capt_moralesg:.
 
WesternA318
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 6:20 am

"Continental's $112-per-flight savings on its Houston-Cancun route is part of an initiative aimed at saving $8 million a year by purchasing extra fuel at lower cost airports."

Hrmm...you think they may be running a scenario of chanign hubs to one with lower avgas? LOL. Instead of IAH or EWR, how bout...SLC and CLE?
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juanchie
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 6:26 am

Let's also keep in mind this has another benefit. By taxining on one engine, you save on engine rotations. In the long run, the engines will last longer and there is no need to run two engines when one will do.


Juanchie
God, forgive me for who I am, and help me be the man I want to be.
 
flyibaby
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 7:03 am

I'm pretty sure that all airlines are doing this now, even the APU useage. The exception is with SW probably because their pilots fly down the taxiway. I used to think it was to be ontime or to give their ramp crews extra time to turn the aircraft, but then I found out it was because the pilots are only paid by how long the trip is scheduled, not how long it takes them. So by taxiing fast they can try and stay below their hours per month and pick up a few additional trips per month.
 
flyibaby
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 7:04 am

I forgot to mention, Independence did a study on this, and found that it costs $1 a minute to run the APU instead of groundpower while parked at the gate. With an engine turning on the ground, about $5 a minute. Therefore the costs savings, and this is just based on the CRJ.
 
ConcordeBoy
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 7:19 am

I'm somewhat surprised they're doing this again.


DC10s used to be taxied out on two engines at UA/AA/CO, with #2 engine started slightly before takeoff.

It was later found that this wore the hell out of #2 engines, with maintenance costs that nearly erradicated any fuel savings.



(though, before anyone asks, this was not cited as a contributing factor to the #2 failure in UA232)
Faire du ciel le plus bel endroit de la terre c'est impossible sans Concorde!
 
planesarecool
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 7:19 am

I wondered why the Delta B767 i saw at Gatwick today was taxiing on one engine, and then when it got to the holding point, there was a kind of hum. It must have been the other starting up.

-Stephen
 
atrude777
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 7:36 am

This engine cutting process ting did start with Delta Express, when they were using Boeing 732's. A pilot noticed how unneccesary it was to use both engines. They were trying to figure out ways to turn arund faster. So they decided as soon as the 732 landed they would switch the right engine off, and taxi on the left so when they got to the gate the ground people could immediatly go to the plane and start taking the bags off without having to wait for the engine to stop for fear of being sucked in. They saw how much time this saved so Delta decided to try it out to the rest of the fleets. Then other airlines caught on. One would think this would be something WN thought of, but as someone pointed out it doesnt benefit them.

Alex
Good things come to those who wait, better things come to those who go AFTER it!
 
Dr.DTW
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 8:09 am

Funny, I was going to post this very same topic.

I noticed a one engine taxi on a 763 on DL from ATL-MIA last month.

IMPORTANT QUESTION: How can a plane taxi with assymetric thrust??

Dr.DTW
 
airxliban
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 8:17 am

just came off an AA MD-80 yesterday in fact where we taxiied on one engine.

i actually didn't realize it, until the pilot said we are number 3 in line for takeoff, there is a UA 752 that is also heading to los angeles in front of us.

in the meantime, we're going to be starting up the other engine and taking off for los angeles.

well whatever it didn't sound exactly like that, but the point was that we were taxiing on one engine.
PARIS, FRANCE...THE BEIRUT OF EUROPE.
 
57AZ
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 8:20 am

The amount of thrust required to taxi is low enough that there is no difference in handling characteristics. Older jet aircraft often taxied on one or two engines but the procedure specified which engine could be used due to design limitations. I believe that the modern systems on twins can usually be driven by either engine. However, on older jets that usually was not the case.
"When a man runs on railroads over half of his lifetime he is fit for nothing else-and at times he don't know that."
 
OttoPylit
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 9:07 am

Atrude777 has it correct. During the mid-90's, Delta asked employees for suggestions in saving money. Pilots suggested that taxiing in on one engine, then taxiing out on the other would save time, but also keep the time on each engine the same. It worked and I assume for the most part is still used successfully. It really doesn't take that much more power to get the plane moving and any more that is used can be backed off once the plane's inertia is pushing the plane along.

Also, when it comes to taxiing a plane, as long as its at slow speeds, the assymetric thrust won't affect the plane any. It's only at higher speeds will the thrust start to interfere with the planes movement.
I don't have a microwave, but I do have a clock that occasionally cooks shit.
 
DL WIDGET HEAD
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 9:26 am

Nope, it's not new. DL has been doing this for years as it really does save on fuel expenses.
 
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Crosswind
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 9:31 am

We evaluated taxiing one one engine last year, with mixed results;

For the A320/321 fleet this became an approved procedure after landing only, saving both fuel and brake wear, as the A320/321 have quite a lot of residual thrust at idle so braking is required with both engines running to keep the aircraft at a safe taxi speed.

For the B757/767 fleet it was rejected. The heavier weights of these aircraft meant that you need to apply a fair amount of thrust on the live engine break away from a standstill, and more thrust than normal to keep the plane moving, negating any other savings you might make. Also the GE-CF6 on the B767 requires a 5 min reccomended cooldown period after landing before shutdown.

It was felt undesirable to delay engine startup on departure for any aircraft in the fleet. Starting all engines on pushback provides some degree of warmup, and also problems that can occur after startup may not always be apparent to the crew, and may not become so until the aircraft has commenced it's takeoff run. For example a fuel leak from within the engine would be reported by your pushback crew, but if you start that same engine at the holding point, there may well be nobody to see it...

Just one operator's experience.

Regards
CROSSWIND
 
AV8AJET
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 9:35 am

We even taxi on one engine at ASA in DFW & ATL especially due to the long taxi time and long lines. We do it when we can, not only does it save fuel but also slows the taxi speed down so you don't have to "ride" the brakes.

IMPORTANT QUESTION: How can a plane taxi with asymmetric thrust??

Power steering helps overcome this, no big deal really.
"To fly or not to fly there is no question!"
 
UN_B732
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 9:40 am

I think jetBlue has done this for a while, but I didn't feel it.
-Mr. X
What now?
 
9V-SPJ
Topic Author
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 9:42 am

Thanks for the replies! Are there certain aircraft in DL's fleet where they taxi on one engine? Does it also depend on the taxi weight of the aircraft?

9V-SPJ
 
WesternA318
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 12:33 pm

Can anyone tell me if the beloved ex-WA 733's taxi with one turning and one umm...sitting?
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isp
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 12:45 pm

JetBlue began doing this Monday 11/29. Also, they are now using GPU's when they never did in the past.

US Airways also taxies on one engine on most of my flights recently.
 
FriendlySkies
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 1:13 pm

On a flight from ATL-ORD on an A319, the pilot used only one engine before takeoff AND after landing. Before hand, we had to sit in the penalty box for a few minutes because left early. If you ever experience it, there is an incredibly high pitched whine when only one engine (IAE) is running on the Airbus. This may have something to do with the lack of sound waves from the other engine, and thus no diffraction from the two sources interacting. Whatever it's caused by, it's annoying as hell! But if it's saving UA money, I can put up with it for 10 minutes.  Big grin
 
ACAfan
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 1:17 pm

Related Question: How much cheaper is a pushback vs. a powerback?
Freddie Laker ... May be at peace with his maker ... But he is a persona non grata ... with IATA
 
Planesmart
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 2:23 pm

Fuel prices may have brought this into focus for some airlines, but it's not a new practice.

In addition to saving fuel, some airlines lease the airframe and engines, while others may own the airframe and lease the engines. Some have a combination.

Engine leases are usually based on a combination of a fixed time period, cycles and running time, so reducing running time can cut variable lease costs, or minimise extra charges applicable if agreed running time is exceeded.

Ideally all engines (whether aircraft, marine or vehicles) require a warm up & cool-down period, so how this translates to engine component wear and longevity is open to some debate, and is probably different for different makes and models.

Airlines track fuel, ownership and maintenance costs of each engine, as well as sharing info with manufacturers, and in some cases, other airlines. If u graph this, there is a point where reduced fuel savings and ownership costs will outweigh extra maintenance.
 
ckfred
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 2:43 pm

I think airlines have been experimenting with ways to save fuel since the oil embargo of 1973.

A friend of mine used to fly 727s for AA between 1989 and 1994. Procedure called for starting the #2 just before entering the runway, and shutting #2 down upon exiting the runway.

Flyibaby:

You aren't kidding about WN planes flying down the taxiways. My friend was at IAH, and a WN plane tried to pass his plane on the taxiway. The captain called the tower and asked if WN was supposed to follow the AA 727 to the departure runway.

The controller gave the WN captain a lot of grief and told him that the next WN plane that tried that would be sent to the penalty box, and a report of the incident would be filed with the FAA in Washington.

 
trnswrld
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 2:47 pm

Pretty good thread here. I will first say that this procedure is nothing new. I have been flying for many many years and I have experienced this uncountable times.
One thing I want to ask that has been previously mentioned regarding "cooldown" times after landing and time for the engine to warmup before takeoff.
I have noticed before especially on MD-80's there would be times that they would literally startup the remaining engine as we were waiting at the holdshort line at the runway. And literally be at takeoff power within a minute or so of starting that engine. Dont these engines require any time to warm up or get to operating temp similar to like say a car? I wouldnt want to floor my car after a cold start on a 30 degree morning. I have taken turbine classes back in college but do not remember studying anything like this. Any input?
Thanks
 
CPDC10-30
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 3:41 pm

Doing this would be terrible with an A32x series aircraft, lucky Delta doesn't have any. First the high pitched drilling sound and then the barking noises. Even when one engine is shutdown at the gate people still get up and look around to see where the barking noise is coming from  Smile/happy/getting dizzy It happens on both the IAE and CFM powered aircraft.
 
AAplatnumflier
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 4:24 pm

Actually it is one of the cost cutting proposals AA and DL passed to save money on fuel. It was a good idea. Along with that they reduced the amount of fuel in their reserves to 5%. The FAA allowed this and now UA is trying to get thos Ok.
 
greaser
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 4:31 pm

So do 747/340s taxi with 2 or 3or 4 engines, because all of the 747s i have flown on have taxied on all 4.
Now you're really flying
 
airxliban
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 4:42 pm

crosswind, what company are you with? not BA i assume...
PARIS, FRANCE...THE BEIRUT OF EUROPE.
 
N743AS
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 5:28 pm

Personally, I'm all about getting to altitude and shutting one down...I found it's a little quieter and fuel burn is reduced. However we do slow a little and the airplane handles funny (we can't figure it out, but I read an article on this problem once). Anyway, I think its genius!

-743AS
If the airplane is one piece, don't cheat on it...ride the bastard down! -Ernest K. Ghann
 
Fiedman
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 6:19 pm

I know turboprops doing a lot I see it a lot with the Dash-8's they taxi in on one engine and feather the second one. And on and off topic maybe someone can either confirm this or correct it but don't four engin airliners shut down one engin enroute to conserve fuel in the air?
Westjet - Canada's National Low-fare Airline
 
AngelAirways
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 8:13 pm

At last people are learning to be efficient and stop wasting.

Hurrah for high fuel prices!
 
Leskova
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 8:35 pm

I've experienced the same here in Europe and in South Africa as well - at least after landing...

Angelairways, you're right about that - now let's hope that the prices go back down quickly and that the airlines keep on using these measures in the long run!

Regards,
Frank
Smile - it confuses people!
 
Planesmart
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 8:43 pm

Fiedman
I know turboprops doing a lot I see it a lot with the Dash-8's they taxi in on one engine and feather the second one.

They feather the port engine so they can disembark passengers more quickly. Saving fuel is a bonus.

Fiedman
And on and off topic maybe someone can either confirm this or correct it but don't four engin airliners shut down one engin enroute to conserve fuel in the air?

Depending on weight and wind conditions, throttling back the 2 outer engines on a 747/A34 might be possible. Those in engineering with access to fleet telemetry will be able to let us know if it really happens.
 
Leskova
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 8:47 pm

And on and off topic maybe someone can either confirm this or correct it but don't four engin airliners shut down one engin enroute to conserve fuel in the air?

While I'm no pilot and don't have any telemetry access, I'll still answer: no.

If you look at the thrust generated by quads compared to the thrust generated by twins, you'll see that it'll always be in the same general area on planes that are roughly the same size.

In other words: quads need the 4 engines roughly as much as twins need their 2 engines.

Regards,
Frank
Smile - it confuses people!
 
Silver1SWA
Crew
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 8:57 pm

I'm pretty sure that all airlines are doing this now, even the APU useage. The exception is with SW probably because their pilots fly down the taxiway.

I don't think that's quite the reason (but I will agree and say, WN are quick around those taxi-ways.). A recent flight from AUS-PHX I was on comes to mind. I swear we were doing a speed comparable to cars on the freeway while taxiing to the runway in AUS. Usually, when you are higher off the ground like in an aircraft you tend to feel you are going slower than the actual speed you are going, but man, the scenery outside my window was zippin' by like it would going 65mph on the freeway in my car.

ANNNNYWAY, WN as far as I know, taxi on two engines at all times, except when pulling into the gate. They often shut one down as they pull in. But prior to departure, the ground crew is not cleared away after pushback until the pilot says they have two good engines...meaning both are started and running. Obviously it depends based on company policy.

It's also common to see some of the prop-driven commuters taxi on one engine.
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
Planesmart
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RE: Delta - Taxiing On One Engine, Is This New?

Sun Dec 12, 2004 8:58 pm

There's no way an engine would / should be shutdown in flight, other than for safety reasons.

Depending on weight & wind conditions (& timetable / slot constraints), it should be possible to reduce throttle settings on 2 of 4 engines, although if flying time is increased, the savings may be very small if not non-existant.

In practice, i suspect it's more likely that when trying to make up time, the settings on the inboard engines may be higher.

HO engineers, please tell us if this happens based on telemetry.
 
Deltacvg
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RE: Delta - Taxiing On One Engine, Is This New?

Mon Dec 13, 2004 12:14 am

..when Taxing up to the gate, DL 757's almost exclusively taxi in on the #2 (F/O's side) engine.

-Beat Army
 
Dazed767
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RE: Delta - Taxiing On One Engine, Is This New?

Mon Dec 13, 2004 12:32 am

I thought I was losing my mind a few times, but I've been on a lot of flights where they did this. USAir for one, every flight I was on with them they did that earlier this summer. On one of my AA flights 2 weeks ago SFO-ORD I think we taxied out on one engine as well.
 
57AZ
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Powerback/shutdown In-flight

Mon Dec 13, 2004 12:42 am

I don't know whether the airlines powerback/shutdown in-flight for fuel/engine conservation. The United States Navy does do this as standard procedure on some of their aircraft, particularly the anti-submarine P-3. At an airshow one year, they had a P-3 fly a practice mission for the crowds at CHA complete with target on the airfield. It was neat seeing the aircraft flying on only No. 2 and No. 3. Due to the autofeather feature, it seemed from the ground that the props were stopped completely. Once he found the "submarine", the FE performed airstart on No. 1 and No. 4 in preparation for the attack. The Navy shuts down engines merely to increase on-station time (flight duration).
"When a man runs on railroads over half of his lifetime he is fit for nothing else-and at times he don't know that."
 
FriendlySkies
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RE: Delta - Taxiing On One Engine, Is This New?

Mon Dec 13, 2004 1:35 am

And on and off topic maybe someone can either confirm this or correct it but don't four engin airliners shut down one engin enroute to conserve fuel in the air?

Well, you can come up with any reason you want, but I think the best and most obvious is that the FAA (and any other aviation admin.) won't let you! That would be considered unsafe operating procedures.
 
Santhosh
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RE: Delta - Taxiing On One Engine, Is This New?

Mon Dec 13, 2004 1:40 am

Is there really a big difference in fuel consumption when taxing with one engine rather than 2 engines? Also even if one engine is used for taxing the thrust settings should be higher to compensate the power from second engines. Right? In that case the fuel used by that single engine on higher thrust setting equals the fuel used in two engines taxing on a lower thrust setting. Please correct me if I am wrong. Also while trying to taxi on a single engine does that aircraft tent to deviate slightly of course due to high thrust from one side of the aircraft and no thrust from the other?

Regards,
George
Happy Landings :)
 
9V-SPJ
Topic Author
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RE: Delta - Taxiing On One Engine, Is This New?

Mon Dec 13, 2004 1:59 am

Santhosh, thats what I was wondering as well. But I think that in the long run, it does save money. I think someone mentioned that power steering is available to keep the aircraft from swivelling off to one side, but isn't there a bit of pressure on the nose wheel to keep the aircraft aligned with the centreline?

9V-SPJ
 
mm320cap
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RE: Delta - Taxiing On One Engine, Is This New?

Mon Dec 13, 2004 2:02 am

FriendlySkies,

Sorry this is so far down below your post, haven't been on the forum in awhile. The reason you hear a high pitched whine on the A319/320 at United during single engined taxi is because we turn on the yellow electric hydraulic pump. That is the whine you are hearing. The reason for doing this, strangely, is passenger comfort. If we don't have the yellow pump running, the Hydraulic PTU (Power Tranfer Unit) will be running. It is basically a hydrualic pump that operates when the hydraulic pressure is more than 500 psi different between systems (green and yellow). This would occur on the single engine taxi because only one engine driven pump (green (left) on United) is running. The PTU sounds like a barking dog and is quite startling to people that don't know what it is.

Miles
 
pilotpip
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RE: Delta - Taxiing On One Engine, Is This New?

Mon Dec 13, 2004 2:08 am

Jet engines at idle aren't very efficient. They are still at about 60% max thrust and sitting at a lower altitude so the consumption can still be thousands of pounds per hour per engine. Assuming 1000 pounds per hour at idle, a 10 minute taxi will save about 170 pounds of fuel. That's a little over 10 gallons. Retail jet fuel here at STL right now is $3.23 so I'd guess the airlines are paying around $1.80 per gallon. That's only $18. That aircraft does 5 legs and the airline has 75 flights at this airport alone. The costs quickly add up. AA started doing this after aquiring TWA when they saw how much money it saved them.

Please get the idea of an airline shutting down an engine in flight out of your head. It's not safe for starters. Second, the loss of performance and added drag is enough to require the running engines to burn more fuel than all of the engines would at a low setting. Third, when a jet engine isn't running, it isn't being lubricated. Engines have very tight tolerances and grinding the bearings at high RPM doesn't help them last long.
DMI

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