OzLAME
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Engine Shut-Down During Taxi

Mon Oct 17, 2005 11:40 am

I recently watched a Boeing 747-400 land and roll out to the upwind end of the runway. After it vacated and was taxiing past me (a couple of minutes after reverse thrust was cancelled) I noticed that No. 4 engine was spooling down. Do crews do this very often, or does it depend on the individual Captain wanting to save a few dollars in fuel?
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Okie
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RE: Engine Shut-Down During Taxi

Mon Oct 17, 2005 12:05 pm

Taxi on one engine on twins, or taxi with two on 4 engine aircraft have pretty much become common place in the US where taxi times are more than a few minutes. The only 3 holer (727) I have been on lately we had short taxi times and all engines appeared to start on the ramp for take off, I can not be sure about taxi to the gate as I was sitting up front and could not tell if any engines were shut down after landing before arriving at the gate.

Okie
 
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HAWK21M
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RE: Engine Shut-Down During Taxi

Mon Oct 17, 2005 12:43 pm

Out here too Some operators of B747s tend to shut off their Outboard Engines after Landing,Considering the Taxi time & Fuel saved.
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MEL
I may not win often, but I damn well never lose!!! ;)
 
bri2k1
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RE: Engine Shut-Down During Taxi

Mon Oct 17, 2005 1:37 pm

It seems to be operator-specific. UA will always taxi on the minimum number of engines, in my experience. I just got off a round trip DEN-MKE on F9, and they left both engines on even a couple minutes after they were parked at the gate. I couldn't explain this one. In both UA and F9 situations, I'm talking about A318/319 aircraft. It must be a company thing.
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Mr.BA
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RE: Engine Shut-Down During Taxi

Mon Oct 17, 2005 9:05 pm

Many times I've seen BA B744s turn off engine no. 3 while taxying to the gate. Haven't seen other airlines done this before but I've read before that saving fuel is one thing and extra safety to the ground crew.

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HAWK21M
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RE: Engine Shut-Down During Taxi

Mon Oct 17, 2005 10:11 pm

Quoting Bri2k1 (Reply 3):
they left both engines on even a couple minutes after they were parked at the gate. I couldn't explain this one.

Probably Awaiting GPU as APU is U/s.
regds
MEL
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phollingsworth
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RE: Engine Shut-Down During Taxi

Mon Oct 17, 2005 10:12 pm

Quoting Bri2k1 (Reply 3):
I just got off a round trip DEN-MKE on F9, and they left both engines on even a couple minutes after they were parked at the gate. I couldn't explain this one.

That makes no sense as you cannot unload luggage or cargo or service significant portions of the a/c when the engines are operating.
 
bri2k1
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RE: Engine Shut-Down During Taxi

Tue Oct 18, 2005 9:02 am

I know, it didn't make sense to me, either. The APU seemed to be operational since I could hear it start up and continue to run, and there was cool air from the vents and the ground air hose was not connected. The ground power cable was connected for several minutes before the engines shut down.
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SuperD
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RE: Engine Shut-Down During Taxi

Tue Oct 18, 2005 10:15 am

Quoting Bri2k1 (Reply 3):
they left both engines on even a couple minutes after they were parked at the gate.

The only time I've ever left both engines running at the gate was when maintenance needed to come on board to check a problem. No one was allowed off then. If there was a delay in deplaning while the engines were running, maybe there was a mx reason. I can't believe they'd let people off while that engine was on. We get a master warning if we open the main door with the number one engine on.

It's not policy for us, but it's strongly recommended to taxi out on one engine. These days, every captain I've flown with does a single-engine taxi. If we're going to be sitting in the same spot for more than 15-20 minutes we'll ask ATC if we can shut both down. (Let's hear it for Newark! Ground-stops and two hour taxis are our specialty!) Anymore, the only time we start both on pushback is if we're at a small outstation and our taxi is going to take all of five minutes.
 
ArmitageShanks
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RE: Engine Shut-Down During Taxi

Tue Oct 18, 2005 11:56 am

I know BA does not allow any engines to be shut down on the taxi in.
 
777wt
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RE: Engine Shut-Down During Taxi

Tue Oct 18, 2005 12:42 pm

Quoting SuperD (Reply 8):
It's not policy for us, but it's strongly recommended to taxi out on one engine. These days, every captain I've flown with does a single-engine taxi. If we're going to be sitting in the same spot for more than 15-20 minutes we'll ask ATC if we can shut both down. (Let's hear it for Newark! Ground-stops and two hour taxis are our specialty!) Anymore, the only time we start both on pushback is if we're at a small outstation and our taxi is going to take all of five minutes.

Thanks for reminding me the 90 min ground delay at 9am in Newark for EWR-AUA trip, my first experience on a CO, and in a 737 with winglets.
 ill 

There was another CO 737 with winglets behind us waiting for the CO 737 I'm on to pushback. All happened was felt like a pushback 10 feet then stop then the PA comes on and say "There's a 90 min ground delay, we don't know why and they won't tell us why"

After 15-20 min, the CO 737 behind me engines were shut down and sitting there and the pushback couldn't complete until that was towed out of the way.

All while I see a BA 777 taxi by after pushback followed by a Virgin A340-500...


What about when your taxing with the No.1 engine running and you want to make a sharp turn to the same side with the No.1 engine running, how would it be completed if the thrust from the opposite side is not avail due it not being running already?
 
midnights
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RE: Engine Shut-Down During Taxi

Tue Oct 18, 2005 1:57 pm

We are encouraged to do all our maint. taxi on one eng to save fuel. Dosen't always happen that way but we try. As for leaving the eng. running at the gate, our flight crews (AA) are encouraged not to start the APU after landing and leave one eng running until the grnd pwr is hooked up.

Quoting Bri2k1 (Reply 3):
and they left both engines on even a couple minutes after they were parked at the gate

Maybe the grnd pwr unit didn't come online and had to be reset...that happens quite often here at DFW. but then our equipment is crap.
 
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HAWK21M
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RE: Engine Shut-Down During Taxi

Tue Oct 18, 2005 4:42 pm

Quoting Bri2k1 (Reply 7):
The APU seemed to be operational since I could hear it start up and continue to run, and there was cool air from the vents and the ground air hose was not connected. The ground power cable was connected for several minutes before the engines shut down.

Maybe GPU Generator u/s.Pneumatics ok.

Quoting 777WT (Reply 10):
What about when your taxing with the No.1 engine running and you want to make a sharp turn to the same side with the No.1 engine running, how would it be completed if the thrust from the opposite side is not avail due it not being running already

Normally the Engine on the Side outboard of the turn to be encountered is kept running.

regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
bri2k1
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RE: Engine Shut-Down During Taxi

Tue Oct 18, 2005 5:20 pm

Quoting HAWK21M (Reply 12):

Maybe GPU Generator u/s.Pneumatics ok.

It is possible. But, the ground power cable was connected. I wish a F9 operator would chime in. They seemed to do the same thing in both DEN and MKE, on two different A318's.

I hadn't flown F9 before, nor a 318. I've flown 319, 320, and 321 though. The electric hydraulic pump on the 318 is piercingly loud, far louder than on the other types.
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kaddyuk
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RE: Engine Shut-Down During Taxi

Tue Oct 18, 2005 5:47 pm

I cant see aircraft taxiing OUT on one engine, why would any aircraft approach an active runway without being in a suitable configuration for departure. All it would take is for a start valve to not-open and they'd be forced to taxi back in for appropriate maint...

I have however seen aircraft taxi in on one engine, AA, BA and VS all have shut engines down whilst on the taxi into the terminal.
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HAWK21M
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RE: Engine Shut-Down During Taxi

Tue Oct 18, 2005 6:10 pm

Quoting Bri2k1 (Reply 13):
Quoting HAWK21M (Reply 12):

Maybe GPU Generator u/s.Pneumatics ok.

It is possible. But, the ground power cable was connected. I wish a F9 operator would chime in. They seemed to do the same thing in both DEN and MKE, on two different A318's.

Sorry Typo.
I meant APU Generator U/s.Pneumatics ok.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
bri2k1
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RE: Engine Shut-Down During Taxi

Tue Oct 18, 2005 6:11 pm

I agree. I can only hope they're following manufacturer procedures WRT elapsed time from startup to full power. Even if they're doing a derated T/O, if the other engine failed, they'd have to firewall the good one.

I can sort of see how, on a long taxi, it saves some fuel to use one engine, especially if there's a long wait, and hence, a lot of idling. But, today was the first time I'd seen it on an RJ. I was on a US (RP actually) Embraer 145 PHL-SYR, and the taxi wasn't even that long, maybe 5 minutes from F15 to 27L. They only fired up one engine at the gate, though, and started #2 AFTER crossing 27R, so it was probably less than 60 seconds from shutdown to T/O power.

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CX Flyboy
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RE: Engine Shut-Down During Taxi

Tue Oct 18, 2005 8:36 pm

On our 4-engined aircraft we are recommended to consider shutting one engine down if conditions permit when taxying in to the bay. We never do it on a single engine just in case we have an engine failure on the remaining engine. The risk is not worth saving those extra dollars.

As for departing aircraft, we always keep engineers on headset until all engines are started and the APU is shut down before we start taxying. If we taxied away and then had problems starting an engine then it would be a pain.
 
SuperD
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RE: Engine Shut-Down During Taxi

Tue Oct 18, 2005 9:24 pm

Quoting Kaddyuk (Reply 14):
I cant see aircraft taxiing OUT on one engine, why would any aircraft approach an active runway without being in a suitable configuration for departure. All it would take is for a start valve to not-open and they'd be forced to taxi back in for appropriate maint...

The times when we have a malfunction starting an engine that requires mx to look at it are very rare. Although there is always the chance, it's so slight that it makes more sense to conserve fuel on the taxi. This is especially true at airports with long taxi times. If we're going to be out there for a while, it's very possible that we could burn so much fuel we'd be below release fuel if we had both engines running all the time. In that case, we'd definitely have to return to the gate and refuel. That has actually happened in rare circumstances. I've seen it come close before when taxiing out on one engine. That's one of the reasons we conserve by going out on one and occasionally shutting both down when we're sitting. The other reason is that naturally the policy saves unbelievable amounts of fuel. The money we save is well worth the slight risk of a malfunction on engine start causing a gate return.

Quoting 777WT (Reply 10):
What about when your taxing with the No.1 engine running and you want to make a sharp turn to the same side with the No.1 engine running, how would it be completed if the thrust from the opposite side is not avail due it not being running already?

The nosewheel is turned by hydraulics powerful enough to turn the wheel on the ground when the airplane is at a complete stop. That's why we're very careful not to engage steering until the towbars are disconnected. If steering were engaged, the hydraulics were powered, and the tiller were moved, the nosewheel could feasibly swing a tug around and seriously hurt someone. So if the nosewheel is turned and you have a jet engine pushing the plane, it will turn in either direction with one engine running. It takes a bit more thrust on one engine, but it works (in an aircraft with two engines).

Quoting Bri2k1 (Reply 16):
I was on a US (RP actually) Embraer 145 PHL-SYR, and the taxi wasn't even that long, maybe 5 minutes from F15 to 27L. They only fired up one engine at the gate, though, and started #2 AFTER crossing 27R, so it was probably less than 60 seconds from shutdown to T/O power.

They have to wait two minutes from shutdown to T/O power on a 145.
 
777wt
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RE: Engine Shut-Down During Taxi

Thu Oct 20, 2005 3:12 am

Quoting SuperD (Reply 18):
Quoting 777WT (Reply 10):
What about when your taxing with the No.1 engine running and you want to make a sharp turn to the same side with the No.1 engine running, how would it be completed if the thrust from the opposite side is not avail due it not being running already?

The nosewheel is turned by hydraulics powerful enough to turn the wheel on the ground when the airplane is at a complete stop. That's why we're very careful not to engage steering until the towbars are disconnected. If steering were engaged, the hydraulics were powered, and the tiller were moved, the nosewheel could feasibly swing a tug around and seriously hurt someone. So if the nosewheel is turned and you have a jet engine pushing the plane, it will turn in either direction with one engine running. It takes a bit more thrust on one engine, but it works (in an aircraft with two engines).

No I don't think you understand my question.

In this case, pushback is already completed and your taxing to the active. On the taxiway you have the First Officer side engine running and you want to make a right sharp turn after stopping for traffic, how would that be completed if the thrust is not avail from the captain side of the aircraft due to it not running already.
 
bri2k1
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RE: Engine Shut-Down During Taxi

Thu Oct 20, 2005 3:47 am

It's the correct answer to the question. The thrust is produced in the rearward direction, not specific to any one side. Since it's assymetrical thrust, there is a turning moment about the vertical axis of the airplane, but it's small enough that the friction of the nosewheel gear against the pavement is sufficient to turn against it. The distance from the engine to the fuselage is generally as small as possible to minimize yaw if an engine fails in flight, so there's a greater distance from the line where the engines are mounted forward to the nosewheel, and it's not difficult for the nosewheel to be able to steer the aircraft into the only operating engine's thrust moment.

Also, most turns won't be made from a dead stop; the plane will already be rolling forwards, at least a little bit. Especially on heavy jets, it would take a significant amount of thrust to get them moving again if they stopped, especially in a turn, so this practice is avoided as much as possible.
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OzLAME
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RE: Engine Shut-Down During Taxi

Thu Oct 20, 2005 11:10 am

I must say I am surprised at the prevalence of taxiing out to the runway without all engines running. Before I saw the 747 the other day the only a/c I had seen moving without all engines running were being repositioned to parking bays or to hangars.

Quoting 777WT (Reply 19):
On the taxiway you have the First Officer side engine running and you want to make a right sharp turn after stopping for traffic, how would that be completed if the thrust is not avail from the captain side of the aircraft due to it not running already.

Even a Metro is able to be taxied on one engine without difficulty. We used to do it all the time; and in Mitsus as well for that matter, although it's a bit harder with an MU-2 as it doesn't have hydraulic steering.
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Silver1SWA
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RE: Engine Shut-Down During Taxi

Thu Oct 20, 2005 2:02 pm

Quoting Phollingsworth (Reply 6):
That makes no sense as you cannot unload luggage or cargo or service significant portions of the a/c when the engines are operating.

Actually this is common when ground power is plugged in uppon arrival. It can be a minute or two from the time a plane comes in, jet way is pulled up and then power plugged in. You have to wait until the jetway is positioned before you can touch the ground power cable as the jetway cannot be operated if the cable is brought down. The engines will not be shut down until a power source is plugged in and working. Sometimes they leave the #1 engine running while #2 is shut down allowing ground personell to move in and start working while this is all going on. Generally at WN, no one is allowed into the zone until both engines are shut down.

Another thing, depending on the length of taxi to the gate, they may leave the engines running at idle for a while. The engines are supposed to be at idle for at least one minute after landing before they can be shut down.

As for shutting down an engine during taxi to the gate, this is quite common. For WN, they will usually shut down #2 before the plane reaches the safety zone at the gate as that is the side the ground crew is standing as the plane comes in. It's just added safety, allows us to move in quicker once plane arrives and of course, helps save fuel. You also see this with aircraft holding out for a gate for longer than a few minutes.

There was one flight that arrived last week that shut down both engines and coasted in before I brought it to a stop. I was like, wow I guess the pressure is on...I better not stop him too short here...haha.
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
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HAWK21M
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RE: Engine Shut-Down During Taxi

Thu Oct 20, 2005 2:11 pm

Quoting Silver1SWA (Reply 22):
There was one flight that arrived last week that shut down both engines and coasted in before I brought it to a stop. I was like, wow I guess the pressure is on...I better not stop him too short here...haha.

Something Similiar happened a Few years ago out here.
Pilot A was Taxying with Pilot B as they approached the Bay with the marshaller directing them.For some Over confident reason Pilot A [In command] cut off both Engines & allowed the Aircraft to coast to a halt right on the Spot. Fantastic!.
On the Return leg.Pilot B was in Command & decided to try the same & unfortunately ran out of momentum 8-10 feet from the Spot.We had to tow it forward.Pilot B was real Embarrased & was Apoligizing constantly for his goofup.Although He did provide a good laugh.As for Mx we waited to tow the Aircraft on the spot before Laughing,as there was an Active Taxitrack behind.Having a Towtruck on the bay at that time helped.
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MEL
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XFSUgimpLB41X
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RE: Engine Shut-Down During Taxi

Thu Oct 20, 2005 3:46 pm

If I am anticipating a taxi of more than 10 minutes, I make it standard procedure to only start one engine off the gate. It saves some gas- and the more gas I have in my tanks when I get in the air, the happier I am.
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bri2k1
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RE: Engine Shut-Down During Taxi

Thu Oct 20, 2005 8:21 pm

XFSUgimpLB41X, what is the fuel flow of a single CRJ powerplant at idle? I can't hardly see the fuel savings, especially against the added wear of a cold start followed by near-immediate full power for a takeoff.
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UAL Bagsmasher
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RE: Engine Shut-Down During Taxi

Thu Oct 20, 2005 11:38 pm

Fuel flow on a CRJ-200 engine at idle is roughly around 400lb/hr.
 
SuperD
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RE: Engine Shut-Down During Taxi

Thu Oct 20, 2005 11:52 pm

Quoting 777WT (Reply 19):
No I don't think you understand my question.

In this case, pushback is already completed and your taxing to the active. On the taxiway you have the First Officer side engine running and you want to make a right sharp turn after stopping for traffic, how would that be completed if the thrust is not avail from the captain side of the aircraft due to it not running already.

see below.

Quoting Bri2k1 (Reply 20):
The thrust is produced in the rearward direction, not specific to any one side. Since it's assymetrical thrust, there is a turning moment about the vertical axis of the airplane, but it's small enough that the friction of the nosewheel gear against the pavement is sufficient to turn against it. The distance from the engine to the fuselage is generally as small as possible to minimize yaw if an engine fails in flight, so there's a greater distance from the line where the engines are mounted forward to the nosewheel, and it's not difficult for the nosewheel to be able to steer the aircraft into the only operating engine's thrust moment.

Thank you, this is correct. The reason I mentioned hydraulic steering is because this is what makes taxiing on one engine easier. In a twin that doesn't have hydraulic steering, making a right turn from a dead stop with the left engine shut down is very difficult. (It is possible. I've had an engine failure before that required a single-engine taxi in a light twin. It was not easy to turn toward the engine, but it was possible.) The aircraft usually has to be rolling before the nosewheel steering can turn the nosewheel, and then with enough power, the aircraft will turn. In an aircraft with hydraulic steering, the nosewheel will easily turn on the ground at a dead stop. That makes the turning a snap. The hydraulics easily position the nosewheel and then with rearward thrust it will turn. It may turn to one side easier than the other, but it works either way. In all fairness, the regional jets I'm familiar with have nearly centerline thrust on a single engine thanks to the rear-mounted engines, but aircraft with wing-mounted engines often do single-engine taxis as well.

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