Shutting down an engine whilst taxiing

[loggerhead]

I took a flight with BA some time ago on a B757. We landed at LHR and started taxiing to the terminal. The crew shut down one of the engines to help save fuel (money). I put though a suggestion to my company on the employees company suggestion scheme that we do the same. The savings were phenomenal even if it were possible only 20-30% of the time.

The company decided not to take up my suggestion mainly due to increased Nose wheel scrub etc.

Do many other company’s follow this as a normal procedure and has nose wheel scrub been increased by that much?

[CrashDive]

According to my B737 Manual - Part B / Flying Procedures / Normal Procedures / Section 2.11.1 / Taxi In Procedure

After a 3 minute cooling period, and at aircraft weights below 46,000kgs, an engine may be shutdown to conserve fuel. If it is anticipated that more than 35% N1 might be required to taxi due to upslope or other considerations, do not shutdown an engine.

Keep both engines running on slippery taxiways.


I'm sure the crews of B757's / etc. have a very similar (weight specific) entry in the their manuals.

[spannerhead]

About12 years ago an Italian reg 146 shut down 2 engines whilst taxiing at CDG. Unfortunately the captain decided to shut down the 2 engines that provided hydraulic power. During taxi he depleted the brake accumulator and the subsequent collision with the terminal jetty resulted in extensive damage to the left wing and No2 engine. I think his reputation took a bit of a knock aswell!!!

[Wino]

Loggerhead,

We did an extensive study of this at my airline and found out that the fuel savings were more than offset by wear and erosion in the remaining engine. Any time you take a jet engine above idle on the ground you start sucking up sand and debris. Even if you don't get the classic fod damage, all the sand that goes through the engine erodes the compressor seals and whatnot making the engine "Leaky" so that it burns much more fuel in flight.

The only time one engine is shut down now is if we are sitting in the penalty box waiting for a gate that is more than 20 minutes away.

Cheers
Wino

[Capt Claret]

Occasionally shut down one & four to help taxi speed control by avoiding light braking throughout the taxi.

One day the APU'll die and I'll think better of the idea! :eek:

[pterodactyl]

Brings to mind an amusing incident at Townsville Airport when there were no aerobridges in the early stages of B737-200 operations.

It was necessary to execute a near 180 degree turn to position at one bay at the terminal. On this occasion there was quite a strong wind blowing at right angles to the park position and a sharp left turn was needed. Being ex DC9 pilots one engine had been shut down as was the custom previously.

So with the right engine shut down and the turn progressing it became apparent that speed would be depleted before the turn was complete with the crosswind on the large fin not helping the turn..... more steering.

Only one thing to do...more power from left engine...but high steer angle on nosewheel.....result less speed!....MORE POWER!!..... no speed!!!

Now with the geometry of high nosewheel steering and a hefty crosswind on the fin opposing the turn and high power from the left engine something had to give!

So the aircraft commenced to slowly back out of there!!!!!

Seriously though it was fortunate that no damage or hurt was done to anyone but it does reinforce the idea that it is wise to consider very carefully before shutting down an engine early during taxy.

Some years later a B767 pilot had adopted the non standard procedure of doing "glide approaches" to the aerobridge with both engines cut. He had been counselled but nevertheless...

He did it again at night and ended up in complete darkness apart from the Emergency lighting and stopped quite a bit out of position. Reckoned the APU had failed but the less charitable ones among us might suspect that it had not been started considering that it functioned OK
subsequently.

Best to follow the recommended procedures don't you think?

[ 18 September 2001: Message edited by: pterodactyl ]

[Canuck_AV8R]

I agree that shutting down and engine on taxi in does require some forethought. If you have to make a sharp turn to get into the parking spot or onto the gate then maybe you should consider which (if any) engine to shutdown. This is all part of the decision making processes that we are paid for. We all make bad decisions but to deny this valuable cost saving measure because of a few isolated incidents is silly.

At our company there has been extensive research performed on both the cost issue and the pros and cons of single engine taxiing. We operate a fleet of 23 B737-200s with approximately 1000 departures a week on a mainly shorthaul domestic operation.

The numbers given to us were similar to the following. If we could save 150 lbs of fuel on 50% of our departures, which is not unreasonable, the fuel savings alone over a 12 month period were in excess of 1 million dollars. This is nothing to turn your nose up at.

I have spoken to our maintenance folks and they have stated that they have not noticed any problems with nose wheel scrubbing or excessive engine wear and tear due to single engine taxiing.

We have guidelines in place some of which include recommended maximum N1 settings and recommended maximum weights for single engine taxi. We are also prohibited from single engine taxiing on contaminated or slippery ramps and taxiways.

As always you should follow your company's SOP and recommendations. I am just providing my point of view.

Cheers


http://www.stopstart.fsnet.co.uk/aircraft/FMSshutup.gif

[scanscanscan]

I recall a rumour that Dan Air had a 727 taxi out on two, and forgot to start the middle engine when cleared for takeoff.
Also Laker did the same in a DC10.
Both aircraft rang all the noise abatement bells and Atc observed a lower than normal climb profile!
Also a Cathay 707 on taxi in, at night, in Tiwan was told to stop by Atc, the new that day sops, required two inboard engines to be shutdown after clearing the runway, this all occured together, the cabin crew threw open the doors and 6 in a rush passengers took the big step and hit the ground at rather a fast rate of descent.
The Cathay Captain under line check asked the check captain "What does the new procedure say about this one then?
Change is not always an improvement.

[rr892igw]

sometime in august,one middle east 744 tried
taxiing with only 2&3 from hanger to the gate in wmkk,it went straight ahead ~200m into a 15m
monsoon drain,breaking the nose just infront and just behind the cockpit.the nose gear went through the main deck floor into the cabin.
i believe a/c can fly with 1 eng,sure can taxi with one....only the correct technique
to be used and precautions to take.
hope this would help.

[Ex Servant]

I would advise caution before trying this. An airline I used to fly down the back for had a thing about getting the pax off as quick as poss. It worked OK until one day, for whatever reason, the other system didn't kick in and the with no brakes to stop the a/c the other prop chewed up a GPU before the a/c stopped. After that all engines stayed on until you stopped. Some years later when jets were introduced the policy was reversed to shut down the left hand engines again to get the pax off quicker. Sure enough within 18 months the same thing happened again, this time with an engine and pylon striking a jetty. It doesn't matter what the reason for the hyd. not working was in either case. If the proceedure's right it takes away the risk. At the end of the day I suppose it's a judgement call. Does the benefit outway the poss risk?

[Intruder]

The 744 needs a LOT of brakes to stay at reasonable taxi speed when light! We can shut down #3 or #2 & 3 for taxiing in, after 3-minute cooldown.

With only #3 shut down, it seldom needs any power above idle, unless tower wants an "expedite" on crossing a runway. With both #2 & 3 shut down, power is needed when maneuvering or climbing.

[thermostat]

If the SOP does not prohibit it and the proper procedure in the manufacturers operating manual is followed then there should be no problem. Some aircraft have enough power to taxi on one and with two engines operating, taxi speed has to be controlled with frequent brake application. This causes hot brakes. The main thing is not to do your own "thing" but follow the procedure in the manual. It is normal to taxi on the engine that provides hydraulic pressure to the brakes for instance, and shut down the engine only after starting the APU.
If you know that a turn will have to be made in the direction of the operating engine then keep the speed up. The problem lies in getting too slow and applying power on the wrong side.
Hope this helps.

[magnum]

From Boeing 777 FCTM:
Taxi-one engine:
"Because of additional operational procedural requirements and crew workload, taxiing out for flight with an engine shut down is not recommended. High bypass engines require warm up prior applying takeoff thrust and cool down prior to shutting down. If the engine has been shut down for several hours, it is desirable to operate as low a thrust setting as practicable for several minutes prior to takeoff.
If taxiing in after landing with an engine shut down, the crew must be aware of system requirements, ie, hydraulics, brakes, electrical. A minimum radius turn should be made in a direction that puts the operating engine at the outside of the turn.
In operational environments such as, uphill slope, soft asphalt, high gross weights, congested ramp areas, and wet/slippery ramps and taxiways, taxi with both engines operating"
My personal oppinion on this is that the workload is too high for the amount of fuel saved after a 12hr leg. It is hard to concentrate for normal duties and even more so with one engine out. It might be ok for 4 engine types, though. There is much more fuel to be saved by other means.

[Fil]

Saw a BA 757 at LHR begin a right handed turn into one of the cul-de-sacs only to be told by ground not to. (I dunno who made the mistake) Fact was, although the 757 had only just started turning a had more than enough space to make a small left back onto the the taxi way it came to a halt and was still there quite some time later. When ATC asked what the problem was they replied difficulty in restarting the right engine. Hence blockage occurred for nearly 10 minutes.

[Mago]

The ATR 42 FCOM states that the engine #1 is to be started during taxi, also in the procedures and techniques chapter were Normal taxi is despicted that there "is NO limitations to go either forward or rearward", it even recommends that the starting of the engine could be performed while taxi is in progress being cautioned to do it where the workload is low enough to monitor it efficiently.
Even in adverse wheather it could be done, by SOP means, when the taxiways are not icy or with slush, but if the OAT is to low you should warm up the engine before take off.
Also when taxi-in, the engine #1 could be stopped allowing at least 1 min. cooling time.
Remember that the ATR does not have an APU and engine #2 has a propeller brake that once engaged on the ground serves as an APU.
In regional airports where taxi-in and taxi-out times are very short this procedure turn out to be time and attention consuming, so normally no operator does it unless there are expected delays of 10 minutes or more while taxiing

[purple haze]

sorry to sound ignorant

what is nose wheel scrub?

cheers

[Cardinal]

Taxiing with only one engine introduces a continuous turning moment into the dead engine. The poor nosewheel has to fight this, and if the forces are high enough the tire may be deflected several degrees despite the aircraft moving straight ahead.
"Slippage" is too mundane a term for our vaunted industry, "scrubbing" sounds much more interesting.

[Chief Stick]

Currently flying the A340/A330,and flew for several years the A320.
Word of caution is supporting what Spannerhead said about the Buses, shutting and engine shuts a color (blue, green or yellow) of the hydaraulic system.
This could result to loss of accumulator and might be more than a nose scrub.
Our airline does not recommend the procedure more to operations with mixed fleet flying.
Cheers

[loggerhead]

So i shouldn't try it on my PA28 then? :D

[Iceman49]

We used to taxi out and in on only 1 engine, however tech ops noticed significant wear on our number 2 engine on the 320.

[HugMonster]

Loggerhead, I don't see any problem with it at all for you.

Provided you pay attention to directional control and brake pressures, taxying on one engine should not be a problem at all.

[moggie]

You need to be careful when doing this - if only when it comes to briefing your colleague.

When I was doing my multi-engined training in the RAF we used the Jetstream to train on and sometimes took 2 trainees and 1 instructor up for a 3 hour flight as this saved airframe/engine cycles. On the occasion in question, I had flown the first 1 1/2 hours under training and my mate was taxying in after flying his 90 minutes.

Just as we pulled into the parking apron, making the final right turn onto stand, the instructor shut down the righthand engine (the one inside the turn) without warning us. My mate in the lefthand seat though "s*it" and shut down the left engine thinking we had a problem. This left the instructor to explain to the engineers why we were shutdown in the middle of the pan waiting for a tug.

Now, 30 seconds of briefing...................

I shall not embarrass the gents in question by telling you where they are working now.

As for the merits of shutting down - on a lightweight VC10 it is a good move as it allows you to lay off the brakes, the remaining engines will not need to come above idle and there is little or no nosewheel scrub (the fuselage is a great place to fit the engines). Either shut down one or one from each side (usually inners as the outers have the reversers) and you still have all electrics and full hydraulics.

Anything that makes a VC10 even a tiny bit quieter has to be a good move.

[ 12 November 2001: Message edited by: moggie ]

[JBravo]

We do it on the Fokker 70 to reduce brake-wear. It has nothing to do with fuel-saving. The F70 has enough power on the remaining engine to do anything, and since the engines are located at the rear of the aircraft it has no impact on stearing capability.

[edit] just one more thing, we only do it during taxi-in. On taxi-out we always use both engines. It saves us the hassle tu return to the gate if a start-up doesn't go like planned.

[ 13 November 2001: Message edited by: JBravo ]

[AC A340]

8 years flying the A320 and we did single eng taxi in on a regular basis. Let the engines cool for 3 mins then when you are going straight with no brake being applied Eng 2 off. All of this is tempered with a degree of airmanship. If it is raining or snowing it is not a good idea. The SE taxi out was also recommended if you were light and it was a long taxi out but it was rarely done. All of this was done without the APU and only once did I hear of someone having a problem. New procedures now call for the APU to be started and this seems to add to the workload and consequently fewer SE taxis are being done. On the A340 we shut down number 3 almost all the time on the taxi in and if you are really light, start the APU and shut down 2 and 3. The A330 also taxis well on one but again you have to be light. After saying all of this nose wheel scrubbing is a non issue with some planning.

[strewth]

In relation to taxiing.....

How often is reverse thrust used to back aircraft out from a gate or other situations. I have seen a C-130 use reverse thrust to back up which resulted in a storm of sand an dust being kicked up and out over the apron (2 engines were hanging off the tarmac) and being blown forwards. Surely this can't be a great idea.

Opinions?

[TechFly]

A lot of good sense coming from everybody!

I am personally using engine shutdown when taxing in.

I guess when can starting having a resume of the argument, respecting who prefers all engines running.

1. Crew discussion and briefing

2. Aircraft type (prop/jet, 2/3/4eng, ..)

3. Airport caracteristics (taxyway/ramp slope, ext./airbridge parking, Homebase, familiar airport, ...)

4. Time (for busy traffic, day/night ops, wet/dry, fog, ..)

5. Aircraft restrictions (see MEL/HIL for APU u/s, generators, indicators, ...)

6. Crew knowledge of SOPs (be prepared for corrective actions: PAX announcement if you lose elect.!, ATC,company frequency, ...)

7. int. left for yr comments!!!


Let's hope for our aviation moving up....

Cheers

[zeroG]

Hello loggerhead

Our airline shuts down the right engine on the way IN, -- never out.
As JBravo states, it has a lot to do with brake wear - and fuel savings. The 737 (300-400-500) will accelerate in idle when light after flight.(not the 600-700) Our ground staff always stands ready at the gate with the ground power plug, and I can then shut down after setting the park brake. We do not (normaly)use the APU either. It works just fine, and keep the engineers happy. BUT it's not mandatory. A winter day demands different thinking.

[NigelOnDraft]

BA 75/76 we are encouraged to shut one down on taxi in to save fuel.

In practice it is only done when the stand is known, so which engine to shut down is known. In addition, most will not do so on E4 ac since the idle thrust is so low, 76 can also be difficult. However, a light C accelerates well on just one engine, so not only saving fuel, but also brakes...

As has been stated, some loss of flexibility if the taxi in plan alters...

NoD

[Jambo Buana]

Talking of scrubbing nosewheels have you ever seen the 320's outside nosewheel lift off the ground during a tight turn. Maybe it's even got fly by wire control of the nosewheels when on one engine and in a turn, to prevent scrub. Now that would be cool!

ps I know that NSW steering is FBW. But the lift on the nosewheel is pretty cool! I also think I know the answer is because of geometry and dynamics, but not for sure.

[DJXL]

On the subject of aircraft using thrust reversers to get out of a stand. This move is known as powerback, and although I´ve read about how to do it in a 737, never seen it in action.

A Do328 used it at Southampton not too long ago. Interesting to see, but you can´t help thinking a tug would have been far less hassle. Not sure how you´re supposed to see where you´re going.

[Mago]

You must never initiate your powerback procedure unless you have a marshall indicating with signals how fast and where to go. also is imperative that both crewmembers have their feet on the floor and NOT on the pedals; to brake you have to take the PL out from reverse and if necessary power up a little to arrest the backward movement.

Here is a little horror story while powerbacking: If anyone of you had flown into Aruba on any high season, carnival, easter, etc.. (that is when you have to hold above the airport in order to get a ramp, because it is so crowded that there is no more space on the ground for you to be)you know how caotic the ramp gets, there are only 17 parking spaces and #12 & #13 are positioned in order for you to be completly downwind, with 25-30 kts winds, so in one of those routinly days groun assigned me #13 and when I was about to enter they called me and instructed me to powerback in (in an ATR 42), I asked for a marshall and they told me to expedite and excersice caution! while powerback on my own, luckily I had another company aircraft waiting on the taxiway next to me, directing me the best he could, my F/O told me that he felt like parking a long truck on a delivery ramp, after that we have to wait for 45 minutes for the pax bus to take the passenger out :rolleyes:

[Alpine Flyer]

We also do single-engine taxiing on the Fokker 70, both after landing (1 min cool-down req.) and before take-off (if expecting delays). As the F.70 has one pump for each hyd system on each engine hyd press is not a concern. You just have to avoid using several hyd powered systems simultaneously because hydraulic flow is lower. With the nice flight warning system on the Fokker there even isn't a single warning or chime when you cut the engine during taxying.

We used to do it on the Dash 8 until it was found that the stand-by hyd pump used to power the left system wouldn't keep up enough flow to keep the brakes powered under all circumstances. Now we only feather the left prop to avoid idle thrust and noise.

[below_the_line_please]

Never tried it myself - but it is posssible on the big stuff to back out with the reversers!
http://www.airliners.net/open.file?id=184632

[strewth]

I can't see how that reversing could possible be good for engines! Oh well... Since I asked I have seen Metro's doing it on a daily basis so I guess it is a pretty common procedure.

Great little picture though

[ 30 November 2001: Message edited by: strewth ]

[moggie]

Yes - you can reverse using thrust reverse but it is not a good idea. I have done it on a VC10 - well the captain did it as he was the one who missed the last exit!- but you must be VERY careful.

It is not good for the engines as there is a lot of hot air ingestion and you must not use the brakes as there is a risk of tipping the aircraft on it's tail. To stop going backwards, you just de-select reverse thrust.

I believe (but have no direct experience) that it is easier with turboprops - mates of mine have done it on C130s.