Shutting down an engine whilst taxiing
 

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?

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

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

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!!!

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

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:

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 ]

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

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.

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.

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?

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.

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.

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.

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.

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

sorry to sound ignorant

what is nose wheel scrub?

cheers

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.

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

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

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.