Taxing on only one Engine - any disadvantages?

[shon7]

Just read an article which said American Airlines now wants pilots to taxi out only on one engine so as to save on fuel?

Any disadvantages in doing this?

[Mad (Flt) Scientist]

Two possible issues, one safety related, one reliability/economic:

By operating with only one engine, care must be taken that all necessary services (hyd, elec, ECS, etc) are adequately powered from the remaining engine (I presume we are talking about twins here). Plus the consequences of engine failure must still be considered; it wouldn't be good to lose all hyd power to the brakes - even with no engine power the aircraft might take a while to coast to a stop. A lot of those issues can be alleviated by running the APU, but there may still be e.g. ECS problems - sometimes the bleed demands can be pretty heavy.

The reliability/economic concern arises from a change to the usage of the engine. The assumptions behind cycle counts etc may be being violated, and certainly in a new mode of operation might reveal new failures, and more likely perhaps lower BTBFs. One thing that comes to mind is that "normally" the engines get a little time to run before going to MTOP for takeoff. If one now goes straight from cold to MTOP, virtually, will there be rubbing/seal wear/etc issues in service, causing reduced engine ecomony and overall higher fuel burn.

Also, if the engine doesn't start (unlikely, but ...) you now have a plane load of upset customers, whereas if they were at the gate it's easier to get them off (not let them on?).

[saudipc-9]

I cannot imagine that today twin jet airliners can be built without each engine being able to assume all the services required for flight! So taxiing out on one would not really be a problem.
Jet engines do not need any warm up time. From start they are up to temp within one minute. They simply do not have the warm up issues reciprocating engines do.
Dash-8's etc have been doing this for years. You just need a few SOP's and it would be quite safe.

[Banana99]

You can only taxy half as fast

[411A]

ASFKAP has hit the nail on the head...needs to be done strictly by the book, with CAUTION. Otherwise, a long serious decidedly unfriendly talk with the chief pilot might result.

[hobie]

pick two out of four and off you go ...... mind you, pick the wrong two and this might happen ......

http://www.airdisaster.com/cgi_bin/view_details.cgi?date=08232001&airline=Saudi+Arabian+Airlines

http://www.airdisaster.com/photos/sa747/3.shtml

cheers ......

[TR4A]

The only real problem with taxing out with only one engine is breakaway power. A higher power setting to start the heavier aircraft moving. Be carefull what is behind you.

[Vox]

Its company SOP’s in the outfit I work for. To clarify, shutting down an engine as we taxi in is. All we do is give the engine 2 mins cooling for the 757 and 5 mins for the 767’s and when the APU is running we shut down the engine on the inside of the turn onto stand. We have the final decision on whether we want to do this. Considerations are conditions of the taxiways and airport, i.e. contaminated paved area or too many tight turns or uphill gradients etc and a/c un-serviceability or insufficient taxi time.

We also shut down the APU if the A/C is on stand for two hours or more, again to save fuel.

We never taxi out on one engine because we need ground crews in attendance for all engine starts. Ground crews’ getting in the way at the holding point is not what we or the airport wants. I also believe that the thrust required to get a heavy 767 moving would be unacceptable and potentially dangerous. We do however slow taxi, in an effort to massage the on time figures for departure. (Just like BA)

Some bright spark worked out that we save huge sums of money on fuel (across the fleet) by doing this per annum and I consider it in the same light as only carrying the fuel you need and not padding unnecessarily. It’s all about being professional operators and saving money without endangering safety. It’s part of your duty and what your company pays you to do.

It’s a bit strange at first, but you get used to it very quickly and it becomes second nature.