AeroTech

Hi,

Is the procedure of a single engine taxiing (for a twin) or fewer engines taxiing (in a trijet or quad) used alot in airlines? Is it an approved procedure? Is it used during taxi-in AND taxi-out?

-What are the benefits and disadvantages of this procedure?

-Is the use of the APU in the gate cost-effective than the use the ground equipments like GPU, ground air conditioning cart,...etc?

Feedback very appreciated. Thank you.
Best regards.

SMOC

In the company I work for no shutting down anything in a twin, and you may shut down 2 (2 & 3) in a quad if you're somewhere like JFK with a very very long taxi time to the runway.

On the way in it's OK to shut down two (2 & 3) if time is suitable and the cooldown times have been met.

Benefit: Saving FUEL and you may still make your destination without a tech stop. (A normal taxi out can cost up to 1.5 tonnes in a 747 and alot more for abnormal).

Disadvantage: when you're heavy you'll look a little silly having to put on a heap of thrust to get moving each time you stop.
If you're unexpectedly cleared for take off when the other aircraft ahead go back to the gate for more gas and you don't have them all turning and burning you may look silly as well (they may require a 5min warm up so start em, warm em, and then shut them down).

I saw a post saying that some US? carriers shut down a donk on the 737s but don't quote me.

Some places charge for ground power etc. so may as well use it, problem is sometimes it's unreliable and also ground aircon can do a poor job in hot/humid weather. Beancounters usually decide where and when APU's should be shut down, but a little common sence is a good start.

renard

There is a procedure published for the RJ aircraft whixh calls for engines 1 and 4 to be shut down if the APU is usable.

It is only mentioned/used in our procedures with respect to contaminaed runways - less forward thrust.

At some airports, vacating runway to brakes on can be a considerable distance and could over a year save a lot of fuel and brake wear.

The only drawback for the RJ is if the APU fails - not uncommon - as it the only main generator. Engine 3 hydraulic stanbt generator would kick in and nose wheel steering would be lost!

LME (GOD)

American shut down one engine on the 777 but only if the apron is dry!

TopBunk

BA do not approve taxying out with engine(s) shutdown, although if you taxy out to a remote holding area awaiting a slot, which could be an hour away, it is then usual to shutdown all engines until about 25-20 minutes before the slot time.

Taxying in, the procedure is available to shut down an engine at pilot discretion if desired in order to save fuel. This applies to 737, A319/32/21 and 747 aircraft (I can't comment on 757/67/77 aircraft). On a shorthaul twin, I believe the saving is about 20kg of fuel per sector, which in itself is not much, but with about 110 SH aircraft doing about 6 sectors per day that equates to about 13 tonnes per day @ about $650 per tonne.

Circumstances which would preclude shutting an engine down would be local restrictions eg T4, local gradients, very short taxi time, etc.

AeroTech

Hi,
Thank you for your posts.

-If the APU is shutdown during single engine taxiing, can the operating engine provide air to both packs?

-Is the ant-ice (wings and engine) is used during single or lower engine(s) taxiing if icing conditions exist? Since the shutdown or the dead engine is not anti-iced engine, can this cause a real problem?

-In certain icing conditions like freezing drizzle, I guess an engine run procedure is required where the engine is revved up to 70% N1 every 30 minutes during taxiing. Are there other similar procedures in icing conditions?
Since the engine must be turned up to 70% N1, it means idle ground is not enough to shed the ice. Does it mean that shutdown engine (in single or lower engines taxiing) will be iced up by the freezing drizzle?

-"In case of freezing drizzle, it seems that the use of engine anti-ice during taxiing is not very efficient since the engine run procedure (70% N1 or more every 30 minutes) in case of freezing drizzle."
What are your comments or opinions on this statement, please?

-Besides single engine taxiing, what are the guidelines provided by the airlines to the flight crew regarding the reduction of the aircraft operating cost? (fuel consumption...)

Any feedback(comment, opinion,...) is very appreciated. Thank you.
Best regards.

blue up

My UK airline will allow taxi-IN on 1 after a set cooling time on the 767/767 but not taxy-OUT. All to do with fire watch on start-up. We also try fuel saving by not running the APU on the ground if we can get GPU power. My own question is....if you switch off the APU air bleed, the EGT goes up and therefore(?) the constant-speed-engine (aka the APU) must be burning more fuel. Someone suggested that the bleed air dump "port" thingy is quite small and therefore the APU needs more fuel with the bleed off than on.
Surely not?

RobertS975

As a frequent passenger on DL, I can tell you that DL taxis out on one engine on just about every twin I have been on- 737s, MD88s, 757s and 767s.

Swedish Steve

One engine can supply air to both packs, but it doesnt matter on the ground. One pack or no packs is sufficient for taxi in.
Wing antice is not used on the ground.
Engine antice is, but only on a running engine.
In freezing fog etc, the engine is not run up during taxy in. The aircraft arrives on the gate with ice on the fan blades which is removed by the ground crew.
Modern engines only have the cowl deiced. The fan blades and spinner are deicied by centripetal force. This does not work below 70%N1.
So after taxying out in freezing fog you must run up the engine to remove the ice before departure. Even this does not always work. Ask SAS about Oslo airport 3 years ago when they failed 3 B737 CFM56 engines the same day in freezing fog.
The RR Trent engine is very susceptible to freezing fog and the core of the engine can ice up. This will stop you as the only real way to remove it is to park the aircraft in the hangar for a while!

Swedish Steve

Ref APU Fuel usage, it depends on the APU.
THe old Garret GTCP85 which was on most old jets was most economical with the bleed off.
Most modern APUs have a separate bleed compressor which runs all the time. With the bleed sw off, the surge valve will open and yes the fuel consumption will get higher.
On my old Tristar, the most economical was APU in min mode, bleed valve open and one pack sw on. This definitely used less fuel than switching off the bleed valve.

Jambo Buana

Boeing do not recommend taxy out on one engine but have no problem taxiing in provided all factors have been considered. Then again in JFK with upto 3 hours at the holding point and a lot of creeping it would make sense to taxyout on one.

My airline (LCC), wants us to start APU taxiing in, only if the delay on stand will be more than a couple of minutes. We use about 6kgs/min/eng 737. The APU uses 2kgs/min 737. Also we do not care about the stop/start cycle of our APUs because the maint price is fixed with a third party. Fuel is most airlines single biggest cost, so saving it is paramount.

On a side note, the rush mentality around LCC turnarounds is ludicrous. Everyone is on a bonus to be speedy. Occasionally this turns into haste and cargo doors etc are opened whilst engines are still running. The best reason to single engine taxy in is to reduce the odds by 50% of sucking in one of those poorly trained baggage handlers! Trust me, just like the Helios accident was entirley predictable, the next accident will be a suck in on a LCC turnaround!!

None

Where can I find this information in written form? Any idea what manual, magazine, newsletter, bulletin?

Propellerhead

A mate of mine used to fly the Fokker 100 and they were allowed to taxi out on one engine. They lined up one day, pushed the thrust levers up to 40% to check for stable, and oops, one was at 40%, one at zero!
Sorry tower, slight technical problem!

Jambo Buana

Pretty sure its in the Boeing Flight Crew Training Manual FCTM under taxiing.

None

Where?
"Taxi - One Engine
Because of additional operational procedural requirements and crew workload,
taxiing out for flight with an engine shut down requires a high degree of crew
awareness. High bypass engines require warm up prior to 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 at as low a thrust setting as practical for several
minutes prior to takeoff.
If taxiing in after landing with an engine shut down, the crew must be aware of
systems requirements, i.e., hydraulics, brakes, electrical. If possible, make
minimum radius turns in a direction that puts the operating engine on 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."

aw8565

At Gatwick where I work an A319 stopped on stand and shut down the engines but unfortunately stopped a little short and the jetbridge wouldn't fit on. A tug was arranged to pull the aircraft forward into the correct position but instead the flightdeck (helpfully - thanks!) offered to restart the engine(s) and pull forward themselves to avoid the delay waiting for the tug. Is this bad for the engines? Running away at cruise power for an hour or two, shut down, then immediately restarted?

Also I remember hearing a story a while ago of a Quantas 744 that was aiming to set the longest (so far) commercial non-stop flight. Can't remember where from/to. The aircraft was apparently towed into position at the beginning of the runway to save the fuel otherwise used on the taxi out. I'm sure that the time between start up and (I'm sure a high power setting for a heavy, fuel-laden) takeoff would have not been more than a few minutes. Surely cold start to high power can't be good? My Vauxhall Astra certainly doesn't like it....

junior_man

We taxi single engine with A 319, 320 & 321 plus 737. No problems with either airplane. Taxi in or taxi out. Taxi in with 1 engine running and APU off if gnd power available. Airbus taxi is with number 1 running, 737 is with only number 2 running. Workload is not hard to start the other engine during taxi out.

Ground power is about $70 an hour cheaper than using the APU on the ground

On-MarkBob

Everything is a compromise, there is no such thing in aviation as a cheap deal!! Single engine taxi has other potentially expensive risks, for example the side load on the nose tyres. (and indeed the structure). Those who are involved with this proceedure keep an eye out for the tell tale signs which are spits in the rubber in the directon of the wheel and chevron splits. There are already documented incidents where the nose wheels have shed the rubber topsides due to high side loads having been imparted upon them (that also occurs due to high speed sharp turns). One incident on an A320 climaxed with an engine failure due to the fact the rubber was injested by the engine on take-off!! Well done chaps for getting her back down safe! - what we're paid to do of course! but very expensive for the price of a bit of extra fuel, and anyway are you paying the bill? If not, use the other engine and let the bean counters have the problem. It might be cheaper in the long term in any case.

In the case of restarting the engines again (above), there is no real problem here so long as the pre-shutdown criterea has been met, (ie. idle for 2mins for example). The big problem is the diversion form the norm as this is when the risk factor escalates dramatically. Make sure all the checklists are properly completed (ie. hydraulic switches on and other important suff), and that the ground crews are clear and not approaching with the baggage, which means you should have a man on the flight interphone telling you it's A-OK and he's normally with the tug! if in doubt wait for the tug, it's OK, it's happened to me and will no doubt happen to many more hence.

Bob.

Taildragger67

First up, it's QANTAS ("There's no 'U' in Qantas... ")

Anyway it was the delivery flight of QF's first 744. You're correct, it was towed out to the strip and ran-up there. Given that they were going further unrefuelled than had ever been done before, they were arguably justified in cutting every corner they could and having them topped to the vents at the get-go. They also used a fuel which had been especially brewed for that flight.

From the Qantas website:
"On 17 August 1989 the first Qantas 747-400, VH-OJA 'City of Canberra', touched down at Sydney Airport after a non-stop flight from London to Sydney. The 17,039 km flight, under the command of Captain David Massy-Greene, took 20 hours, nine minutes and five seconds and established a new world distance record for a commercial aircraft."

That absolute record was broken a few years back by a 777-200 (although that aircraft was in a lighter weight category, so the Qantas 747 record stood in the heavier category) which itself was broken last year by a 777-300LR which flew Hong Kong-London (and so took both the absolute and higher-weight category records). I'm not sure if any Airbus aircraft had beaten the Qantas 747's record before the 777s did.

junior_man

We have been doing single engine taxi for over 10 years without incident.
Not a big deal to do. If you are heavy you start out with a turn towards the non running engine and that avoids large loads on the tires and nose gear.

Not much work to do it.

A 320, to start second engine:
yellow hyd pump OFF
X bleed Auto (usually there anyways)
IGN selector to start
engine master ON

To shut it down taxiing in
Yellow pump ON
Engine master OFF