A320 single engine taxi out threats

[oicur12.again]

I joined my new airlines less than a year ago and SOP permits single engine taxi out. Great idea for fuel savings but if not handled well can also present threats.

Our procedure is to start the second engine at a time to permit 3 minutes warm up prior to taking the runway.

What I find disconcerting is that single engine taxi obviously requires the delaying of after start check list/flight control checks/before takeoff checklist until the second engine is started and sometimes almost on the runway.

This requires the FO to be heads down and pretty much out of the loop as the aircraft approaches the hold with converging traffic, frequency changes and takeoff instructions etc.

Our company recently had a runway incursion as a direct result.

I have flown Airbus at many other airlines but never before have I seen single engine taxi.

I am wondering what other carriers do it and how it is handled.

I am especially puzzled by the fact that we save a small amount of fuel on taxi out, force the PM to be heads down at the most critical point of the taxi then burn the fuel en route to catch the commute home flight????

Seems kinda pointless!

[FlightDetent]

I think the same. Hence the question here: http://www.pprune.org/tech-log/580812-a320-one-engine-taxi-out.html#post9422235

The present base have average taxi out times 15 minutes, 10 more when busy. I am slowly leaning towards trying one day... but exactly as you point out, would already start the 2nd when 3 to depart and 2 more to land, i.e. approx 7 minutes to go.

[Denti]

Dunny why, but my company decided quite some time ago that single engine taxi out is only approved on the A330, not the A320. Both are flown by the same pilots in mixed fleet flying. Single engine taxi in however is approved and encouraged on all fleets. The concern might be about misjudged engine starts, the PM (which is the captain on FO sectors) being head down and so on. But then, we moved from a policy of doing flight control checks before starting to taxi and no checklists from the start of taxi until being parked to the normal airbus SOPs which have us quite a bit head down during critical phases anyway.

[Check Airman]

This requires the FO to be heads down and pretty much out of the loop as the aircraft approaches the hold with converging traffic, frequency changes and takeoff instructions etc.

Agree with this 100%

My company does SE taxi, and the delayed items (flight controls, SEC resets etc) combined with the long checklist, have cause me to be heads down until practically reaching the runway on several occasions.

Of course, if the other fellow messes up the taxi instructions, I'll be called into the office as well.

[PENKO]

The actions to start the engine take about 7 seconds.
The after start actions take about 5 seconds.
The checklist another 10 seconds max.

All other checks (flight control checks etc.) would be done on the taxi out anyway.
What is the problem? Surely you can find a spare 22 seconds during a long taxi?

[tdracer]

Correct me if I'm wrong (as if you guys wouldn't :E), but I don't think autostart is basic on the A320 (perhaps it is on the more recent production). No autostart means someone needs to be 'heads down' during the entire start sequence unless you want a tailpipe full of molten metal.
As a propulsion guy, 3 minute warm up is really short for initial start to takeoff power. If you're talking a quick turn-around it may be OK since the engine never really cooled off, but after an overnight that's a big thermal shock to the engine (compressor rub/permanent performance loss - in an extreme case it can cause a surge). Five minute warm up is the minimum I'd recommend.

[flyingchanges]

3 minute warm up is really short for initial start to takeoff power. If you're talking a quick turn-around it may be OK since the engine never really cooled off, but after an overnight that's a big thermal shock to the engine (compressor rub/permanent performance loss - in an extreme case it can cause a surge). Five minute warm up is the minimum I'd recommend.

We lease the engines...

[tdracer]

We lease the engines...
OK, but you still buy the fuel...

[flyingchanges]

Doesn't come out of my check (yet):eek:

[TSIO540]

I fly IAE equipped 320's..

We have auto-start that requires monitoring only starter time limits should an ECAM require cranking.

If Auto-start is available, it really does take about 5 seconds to initiate the start; and the after start flow takes about 10 seconds... Very easy.

The manuals we have require a 3 min warm up if the engine has operated in the last 2 hours otherwise it is 5 minutes; however our S/E taxi out procedure calls for start initiation 10 mins prior to takeoff as an additional layer.

Airmanship points.. If for any reason the workload is higher than taxiing in a straight line with an automatic start, you shouldn't be taxiing.. so stop! Tell ATC you need 3 mins at the holding point before ready. If there are expected difficulties on the taxi or you have relevant defects, keep a standard two engine taxi.

The threats with SE taxi IMO are forgetting to check the ground crew are clear, forgetting engine anti-ice, tight left turns and anyone in the other seat with low experience (to monitor me or the start).

From a commercial perspective, if you're flying older machines you might not detect faults until at the runway which at most major ports will mean you can't get a gate on your return (outer bay only) where as before you taxi you can usually reclaim your departure gate.

[PENKO]

tdracer, single engine taxi out is not allowed with a cold engine...it needs to have flown less than 6 hours prior.

There was a lot of scepticism in my outfit when the procedure was adopted, but there really is nothing to it once you get used to the flow (i.e. after two or three flights).

[Fursty Ferret]

Correct me if I'm wrong (as if you guys wouldn't ), but I don't think autostart is basic on the A320 (perhaps it is on the more recent production).

You're wrong. The FADEC will catch any problems and dry motor the engine if necessary.

I don't bother with timing start up as I know I can do an attempted start; an auto-crank; and a second manual start within the time limits. If it doesn't start after that I want to know why and the subsequent return to stand for engineering input will more than suffice for cooling time. :-)

[sierra_mike]

single engine taxi out is not allowed with a cold engine...it needs to have flown less than 6 hours prior.

PENKO, what engines do you have? can't find a reference on that for the CFMs

[bugged on the right]

I'm sure the aircraft won't let you carry out your own vmcg investigation will it?

[PENKO]

sierra_mike, it's from our OMB

[sierra_mike]

PENKO i thought so :E IAE engines? can't find such limitation in our OMB but we have CFMs

[FlightDetent]

A credible gentlemen suggested once, that on CFMs, for a cold engine ...

warm-up time up to 13 minutes (until the last one of them) provides increased TT margin and reduced wear preferential to any fuel savings.

That's why I actually asked the question in the other thread.

[oicur12.again]

Penko

"All other checks would be done on the taxi out anyway"

True, however my point is that when conducting a 2 engine taxi out, these are usually completed before arriving near the runway, often way before. The length of taxi time is not relevant.

Because we do not do any checks or actions with single engine taxi out until after the second engine start, we are simply bringing these items with us closer to the runway where we are meeting other traffic, checking for landing traffic, switching radios and making be seated PA's.



"Surely you can find a spare 22 seconds during a long taxi."

This morning we timed our procedures from commencment of second engine start. It took just under 3 and a half minutes to start the engine, complete after start scan, read after start check list, conduct flight control check both sides, mini brief, before takeoff checklist to the line, be seated PA, before takeoff scan and before takeoff checklist below the line.

PM was heads down almost the entire time and only joined the party crossing the hold line.

For info, our FCTM requires PM to "monitor the start sequence" and FCOM requires us to check "main and secondry idle parameters".

Anyone who trusts FADEC to start an engine without monitoring it has never seen FADEC get an engine start wrong costing many $$$$.

Just not worth saving the small amount of fuel IMHO.

TSIO540

"Tell ATC you need 3 minutes at the holding point....."

If you asked ATC for this in Chicago at peak hour because you mistimed the start, it would probably be the last time you ever saw Chicago.

[PoppaJo]

Is this just an American thing?

Never seen it in Australia or Asia. Seen it on JetBlue, Virgin, Southwest and the rest of them.

[PENKO]

iocur, that's not our decision to make. If our beancounters think single engine taxi benefits profit overall, who are we to say the contrary?

But honestly, I like the procedure. It's time efficient and if done well, of little impact on the operation. You just need to be sensible about it.

Our engines are CFM...

[TSIO540]

TSIO540

"Tell ATC you need 3 minutes at the holding point....."

If you asked ATC for this in Chicago at peak hour because you mistimed the start, it would probably be the last time you ever saw Chicago.

[/QUOTE]

I totally agree.. In Hong Kong you'd be spanked for that too. WRT asking for 3 mins.. I mean a delay owing to SE taxi should not occur with good judgement unless there is a tech fault. With that in mind, don't be a d#%k to ATC, tell them while there is an opportunity to get you out of the way.

One particular operator was taxiing SE in front of us at about 5kts (steady). The controller asked if there was a tech issue. They said "no, it's a new company policy to taxi on one engine!"

The ATC supervisor then advised to "expedite or you can 'company policy' next right into V4 (disused taxiway) and hold until you're ready to taxi faster"

[PENKO]

And that's why we are paid a nice salary: to judge when or when not to...
Don't blame single engine taxi for some pilot's inability to apply common sense. If you know that you will hold up traffic because of single engine taxi, then either don't do it, or increase the thrust on your live engine. Not rocket science.

[CaptainMongo]

I two engine taxi when it makes sense (warm up requirements, short taxi to RWY, required by local procedure, heavy weight at high altitude airport, contaminated taxi ways, etc.)

I single engine taxi from the gate all other times. SE taxi allows me to: call for taxi about 60-90 seconds earlier, saves fuel, helps prevent hot brakes on a quick turn A/C (no brake fans at our company) I also find it easier to taxi SE.

Our checklists are built with SE taxi in mind. After engine start we accomplish the control check and read final items (5 of them - no briefing items). Our fleet has spent a significant amount if time modifying our checklists to prevent our FO's from being heads down during this process.

If I were at an airline which didn't have this SE taxi "culture" built into it, I could see how it could be uncomfortable, for us it is SOP.

[Fursty Ferret]

. Tell ATC you need 3 minutes at the holding point....."

Maybe ATC should give more than three minutes notice of position in takeoff sequence?

[sonicbum]

Our checklists are built with SE taxi in mind. After engine start we accomplish the control check

That's a good point here. Did your airline liaise with Airbus to ask for a no objection in performing the FLT CTL check with 1 engine running ?

[Amadis of Gaul]

Operated out of ORD yesterday. Started single-engine, came out on A21, right turn on A, left on A17, left on D, started the second engine when joining D, had plenty of time before we got to 22L.

Really not that hard.

[Uplinker]

Makes me laugh.

In our crew room there are these posters from ATC emphasising how important the taxi phase is and how we should avoid distractions; both heads looking outside and agreeing all clearances etc.

So what do we do? Bring in single engine taxi out. Brilliant ! That won't cause any extra distractions will it ?!?!?!

We follow Airbus SOPs and don't do control checks until after both engines are running.


.

[PENKO]

How did they manage single engine taxi on the DC 9 with a checklist 3x as long and no autostart?

[EcamSurprise]

So what do we do? Bring in single engine taxi out. Brilliant ! That won't cause any extra distractions will it ?!?!?!

Oh come on.
We do flight control checks et all while taxiing on 2 engines.

Is it REALLY that more distracting for PM to go "Pump off, Bleed on. Ign. Starting eng 2".
No. If you allow yourself enough time (airmanship!) then there is no rush. There is no real extra distraction.

I am sure the next reason we will hear here is "but there might be a fuel leak!". Which usually comes from the guy who disconnects the ground crew before Eng 2 has even starting turning anyway.

[oicur12.again]

Poppajo

I have not seen single engine taxi in my previous 6 airlines that operate 320/330 in aus/asia/pacific.

Penko,

"Thats not our decision to make".

Its not my decision, i am a simple line pilot. But it is up to flight ops to balance the competing interests of safety and profit. Some do this well, some dont. Bean counters are important but they should never be permitted to be the sole driver of operational policy!

Captainmongo

Great point. Our company does not have SE taxi culture and as such the procedure is rather cumbersome and not very well thought through, IMHO.

Sonicbum,

I suspect the entire SE taxi procedure is done without much support from Airbus.

Ecamsurprise

Many airlines now do the flight control checks stationry before taxi. Both sides.
And I suspect you did not read my second post on the subject, there is a lot more to it than pump/bleed/start. Remember airlines have different procedures and my airline probably does it differently to yours.

[CaptainMongo]

Just like we only manage errors and not eliminate them we only manage distractions. We don't eliminate them.

Can SE taxi be a distraction for a FO? Sure if he or she hasn't been properly trained, or if the Captain isn't taking into account FO work load or experience or any number of other factors a good Captain should be evaluating to determine whether a two engine taxi is a safer course of action.

I conduct initial operating experience line events and our FO's flying the line for the first time are very comfortable and competent performing duties using SE taxi. Do I call for second engine start on the first leg of IOE earlier than I normally would - of course, by the second or third leg - usually not. Our FO's are conditioned through their simulator training to expect to taxi SE (as are our Captains)

The Captain calls for the control check after the second engine is started. Our procedure does not require the Captain to look inside the cockpit during the control check, the FO monitors the correct displacement on the F/CTL page.

As I stated earlier, I find SE taxi, when appropriate, easier - I'd rather taxi with idle or just above idle power than ride the brakes. Finally SE taxi is encouraged at our airline, it is not mandatory.

[Johnman]

Brake life and fuel savings may govern company policy on permitting aircraft to taxi with one engine shut down.
However, if taxiing out with one engine shutdown, the flight crew should be aware of the following:
It is recommended to retain the use of Engine 1 during taxi to maintain the accumulator pressure of the blue hydraulic system.

If taxi is performed with Engine 2, the flight crew should check the accumulator pressure of the blue hydraulic system.

Slow or tight turns in the direction of the operating engine may not be possible at high Gross Weights.

It is not possible for ground personnel to protect the engine against fire, when the aircraft moves away from the ramp.

The remaining engines should be started with sufficient time for engine warm-up before takeoff

Any faults encountered during, or after, starting the remaining engine may require a return to the gate for maintenance. This could result in an additional departure delay.

Taxi with one engine shut down may require higher thrust than usual. Caution must, therefore, be exercised to avoid excessive jet-blast and the risk of Foreign Object Damage (FOD).

It is recommended that the flight crew use the APU. However, APU bleed should be switched off, in order to avoid ingestion of exhaust gases by the air conditioning system.

[Finns]

Is there any difference (on arrival) between .
PRK BRK..... on
Y ELEC PUMP .... off
ENG 1 ....... shut down

And (parkbrake on)shut down the eng 1 first then turn off the y elec pump ?

[pineteam]

Hi Finns,

Yes it’s in this specific order to allow the PTU self test. Pay attention next time you switch off both engines you will see the PTU memo on the lower ecam.

EDIT: Can’t find the info in the FCOM to back up what I said above... I might be wrong but I’m sure it’s something to do with the PTU...

[EGPFlyer]

The PTU will run if you have both engines off and the Y pump on.

[Fursty Ferret]

Is there any difference (on arrival) between .
PRK BRK..... on
Y ELEC PUMP .... off
ENG 1 ....... shut down

And (parkbrake on)shut down the eng 1 first then turn off the y elec pump ?

No - the yellow pump is a PM task and independent from the engine shut down which is the important bit. Set the parking brake, confirm it's on, and shut down ENG 1. There's no requirement to wait for the pump to go off, although I delay it a second or two to ensure the accumulator is topped off when the park brake is set.

[MD83FO]

Fusty Ferret, I agree, but the standards office here wants this things to be read off the FCOM, as it is a supplementary procedure requiring the pump to be switched off before the engine is.
I hate when I cant use common sense only because thats the way the manual it's written, there are sooo many things like this in operation.

[Nil further]

AFAIK Single engine taxi out is not an approved Airbus SOP on the 320 series ,they have ‘ no technical objection’” which means that airlines can get away with doing it . It is not however an Airbus SOP according to our Airbus guru.

[KingAir1978]

I don't work for an airline that uses single engine taxi-out. Just out of curiosity, when does the MEL applicability cease in your operation? It can't be 'when the airplane moves under its own power'...

[FlightDetent]

Nil further: the Airbus FCOM suggests otherwise.

KingAir1978: Why not? Dispatch Phase <-aircraft moves-> Flight Phase

[hph304]

How do you manage the probability of tailpipe fire or leakage of the fuel valve after engine start? Also working for a non SE taxi out operator.

[Dracarys]

These things don't happen very often. The only difference if it happens during a SE taxi appears to be that you wouldn't have ground crew anymore. But what difference does that really make? Or have I missed your point? :confused:

[KingAir1978]

Nil further: the Airbus FCOM suggests otherwise.

KingAir1978: Why not? Dispatch Phase <-aircraft moves-> Flight Phase

What if you have a start valve stuck closed on the second engine start? Just wondering how these companies have organised their legality, that's all.


Dracarys, I agree that tailpipe fires are extremely rare. However, if the ground crew are there, they can at least warn you of it. An engine tailpipe fire, doesn't necessarily trigger an engine fire warning.

[Dan Winterland]

My airline has gone over to the procedure on both A320s and A330s. The wording in the ops notice promulgating it is that the procedure "should be considered". Guidance is given that at high weights, slippery conditions, airports with slopes and high workload should all be taken into account into making that decision. It's not mandatory - and it relies on a suitable application of airmanship.

In reality, we have had few issues. In the first few months, I have only seen two safety reports relating to the procedure indicating that it is being applied with due consideration to the threats. Personally, I have only had two problems. One being a turn through 135 degrees with the live engine inside the turn which couldn't be done, requiring us to start the other one. The second being a runway change at a busy airport. I shan't be doing the procedure in either of these places in future.

The only thing I have noticed is that at high weights, the extra power needed results in a fuel burn double that of idle, which negates the fuel saving. And there is a bit of NWS input required to keep straight - which means more $s on tyre wear.

And also, I've noticed the procedure is more popular towards the end of the month when the guys realise they will be in overtime. Not so much of a saving after all!

[vilas]

When fuel prices rise significantly etaxi will be will become the preferred option.

[Nil further]

Flight detention

You’ve misquoted me there , not what I’ve written ,care to remove ?

[FlightDetent]

NF: I did not quote you at all, it was a disagreeable reply to your post.

KingAir1978:

1) The legalities are sorted the usual way, no need to modify anything. In case you got a start valve stuck, you try again and if unlucky then taxi back to get an engineer with a wrench, or take another decision. You are already in the flight phase.

Speaking of LEGALITIES, in case the same happened during convnetional Push-Back, you do NOT get to try one more time. It is a return to stand, Tech Log entry, and then MX. First movement under own power / dispatch phase and all ....

2) For tailpipe fire: In order to action the appropriate C/L you need to be told, true. But in a place where you'd actually perform an OEI t-out, there will be plenty of people to advise you of the fact.

3) Fuel leak during engine start - that's a good one! Unlike tailpipe fires, or start valve failures, this actually happens now and then. I assume you have this in mind
3877
(CFM engines)

[hph304]

That's the one I meant! Happens about twice a year to me. I guess the safety department will have had a proper look at their matrix regarding these issues..

[Derfred]

My airline does SE taxi-in, but never out.

Question: for SE taxi-out, how much breakaway thrust is permitted on one engine on an uphill slope at heavy weight? I imagine it would be much more than is considered "normal" in my airline on two engines.

[FlightDetent]

Derfred:

a) There is no on-ground thrust limitation in AFM.
b) There is no on-ground thrust max allowable value in FCOM.
c) Hard to comment on any company in-house restrictions (we aint' got any)

How much would you take as an acceptable max thrust on apron in standard ops? My personal value - reasons unknown - is 40% N1. As well it seems that's exactly where the FF of one engine becomes roughly equal to the idle burn with both ENG running.

As a matter of fact, jet blast is the same or let's say it stays N2 dependent irrespective of slope, AUM, taxi phase, or even the number of engines. What I mean to say is that whenever I need more than 45% N1, the planning was not done properly.

[Cough]

We had a max 40% N1 for 319-321 which was in the FCOM.

If we pushed to face uphill then we started both. This isn't a procedure we had to do...

[FlightDetent]

Cough could you have a look and send a reference? I would be most happy to see if the 40% is actually written somewhere by Airbus themselves.

[Nightstop]

I do OETD a lot. When 40% N1 isn’t sufficient to get moving, I find a little temporary NWS input away from the live engine does the trick :ok:

[Sciolistes]

If there are like to be delays at the hold then single engine taxi would seem to be worth it and all the fiddling about associated with it can be done in the queue. It is also useful when against the clock on a slot and can save a minute by starting just one engine and releasing the engineer then immediately starting the second engine with the taxi clearance.

What I don't understand is why so many are so keen with a standard 10 min taxi for all the reasons mentioned above.

Taxi in shutdown pretty low risk.

Just a couple of thoughts in general. With SET, taxiway slope, crossing active runways, taxiway condition, complex or narrow taxiways, heavy ATC, aircraft weight, etc, etc all have to factored in. SET is not suitable when thrust, control and distraction issues are likely.

[Cough]

FlightDetent - I'll try and have a peek over a FCOM soon - My manual set was changed to the Plastic Boeing so I have no easy FCOM to browse any more.

Standby...

Ed to add - Finally looked, and yup as noted below, the reference has gone.

[dream747]

In the past, under Normal Procedures taxi, it was worded in a way that the maximum breakaway thrust to be used is 40% N1. If memory serves me right, a year or so ago during one the manual updates, it has been re-worded, to say that the crew may need to use up to 40% N1 to get moving at heavy weights. Then with the recent mega change in the manuals, this 40% figure is totally removed.

[pineteam]

Heard from my friends flying the A320 with CFM engines, you need most of the time to had some power to taxi with both engines running. I guess it can easily be an hassle to do single engine taxi out? I only did once in Beijing single engine taxi out on A321. But with IAE engines even on single engine, you barely need to add power. A light A319 will even accelerate above 30 kt with one engine on idle power.

[RudderTrimZero]

A few skippers at a previous airline bent the SOP a bit and personally I liked it. Home base was notorious for >45 minute taxi out times in the winter, so they started all engines as per normal and then once on the taxi way on which the queue began to form, shut one down with a view to starting it up again once 4 or 5 aircraft were in front. Any SOP that wants you to consider it for a taxi time of less than 15 minutes is bean-counter bollocks that will ruin your day one day and should be ignored.

[PENKO]

Heard from my friends flying the A320 with CFM engines, you need most of the time to had some power to taxi with both engines running..

Your friends are wrong. The 320 will accelerate with both engines running on the ground.

[Jimmy Hoffa Rocks]

I do OETD a lot. When 40% N1 isn’t sufficient to get moving, I find a little temporary NWS input away from the live engine does the trick :ok:

When one uses 40% in one engine you lose pretty much all the fuel savings.

One engine taxi fuel savings is not calculated with the fuel flow at 40% to get moving. Right ?

it defeats the purpose with the safety margin of having someone monitor your engine start visually gone.

As stated before have missed frequency changes and heads down, have caused taxi issues for us, increasing workload,

not worth it unless your are number 12, in a easy taxi environment.

In a short taxi scenario. ( A long wait at the holding point is another thing ) Go ahead to save your bosses 15 kgs of fuel, if you have to go back to the parking for engine problem or have a taxi incident, or rushed checklist thats your choice? Is it really worth it to save your managers maybe 20kgs of fuel?

[Dan Dare]

I've lost count of the times SET aircraft fail to be ready at a time I could depart them. I normally then log the difference between actual airborne time and when they should have been airbrone and it is usually 5-10 minutes. Additionally the opportunity to use the runway can be lost, delaying every subsequent departure for for the rest of the day until runway utilisation is not limiting movements. One aircraft not ready at their base could cumulatively cost their company (aircraft that follow) an hour of extra delays at a busy airfield.

[FlightDetent]

Excellent inputs showing what a multi-headed hydra SETD is. Thanks a lot Dan for the view from across the tower windows! Dare I say your experience would include a certain citrus fruit operator at their major base nearby Horley? If those guys can't get it right without shooting their foot...

[CaptainMongo]

Our baseline flight planning is two engine taxi which equates to 30 pounds per minute. Single engine with APU running equals 18 pounds per minute. We average about 15 minutes taxi time for each flight across our operation. We operate about 166 319/320 aircraft. I won’t do the public math, but the yearly savings using SE across the fleet is in excess of $1 million.

That is well and good but I would leave with this thought - Safety is paramount on the flights we conduct, it is absolute and our first priority, but can operating our flight as efficiently as possible lead to an increase in safety?

Each pound of fuel you save on your flight you put in your pocket for your use on your flight if you need it. A hundred pounds on the ground, a hundred on climbout, a few directs, CI monitoring, optimum altitude cruise, etc and over the course of a flight one might save 3, 4, maybe 500 pounds of fuel. All fuel saved for your use on your flight if you need it. If you don’t need it, fine, give it back to the company but if you do need it, like I did a few months ago when the gear didn’t come down on the first try (and second try for that matter - third time a charm) I was happy that I operated my flight as efficiently as possible to that point to give me a few extra precious minutes to sort that issue out.

[pineteam]

Your friends are wrong. The 320 will accelerate with both engines running on the ground.

Well I asked my friend again and he confirmed what I said: Most of the time on the 319 they need to add power to get moving after releasing the parking brake. but they do operate often quite heavy tho.