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A320 single engine taxi out threats

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A320 single engine taxi out threats

Old 19th Aug 2016, 18:38
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A320 single engine taxi out threats

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!
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Old 19th Aug 2016, 18:52
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I think the same. Hence the question here: http://www.pprune.org/tech-log/58081...ml#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.
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Old 19th Aug 2016, 19:25
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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.
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Old 19th Aug 2016, 20:49
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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.
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Old 19th Aug 2016, 23:39
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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?
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Old 20th Aug 2016, 00:21
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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). 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.
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Old 20th Aug 2016, 01:13
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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...
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Old 20th Aug 2016, 01:19
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We lease the engines...
OK, but you still buy the fuel...
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Old 20th Aug 2016, 03:16
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Doesn't come out of my check (yet)
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Old 20th Aug 2016, 05:29
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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.
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Old 20th Aug 2016, 09:58
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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).
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Old 20th Aug 2016, 10:13
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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. :-)
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Old 20th Aug 2016, 14:46
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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
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Old 20th Aug 2016, 15:01
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I'm sure the aircraft won't let you carry out your own vmcg investigation will it?
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Old 20th Aug 2016, 15:37
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sierra_mike, it's from our OMB
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Old 20th Aug 2016, 15:49
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PENKO i thought so IAE engines? can't find such limitation in our OMB but we have CFMs
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Old 20th Aug 2016, 18:26
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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.
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Old 20th Aug 2016, 21:18
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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.
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Old 20th Aug 2016, 22:00
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Is this just an American thing?

Never seen it in Australia or Asia. Seen it on JetBlue, Virgin, Southwest and the rest of them.
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Old 21st Aug 2016, 00:56
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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...
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