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Dano1977
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Engine Revving On Taxiway?

Sat Oct 12, 2013 6:18 pm

A few hours ago, I flew on Monarch Flight ZB7253 from Venice to London Gatwick.

G-OZBE - Built 2002
Airbus A321-231
IAE V2533-A5


After pushback and engine start we held on the taxiway for a few minutes, then the engines spooled up to whatever power setting and you could feel the Airbus being held against the brakes for a sustained period of about 30-45 seconds. This happened twice.

Then instead of going along the taxiway, we backtracked along rwy 22R/04L (The active rwy) again with what seemed like the engines being spooled up to higher than normal taxi speed settings.

By backtracking the active, we made a Delta 767 wait at the holding point for rwy04L and a couple of other aircraft.


Take off and the flight were normal and we landed on time.


Just curious as to why.
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EGGD
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RE: Engine Revving On Taxiway?

Sat Oct 12, 2013 6:26 pm

It is quite difficult to say with any authority why this would happen. The most obvious situation where more thrust than usual is used whilst not on the runway is whilst performing a crossbleed engine start. This is where the aircraft has no Auxiliary Power Unit to provide air to the engines for the normal start sequence. In this instance, the first engine is started with a pneumatic ground unit attached to the aircraft and once the engine is started, the aircraft is pushed back. Once on the taxiway, the running engine is advanced to a certain thrust level and the bleed air from that engine is used to start the second engine. This would be the most likely scenario in my opinion, the extended taxi for departure I cannot link to this explanation but it could be completely unrelated, a taxiway closure/blockage or traffic flow control (I have never flown to Venice).
 
LittleFokker
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RE: Engine Revving On Taxiway?

Sat Oct 12, 2013 6:49 pm

Quoting Dano1977 (Thread starter):
Then instead of going along the taxiway, we backtracked along rwy 22R/04L (The active rwy) again with what seemed like the engines being spooled up to higher than normal taxi speed settings.

By backtracking the active, we made a Delta 767 wait at the holding point for rwy04L and a couple of other aircraft.

Is it possible that LGW was in some kind of ground delay program, and your flight's wheels up time had been moved up, so VCE ATC moved your flight to the front of the line to expedite departure? That's the most plausable scenario I can come up with.
"All human activities are doomed to failure." - Jean Paul Sartre
 
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Dano1977
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RE: Engine Revving On Taxiway?

Sat Oct 12, 2013 7:10 pm

Quoting EGGD (Reply 1):

Nope we definitely started both engines on the pushback - heard the PTU (barking dog sound) come on then go off as the second engine was started/completed start.




Quoting LittleFokker (Reply 2):

We left on time, which was amazing due to the chaos that Venice airport is on Cruise ship change over day....
Children should only be allowed on aircraft if 1. Muzzled and heavily sedated 2. Go as freight
 
LittleFokker
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RE: Engine Revving On Taxiway?

Sat Oct 12, 2013 7:16 pm

Quoting Dano1977 (Reply 3):
We left on time, which was amazing due to the chaos that Venice airport is on Cruise ship change over day....

That might actually support my theory. Perhaps, initially, your flight was given a delayed time (~30 minutes, perhaps) to space out arrivals into LGW. However, if there were lots of connections to other ZB destinations (or the aircraft's next flight may have been a high on time priority flight), maybe the flight's priority was higher than usual, and the wheels up time was moved up to an on-time slot. Hard to say without being in ZB's operations headquarters, but it's very possible that's what occured.
"All human activities are doomed to failure." - Jean Paul Sartre
 
mjgbtv
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RE: Engine Revving On Taxiway?

Sat Oct 12, 2013 8:00 pm

Burning excess fuel?
 
PGNCS
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RE: Engine Revving On Taxiway?

Sat Oct 12, 2013 8:03 pm

Quoting Dano1977 (Thread starter):
Just curious as to why.

Unless one of the two pilots operating the flight is reading this posting, there is no way anyone here can answer without it being pure speculation. Which begs the question why didn't you ask the crew when you got off the plane? They could have actually given you a genuinely informed answer.
 
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Dano1977
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RE: Engine Revving On Taxiway?

Sat Oct 12, 2013 9:56 pm

Quoting PGNCS (Reply 6):

I wish I had of done now.

But there was no announcement from the flight deck, So i assumed it may be some procedural check that may happen from time to time or due to the short taxi time to the runway, I think either the CFM or IAE need a minimum warm up time before take off power is applied.

But I will say one thing... It's the first time on an A321 that I have ever been forced into the back of my seat on the take off roll...
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prok
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RE: Engine Revving On Taxiway?

Sun Oct 13, 2013 11:05 am

As PGNCS already said, we'll never know what happened.
What comes to mind is a bleed air valve fault (stuck). Sometimes by adding some power you can easily resolve such issues.
Normally 04L is used as taxiway only at VCE and you taxi the last part of 04L to 04R which is the standard rwy for arrival and departure.
Full thrust takeoff makes sense to gain some attitude as there are some climb restrictions for crossing the Alps.
Hope this helps!
 
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DarkSnowyNight
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RE: Engine Revving On Taxiway?

Sun Oct 13, 2013 1:59 pm

Quoting Dano1977 (Thread starter):
Just curious as to why.

Fueling overshot.

Of course I don't know that with any certainty, but I've seen it happen enough times. If they're trying to just smoke off a few hundred pounds to get close to dispatch TOW again, this will save a lot of time rather than de-fueling.

If they elect OTOH to defuel, there a few huge problems. First, the fueling company can only take fuel off a plane into a tanker specifically dedicated to that airline (at least for that day/shift/etc). It cannot be put back into a general pool or into the pit (per both FAA & EASA regs). Most fueling companies don't actually have tankers standing by for this purpose, so they'd be real lucky to find one.

Secondly, de-fueling is a much slower process than fueling, as the PSI alottment for this is quite a bit less than fueling ops, and of course you still have the same set up times, etc.

Those both will cause a delay that nobody wants. So, better to just burn it off if we're talking about a discrepancy of anything less than a few thousand pounds.

Quoting PGNCS (Reply 6):
Unless one of the two pilots operating the flight is reading this posting, there is no way anyone here can answer without it being pure speculation.

Yup. I had my theory above, but I'm sure it could have been a few other things too.
You Sir, are a very funny lady.
 
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Dano1977
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RE: Engine Revving On Taxiway?

Sun Oct 13, 2013 3:24 pm

Quoting prok (Reply 8):

Yeah I noticed we circled round the airport while climbing out, and there wasn't the usual throttle back/Noise abatement and assumed it was because of the Alps/Dolimites(sp?)


Thanks for the answers.

Dano1977
Children should only be allowed on aircraft if 1. Muzzled and heavily sedated 2. Go as freight
 
mcdu
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RE: Engine Revving On Taxiway?

Sun Oct 13, 2013 4:19 pm

Was it chilly and first flight of the day. Engine oil temps need to come up or lest you wait. Something above idle will expedite the process. Airbus has a NO TAKEOFF oil temp ECAM alert that is tied to oil temp
 
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Dano1977
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RE: Engine Revving On Taxiway?

Mon Oct 14, 2013 4:47 pm

Quoting mcdu (Reply 11):

The flight had arrived from London Gatwick - and had a turn around time of about 1hr 20mins

the temp was around 11/12 degrees centigrade or 53 Fahrenheit
Children should only be allowed on aircraft if 1. Muzzled and heavily sedated 2. Go as freight
 
musang
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RE: Engine Revving On Taxiway?

Tue Oct 15, 2013 12:57 pm

Quoting prok (Reply 8):
Full thrust takeoff makes sense to gain some attitude as there are some climb restrictions for crossing the Alps.

Can't imagine the 321 is that weak. Even if you get an immediate left turn towards Vicenza (where you would end up if going to London) there is no rush to climb. There is no emergency turn procedure (engine failure scenario) for the 737s I fly to VCE, which means no terrain close enough to matter, and we never have to worry about sufficient altitude to clear the Alps. Perhaps a heavy 321 is different.

Quoting Dano1977 (Reply 10):
Yeah I noticed we circled round the airport while climbing out, and there wasn't the usual throttle back/Noise abatement and assumed it was because of the Alps/Dolimites(sp?)

Some of the standard departures involve a long right turn from the north west runway, back to just south of the overhead.

About the thrust reduction after take-off - this isn't inevitable, and there's another thread about it. Take-off thrust is usually higher than climb thrust, but if it takes off with reduced thrust, as it might with a long runway (like VCE) and lower than max weight, there may be little thrust reduction to notice.

Perhaps an Airbus driver can comment, but there is probably an option to over-ride the thrust reduction after take-off like there is on the 737. A nervous crew might have taken this option with the Alps in mind, but I find that difficult to imagine based on how distant they are from VCE. I'd go with my theory that they took off with thrust reduced so much that there was hardly any further reduction to climb thrust.

No idea why it would be spooling them up on the taxiway though. We'd do this to shed ice from the fan blades in icing conditions, but not in the ramp, and one engine at a time.

Regards - musang
 
Fabo
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RE: Engine Revving On Taxiway?

Tue Oct 15, 2013 4:32 pm

Quoting musang (Reply 13):
Perhaps an Airbus driver can comment, but there is probably an option to over-ride the thrust reduction after take-off like there is on the 737.

You would physically move the levers to a lower detent on reduction. Or in case you wanted for some reason to keep TOGA power, you would not move the levers.

Quoting musang (Reply 13):
I'd go with my theory that they took off with thrust reduced so much that there was hardly any further reduction to climb thrust.

More likely.

Quoting musang (Reply 13):
No idea why it would be spooling them up on the taxiway though. We'd do this to shed ice from the fan blades in icing conditions, but not in the ramp, and one engine at a time.

I suppose the "burn excess fuel" theory makes some sense. If they were near MTOW... I don't really know how close the MZFW-MTOW gap is to TO fuel for VCE-LON run, but I can imagine that taxi fuel was lower than anticipated, especially as they went ahead of queue.
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