A320/A319/A321 take off performance.

[nodelay]

To the Airbus Pilots.

This follows on from a thread posted on the ATCO forum about the use of the phrase 'expedite'.

At my unit we have a good mix of Airbuses and Boeings, (and a few others!!), smalls, mediums and heavies. It is a fact of life that the requirement to move more traffic in a shorter period of time is on the increase. As an ATCO I have to provide, above everything else, a safe service. Orderley and expedition come second. That said I could not afford to be sitting there as the tower controller, with a strong headwind, using 6 mile gaps (one in, one out), giving landing clearances at 2.5 - 3 miles. So, the gaps are tailored for the weather conditions and types of aircraft, and as an example when the the sky is 8/8s blu the ideal landing clearance is given at between 1 - 1.5 nm.

When I clear an a/c to take off I expect it to roll imediately. However I am becoming more aware, especially now we have an increase in the numbers of airbuses operating from my unit (A321/20/19's), that I am having to 'jivvy' the traffic up a lot more to accomodate these types on departure i.e. Instruct the landing a/c to 'expedite vacating', instruct the departing Airbus to be ready immediate and warn the second inbound to expect a late landing clearance. If I don't do this then I find the Airbuses, in contrast to the B73's seem to sit on the runway for an age, having been cleared for take off, before commencing their roll, thus compromising the inbound.

This seems to be a general observation amongst many of my colleagues. Any thoughts or feedback would be greatly appreciated and would help us all immensely. Also, how many of you actually respond to instructions like "after landing expedite vacating, etc." Be honest, does it make you react any quicker?

[Busdrvr]

An interesting observation! I have been on the 319/320 for about five years now. I have also flown other type jets, and I can't say I have really noticed any real difference in the time to roll, for any of them. Perhaps there is, I have never really noticed, but, I do not do as many expedited T/O's as you clear to be done. As for the second question, I think most pilots will try to accomidate, but when that request comes too late, or even at an inappropriate time. ie. Right at touchdown, before we have time to slow, I tend to ignore any requests.

[square leg]

Some operators use a mix of engines, i.e. on one Airbus you might find a CFM56 engine with a Double Annular Combustor (DAC) and one with a Single Annular Combustor (SAC).

These engines have different spool up times from IDLE and thus must first be stabilised at 50% N1 before they can then be both advanced to TOGA thrust. This takes a tad longer than a "normal" T/O.

Otherwise, the only other reason I can think of is that some operators might use their own checklists (as opposed to AI CL's) which could be more tedious to complete.

I say this because I've seen some really weird (long/confusing) CL's left behind in the sim from other operators.

Theoretically, once lined up, one should be ready to roll with all Checklist (CL) work completed.

[4MONU]

I'm a 737 driver, and personally feel I take too long to commence my roll. Company procedures requires me to complete 4 items on the checklist only AFTER being cleared for Take-off.

The competition flies 320's, and their auto-thrust gate is set at staert of Tx from Tower for T/O clearance.

So its just Proc's I guess.

[Carnage Matey!]

Can't think of any good reason for the delay on an Airbus. At BA all we do is set N1 50%/EPR 1.05, check the engines are stable and away we go. Shouldn't take any longer than 4-5 seconds to achieve that. The only time we'd need longer is in icing conditions ( temp at or below 10C, visible moisture) when we'd need a 15-30 second run up depending on engine type and we'd tell you about that before we accept the line-up clearance.

On the subject of being asked to expedite vacating, if you tell us in good time (like above 500 ft) we'll do our best. If you tell us when we're doing 130kts down the runway its all a bit too late and its usually quicker to just go for the exit you were planning for than to slam on the brakes, miss the closer exit then have to taxi to the originally planned exit at 20kts.

[NWSRG]

"Some operators use a mix of engines, i.e. on one Airbus you might find a CFM56 engine with a Double Annular Combustor (DAC) and one with a Single Annular Combustor (SAC)."

Square Leg,

Does this mean that you could have two versions of one engine type on the same aircraft? I never knew that. Would the FADEC ensure that the two matched in flight?

...or maybe I am picking you up wrongly!!

[Lemurian]

NWSRG,
Square leg meant just that.
The maintenance procedure is quite straightforward and to the pilots,the mix is transparent.
You'll get a warning "Engine mismatch" message during start-up,reminding you of the different spool-up times,as SL said.And that's it.

[square leg]

Hello NWSRG,

Lemurian answered the question for me. I am not a technician, but yes you do get engine intermixes. That is, let's say two "different" CFM 56's. They both would have the same thrust, but they might have different FF, EGT, and possibly a slightly different negligible GND IDLE. But other than that there's not much diffs. The other difference is the restart envelope, the SAC being the better performer.

The SAC is more environmentally friendly and thus where possible, the older DAC's are being swapped/replaced/modified slowly but surely.

I think that on MD 80/90's it is/was common practice to have different engines on one A/C. I thought that I once saw an SAS MD80 or 90 with a V2500 and an older smaller engine (P&W?). I might have seen incorrectly.

[NWSRG]

Thanks folks,

you learn something new every day!

[747FOCAL]

Its a French thing........ "We will go when we feel like it......." :E


square leg - I think you did not see what you thought you did. MD-80s and 90s will not have different engines side to side. By different I mean one low bypass and one High bypass ratio engine. :)

[T O G A Boy]

I havent noticed taking a long time to commence the take off roll. we usually have the checklist list finished just as we are entering the runway. the only reason for delay i can think of, is that sometimes certain people would like to request for departure and their checklists are not finished so that the approaching AC couldnt get a landing clearance thus delaying the take off till the landing of the other a/c. i could be wrong though, but thats most likely. and as carnage said , if we are asked to expedite or to plan to vacate via a certain exit while in the air then i believe it can be accomodated. but on the runway its a far too late...

[BOAC]

We've had this discussion before! IF ATC can give some clues as to when we are likely to roll, engines can be 'spooled up' in readiness (and it is difficult for us pilots to work out from a call-sign which SID the preceding is on).

I have been 'caught' by surprise by being cleared to roll at LGW just after the first a/c rotated, and also by sitting at 'spool-up' for 30 seconds when I wasn't cleared as I expected. Some way of 'indicating' without compromising safety would be good.

In terms of landing/expediting, Carnage has said it all
On the subject of being asked to expedite vacating, if you tell us in good time (like above 500 ft) we'll do our best. If you tell us when we're doing 130kts down the runway its all a bit too late and its usually quicker to just go for the exit you were planning for than to slam on the brakes, miss the closer exit then have to taxi to the originally planned exit at 20kts.

Best if you can tell us by 1000ft ARTE really, as there may be things which need to be rebriefed if exit points change, and there are a lot of 't's to be crossed and 'i's to be dotted in modern SOPS!

[Lemurian]

Hi all,
It is true,as Carnage and Boac say that an early notice to expedite vacating the runway from the ATC would be welcome.

On short final,especially at LHR,I would display rose and 10Nm range.This would show on TCAS the traffic in front and behind me.Assuming some 2mins/Nm,I could then have an accurate idea on how/where I would exit the runway without disturbing the following a/c landing.

Anything that increases SA should be used.