Air France A343 departing St. Maarten (SXM)

[Check Airman]

Hi all,

Something’s been puzzling me for a few days now. Air France sends the A343 to TNCM, which boasts a whopping 7000ft (2100m) of pavement. Given that this plane is not known for performance, how do the crews manage it, especially since most of the time you’ll be around ISA+15? Are there special procedures, such as CONF3 and full power all the time? What’s the typical maximum takeoff weight you can manage from this airport?

Thanks

[RingwaySam]

Im no pilot, but when I was in St. Maarten the AF A340s used every single bit of runway possible. While we were there they also requested a 27 departure even with a slight tailwind, so they must have been heavy that day. I don't think the hot and humid conditions would help much either would they?

27 Departure...
http://www.jetphotos.net/viewphoto.php?id=5994297&nseq=27

[Check Airman]

Thanks Ringway!

Any pilots care to comment?

[FE Hoppy]

Where are they going to? straight across the pond or to a nearby longer runway?

Did this route on a Tristar when AOM were grounded, we were scheduled via somewhere else on the way back.

[Check Airman]

They seem to go straight across the pond. I would have thought that the A330 would be a bit better, given the runway.

[NG_Kaptain]

When I used to fly through SXM AF used to fly the 74's from Paris to St Martin then down to Guadeloupe before doing the crossing. We were performance limited on the MD83 from SXM so I really don't see how the 343 could make the crossing. I'm on the Bus now and my previous carrier used to do the crossing to LHR and MAN on the 343 via BGI, UVF or ANU. Barbados, St Lucia and Antigua respectively.

[XPMorten]

Was a passenger CDG - SXM - CDG on an AF A343 a few weeks ago.

http://www.airliners.net/open.file/1277707/L
http://www.airliners.net/open.file/1083403/L/

M

[mustpost]

Lots of vidjoes (as we say in Scotland) on youtube of this excercise - looks scarier than it probably is. Just type in the name

[Robini]

You cant takeoff from SXM with either A330 or A340 if you arent VERY
weight restricted.

What i now you calculate the maximum takeoff mass that you can carry
off the runway in the conditons that exists at that moment and then
take the fuel that is needed and at the last you will se how much pax/cargo
you can take with you on that flight...
I hope this helps!

//Robini

[RingwaySam]

I wouldn't be so sure it's weight restricted. A friend of mine has been twice and said it was pretty much full on the way back from his last flight - Saying that I can't see them taking much cargo from SXM to CDG, but im not Pilot. Hopefully an Air France A340 pilot will eventually reply.

I've seen a few A340-300 takeoffs, some around the same duration of SXM-CDG and they climb out very slowely, so possible de-rated. The angle the Air France goes out, it wouldn't suprise me if it was full power.

Interesting thread though. I'd love to know.

-Sam

[Robini]

An A340 CAN'T takeoff from SXM with MTOM.
You can't either say how heavy the plane is that depends on a lot
of factors such short runways (like TNCM) etc...with other words
impossible... All i know for sure as i said from the beginning it's not
possible for the A340 to takeoff at SXM with MTOM.
And maybe the wind was very good and allowed a little bit of cargo too,
who knows??

//Robini

[bjornhall]

They seem to go straight across the pond. I would have thought that the A330 would be a bit better, given the runway.

A330 & A340: Same installed power, twin vs quad => A340 has better takeoff performance at the same weight...

I thought the reason they use the A340 is its impressive short field performance at low weight.

A peek in the FCOM reveals the maximum takeoff weight if runway limited (2100 m) at ISA+15 to be about 210 tons (CONF3). Further FCOM thumbing suggests about 50 tons of fuel to get to CDG (no wind, ISA, including reserves), so that would leave some 30 tons left for payload. Approximate figures, obviously!

So I suppose there's no magic involved... :)

[5 RINGS]

Quote:
"Hopefully an Air France A340 pilot will eventually reply."
Unquote.

I hardly believe in this, based on the poor English level heard from AF birds on R/T...:E

[Capn Bloggs]

I think they're doing a TCAS Climb to avoid that albatross, otherwise they'd be much lower so that the beachgoers could get a better view. :}

[Check Airman]

A330 & A340: Same installed power, twin vs quad => A340 has better takeoff performance at the same weight...

I thought the reason they use the A340 is its impressive short field performance at low weight.

:eek::eek::eek:

Verify we're talking about the AIRBUS A340 here? And not another A340 made by some other company?

The AIRBUS A340 has CFM56 engines, as do the A320 and 737.

The A330 has CF6 engines.

The CFM56 is rated at 34,000lb, while the CF6 is rated at 68,000lb

The only time I've ever seen a 340 with an impressive climb rate was when it went on a 100nm sector. That doesn't happen too often, so I can hardly say it counts.

[Robini]

Check Airman,
Yes you have right that the A330 has 68,000lb-72,000 lb.
BUT the A330 has one engine on every wing while the 340 has
2 engines on the wing...Simply 68-72,000 lb on every wing on the
330, and the 340 has 36,000 lb on every engine it will be 36*2=72,000lb
on every wing (340) and that's the same as the 330.

//Robini

[bjornhall]

The CFM56 is rated at 34,000lb, while the CF6 is rated at 68,000lb

:confused: 4 x 34,000 = 2 x 68,000 ; same power & almost identical aerodynamics => same performance

3 x 34,000 > 1 x 68,000 ; N-1 performance better for A340, at equal weights

This means that the A340 has higher maximum TOW than the A330 at any given runway (when runway limited!), and can thus carry the same payload further. Unsurprising; that's what it was designed for!

Twin: N-1 limiting; will only observe limit performance with an actual engine failure.

Quad: Usually N limiting; will observe limit performance on every takeoff.

So the A340 appearing to have less performance when it actually has better short field performance than the A330 (at equal weights) is not inconsistent.



At least that's how I understand these things... :zzz:

[Check Airman]

Guys,

Are you really saying that the A340 will equal or better the A330?

:=

So it's established that they each have equal thrust outputs (68*2=34*4=136)

BUT

MTOW for the A330 is 507,000lb
MTOW for the A340 is 606,000lb

You can't look compare the planes at equal weights, as this is unrealistic because they are different planes. You'd have to normalize the weights by looking at each of them at the same relative weight. The easiest way to do this is to look at the MTOW. You'll see tat with the same thrust, the A340 will have to haul some 100,000lb extra. All the wing design in the world won't compensate for that.

To further illustrate that your argument is invalid, consider a 767 and a 747. Both are powered by the same RR engines. If they're both at the same weight (400,000lb), which one do you think will perform better? You think it's a fair comparison?

[Robini]

Check Airman,
You can't compare a B767 and a B747 because they are TOTALLY different
airplanes and even if they had the same power to weight ratio the performance wouldn't be the same.Many things like wing construction etc..
is playing a very big factor when it's about performance.

The 330 and 340 are almost the same aircraft , and they have the same
wing construction. What would the prestanda difference be if the aircraft
construction is the same and they had the same power to weight ratio??
Nothing i guess...

[bjornhall]

Ok, maybe I am missing what you are saying, so pardon me if I am stating the blatantly obvious here... However:

The principle behind the A330 and A340 is that they are the same basic airplane, differently optimized. The A330 is optimized for shorter flights, and thus has lower weights, whereas the A340 is the same aircraft optimized for longer flights and higher weights. This optimization is done by using four engines versus two, for the same installed power. Spreading the power over more engines, to be less penalized by engine out performance, is what gives the A340 its additional 50 ton MTOW (structural); aerodynamically they are equivalent. And both are designed to carry the same payload.

This means that, contrary to the B767 vs B747, it does make perfect sense to compare the A330 with the A340 at roughly the same weight. Specifically, the comparison should be made at the same payload. This reflects the fact that for the given payload, you have the choice of using either the A330 or the A340. The A330 has lower fuel burn, so if it can fly the mission it is the more economical choice. But the A340 has a higher maximum weight, so it can fly the missions that the A330 can not handle.

I can't see the point of comparing the two at MTOW; that is of no help when you try to decide which has the better performance for a given mission.

Consider then the flight from TNCM to LFPG; let's call it 3,700 nm, ISA, no wind. We are choosing between the A330-300 and the A340-300. Figures are approximate, but should be accurate to within 5 tons or so.

For the A340: MTOW 210 tons (rwy limited), trip fuel 45 tons, reserve + alternate about 5 tons, leaving a ZFW of 160 tons. DOW is roughly 130 tons, so we can have a useful payload of 30 tons.

For the A330: DOW roughly 125 tons (lighter due to fewer engines), payload of 30 tons gives a ZFW of 155 tons, trip fuel roughly 40 tons, reserve + alternate also 5 tons to keep it simple. This means TOW is 200 tons.

So for a fair comparison between the A330 and the A340 for this flight, we should compare the performance of the A340 at 210 tons to that of the A330 at 200 tons.

The A330 is a little lighter to begin with, and it uses a little less fuel to carry the same payload the same distance. But it is just a 10 ton difference for this flight; certainly not 50 tons!

I don't know if an A330 at 200 tons could take off from St. Marteen, but given that it is only 30 tons less than its structural MTOW I'm guessing it could not.

I think it is safe to say that for any given payload and distance, the A340 will have better takeoff performance than the A330; i.e., it can take off from a shorter runway if needed. There are three reasons why we don't observe that in practice:

1) The A330 is more economical, provided it is capable of making the flight, so you don't typically see an A340 on a trip that an A330 could fly. Thus you rarely get to compare the two at equal weights.

2) If the A340 is used anyway, it will not use full power, so we don't see its actual performance.

3) A twin, being more over powered with all engines running, will necessarily appear to have better takeoff performance when there is no engine failure.

If I'm speaking a bunch of nonsense, hopefully someone will tell me so... ;)

[Robini]

Bjornhall,

sorry if i react on small things but the A332 has a DOW at 125 t but
the A333 has a higher DOW than the 332 (DOW for A333 is 128 T).

At the second you can't say if the 340 would use max power or not
that depends a lot of the weight and the actual QNH.

[XPMorten]

Check Airman,

Like Robini says, they have the same wing. Also, comparing MTOW numbers is a bit academic in this case. The empty weight OEW for the
A343 is 5T more than the A333.
If you look at the ROC tables you will see that the A333 actually has
better climbrate for the same PAYLOAD as the A343 (Lo).

I'm no pilot, but my guess is having 4 engines will give better
performance in an engine out scenario which gives the A340 an edge
in this case.

http://www.xplanefreeware.net/morten/DOCS/333_343.jpg

[Check Airman]

OK, we seem to be moving towards raw performance here...

Robini, you seem to see my point a bit. You can't compare different planes. 767/747 is indeed an extreme case. You MUST minimize all variables in order to make a fair comparison. You can't talk about payload in performance. No performance tables I've ever seen have dealt with payload, only gross weight. The plane only knows what it's weight is, and it will perform accordingly, it doesn't care if the weight is payload, fuel, or part of the structure. Weight is weight.


I can't see the point of comparing the two at MTOW; that is of no help when you try to decide which has the better performance for a given mission.

Can you suggest a more generally applicable value to use?

3) A twin, being more over powered with all engines running, will necessarily appear to have better takeoff performance when there is no engine failure.


This is true. Twins have a 50%surplus, and quads only have a 25% surplus.

After writing that, how can you argue that an A340 will outperform an A330?

Comparing them at the same weight is useless. An A330 at 500,000lb is nearly maxed out. An A340 at the same weight still has a FAR way to go before MTOW.

For the record, I've been discussing the A332, since more have been built. When they're both empty, the 330 is lighter. It will climb faster. When they're full, the A340 is MUCH heavier. It climbs MUCH slower.

This isn't by any means an academic issue. The 340 has a reputation for climbing slowly- hence my initial question.

[bjornhall]

You asked about performance when taking off at St. Marteen, and said you thought the A330 would be a better choice due to its better performance.

I believe considering the same payload is the most illustrating and useful comparison to make in order to answer that question.

Doing so, the conclusion is that the A340 can indeed manage St. Marteen - Paris non-stop with a useful payload whereas the A330 can not, and we can readily understand why that is so (right?).

If you compare other weights you might get other answers, but I don't see what that has to do with the ability of the two aircraft to fly from St. Marteen to Paris.

This is true. Twins have a 50%surplus, and quads only have a 25% surplus.

After writing that, how can you argue that an A340 will outperform an A330?

Surely you will agree that the performance that matters when flight planning is the performance you get from the performance tables? And those tables take engine failures into account. To me, "better takeoff performance" means "can take off from shorter runways, or carry more payload from a limiting runway". In that specific sense, the A340 outperforms the A330.

The 340 has a reputation for climbing slowly

I don't much care about reputations... ;) It's the data that matters!

There must be a million threads here that deal with the 'raw performance' and reputation of the A340 and its competitors, maybe we don't have to go there again... I was merely interested in the St. Marteen question.