777-300 too heavy for ORY?

[RevMan2]

La Tribune (also picked up by FT Deutschland) reporting that Aeroports de Paris is concerned about possible runway damage when AF replaces its 747 longhaul services with 8 777-300s in ORY as from 2006.
380s aren't a problem supposedly, due to weight distribution of 25t per MLG wheel vs 28t for 777-300.
Bill for strengthening the runway to be shared between ADP and AF.<p>
A pretty good rumour, if you ask me...

Update
AF has them kitted out in all-Economy for the Caribbean services, with few options for using them on other routes.
Price tag for runway strengthening estimated at €100m.
Oooops....


_________________________________________________
Of course, that's just my opinion..I could be wrong

[crazypilot]

Yeah....this was also reported on ATI today:

773ER works out at a few more tonnes per mainwheel than a 744ER does....773 = 27 tonnes vs around 23.8 on the 747.

Orly faces runway upgrade headache to handle 777-300ERs

Paris airports operator Aeroports de Paris (ADP) is discussing options to reinforce the runway at the capital’s Orly Airport after discovering that it could be damaged by intensive operations by Air France’s Boeing 777-300ERs.

Air France – which already operates 777-300ERs from Paris Charles de Gaulle – is planning to station seven of the type at Orly from May 2006 to be used on dedicated routes to French territories.

But while Charles de Gaulle’s runways are strong enough to withstand frequent operations by larger aircraft, Orly’s will need upgrade work to handle the 777s.

Paris Orly has three runways, the longest of which is the main 25/07 strip. Air France says: “Examination of the resistance values published for the longest runway at Orly Airport did not appear to suggest difficulties in receiving Air France’s 777-300ERs.

“It appears that the actual technical state of the pavement nevertheless requires reinforcement before intensive use of these Boeings.”

A spokeswoman for Air France says the airline is in talks with ADP regarding measures to strengthen the airport’s surfaces. She says that there is “enough time” to carry out the work before Air France introduces the aircraft to Orly next year.

Each of the two main-gear legs on the 777-300ER supports 46% of the aircraft’s weight and this is spread between six wheels. The 777-300ER has an all-up mass of 352t.

In contrast the Boeing 747-400ER, while having an all-up mass of 414t, carries its weight on four main-gear legs each supporting 23% of the aircraft’s weight. Each main-gear bogie has four wheels.

This means that the 777-300ER, despite being the lighter of the two, potentially concentrates a greater load on each individual wheel.

Air France is not intending to alter its plans to base the 777s at Orly and insists ADP should bear the responsibility for funding the reinforcement work.

“It should be ADP [that bears the cost] because we pay taxes to the airport,” says the Air France spokeswoman. “That’s what they’re for.”

Discussions over the issue have been taking place since last month. ADP is declining to comment on the issue of financing any alterations. A spokeswoman for the Orly operator says that the airport was not designed to deal with frequent operations by the largest aircraft types, expecting such services to be routed primarily through Charles de Gaulle.

“It had been decided that Charles de Gaulle was the most appropriate to handle large aircraft. Orly wasn’t supposed to handle them,” she says.

“Orly has the ability to handle [these] aircraft in special or rare cases – when there is a diversion, for example – but the problem with the Air France aircraft is to do with handling them many times daily. There’s a big difference between handling large aircraft once or twice a year, and several times a day.”

Although Boeing is aware of the matter, says a spokesman for the manufacturer, the company wants to avoid becoming involved in a debate which, it claims, is between the airline and the French airport authorities – arguing that the issue is nothing to do with the design of the aircraft but rather the airline’s choice of where to operate the twin-jet.

(source: Air Transport Intelligence)


CP

[TheOddOne]

100 million euros sounds WAY over the top, to me.

We put a mega over-slab on top of our main runway at LGW a few years ago to cure some reflective cracking problems from the old concrete runway built in the 1950s. That came in at under £20million and included a complete replacement of all the CATIII lighting as well.

As you know, we're the busiest single-runway airport in the world with many 777 rotations a day, as well as A330, 747, DC10 767 and other heavies. We keep on top of the maintenance of course with frequent night closures and Northern runway ops but we're vey pleased with the way the main runway is standing up to the pressure.

The main problem we found after all the work was everyone complaining about the lights being too bright, even on 3% setting, as they finally now meet the spec!

Perhaps ORY have some hidden agenda and are using this as an excuse???

Cheers,
The Odd One

[keel beam]

100 million Euros for Orly and £20 million for Gatwick? that is the sort of exchange rate I like for my travels in europe:D

[acm]

don't worry,

ADP will reinforce the runway for Air France by increasing others airlines landing fee.:rolleyes:

[lasernigel]

Not wishing to gloat too much.But isn't this one in the eye for 747 focal and his glorious Boeings???:p :p :D :D

[singleseater]

Having just done a few sectors in a B77-300 ER and looked at the loading data as supplied by B
Max T/O 341 T
Percentage per Main gear 46
So each Main Gear is taking 156.9 T
6 wheels per Boggie and the wheel loading is 26.2 T
Less than that quoted for the 747-4 and certainly less than the 777-300 at 299.3T max T/O

[Seloco]

Singleseater:

How can the -300ER loading per wheel be less than a -300 if the latter has a lower MTOW and the same number of wheels? If that were true using your numbers, the total maingear loading on a -300 would, at greater than 2 x 156.9 = 313.8T, be more than the total weight (299.3T); ie does not compute!

[Konkordski]

Perhaps it's me but the calculation from the article above seems pretty clear.


Each of the two main-gear legs on the 777-300ER supports 46% of the aircraft’s weight and this is spread between six wheels. The 777-300ER has an all-up mass of 352t.

In contrast the Boeing 747-400ER, while having an all-up mass of 414t, carries its weight on four main-gear legs each supporting 23% of the aircraft’s weight. Each main-gear bogie has four wheels.

This means that the 777-300ER, despite being the lighter of the two, potentially concentrates a greater load on each individual wheel.


This data means 27 tonnes per wheel for the 777-300ER but only 23.8 tonnes for the 747-400ER.

[humble_dor]

Let's consider these distances

http://gc.kls2.com/cgi-bin/gc?PATH=ory-ptp%2Cory-fdf&RANGE=&PATH-COLOR=&PATH-UNITS=nm&SPEED-GROUND=&SPEED-UNITS=kts&RANGE-STYLE=best&RANGE-COLOR=&MAP-STYLE=&ETOPS=180

and this payload range

http://www.boeing.com/assocproducts/aircompat/acaps/777rsec3.pdf

The needed take-off weight is less than 625,000 lbs (283,000 kgs).

Percentage per Main gear 46
So each Main Gear is taking 130 T
6 wheels per Boggie and the wheel loading is 21.7 T

What's the problem ?

[ReadMyACARS]

What is the critical stage of runway use, take off or landing?

If the problem is the stress an aircraft causes to the pavement, then the greatest force will occur on landing not take off. If this is the case should critical weight be the max landing weight and the force each bogie transmits instead of the MTOW, which was focussed on in the article?

RMA

[Konkordski]

If the problem is the stress an aircraft causes to the pavement, then the greatest force will occur on landing not take off.



Is that necessarily true, given that a landing aircraft is usually minus a substantial quantity of fuel and given that the aircraft doesn't use the runway to stop falling - the wings still provide lift at the point of contact - but rather to gradually settle its weight back on the ground?

[TheOddOne]

Actually, the greatest strain on the pavement is when turning. The 747 inner bogies steer, as does the aft axle on each bogie on the 777 but there is still a great stress caused as an a/c lines up or vacates.

Also, it's not just a simple matter of mass divided by number of wheels; there's the actual footprint of each tyre to be taken into account, wheel size, tyre pressure and so on. All International airports are required to publish their pavement strengths and the a/c mass that they can support, but I can't find the data for Orly. (LGW is in the UK AIP, PCN 78)

Here's some useful background reading material from the FAA:

Pavement Classification Number (PCN) paper (http://www.faa.gov/arp/publications/acs/5335-5_pt1.pdf)

Cheers,
The Odd One

[greek-freak]

The Odd One is right here, calculating the ACNs for aircraft seems to be an obscure art with weird formulas and is not that evident at all. I do not recall the details anymore, but I remember from a lecture at univesity that there was a problem with the 777 since it has three axes instead of the usual two on the main landing gears and that Boing did some rather questionable calculations to obtain a three-axes fromula.

Sorry, I do not remember any more details, only that there was a problem with 777 due to the different main gear configuration.

[Konkordski]

...that there was a problem with the 777 since it has three axes instead of the usual two on the main landing gears and that Boing did some rather questionable calculations to obtain a three-axes fromula.



I don't know about it being questionable, but I understand that the FAA doesn't officially recognise the six-wheel bogie calculation so the figures have to be taken with a certain degree of faith.

[ReadMyACARS]

Actually, the greatest strain on the pavement is when turning

Yes, TheODDOne I was actually wondering that as I was typing.

You can find the French AIP here
http://www.sia.aviation-civile.gouv.fr/html/frameset_encoursMSE_uk.htm


These are the relavent figueres for Orly
Rwy PCN Construction Material
02 60 R/C/W/T béton / concrete
06 80 F/C/W/T béton bitumineux / bituminous concrete
08 66 R/C/W/T béton / concrete

[OverRun]

Thanks for that useful background reading material from the FAA - TheOddOne.

ReadMyACARS, the critical stage of runway loading is takeoff not landing. Runway loading is (very approximately) equal to the tyre load squared - so the heaviest tyre load (which is usually at takeoff) means more equivalent load (there are many variants to this such as the 4th power law, 7th power exponent, etc), but in practical terms it means that the weight of the landing aircraft can often be ignored in the design calculation.

Turning aircraft impose other stresses on the surfacing. And if the surface is asphalt, the visco-elastic nature of bitumen means that slow rolling or stopped aircraft raise other loading issues. But thesde are outside the ACN/PCN issue.

The loading at the moment of landing is ignored. From an earlier PPRUNE post (and reproduced there with appropriate acknowledgment)
http://www.geocities.com/profemery/aviation/airport_design_data.html
Maximum force allowed on tarmac on landing
= desirably zero because just at touchdown, almost all the lift should still be taken by the wings. If hits the tarmac with any force that implies the wings have fallen off, which is a Bad Thing. Longitudinal and lateral forces due to tyre spinup exist, but are not calculated. Instead the type of surfacing (asphalt, concrete, chip seal) is chosen according to the size and frequency of aircraft.

As for the ACN/PCN method - well the best description of its problems is given in Boeing document D6-82203: - "there is a great amount of uncertainty … as to exactly arrive at a PCN". The method isn't intuitive or friendly to use.

Now on top of the PCN method uncertainty, designing for the B777 six wheel bogie has got most people totally perplexed. The problem with the Boeing 777 gear is that it is way beyond the old method for calculating ACN/PCN (and the antique systems for evaluating pavement loading). That method is derived from equivalency upon equivalency upon equivalency. It was a great concept back years ago for the single wheel DC-3, which was then adapted to the DC-4, and adapted to the DC-10 and adapted to the DC10-30 (with the centre gears) and …… but it can't handle the 6 wheel gear.

The current FAA design charts are generally good and I use them often, but the best system for dealing with aircraft such as the B777 and new undercarriage systems is to use a more fundamental approach such as the South African mechanistic method (SAMDM) bolstered with appropriate transfer functions. This is outside the American framework and they are having to work hard to catch up.

As for the La Tribune story about the B777 compared to the B747 - well Airbus won’t say this and Boeing is too close to the issue, but the concern is all eurocr*p. Put simply, if the runway takes a 747 then it takes a 777. crazypilot - calculate the wheel load for a few Airbus aircraft and you will find it is in the 27-28 tonne bracket as well.

I'd be pleased to trade stresses and strains if anyone differs on this - say a target pavement of 125mm asphalt on 300mm cement stabilised base on 300mm subbase on an A subgrade.