runway width requirements

[Prof2MDA]

Would be curious to see what the experienced members here feel is appropriate for minimum runway width requirements for the A-380 and your rational behind your opinion, i.e. 45 vs 60 meter.

Also, does anyone have easy access to the following specs for the widest of each of the following aircraft/families, either from centerline or total span:
A380, B777, A340, 747-400

main landing gear width

outboard engine width (outboard to outboard)

wingspan

cockpit height

I'm on a trip right now, so don't have the numbers with me, and not all of this is on the websites, plus with dial-up, searching it out is a bit problematic. If you could list sources as well, that would be appreciated.


Thanks.

[john_tullamarine]

ah .. interesting question.

The standard requirements are geometry based rather than having a rational handling basis.

Many years ago Australia was the one country which implemented an ICAO recommendation to require a rational handling assessment for aircraft intended to be operated from lesser width runways.

As part of the various test programs which were done, and the regulator's development work on the subject, it became very obvious that more than a few aircraft sensibly needed more than the prescribed geometry-based limit widths .....

[Prof2MDA]

John

Is that study available at all?

[john_tullamarine]

.. see your emails ..

[Intruder]

For the 744:

Cockpit height: about 37'

Wingspan: 213'

Turning diameter of outboard gear: 153' (with body gear steering operational)

I don't have the other figures handy.

[Noise Unit]

Prof2MDA

With regards the A380 - the following link should provide much of the information you require (particularly chaps 4 & 9).


http://www.airbus.com/product/a380_planning.asp

There are some similar documents on the Boeing website

[OverRun]

Prof2MDA

Unfortunately I'm also away from the reference books and high-speed connections, but at least I'm at the beach while doing so.

As indicated by Noise Unit above, some web sources are:

FAA site which has some of the required aircraft information in AC150 - their 150/5300-13 Airport Design. Warning - this is a large file and the latest aircraft variants are not included:
http://www2.faa.gov/arp/150acs.cfm?ARPnav=acs#Airport_Planning

and the excellent Boeing site which has the individual airport planning guides for their various aircraft:
http://www.boeing.com/assocproducts/aircompat/plan_manuals.html

I also came across a USA study on The Operational and Economic Effects of New Large Airplanes on United States Airports (halfway down the page at http://www2.faa.gov/arp/engineering/index.cfm?ARPnav=engineer
It seems that they have looked at some of the runway cost implications for the new large aircraft at USA airports and quite a few runways have to be widened . . . .

Interesting to learn about the rational method of determining runway width. JT - if you could send a copy of the report my way, I'd also be very interested to read it.

I presume runway width devolves to at least four issues:

OPERATIONAL the foundation issue of aircraft travelling at high speed just above or on the runway, including sideways drift due to crosswind, differential braking and/or differential friction, and width to cope with aircraft wander.

RUNWAY EXIT/ENTRY including pilot sight lines and the fillets (widening of the corners at the taxiway/runway intersection because the larger aircraft cut the corner in the turn). Most people use aircraft tracking/turning software to "drive" the aircraft through a turn and the necessary widening of corners/fillets can be easily found. The A340-600, for example, requires quite a lot of work in widening fillets because its long wheelbase increased the tendency to 'cut the corner'.

FOD protecting engines overhanging the runway strip of grass/soil/sand. Tackled in part by requiring additional sealed/surfaced width each side - often called sealed shoulders. Runways with 747 operations typically have additional [low strength] sealed pavement along the edges. So the 45m wide runway very often has 60m or more of surfaced/sealed width.

180 DEGREE TURN on the runway. Aircraft maximum steering angle and cockpit sight should play a role here, as would the provision (or absence) of turning nodes. Even though most aircraft can turn sharply (the 767-400 will get around in something like 42.5 metres width at maximum steering angle if memory serves me), it is not so easy to see what is happening from the cockpit, and I would suggest that some slight misjudgement of positioning can be expected in practice. This could easily lead to running off the high strength runway and bogging (no-one mention a pukka 747 at Perth - or should that come under the heading of inadequate shoulder delineation). The use of maximum steering angle in geometric design for determining runway width is asking for trouble.

[john_tullamarine]

OverRun ..

I am not aware that CASA (I think they were DOT-ATG at the time .. ) released a report on the work done.

The concerns were purely operation .. regarding

(a) CL deviations during a failure for reject/continue cases

(b) worst case considerations for the wet runway case

(c) late final landing manoeuvring following a misaligned letdown and a side-step manoeuvre .. wonderful to watch from the ground ..

The main thing to come out of the work was that the lateral deviations can be a bit hairy depending on the proximity to Vmcg at Vef and, of course, depending on crosswind. The general concensus was that some aircraft ought not to be operating on the ICAO standard widths as a critical failure could produce useful journalistic copy on page one.....

We still have to catch up for an ale so I can regale you then with stories of the work done ....

[OverRun]

JT- interesting stuff. There is a slight but worrying trend amongst airport engineers who question the need for the runway to be homogeneously provided across the full width. They see the rubber deposits in the touchdown zone concentrating around the centreline (and forming what is almost a textbook example of normal distribution with quite a small standard deviation). This leads them to believe that the outside edges are never used, and so economies can be had in the upkeep of the runway.

There are certain fine tuning things that can be safely done, such as reducing the pavement depth at the runway edges based on the reduced trafficking at the edge. However when this thinking leads to economies like grooving only the central 30m on a 45m wide runway, or resurfacing only the central 15m or 22m, then the whole thing gets marginal. This discussion will be useful stuff to throw into the debate. Many years ago, I managed to drift a 707 off the runway into the grass of the runway strip during landing, which gave me an everlasting understanding of the value of width. The DoT ATG stuff is more scientific and easier to use in teaching.

Look forward to catching up over an ale - I'll drop you a line next time I'm travelling east of the rabbit proof fence.

[john_tullamarine]

OverRun, I concur with your concerns... had I been able to spare the time to attend, I would have caught up with you during the recent Perth Bash ... however, with my present job, it is now likely that you have more occasion to travel than do I ..

Some thoughts which might be of interest to those following the discussion ....

(a) there is not much of a problem associated with more or less maintaining or hitting the centreline when things are going well ... why, I can even recall the odd landing where I managed both the centreline and a smooth touchdown ...

(b) my reading of the tea leaves is that the ICAO numbers address routine geometric considerations but give inadequate consideration to the reasonably anticipated centreline deviations in emergency situations.

(c) for the takeoff failure case, the main problems are

(i) proximity at Vef to Vmcg .. at speeds reasonably well above Vmcg, the deviation is minimal for a competent pilot. However, as the failure speed reduces toward Vmcg, the deviation becomes rapidly and entertainingly significant ... tending, in the limit, to a very rapid and total loss of directional control and a walk in the grass ... in the absence of a throttle chop.

(ii) such involvement as I have had in this work suggests that the continued takeoff is more critical than the reject

(iii) the control effects significantly relate to (aft) CG, and nosewheel cornering force capability... in the testing programs, the case was taken to the certification extreme of having no steering capability to address runway surfaces with little or no usable friction (wet, very slippery, ice, etc.)

(iv) the effect of crosswind is either stabilising (downwind failure) or destabilising (upwind failure). As we generally don't get into guessing which side will have the failure, it is reasonable to consider the destabilising case. It should be kept in mind that Vmcg is determined for nil crosswind (US) or 7 kt (older UK standards).

The typical effect of crosswind on Vmcg varies from around 0.5 kt/kt (twins) to well in excess of 1 kt/kt for 4-motored beasties .... considering that we cheerfully depart in crosswinds of 20-40 kt depending on Type ... this might easily mean, during a Vmcg-limited V1 schedule, that the pilot is faced with a failure many knots below the REAL Vmcg of the day.

With the training emphasis on doing things by rote, this would easily result in a very surprised line pilot doing all the "right" things while watching the aircraft rapidly depart the runway edge into a ground loop with probable catastrophic results. This is one of the reasons why, when I was involved with training programs, I always put the trainee in this sort of situation to emphasise the need to consider the interaction of minV1 and crosswind ... the effectiveness depended on how the sim was set up .. but, in those which were set up well ... the lesson was salutory ..

(d) for the landing case, the main concerns are

(i) pilot mishandling which can only be addressed by training and concurrency requirements, assuming a basic skill level in the individual

(ii) misalignment off an instrument let down .. typically a non-precision runway approach in minimum vis situations. For a reasonably experience and competent pilot, the resulting sidestep manouvre, while interesting, need not necessarily be hazardous providing that the missed approach is exercised if the misalignment is more than minor or the profile cannot be maintained during the sidestep.


Following on from OverRun's comments on airports engineering's penny-wise, pound-foolish philosophies, I can only concur ....

(a) if nothing goes wrong during the operation, then we don't need more than a minimal pad outside the mainwheel footprint.

however ...

(b) if it all turns to custard, the more the better .... I am reminded of a colleague's report relating to his transition to egg-beater machines in respect of the initial hover training ... something along the lines of ... "I started off in a big area in a big aerodrome .. but needed the whole of Queensland before I got it under control ... "

(c) if we go down the path of not worrying too much about the infrequent extreme situation when it comes to airports engineering practice, then we might as well not bother with any training .. etc. ... and just recruit PacMan-proficient 6 year olds to fly our airline transports.

[OverRun]

The value of this discussion is that it highlights the rational basis for the determination of the runway width standard. Sometimes with the passage of time, the rational basis gets a bit lost, and it becomes harder to see how the standard fits to the context of new developments and new aircraft [what a neat way of bringing the discussion round to the original basis of this post].

For runway width, I don't think requirements for each class of aircraft have changed since DC-3s were still in airline service. It could be simplistically argued that the now exclusive use of tricycle undercarriage in RPT aircraft means an increase in controllability and so a decrease in runway width requirement. Or it could be argued that the use of autoland means more accurate landings and a decrease in runway width requirement. These are empirical arguments which seem superficially attractive.

They miss the rational basis for the standard that JT outlined eloquently above, part of which is the takeoff case. And his point that if the critical engine fails at Vef just above Vmcg, and the runway is wet (with poor friction), and there is a cross-wind blowing which significantly increases the real Vmcg (to above Vef), then the nosewheel steering and rudder authority can be insufficient to control the aircraft and a rapid sideways departure can occur. Quite a believable scenario. All the requirements for runway width (and shoulder and runway strip) could come into play.

What was interesting in the certification assumptions, and missed by myself initially not being a performance engineer [thanks Santa for my copy of Swatton], was the detail of the definitions:
Vef is the speed at which, for the purposes of performance calculations, the critical engine is assumed to fail; it is never less than Vmcg.
Vmcg is the minimum control speed on the ground at maximum takeoff power such that, if the critical power unit becomes inoperative, it is possible by aerodynamic means alone without the use of nosewheel steering, using normal piloting skills to maintain a parallel path not more than 30 ft (9m) laterally from the original path.

This started me thinking about the original question by Prof2MDA on runway width. Taking the design? normal? engine failure case on takeoff where Vef is just above true Vmcg. The aircraft will probably have wandered slightly off centreline during takeoff anyway; I don't have the relevant research to hand, but from memory a normal aircraft wander could be up to say 5m off centreline. Then given a wheeltrack (distance between the outer tyres of the outer main gears of approximately 12.6m for a 747-400, this places the outer tyres at (12.6/2 + 5=) 11.3m off centreline. Then have an engine failure just above Vmcg and experience a parallel path departure of 9m allowed in the regs, and the outer wheels are now (11.3 + 9 =) 20.3m off centreline. If the minimum clearance between the outer tyre and the edge of the runway was set to be 1.5m (my estimate to allow for load spreading in the lower pavement), then that is equivalent to a minimum runway width of (20.3+1.5)*2 = 43.6m. Hmm - doesn’t leave much fat in a 45m wide runway. And it doesn't leave anything for JTs scenario with a crosswind. I don’t have the A380 gear width information to hand to redo the calculation for that aircraft - but I also wonder how THAT fits runway width.

[john_tullamarine]

.. food for thought, is it not .... ?

As a minor comment, the Vmcg CL deviation limit varies depending on design standard but the thrust of the argument is still more than valid ....

When it is all going reasonably OK, any half-competent pilot can stay somewhere near the centreline .... in a critical failure situation, competence may have not too much to do with the outcome if the aircraft is in the grass before the pilot can capture the initial excursion .. especially with the V1-go typical mindset's making an above V1 cut very difficult for the non-certification minded pilot ...

[OverRun]

Got an update on runway width requirements for the A380. The jury is still out around the world on the runway width regulations. Airbus reckon 45m (150 foot) is just OK, some of the FAA are worried and want 60m wide runways, while their flying ops people seem relaxed about using 45m runways.

The problem is that the A380 is on the borderline of two 'design groups', and the 'design groups' were little more then stabs in the dark to cater for these new larger aircraft which hadn't been built at that stage.

Anyway, to bring some maths to the table: the A380-800 wheeltrack (distance between the outer tyres of the outer main gears) is approximately 13.8 metres.

Taking the design? normal? engine failure case on takeoff where Vef is just above true Vmcg. Add aircraft wander off centreline of 5m. Then given a wheeltrack of 13.8m for a A380-800, this places the outer tyres at (13.8/2 + 5 =) 11.9m off centreline. Then have an engine failure just above Vmcg and experience a parallel path departure of 9m allowed in the regs, and the outer wheels are now (11.9 + 9 =) 20.9m off centreline. If the minimum clearance between the outer tyre and the edge of the runway was set to be 1.5m (my estimate to allow for load spreading in the lower pavement), then that is equivalent to a minimum runway width of (20.9+1.5)*2 = 44.8m. Hmm – that's a 'just fit' on the 45m wide runway. And it doesn't leave anything for JTs scenario with a crosswind. No wonder the authorities are debating what to do with their requirements for existing airports. The FAA has said that all NEW runways must be 60m wide. But that still leaves a lot of existing runways. . . . .

And if you can borrow an A380 and want to try it out for runway width, here is the ACN chart to see if you'll bog it down before you can run it off onto the grass.
http://www.geocities.com/profemery/aviation.html
There is also a layout of the gear. 20 tyres on the main gears :eek:

Call the refuellers - fill it up and check the tyres, sport. She'll take about 85,900 US gallons and give me 210 psi in the slicks.

[mymymy]

A340-300 dimensions

MLG width - 35' 0.6" (gear centerline to centerline)

Outboard engine width - 128' 7.4" (nacelle centerline to centerline)

Wingspan - 197' 10.0" (top of winglet to top of winglet)

Cockpit height - Hey, 3 out of 4 ain't bad :)

Wow, my first post

mymymy

[enicalyth]

megajets are rather more forthcoming than hairbrush and the AC 380 pdf is a straight crib of what boring have been doing for years.

www.boeing.com/assocproducts/aircompat/plan_manuals.html

whenever i try to get similar data on scarebuses other than the A380 those awfully nice hairbrush people just pit me on the newsletter list and totally ignore my requests.

thank you (sir) noel forgeard, my feelings exactly

[mutt]

[QUOTE]especially with the V1-go typical mindset's making an above V1 cut very difficult for the non-certification minded pilot ...

J_T, would you care to expand on this?

Thanks.

Mutt.

[john_tullamarine]

Simple, Mutt ... for the strong destabilising crosswind case, a min V1 failure, depending on CG etc., may render the aircraft uncontrollable. The typical airline pilot's mindset is that V1 means go... but if the tracking becomes uncontrollable, the need is to stop .. even if the speed is above V1 ... and this is not an easy thing to do for someone who has not had exposure to the problem.

[411A]

Australia seems to have been rather keenly aware of runway requirements, especially length, for quite some time.

Many years ago when I was flying 707's to Australian destinations, we received updated runway performance charts that reduced the available runway distance by the amount of length it took to line up from a 90 degree intersection....150 feet.

Considering that we were nearly always rotating close to the far end, a very worthwhile exercise, IMO.

[john_tullamarine]

I can't put hand on heart and say Australia was either the first or only ... but the antecedents of the present Regulator put in place requirements for both lineup allowances (starting with Qantas .. I have copies of some of the original correspondence in the files somewhere - this addressed 90/180 degree turns and a sensible measure of wheel clearance from runway edge/end) and runway width demonstration of suitability.

Like most things ... if all is humming along smoothly, these sorts of things don't have a routine or immediate effect ... but, when it all turns to custard ....