Airbus A380 operations at alternate airports aacg november-2004 Version 2 draft introduction

November-2004

Many airports need to adapt their airside infrastructure. Upgrading runways, and taxiways, relocating taxiways and even relocating aircraft stands and buildings to provide sufficient wingtip clearance, are examples of the works that several airports may need to carry out before the A380 enters service.

For airports which will see the A380 frequently such changes to the infrastructure may be reasonable. When an airport operates close to its full capacity, efficiency of operations is a prime factor as well as safety.

Examples of airports, where large scale infrastructure changes could be economical, include the large continental gateways, and those airports whose home-carriers have ordered the A380 aircraft: for example, London-LHR, Paris-CDG, Frankfurt, New York-JFK, Los Angeles, Singapore, Hong Kong, Sydney, Dubai etc.

For those alternate airports, large scale changes to their existing airside infrastructure would be financially excessive and never be economical. On the other hand, especially in the case of a filed alternate, a minimum should be done to properly handle the aircraft and its passengers.

This is not substantially different than what is regularly done at airports who receive the occasional visit of an airplane bigger than their design aircraft: An 124, or even B 747 in many “old” airports.

This document aims to provide guidance for operators and States on the use of alternate measures, operational procedures or operating restrictions, in combination with the minimum level of infrastructure requirements at possible alternate and even lower frequency use airports. States and airport operators are encouraged to review the guidance in this document, but as with the AACG Common Agreement Document (destination airports), it must be clearly understood that the final safety based decision at a particular airport remains the responsibility of the State and the airport operator.
The proposed procedures are based on the current state of knowledge, as used for the December 2002 AACG recommendations. Several Aeronautical studies are on-going at this time and they could result in lower requirements than those proposed by the AACG (most noticeably for points which the AACG had left open in December 2002, such as OFZs, holding point position and runway to taxiway separation). Use of possible outcomes from the uncompleted studies would be premature.

However it is possible that the outcome of some of these studies, expected within the next year, could render several proposed operational procedures unnecessary.

While ICAO member states are encouraged to fully implement the new code F requirements for the development of their airports, it has also become clear that many states will have difficulties in complying with these specifications for the upgrade of their currently existing facilities. For this reason ICAO developed a circular for New Larger Aeroplane Operations at Existing Aerodromes. This circular identifies all issues which are of relevance to the operations of NLAs and proposes possible mitigation measures for accommodation of NLAs at those airports that are unable to comply with annex 14, code F provisions. The circular does not specify what is acceptable and what is not: the responsibility remains with the local authority. The State should decide on the suitability of lower requirements than those given by Annex 14, based on aeronautical studies. The principle is that safety requirements must be met, however efficiency of operations should also be considered, especially for airports which have a very low number of A380 movements and therefore whose infrastructure is unlikely to be code F (or AACG)-compliant.

Together with ICAO Annex 14 the AACG recommendations form a basis for the infrastructure requirements at existing airports.

• 
  ICAO, Annex 14,
  

• 
  ICAO, Circular on New Larger Aeroplane Operations at Existing Aerodromes,
  

• 
  Common Agreement Document of the A380 Airport Compatibility Group,
  

• 
  The case of a planned alternate, where the airport is regularly declared in the flight plans of an airline as the alternate in the case of unavailability (most of the time for weather conditions) of the destination airport. In this case, the conditions of accommodation can – and should – be negotiated in advance by the airport with the airline and the ATC services. There may be some restrictions to “normal” operations, but they should not be disruptive – if only because, in the case of bad weather, the A380 is unlikely to be the only diverted aircraft and the alternate airport also has to handle its own traffic.
  

• 
  The case of an unplanned diversion airport, most likely to be used for an aircraft emergency. In such a (rare) case, temporary disruption of operations at the alternate airport is to some extent tolerable.
  

The level of the operating restrictions that can be tolerated will be higher in the second case.

Annex 14 prescribes a runway width of 60m for Code F aircraft. Many long-range traffic airports however, and certainly those that will be filed as an alternate, have runways which are expected to comply with ICAO Code E requirements, i.e. a width of 45m.

Subject to the A380 being certified on 45m wide runways, the AACG recommendations state that a 45 meter wide runway can be used for Airbus A380 operations.
No specific alternative measures, operational procedures and operating restrictions are proposed for operations of an A380 on a 45 meters wide runway.
Runway strength

The runway need only support the reduced operating weight at an alternate (airlines have quoted maximum MLW and two hours fuel) and the infrequent use would allow pavement concession action for the appropriate bearing strength.

For destination airports, AACG recommendations state that a 45 meter wide runway with 7.5 meter shoulders on both sides can be used for Airbus A380 operations if the runway is also provided with additional “outer” shoulders. These outer shoulders should be prepared for jet blast protection, engine ingestion protection, and for supporting ground vehicles and their width should be at least 2x7.5m.

The use of 2* 7.5 meter shoulders in Code E alternate airports instead of 2*15 meter wide shoulders (including the AACG “outer” shoulders) could therefore be an issue.
For an alternate airport, upgrading the total runway + shoulder width to 75m is mostly not viable. To find whether, and under what conditions, the A380 can be operated on code E runways and shoulders, the focus should be put on the intended use of the “outer” shoulder.

1. 
   Jet blast and engine ingestion protection.
   

Use of a runway at a landing alternate is likely to happen on short notice. Specific preparation of the runway and runway shoulders is not necessarily possible within the available time frame. However the landing does not present a specific risk and therefore special procedures are not necessary (although runway inspection is advisable).

In the take-off case more time is available and the departure of an A380 can be coordinated with other traffic and the need to inspect the runway,(if a 75m wide runway area is not already inspected on a regular basis). Runway inspection must be carried out immediately after take off to check that no loose objects have been blown onto the runway. In addition, a de-rated thrust may be used for takeoff at alternate airports, further reducing the engine hazard. It should be noted that the ingestion risk occurs in the very early part of the takeoff roll, below about 35 knots. A special procedure would be required for A380 operations on 45m runway without inner shoulders

2. 
   Supporting ground vehicles
   

Rescue and Fire Fighting vehicles are designed for operating over short distances on the natural soil of the runway strip. The lack of 7.5 meters of “outer” shoulder does therefore make no difference between code E and A380 operations.

3. 
   Bearing strength
   

Future A380 operators have indicated that a take-off weight limitation, based on MLW + 2 hours fuel, is acceptable.

The outer shoulder does not have to be designed for the occasional passage of an aircraft. Some states / airports are studying the possibility of having the outer shoulder functions performed either by a stabilized surface (which is a possibility also mentioned by the ICAO NLA circular) or even by a well tended grass surface.

As stated in the AACG Common Agreement Document, the decision on the bearing suitability of the shoulder (composition and thickness) is the responsibility of the airport or national authority. The authority is able to declare a limiting takeoff weight for the A380, based on the gear layout, in the AIP or pavement concession documentation
Proposed alternative measures, operational procedures and operating restrictions for airports that cannot comply with ICAO requirements or AACG recommendations related to shoulder width (in combination with at least 45 meter wide runway).

• 
  Runway and shoulder FOD inspection must take place before each A380 take-off if a 75 meters wide runway area is not inspected on regular basis.
  
• 
  Runway and shoulder FOD inspection must take place after each A380 take-off.
  
• 
  Restrictions on actual take-off weight if the airport pavement PCN is not sufficient to handle an A380 at MTOW; airlines will judge whether the published PCNs are appropriate for their outbound flights. MLW plus two hours fuel would appear to be a good measure for the majority of cases
  

[Comment: When possible it is advised to have runway and shoulder FOD inspection before and after each A380 landing]

4. 
   Runway edge lights
   

Tests have been carried out to see if light fittings, currently available on the market, can withstand blast profiles comparable with an A380 engine. The results of these tests will soon become available³.

Alternatively, the airport or local authority can perform runway edge light inspection after each A380 departure (which may well by required for FOD reasons). As the outer engines of an A380 are not fitted with thrust reverse systems, it is not required to perform a runway edge light inspection after the landing of an A380.
Proposed alternative measures, operational procedures and operating restrictions for airports with non blast resistant elevated runway edge lights on a 45 meters wide runway.

• 
  Runway edge lights inspection after each A380 departure.
  

The ICAO Annex 14 Code F taxiway width is 25m, or 2m more than Code E. The A380 has a wheel track 0.3m larger than the Code E limit.

Extensive deviation studies, carried out at several airports around the world, have shown that the deviation of large aircraft (code E) is much less than the 4.5 meters margin used in the formula to determine the taxiway width. Results show that a deviation of less than 2.5 meters is a very realistic value under the condition that proper guidance such as centre line lights and markings or equivalent guidance is provided for night or low visibility operations.

Additional to the above, it can be stated that the outer main gear wheel span of the A380 is such that the actual wheel to edge clearance (4.3m) is more than the 2.5 meters if the aircraft is taxiing on a code E taxiway.

If the taxiways are not provided with proper guidance or if the airport / local authority does no feel comfortable with the use of 23 meter wide taxiways, the use of “follow me” guidance can be a solution.

To facilitate the movement of an A380 on curved taxiways and on junctions / intersections of taxiways with runways, aprons and other taxiways, fillets should be provided. The design of the fillet should ensure that a minimum wheel to edge clearance is maintained, based on Cockpit over Centre Line (COCL) steering technique. ICAO requires a minimum wheel to edge clearance of 4.5 meters for curved taxiway segments Also the AACG recommendations mentions a 4.5 meters wheel to edge clearance for curved taxiways, however in some states the use of smaller wheel to edge clearances (i.e. 2.5 meters) for the design of taxiway fillets is under certain conditions accepted.

• 
  Reduced wheel to edge clearance
  
• 
  Use of judgemental over steering
  
• 
  Additional markings for over steering guidance.
  
• 
  Publication in the appropriate aeronautical documentation is required.
  

Both ICAO Annex 14 and the AACG Common Agreement Document recommend a 60 meters wide strip to be protected against shoulder erosion and engine ingestion risk. The shoulders could build up of a paved, a stabilized or a natural surface (experienced at CDG for many years). The A380 engine ground clearance is a factor. The inner engines are 0.5m higher and the outer engines 1.2m higher than the 747-400 ones, which would decrease the ingestion and jet blast risks. If the airport / local authorities does not feel comfortable with the shoulder surface in combination with A380 operations, the possibility remains to taxi with both outboard engines idle or even shut-off. The feasibility of this must first be confirmed by the manufacturer.

If it is required that the outer engines being shut of, special attention should be given to tight curves where normally asymmetric power is used to move the aircraft through the curve.

• 
  Taxing with outboard engines on idle thrust.
  
• 
  In the extreme case the airport authority could require taxiing with outboard engines shut-off (feasibility to be confirmed by manufacturer) or the aircraft could be towed.
  

• 
  Publication in the appropriate aeronautical documentation is required.
  

1. 
   Landing of an A380 on an non instrument runway, Runway – taxiway separation is 107.5 meters,
   

2. 
   Landing of an A380 on an instrument runway, Runway – taxiway separation is 182.5 meters,
   

3. 
   Take-off of an A380, runway – taxiway separation is 107.5 meters,
   

4. 
   Take-off of an A380, runway – taxiway separation is 182.5 meters,
   

5. 
   Taxiing of an A380 on a parallel taxiway, runway – taxiway separation is 107.5 meters,
   

6. 
   Taxiing of an A380 on a parallel taxiway, runway – taxiway separation is 182.5 meters,
   

• 
  When an A380 uses the parallel taxiway next to a runway, operations on that runway should be restricted or even halted if the runway – taxiway separation is less than 115 meters (under visual conditions).
  

[Comment: in annex 14, the width of the runway strip is a permanent characteristic attached to the runway, not to the type of operations and the aircraft size. It may be necessary to note that proposals b, d, and f consist in saying that an instrument runway in visual conditions can be operated with the clearances of a non-instrument runway, with an acceptable level of safety. In practice, this may need to be validated by ATC services]

1. 
   For collision risks, the distance between runway holding point and runway centre line will be determined by the biggest aircraft that can use the runway as well as the geometry of the aircraft at the holding position.
   
2. 
   The other purpose is to prevent unacceptable interference with the ILS signal. During ILS CAT II/III operations, the runway holding positions needs to be positioned in such a way that the critical and the sensitive areas are free of any aircraft movement on the ground
   

For code E the minimum distance for the runway holding position is 90 meters, for code F this distance is 107.5 meters. These distances are based on

“an assumed aircraft with a tail specific height (code E; 20 meters, code F; 24 meters), a distance from nose to the highest part of the tail (code E; 52.7 meters, code F; 62.2 meters) and a nose height (both code E and F ; 10 meters) holding at an angle of 45º or more with respect to the runway centre line, being clear of the obstacle free zone (OFZ)” .
As can be concluded from above the Runway Holding Position is not only a function of the size of the Holding aircraft, but also of the dimensions of the Obstacle Free Zone (OFZ) ⁷.
As an interim solution, operational procedures can be implemented which prevent aircraft coming near the runway in case of the occasional A380 landing. If the airport is equipped with ILS CAT II/III holding positions, these could be used for this purpose. Similar restrictions are already published on airport charts.
Proposed alternative measures, operational procedures and operating restrictions for airports that can not comply with ICAO requirements or AACG recommendations related runway holding positions.

• 
  Holding aircraft further from the runway in case of an A380 landing may be required (i.e. the ILS CAT II/III holding positions).
  
• 
  Holding aircraft at the parallel taxiway, away from the runway entry taxiway.
  

• 
  Establish the appropriate ATC procedure.
  

Studies and simulations⁸ are being performed to find out if an A380 on a parallel taxiway and at holding positions gives more interference to the ILS signal than the current large aircraft. The size of the tail fin is under special consideration.

Preliminary results shows that the effect on the ILS signal is strongly related to local conditions and therefore a standard and uniform solution can not yet be provided. Also the acceptable level of disturbance is not the same at all airports and in all states.
If an alternate airport expects to handle diverted A380 operations during low visibility conditions, special attention should be given to this kind of operations. An operational plan must be set up to guarantee that the ILS signal is not disturbed or alternatively that operations at the runway are temporarily restricted.


3.7 Taxiway minimum separation distances
To reduce wingtip collision risk to an acceptable level, minimum separation distances for taxiways and taxilanes are implemented. For this, ICAO has specified separation distances for the different aircraft categories and taxiway / taxilane situations. For code F, these minimum separation distances are based on extrapolation of the distances given for code E. However, risk assessment, as well as operational experience with code E aircraft, has shown that large aircraft can be operated safely on taxiways with smaller separation distances than those given by ICAO.

AACG recommendations for minimum separation distances are based on these risk assessment and operational experiences. The results of the taxiway deviation studies carried out by London-LHR, Frankfurt, Amsterdam and Paris-CDG were used for these recommendations.

1. 
   Parallel taxiways (Taxiway centre line to taxiway centre line)
   
2. 
   Taxiway centre line to object
   
3. 
   Aircraft stand taxilane to object
   

In ICAO Annex 14, the minimum distance between two parallel taxiways is given as 97.5 meters for code F aircraft. AACG recommend a distance of 91 meters if proper guidance, such as centre line lights or equivalent guidance, is provided for night or low visibility operations.

Many alternate airports will have parallel taxiways which are designed for code E aircraft. A separation distance of 80 meters will in those cases normally be available. This does not mean that the A380 cannot make use of one of the two parallel taxiways. If an A380 operates on one of the taxiways, the other taxiway will be restricted for use by aircraft smaller than code E.
The ICAO requirement for parallel taxiways to be separated by 97.5m gives a margin of 17.5 meters when two A380 aircraft taxi on parallel taxiways. The AACG recommends 91 meter which results in a margin of 11m.

The maximum wingspan for the other aircraft in the case that an A380 taxies on parallel taxiways separated by only 80 meters can easily be calculated: taxiway separation minus half wingspan of A380 minus margin equals half wingspan of the aircraft on the other taxiway.

80 meters – 40 meters – 17.5 meters = 22.5 meters or a maximum wingspan of 45 meters (i.e. aircraft like A310, A300 and B757).

80 meters – 40 meters – 11 meters = 29 meters or a maximum wingspan of 58 meters (i.e. aircraft like B767 and MD11).

• 
  Restrict aircraft operations on the taxiway not used by the A380, to aircraft with a maximum wingspan of 45 meters.
  
• 
  If proper guidance is given, this restriction can be lifted to a maximum wingspan of 58 meters.
  
• 
  If necessary, procedural separation must be provided.
  
• 
  Publication in the appropriate aeronautical documentation is required.
  

• 
  Establish appropriate ATC operational procedures.
  

For taxiway to object clearance, ICAO requires 57.5 meters while AACG recommend 49 meters if proper guidance is available. However both accept lower separations distances for taxilanes based on the fact that taxiing is more accurate on taxilanes. Although recent taxiway deviation studies have not found any relation between taxi speed and deviations from the taxiway centre line, it is still one of the reasons why ICAO allows smaller clearances on taxilanes. Extra caution on the more congested apron area could also be a factor in better taxilane accuracy.

If proper guidance, like for example taxiway centreline lights, is available, an A380 could be operated on a code E taxiway (47.5 meters separation distance to object).

• 
  Use of code E taxiways with warnings to exercise caution, and possibly reduction of taxi speed (taxiway to object clearance = 47.5 meters)
  
• 
  “Follow me” guidance or marshalling can be used.
  
• 
  In an ultimate step, towing the aircraft can be an option (if taxiway to object clearance less than 47.5 meters)
  
• 
  Publication in the appropriate aeronautical documentation is required.
  

For aircraft stand taxilanes ICAO requires 50.5 meters clearance to any object while AACG recommend 47.5 meters if proper guidance is provided. Further reduction of the separations distances is difficult and will result in higher and probably unacceptable risk of wingtip collision.

If separations of 50.5 (ICAO) or 47.5 meters (AACG) can not be guaranteed, the use of “Follow me” guidance or marshalling but also towing the aircraft are possible solutions.
Proposed alternative measures, operational procedures and operating restrictions for airports that can not comply with ICAO requirements or AACG recommendations related to aircraft stand taxilane – object clearance

• 
  “Follow me” guidance or marshalling can be used.
  
• 
  Towing the aircraft on the taxilane.
  
• 
  Publication in the appropriate aeronautical documentation is required.
  

• 
  Temporary downgrading adjacent aircraft stands.
  
• 
  Towing the aircraft on to the stand.
  
• 
  Use of remote / cargo stands or “roll-through” parking positions for handling the A380.
  
• 
  Publication in the appropriate aeronautical documentation is required.
  

[Comment: In the case of an airport regularly filed as an alternate, it may be advisable to have a few marked remote A380-capable stands (possibly downgrading adjacent stands), accessible by A380s under their own power]

• 
  Bridge width,
  
• 
  Blast protection,
  
• 
  Accessibility for rescue and fire fighting vehicles and
  
• 
  Structural maximum load, also applicable to tunnels underneath taxiways (and runways)
  

For the width of a taxiway bridge, AACG recommends a minimum of 49 meters (ICAO requirement 60 meters minimum). Smaller bridges are acceptable if a proven method of lateral constraint is provided. If the taxiway bridge is designed for code E aircraft, the width of the bridge will be 44 meters minimum. In that case, an A380 can only use that taxiway bridge if lateral constraint is provided. If not, the A380 may not use that taxiway bridge, under its own power. Towing the aircraft over the bridge is a possibility. Connecting and disconnecting time requires consideration. As the number of A380 movements is very low, the operational disturbance may be acceptable.

• 
  Towing the A380 over the taxiway bridge
  
• 
  Publication in the appropriate aeronautical documents that the A380 may not taxi under own power over the bridge is required.
  

If the width of the taxiway bridge is such that the outboard engines overhang the bridge structure, blast protection of areas below the bridge may be necessary. In case jet blast protection can’t be provided over a width of 60m, taxiing with the outboard engines on idle thrust or even shut-off is a possibility.

• 
  Taxing with outboard engines on idle thrust.
  
• 
  In the extreme case the airport authority could require taxiing with outboard engines shut-off (feasibility to be confirmed by manufacturer).
  

• 
  Publication in the appropriate aeronautical documentation is required.
  

Access should be provided to allow rescue and fire fighting vehicles to intervene in both directions. This is however not a specific A380 issue. The wingspan of code E aircraft also exceeds the width of a code E taxiway bridge.

If the width of the bridge is not enough to provide vehicle passage on the bridge, when occupied by an A380 or any other large aircraft, an alternative path for RFF vehicles must be provided. This path could be a service road with separate service road bridge. On large airports, more than one RFF station is mostly provided. In most cases, a solution could be to intervene from both sides of the taxiway bridge if the RFF stations are not located on the same side of the bridge. Specified response times should be taken into account.

If an alternative path for RFF vehicles or response times from one of the RFF stations can not be guaranteed the solution could be to strategically position RFF vehicles on both sides of the taxiway bridge for an A380 passage. As the A380 passage is only occasional, the disturbance of this procedure should be acceptable.

• 
  Strategically position RFF vehicles on both side of the taxiway bridge.
  

The maximum load of the bridge or tunnel is a prime factor in determining the capability for A380 aircraft. Taxiway bridges and tunnels designed to be capable of supporting a B747-400 at MTOW, are in any case capable of supporting a A380 on arrival. The Maximum Landing Weight (MLW) is less than the MTOW of a B747-400. The bridge should also be capable to support an A380 on departure as the airlines have quoted that the actual take-off weight in practice will be limited to maximum MLW + 2 hours fuel (comparable to a B747-400 at MTOW). In that case no special procedures are required.

• 
  Publish the weight limitations on A380 taxi routes
  

As the A380 movement is occasional, the operational disturbance could well be acceptable in relation to the enormous investment for upgrading the infrastructure. As these investments cost will be reflected into the operational charges of the airport, the other airlines will probably accept the occasional disturbance a diversion will cause.

If an A380 can not operate on the taxiway parallel to the runway, taxiing on the runway becomes necessary. Turning pads at the end of the runway must then be available.

Back tracking on the runway after landing or before take-off is not uncommon and normal practice on many airports around the world. It is uncommon on airports where parallel taxiways next to runways are provided and where normally traffic volume is high. Back tracking on the runway could in that case not only cause operational disturbance (runway is blocked for a longer time), but could also be source of additional runway incursion risk. Caution should be made for alternate airports where in practice only the occasional A380 movement needs taxing on (part of) the runway.
Taxiway bridges

The taxi route between an aircraft stand and the runway can contain taxiway bridges or tunnels. As mentioned in paragraph 3.7, taxiway bridges can be critical not only in width but certainly also in bearing strength. If that is the case, it is wise to define taxi routings that bypasses the taxiway bridge or tunnel. Sometimes this will not be possible as the only route between runway and terminal area will be over the taxiway bridge / tunnel. In that case, it is advisable to look for a parking position somewhere between the runway and the Taxiway Bridge / tunnel. In the extreme situation this could be part of the taxiway system or even a non used runway.

The following items are a relevant but not exhaustive list.

The need to upgrade the RFF equipment should be assessed with regard to the national and international regulations. ICAO, FAA as well as JAA have requirements on RFF services on alternate airports. It is the responsibility of the local authority to determine acceptability of the available RFF services and equipment.

The blast issues raised in the “runway” paragraph are also valid for snow removal. It is therefore necessary that airports, which can be filled as an alternate, prepare a plan for runway snow removal based on the characteristics of the A380.

Normally, ground servicing can be achieved with GSE commonly used by other wide body jets (main deck service). Attention must be given for ground service equipment which can be specific for A380 operations. This could be:

• 
  a capable tow truck and suitable tow bar at alternate airports where towing the aircraft is unavoidable
  
• 
  Suitable de-icing equipment
  

In the case of a filed alternate, the servicing of the aircraft, its passengers, cargo and baggage should be prepared in advance; the airline should ensure the availability of the relevant handling equipment.

This is not substantially different than what is already common practice at many airports who accommodate the occasional visit of an airplane bigger than their design aircraft: for example, an An-124, or even B 747 at many existing airports.

References

• 
  ICAO, Annex 14,
  

• 
  ICAO, Circular on New Larger Aeroplane Operations at Existing Aerodromes,
  

• 
  Common Agreement Document of the A380 Airport Compatibility Group,