Download FAA Engineering Brief (EB) No. 78, Linear Equations for ... and more Study notes Engineering in PDF only on Docsity!
Federal Aviation
Administration
Memorandum
Date: SEP 282 01 2
To: All RegiOn ~ er , Airport Division
From:
Prepared by:
~:~ o~ger, Airport Engineering, AAS -l 00
George Legarreta, Civil Engineer, Airport Engineering, AAS - I 00,
x
Subject: Engineering Brief No. 78, Linear Equations for Evaluating the
Separation of Airplane Des ign Groups on Parallel Taxiways and
Taxiways to FixedlMovable Objects
Engineering brief (EB) No. 78 provides industry and FAA Airports Regional Division
Managers seven linear equations to evaluate proposed modification- ta -standards (MOS)
on the separation of parallel taxiway centerlines and the clearance of taxiways centerlines
to fixed/movable objects.
The EB has several primary goal s. First, the EB formalizes our systematic methodology for all Airplane Design Groups (ADG) to demonstrate when a proposed MOS provides an acceptable level of safety. Numeric values from a proposed MOS that cannot provide an acceptable level of safety always triggers an internal review with the other FAA Regional lines of business (LsOB). Second, the EB grants FAA Airports Regional Division Managers the authority to approve proposed MOSs using the linear equations to
accommodate airplanes on existing taxi systems that provide acceptable level of safety.
One exception to Regional approval authority is proposed MOS involving ADG VI
airplanes, such as, the Airbus A380 and the Boeing 747-8. Lastly, the EB clarifies that
because these linear equations fonnerly provided in AC 150/5300- 13, Airport Design, were coordinated and approved by the other FAA LsOB , no further MOS coordination is nonnally necessary beyond the FAA Airports LsOB when a proposal provides an
acceptable level of safety. However , coordination will be prudent whenever operational
restrictions and/or standard operating procedures (SOP) and inter-LOB agreements are necessary.
Attachment
FAA
Airports
Engineering Brief No. 78
Linear Equations for Evaluating the Separation of Airplane Design Groups on
Parallel Taxiways and Taxiways to Fixed/Movable Objects
Part 1: Background
This engineering brief provides industry with seven linear equations to evaluate proposed modification-ta-standards (MOS) on the separation of parallel taxiway centerlines and the clearance of taxiways centerlines to fi xed/movable objects. The primary goal of this engineering brief is to establish a systematic methodology for all Airplane Design Groups (ADG) to demonstrate when a proposed MOS provides an acceptable l eve l of safety. A resulting numeric value provides an acceptable level of safety when it is smaller or equa l to the existing parallel taxiway CL-to-CL separation or t he existing taxiway CL to a fixed /movable object clearance.
A request for a MOS should be done only as a last resort by an airport operator after an exhaustive evaluation of all alternatives to meet design standard(s). In some cases where meeting the standard is not practicable a MaS can be reviewed. However , the airport operator should always keep the 20-year planning period in mind as to not restrict the growth of the airport to accommodate other lar ger airplane wingspans within the same ADG.
Because these linear equations were coordinated and approved by the other FAA lines-of business (LsOB), no further coordination is normally necessary beyond the FAA Airports LOB when a proposal provides an acceptable level of safety. However, their use does not exclude FAA Airports to determine if further internal coord ination is necessary. For example, internal FAA coordination will be prudent whenever a submitted proposed MaS Involves operational restrictions and/or standard operating procedures (SOP) and where inter-LOB agreements are necessary. Some other common areas needing resolution may include jet blast mitigation on curved sections of a taxi route and vehicle-object height restrictions for nearby service roads. Numer ic values from a proposed MaS that cannot provide an acceptable level of safety always triggers an intemal review with the other FAA Reg ional LsOB and AAS-1 00.
Although all seven linear equations use the parameter of airplane wingspan, a major difference exists. Four equations , referred to as Single ADG , require only one wingspan input while the remaining three equations, referred to as Dual ADG , require two wingspan inputs. Lastly, the latter three equations only apply to parallel taxiway CL-to-CL separations, not clearances for twy C L to fixed/movable objects.
Table 4-1 of Adv isory Circular 150/5300-13A, Airport Design', provides the separation and clearance standards for parallel taxiway centerlines (C L), taxiway CLs to a fixed or movable
1 Advisory circulars are availab le for free at t he following web site: http·Mw,w.fa a.gov/aimorts!resources/adyisorv circularJI.
Enginee ri ng Briel No. 78 Iss ued 91 281 2012 Page 1 of 8 AAS -l 00
Part 3: Modiflcation-to-Standards (MOS) Applications for Single Wingspan
Although new construction or reconstruction of an existing taxi system is built to the design standards, site conditions that are not practicable to improve CQuid limit the available separation
and clearance. In response to such difficulties, AC 150/5300-13A refers to the use of these four
linear equations in conjunction with a lower wingspan value to determine if an acceptable level of safety can be achieved for the site condition(s). In dealing with such circumstances , airport operators should use the linear equations to support their proposed modification-te-standard (MOS). Such usage results in short narrative proposed MOSs that show the linear equation computation(s) with no further supplementary, in-depth supportive documentation. However, their use does not exclude additional review by FAA Airports to determine if further coordination is necessary with other FAA lines of busin ess. For example, a submitted proposed MOS may involve an internal FAA evaluation of various operational im pacts needing resolution , such as jet blast mitigation, vehicle height restrictions for nearby service roads, etc.
Procedurall y, users of table 1 should initially apply taxiway equat ions #1 and #2 rather than taxilane equations #3 and #4 since the former equations may avoid the introduction of FAA approved operational limitations, while the latter equations will include limiting measures. Part 4 provides an actual case study to illustrate the process and the possibility to avoid limitations.
Part 4: Case Study: MOS Application for the Boeing 747-8 - Airplane Design
Group VI
The Boeing 747-8, an ADG VI airplane that began operations in late summer 2011 , is serving
airports designed for ADG V 8747 -100/200/400 service. Table 4-1 illustrates the immediate
impacts by an ADG VI airplane on the existing ADG V taxiway system. That is, the standard taxi CL separation for parallel taxiways for the ADG V Boeing 747-400 measures 267 feet; for the ADG VI 8747-8 , it measures 324 feet-an increased CL - to-CL separation of 57 feet. Consequently, airport operators that receive this ADG VI airplane , but not expecting to accommodate a larger ADG VI airplane within the 20-year planning period , may need to submit a proposed MOS for deSignated 8747-8 taxi routes. Fortunately the imp act to the parallel taxiway CL-to-CL separation is less because the 8747-8 wingspan measures 224.5 feet, which places it toward the bottom of the ADG VI wingspan range (214 feet but not over 262 feet). The design objective for the B747-8 or for any airplane is to find a solution that allows taxiing operations without any operational limitations.
(1) Airports 8uilt to Fonner FAA Taxi Separation Standards. Prior to the 1980s,
airports serving air carrier traffic were built with greater parallel taxiway CL-to-CL separations^2 , e .g ., 300 feet. This raises the question whether a MOS is necessary for simultaneous B747-8s operating on such parallel taxiways.
Applying equalion #1 from table 1 fo r the 8747-8 with a wingspan of 224 .5 feet yields:
Result #1 S l-S747-Uuiway :;; 1.2 x 224.5 feet + 10 feet :;; 279.4 feet.
Since the resulting value is less than the available 300-foot CL-to-CL separation, no MOS is required.
2 Cancelled AC l5OJ5335-1A. AllPOrt Design Slandards _ AilPOrts Served By Alr Carriers - TaxiYIays. Engineering Brief No. 78 Issued 912812012 Pag e 3 of AAS-l
(2) Airports Built to Current FAA Taxi Separation Standards. In 1989 AC 150/5300·
13 was introduced. It promulgated lower taxiway and taxilane separation and clearance design
standards that continue today under AC 15 0/5300·13A. It reduced the pa rallel taxiway CL·to·CL
separation for ADG V from 300 feet to 267 feet. Was there an impact? It depends on the airplane wing span under evaluation.
Result #1 from above already confirms that this operation requires at least 279.4 feet, greater separation than the current 267 -foot design standard. Hence, the airport operator should apply taxi lane criterion , equation #3 to find out whether the operation can continue with an FAA conditionally approved MOS with limitation(s).
Result #2 8 3_B7 47_8 Taxilan e = 1.1 x 224.5 feet + 10 feet = 256.95 feet.
Since the resulting value is less than the available 267-foot CL-to-C L separation , the airport
operator's MOS has merit if it inc ludes some appropriate FAA-approved operational
limitation(s). A common mitigation measure used by airport operators is to restrict the taxiing speed of the larger, less taxied airplan e. Field research conducted by the FAA on the taxi CL wander behavior of larger airplanes indicated that 15 mph was a defining speed threshold between taxilane operations and taxiway operations. Another commonly used mitigation option is to restrict the ma ximum wingspan for the other airplanes operating on the adjacent parallel taxiway. In either case see the Necessary Precautions Box in Part 1 when dealing with taxilanes.
Part 5: Industry Inquiry· Procedure for Parallel Taxiways Serving Different
Airplane Wi ngspans
A common inquiry by industry is how to accommodate two different airplanes within the same ADG or from within different AOGs on an existing parallel taxiway system. Industry inquired because li near equations #1 • #4 are limited to a single airplane wingspan (variable). For example, figure 1 shows one inquiry by Port Authority of New York and New Jersey for JFK International Airport that received an FAA-approved conditional MOS for parallel Taxiways A and B to handle simultaneous Airbus A380 and the Boeing 747·8 taxiing operations. T he submitted MOS showed only a 41-foot wingtip-to-wingtip separation between the A380 and the B747·8 for the existing parallel taxiway CL·to·CL separation of 284 feet. Table 4·3, from the
previous edition of AC 150/5300·13 whose values remain in effect today, is reprinted below to
illustrate the standard wingtip ctearance standards among the ADGs for taxiways and taxi lane applications.
Eng i nee ring Br ie f No. 78 Is su ed 912812012 Page^ 4 of 8 AAS·
ITEM (^) Airplane Design Group
I II II I IV V VI
Taxiway Wingtip 20 ft 26 ft (^) 34ft 44 ft (^53) ft 62 ft Clearance 6m 8m to .5 m 13.5 m 16m 19 m Taxilane Wingtip 15 ft 18 ft (^22) ft 27 ft 31 ft 36 ft Clearance 4.5m (^) 5.5m 6.5m 8m 9.5 m 11 m
Table 4·3. Wingtip clearance standards (Fonner AC 150/5300·13)
Part 6: Dual Airplane Design Groups Linear equations for Parallel Taxiway Centerline Separations
To exped ite future MOS proposals involving only parallel taxi designs , the Airport Engineering Div ision (AAS-100) developed three new linear equations shown in table 2 for ch ange 17 for the previous edition of AC 150/5300·13. Table 2 is applicable to all ADGs for evaluating two airplane wingspans within the same ADG or different AOGs on exist ing paralle l taxi designs.
New Parallel Taxiway Centerline Linear Equations for Dual Airplane Design Group Evaluations (All Airplane Design Groups)
Equation #5 for Dual Parallel Taxiway Application
1.2 x [(WS, + WS , ) 12] + 10 feet = CL·to·CL Separation
Equation #6 for Dual Parallel Taxilane Application 1.1 x ((WS, + WS,) 12] + 10 feet = CL·to-CL Separation
Equations #7 for Mixed Parallel Taxiway and Taxilane Application
((1.2 x WS, + 1.1 x WS,) 12] + 10 feet = CL·to-CL Separation
NOTE: The red-coded 1.1 coefficient multiplier implies that a taxiing
speed limitation is required on the corresponding wingspan(s).
Table 2
Part 7: Rationale for Table 2
Table 2 incorporates the rationale behind table 4-3 which uses the concept of creating a ~ safety
wingtip box [SWB)" between the wingtips of two identical airplane wingspans and between the
wingtip of an airplane to a fixed/movable object. For example , 62 feet is the SWBAOGVl-T.xiw.y for
ADG VI parallel taxiways (obtained by subtracting the table entry from the corresponding maximum wingspan of the AOG). For reference ,
Eng ineering Brief No. 78 Issued^912812012 Page^6 of^8 AAS·
Result #3 (^) SWBADG Vi. Taxiw~~ :::: 324 - 262 :::: 62 feet Result #4 (^) SWBAOG V-T axiw ~y ;: 267 - 214 :::: 53 feet
For airplane wingspans within a given ADG, such as the B747-8 with wingspan of 224.5 feet,
use equation #1 with 1.2 x 224.5 + 10;: 279.5 feet, then subtract 224.5 to obtain SWBB 74 7.S. Taxiwll y·
Result #5 SWBB 7 4 7. 8.T~K i way :::: 279.5 - 224.5 :::: 55 feet
The same process, but using equation #3 , determines taxilane SWBs.
Result #6 SWB AOG VI-Ta xil ane = 298 - 262 = 36 feet
Result #7 SWBADGV.Taxilane = 245 - 214;: 31 feet
Result #8 SWBB747 .s.Taxilan e = 257 - 224. 5:: 32.5 feet
Table 2 uses the same SWB concept but takes the average of two SWBs associated with the two airplane wingspans being evaluated. Take note that the green color-coded coefficient 1. implies no operational limitation. In contrast, the red coefficient 1.1 requires some operational limitation.
Part 8: Design Process for Table 2 and JFK Proposed MOS from Part 5
JFK MOS Proposal- Allow Simultaneous Airbus A380 and Boeing 747-8 Operations on Parallel Taxiways A and B.
Figure 1 illustrated that the available parallel taxiway CL-to CL separation is 284 feet with a 41 foot SWB wingtip-to-wingtip separation. Procedurally start with Case 1 equation #5, then equation #7, followed by equation #6 shown below.
Case 1 Equation #5 - Evaluate Dual Taxiway Criterion to avoid any operational
restrictions
Use 1.2 x [(WS, + WS,) 12J + 10 feet = average CL-to-CL separation
1.2 x [(261 .7 + 224. 5) 12J + 10 feet = 301 .7 feet
Result: There is insufficient separation because the average CL-to-CL separation of 301 .7 feet exceeds the available 284-foot CL-to-CL separation.
Case 2 Equation #7 - Evaluate A380 Taxilane Criterion and 8747·8 Taxiway Criterion to avoid operational restrictions on one airplane
Use [(1.2 x WS, + 1.1 x WS,) 12J + 10 feet = CL-to-CL Separation
[(1.2 x 224.5 + 1.1 x 261.7) 12J + 10 feet = [(269.4 + 287.9) 12J + 10 = 288.6 feet
Result: There is insufficient separation because the average CL-to-CL of 288.6 feet exceeds the available 284-foot CL-to-CL separation.
Case 3 Equation #6 - Evaluate Dual Taxilane Criteria to permit the operation but with both airplanes having restrictions
Eng ineering Brief No. 78 Issued 912812 012 Page^^7 0t AAS·
