[Federal Register Volume 59, Number 176 (Tuesday, September 13, 1994)]
[Unknown Section]
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From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-22620]


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[Federal Register: September 13, 1994]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM-53; Notice No. SC-94-3-NM]

 

Special Conditions: Jetstream Aircraft Limited Model 4100 Series 
Airplanes, Main Cabin Aisle Arrangement

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed special conditions.

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SUMMARY: This notice proposes to amend special conditions issued to 
British Aerospace Public Limited Company (BAe) (Currently Jetstream 
Aircraft Limited) for the BAe Model 4100 airplane. This airplane has a 
novel or unusual design feature associated with the main cabin aisle 
arrangement. Special Conditions No. 25-ANM-45 were issued on July 9, 
1991, addressing this unusual arrangement, and included a limitation on 
passenger capacity. The applicant has requested that the special 
conditions be amended to increase the passenger capacity limit from 29 
to 30 passengers. Since the special conditions were issued the 
applicant has changed the company name and revised the model number of 
the airplane. This amendment of the special conditions should also 
reflect these changes. Since the applicable airworthiness regulations 
do not contain adequate or appropriate safety standards for this 
particular design feature, this notice contains the additional safety 
standards which the Administrator finds necessary to establish a level 
of safety equivalent to that established by the airworthiness standards 
for transport category airplanes.

DATES: Comments must be received on or before October 3, 1994.

ADDRESSES: Comments on this proposal may be mailed in triplicate to: 
Federal Aviation Administration, Transport Airplane Directorate (ANM-
100), Attn: Docket No. NM-53, 1601 Lind Avenue SW, Renton, Washington 
98055-4056; or delivered in triplicate to the Transport Airplane 
Directorate at the above address. Comments must be marked: Docket No. 
NM-53. Comments may be inspected in the Rules Docket weekdays, except 
Federal holidays, between 7:30 a.m. and 4:00 p.m.

FOR FURTHER INFORMATION CONTACT:
Jeff Gardlin, Regulations Branch, ANM-114, Transport Airplane 
Directorate, Aircraft Certification Service, FAA, 1601 Lind Avenue SW., 
Renton, Washington 98055-4056; telephone (206) 227-2136.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in the making of 
these proposed special conditions by submitting such written data, 
views, or arguments as they may desire. Communications should identify 
the regulatory docket or notice number and be submitted in triplicate 
to the address specified above. All communications received on or 
before the closing date for comments will be considered by the 
Administrator before taking action on this proposal. The proposal 
contained in this notice may be changed in light of comments received. 
All comments submitted will be available in the Rules Docket for 
examination by interested persons, both before and after the closing 
date for comments. A report summarizing each substantive public contact 
with FAA personnel concerning this rulemaking will be filed in the 
docket. Persons wishing the FAA to acknowledge receipt of their 
comments submitted in response to this notice must submit with those 
comments a self-addressed, stamped postcard on which the following 
statement is made: ``Comments to Docket No. NM-53.'' The postcard will 
be date/time stamped, and returned to the commentor.

Background

    On May 24, 1989, BAe Public Limited Company (currently Jetstream 
Aircraft Ltd.) applied for a type certificate for the BAe Model 4100 
(currently Jetstream Model 4101) airplane in the transport airplane 
category. The Model 4100 was to be a derivative of the Model 3100, 
which is a small airplane and is certificated under the provisions of 
part 23. Like the Model 3100, the Model 4100 was a low wing, twin 
engine turbo-prop design. The fuselage was stretched, however, to seat 
29 passengers in a three-abreast arrangement. Since the Model 4100 
airplane had the same fuselage cross section as the Model 3100, it did 
not have a traditional main cabin aisle arrangement.
    Section 25.815 species the minimum aisle width dimensions for 
transport category airplanes based on the passenger capacity. For 
airplanes with 20 or more passenger seats, a minimum 15-inch width at 
heights 25 inches or less above the main aisle floor and a minimum 20-
inch width at heights greater than 25 inches above the floor must be 
maintained. Aisle width is measured at any point along the aisle, 
normal to the centerline of the aisle. The main aisle envisioned by the 
regulations would run in a straight line from one end of the passenger 
cabin to the other and would satisfy these width criteria. Long 
standing FAA policy has permitted slight deviation from a straight line 
where there is a transition from one cabin section to another, or where 
there are interior features which dictate that the aisle move 
laterally. For example, from tourist class to first class there may be 
a change from five-abreast seating to four-abreast seating which moves 
the aisle centerline laterally. This has been accepted provided the 
required widths are maintained at all heights normal to the path that 
an individual would take. This type of offset normally occurs at one or 
two points in a main cabin aisle. In addition, there is no offset 
permitted in the aisle vertically; that is, the required 15-inch 
dimension must lie completely below the projected 20-inch dimension at 
all points along the aisle.
    The Jetstream main cabin aisle arrangement utilizes an offset at 
each seat row. The left and right seat assemblies are offset from one 
another longitudinally such that the seatbacks are not opposite each 
other across the aisle. This arrangement permits a 20-inch measurement 
between seatbacks (at an angle to the airplane centerline) and the 
required 15-inch dimension is maintained within the projected 20-inch 
dimension vertically. Thus the ``required aisle'' is not a straight 
line from one end of the cabin to the other, but a series of 
alternating angular segments from seatback to seatback. Nonetheless, 
there is a straight path along the cabin length, and the aisle floor 
does not deviate from side to side at all. The projected aisle width 
along this straight path reaches 20 inches at a height of 43 inches 
above the floor, which is the typical seatback height for transport 
airplanes. Another feature of the design includes the use of overwing 
exits which are offset longitudinally, corresponding to the seat 
positions on the left and right of the airplane.
    In order to provide design standards for the novel and unusual 
aisle configuration in the BAe Model 4100 airplanes, the FAA issued 
Special Conditions No. 25-ANM-45 on July 9, 1991. The criteria used to 
develop Special Conditions No. 25-ANM-45 utilized the existing 
regulations, and made certain favorable design features in the Model 
4100 mandatory. Special Conditions No. 25-ANM-45 are summarized as 
follows:
    a. There are no more than 29 passenger seats with no more than ten 
seat rows on either side of the aisle;
    b. The interior arrangement includes one pair of Type II and one 
pair of Type III passenger emergency exits;
    c. In addition to the requirements of Sec. 25.815, the projected 
aisle width is at least 20 inches measured at a height of 43 inches 
above the aisle floor;
    d. The Type III exits and adjacent seat rows are offset 
longitudinally such that persons approaching an exit from one end of 
the cabin may use the exit without interfering with those approaching 
the other exit from the other end of the cabin;
    e. The location and part number of each passenger seat must be 
defined by a drawing approved by the FAA or foreign civil airworthiness 
authority. The seat arrangement may not be reconfigured without FAA 
approval; and
    f. An evacuation demonstration must be conducted to demonstrate the 
efficacy of the aisle arrangement.
    The content of the special conditions was based, in part, on the 
maximum passenger capacity proposed by BAe. The specific limitation of 
29 passenger seats was the maximum capacity requested by BAe, but the 
FAA considered that the fact that this capacity was well below the 
maximum that could be allowed for the installed exit combination was a 
significant factor in acceptance of the aisle arrangement.
    Subsequent to issuing the Special Conditions 25-ANM-45 and prior to 
issuance of the Type Certificate for that project British Aerospace 
Public Limited Company changed its name to Jetstream Aircraft Limited 
and changed the model designation for the airplane from BAe Model 4100 
to the Jetstream Model 4101. Type Certificate A41NM was issued to 
Jetstream Aircraft Limited on April 9, 1993 for the Jetstream Model 
4101 airplane. It is now anticipated that additional models of the 4100 
series may be added to this Type Certificate in the future. In addition 
to the Model 4101, Special Conditions No. 25-ANM-45 would be applicable 
to any other Jetstream Model 4100 series airplanes that incorporate the 
same novel or unusual aisle configuration.

Type Certification Basis

    Under the provisions of Sec. 21.101, Jetstream must show that 30 
passenger Model 4100 series airplanes comply with the regulations in 
the type certification basis established for the 29 passenger Jetstream 
Model 4101 airplane. The type certification basis for the Model 4101 is 
as follows:
    The certification basis for the Model 4101 is established in 
accordance with Sec. 21.29, using the Joint Aviation Regulations (JAR) 
as a reference point, with appropriate additional requirements 
incorporated to provide an equivalent certification basis to the FAR 
requirements for U.S. certification. British Aerospace and the Civil 
Aviation Authorities (CAA)-UK elected to have the type certification 
basis be the following:

--JAR 25 as amended through Change 12 dated May 10, 1988;
--JAR 25 Orange Paper Amendment 88-1 effective October 18, 1988;
--JAR 1, definitions as amended through Change 4 dated June 1, 1987; 
and
--any additional part 25 paragraphs necessary to provide a composite 
type certification basis equal to the required part 25 type 
certification basis.

    Based on Secs. 21.29 and 21.17 and the type certification 
application date, the applicable U.S. type certification basis was 
established as follows:

--Part 25 dated February 1, 1965, as amended by Amendments 25-1 through 
25-66;
--any applicable special conditions issued;
--any applicable exemptions granted;
--any equivalent safety findings made;
--the fuel venting requirements of Special Federal Aviation Regulation 
No. 27, including Amendments 27-1 through the latest amendment in 
effect on the date the Model 4100 is type certificated, and
--Part 36, including Amendments 36-1 through the latest amendment in 
effect on the date of TC.

    If the Administrator finds that the applicable airworthiness 
regulations (i.e., part 25 as amended) do not contain adequate or 
appropriate safety standards for Jetstream Model 4100 series airplanes 
because of a novel or unusual design feature, special conditions are 
prescribed under the provisions of Sec. 21.16 to establish a level of 
safety equivalent to that established in the regulations.
    Special conditions, as appropriate, are issued in accordance with 
Sec. 11.49 after public notice, as required by Secs. 11.28 and 
11.29(b), and become part of the type certification basis in accordance 
with Sec. 21.17(a)(2).
    Special conditions are initially applicable to the model for which 
they are issued. Should the type certificate for that model be amended 
later to include any other model that incorporates the same novel or 
unusual design feature, or should any other model already included on 
the same type certificate be modified to incorporate the same novel or 
unusual design feature, the special conditions would also apply to the 
other model under the provisions of Sec. 21.101(a)(1).

Novel or Unusual Design Features

    The 30 passenger seat version of the Jetstream Model 4100 series 
airplanes incorporate(s) the same novel or unusual aisle configuration 
as described above for the 29 seat version.
    As in the case of the 29 seat version, the required main cabin 
aisle widths would be established using measurements taken between 
seatbacks, which form a path in angular segments. The aisle width 
measured normal to the fuselage centerline above 25 inches from the 
floor, would extend from the seat back to the opposite cabin sidewall. 
Thus, while the required 15-inch dimension at cabin heights below 25 
inches from the floor would be completely within the projected 20-inch 
width vertically, the 20-inch position would not be centered over the 
15-inch position (See Figure 1.)

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    In establishing Special Conditions No. 25-ANM-45, the FAA carefully 
evaluated the relevant design parameters of the BAe Model 4100 and 
determined that the main aisle configuration is clearly not what was 
envisioned by the regulations. The regulations do not specifically 
prohibit the arrangement proposed; however, the policy in effect is 
predicated on a largely straight aisle which has only one or two 
lateral deviations; in other words, a traditional cabin arrangement. 
Therefore, special conditions were developed to establish design 
criteria which result in a level of safety equivalent to configurations 
on which the regulations were based.
    Jetstream has requested that the FAA amend Special Conditions No. 
25-ANM-45 to allow a maximum passenger capacity of 30, to account for a 
new customer demand, and be responsive to the market. In their request 
Jetstream contends that there is no technical basis for the limitation 
on passenger capacity, and that the Joint Aviation Authorities (JAA) 
have, in fact, already granted such approval. Jetstream has proposed 
that on the basis of harmonization with the JAA, the FAA should 
consider their request favorably.
    Jetstream further contends that the evacuation demonstration 
conducted in accordance with the special conditions for the 29 
passenger Model 4101 illustrated that there is no impediment due to the 
aisle arrangement for 30 passengers. Jetstream argues that the concern 
that prompted the requirement was therefore demonstrated not to exist.
    In developing the special conditions, the FAA took account of the 
several favorable cabin safety features that the 29 passenger Model 
4101 incorporates. One of the major features was the good exit-to-
passenger ratio for the number of passengers requested. That is, one 
pair of Type II exits and one pair of Type III exits for 29 passenger 
seats, where the regulations allow up to 39. In this regard, 29 
passenger seats was the largest arrangement proposed for a US customer. 
Consequently, the FAA did not consider a greater passenger capacity, 
and the issue of harmonization did not come up.
    With respect to the evacuation demonstration conducted in 
accordance with the special conditions, this demonstration was a 
modified version of the demonstration specified in part 25, Appendix J. 
The principal modification was the use of a single exit (in this case, 
the forward Type I exit) instead of one half of the total number of 
exits installed. The demonstration was conducted this way in order to 
provide for maximum usage of the aisle, by the maximum number of 
passengers. While this demonstration was completed in 54 seconds, the 
resultant overall rates of egress were not particularly fast for this 
type of exit. In addition, the evacuees appeared to steady themselves 
on seatbacks to a higher degree than is typically seen in such 
demonstrations. Thus, while there was no clear obstruction due to the 
aisle, the overall egress rates did seem to be somewhat reduced. The 
FAA therefore considers that the aisle arrangement should result in a 
limit on maximum passenger capacity that is reduced over the 
theoretical limit in the regulations.
    Jetstream has requested that the FAA increase the current limit, 
which they believe is arbitrary, and allow up to 30 passengers in 
accordance with same special conditions. As noted by the applicant the 
demonstration conducted for approval of the 29 passenger version Model 
4101 did include 30 occupants in the passenger cabin (to account for 
the JAA approved arrangement) and was completed well within the 
allowable time. Therefore, from the standpoint of amending the special 
conditions, an additional demonstration would not be required. While 
the limit of 29 passengers is somewhat arbitrary, the FAA must consider 
whether other conditions should apply if the limit is raised.
    One of the existing conditions is that there be no more than ten 
seat rows on either side of the aisle. The 30 passenger arrangement 
proposed by Jetstream still complies with this requirement. In fact, 
the additional seat is located on the left side of the aisle at the 
extreme rear of the airplane, and does not produce the same kind of 
aisle offset that occurs throughout the cabin. This is because the seat 
is opposite a windscreen at which point the aisle leads into the 
passageway for the aft exit.
    These special conditions are intended to provide requirements which 
result in a cabin aisle that is as effective and safe as those 
envisioned by the regulations for the maximum number of passengers on 
the airplane. Where appropriate, requirements have been drawn from 
existing regulations. In other cases, new requirements were developed 
to preserve the level of safety which is inherent in the design of more 
conventional aisle arrangements. The FAA considers that an additional 
passenger does not invalidate the existing special conditions. It is 
noted however, that further increase in passenger capacity would 
violate one of the other conditions because it would result in more 
than ten seat rows on at least one side of the aisle. Therefore, any 
increase beyond 30 passenger seats would very likely require the 
development of additional conditions. As noted above, the FAA has 
determined that the staggered aisle should limit the passenger seating 
capacity to something less than would otherwise be allowed by the 
regulations. Under the terms of these special conditions, 30 is 
considered to be the reasonable maximum.
    As in the case of Special Conditions No. 25-ANM-45, an evacuation 
demonstration would be required for the 30-passenger version. Since the 
applicant chose to conduct it with 30 rather than 29 passengers, the 
evacuation demonstration conducted for the 29-passenger version would 
show compliance with this requirement for the 30-passenger version as 
well.
    Accordingly, in addition to the requirements of Sec. 25.815, the 
following amended special conditions are proposed for Jetstream Model 
4100 series airplanes with a staggered main aisle. Other conditions may 
be developed as needed based on further FAA review and discussions with 
the manufacturer and the Civil Aviation Authority (CAA).
    As discussed above, the proposed special conditions would be 
applicable initially to the 30 passenger version of the Jetstream 
Aircraft Limited Jetstream Model 4101 airplane. Should Jetstream apply 
at a later date for a change to the type certificate to include another 
model of the 4100 series incorporating the same novel or unusual design 
feature, the special conditions would apply to that model, as well, 
under the provisions of Sec. 21.101(a)(1).
    Jetstream, in their petition, requested that the amended special 
conditions be promulgated without delay as a final rule and in time to 
permit delivery of 30 passenger airplanes during August 1994. The FAA 
has determined that public comment would be in the public interest, but 
will shorten the comment period to 20 days in order to expedite the 
issuance of the final special conditions.

Conclusion

    This action affects only certain novel or unusual design features 
on one Model of airplanes. It is not a rule of general applicability, 
and it affects only the manufacturer who applied to the FAA for 
approval of these features on the airplane.

List of Subjects in 14 CFR Part 25

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amended Special Conditions

    Accordingly, the Federal Aviation Administration proposes the 
following amended special conditions for Jetstream Aircraft Limited 
Model 4100 series airplanes with an offset main cabin aisle.

PART 25--[AMENDED]

    The authority citation for these special conditions is as follows:

    Authority: 49 U.S.C. 1344, 1348(c), 1352, 1354(a), 1355, 1421 
through 1431, 1502, 1651(b)(2), 42 U.S.C. 1857f-10, 4321 et seq., 
E.O. 11514; 49 U.S.C. 106(g) (Revised Pub. L. 97-449, January 12, 
1983).

    1. Jetstream Model 4100 series airplanes may be approved with an 
offset main aisle provided:
    a. There are no more than 30 passenger seats with no more than ten 
seat rows on either side of the aisle;
    b. The interior arrangement includes on pair of Type II and one 
pair of Type III passenger emergency exits;
    c. In addition to the requirements of Sec. 25.815, the projected 
aisle width is at least 20 inches measured at a height of 43 inches 
above the aisle floor; and
    d. The Type III exits and adjacent seat rows are offset 
longitudinally such that persons approaching an exit from one end of 
the cabin may use the exit without interfering with those approaching 
the other exit from the other end of the cabin.
    2. The location and part number of each passenger seat must be 
defined by a drawing approved by the FAA or CAA-UK. The seat 
arrangement may not be reconfigured without FAA approval.
    3. An evacuation demonstration must be conducted to demonstrate the 
efficacy of the aisle arrangement.

    Issued in Renton, Washington, on August 30, 1994.
Stewart R. Miller,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 94-22620 Filed 9-12-94; 8:45 am]
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