[Federal Register Volume 59, Number 229 (Wednesday, November 30, 1994)]
[Unknown Section]
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From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-28286]


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[Federal Register: November 30, 1994]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM-53; Special Conditions No. 25-ANM-45A]

 

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

AGENCY: Federal Aviation Administration, DOT.

ACTION: Amended special conditions.

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SUMMARY: These amended special conditions are issued to Jetstream 
Aircraft Limited for the Jetstream Model 4100 series airplanes. 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 (to British Aerospace Public Limited Company (BAe)), 
addressing this unusual arrangement, and included a limitation on 
passenger capacity. The applicant has requested that Special Conditions 
No. 25-ANM-45 be amended to increase the passenger capacity limit from 
29 to 30 passengers. Since Special Conditions No. 25-ANM-45 were 
issued, the applicant has changed the company name and revised the 
model number of the airplane. These amended special conditions reflect 
those changes. Since the applicable airworthiness regulations do not 
contain adequate or appropriate safety standards for this particular 
design feature, these amended special conditions contain 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.

EFFECTIVE DATE: November 30, 1994.

SUPPLEMENTARY INFORMATION: On May 24, 1989, BAe (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 specifies the minimum aisle width dimensions for 
transport category airplanes based on the passenger seating 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 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 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 Special Conditions No. 25-ANM-45 is 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 the issuance of Special Conditions No. 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. Also, the specific model of the 4100 series in question was 
identified as 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 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 of 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 Jetstream Model 4100 series 
airplanes incorporate 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 portion would not be centered over the 
15-inch portion. (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 seating 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 exists and one pair of Type III exists 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 seating 
capacity, and the issue of harmonization with JAA requirements 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 passenger seats 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 passenger seats 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 is consistent 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 were drawn from existing 
regulations. In other cases, new requirements were developed to 
preserve the level of safety that is inherent in the design of more 
conventional aisle arrangements. The FAA considers that an additional 
passenger seat would not invalidate the basis for the original finding 
of equivalency. It is noted however, that any 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.
    Accordingly, in addition to the requirements of Sec. 25.815, these 
amended special conditions are issued 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 amended 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, these amended 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 
determined that public comment was in the public interest, but 
shortened the comment period to 20 days in order to expedite the 
issuance of these amended special conditions.
    Notice of Proposed Special Conditions No. SC-91-4-NM for the 
Jetstream Aircraft Ltd. Model 4101 airplane was published in the 
Federal Register on September 13, 1994 (59 FR 46939). Comments were 
received from two labor organizations and two airlines.
    Both operators comment on the improved productivity that could be 
realized with the additional seat on the Jetstream 4101 and strongly 
support the proposed amendment. One operator notes that the Joint 
Aviation Authorities have already approved the airplane for 30 
passengers and only the FAA special conditions limit its capacity.
    The third commenter is not in favor of the proposed amendment to 
the special conditions. This commenter argues that the exit arrangement 
and flight attendant seat location on the airplane are confusing and 
awkward. The commenter specifically criticizes the location of the 
flight attendant seat and the potential for the flight attendant to 
disrupt evacuation through the right rear exit. The FAA does not agree 
that the exit arrangement on this airplane in conjunction with the 
flight attendant seat location is in any way inadequate. The exit 
arrangement complies fully with all applicable regulations and provides 
good uniformity for the number of passengers on board. The FAA also 
participated in an evaluation of the flight attendant's ability to 
assist passengers through the right rear exit and found that this could 
be accomplished quite effectively.
    This commenter also does not feel that the emergency evacuation 
conducted as part of the original special conditions was adequate, and 
should be repeated before an increase in passengers could be 
considered. The commenter notes that there has been a change to the 
regulations regarding evacuation demonstrations since the issuance of 
the special conditions and believes that the new provisions were not 
complied with in the original demonstration. This commenter also 
questions whether the demonstration met the FAA's stated objective of 
maximizing the number of passengers who must use the aisle, and feels 
that the aft right-hand door should have been used for the 
demonstration. Additionally, the commenter interprets FAA comments to 
mean that the passengers were ``zig-zagging'' around the seats backs. 
The commenter also suggests that Jetstream should relocate the flight 
attendant seat to the forward bulkhead. The commenter believes that 
this would enhance both passenger and flight attendant safety. This 
last comment is not germane to these amended special conditions.
    With respect to the demonstration conditions, these were chosen by 
the FAA for the purpose of complying with the special conditions, and 
not to show compliance with the specific regulations regarding 
evacuation demonstrations. Therefore, changes to these regulations 
since the special conditions were issued are not relevant. In any case, 
the new provisions in the regulation were encompassed in the 
demonstration done for the special conditions.
    In regard to the second concern, that the demonstration did not 
maximize usage of the aisle, the FAA does not agree. The evacuation 
demonstration was conducted with a full passenger and crew complement 
using only the forward entry door. This scheme was chosen for several 
reasons. First, the end of cabin location meant that passengers at the 
extreme end of the cabin would have to traverse the entire cabin in 
order to reach an exit, thus making maximum use of the aisle. Second, 
the forward exit, a Type I exit, was specifically selected because it 
was expected to provide for an increased evacuation rate capability 
over the aft exit, which is a Type II. Thus, the door rate would not 
mask any effect due to the aisle. Had the aft exit been used, it is not 
clear that the rate capability of the door is sufficiently higher than 
that of the aisle to identify effects due to the aisle only. In 
addition, the aft location of the flight attendant seat meant that 
passengers had to negotiate the aisle without crew assistance, which is 
the more critical case.
    Finally, the FAA's observations of the evacuation demonstration, as 
expressed above, were not intended as an implication that passengers 
were required to ``zig-zag'' around the seat backs. The passengers 
proceeded in a straight line along the aisle, but did seem to use the 
seat backs as hand-holds to a higher degree than is usually seen.
    In summary, the FAA will not require a new evacuation demonstration 
since the results of the previous demonstration are still valid.
    The fourth commenter opposes the amendment to the special 
conditions, and reiterated opposition to the original special 
conditions. The commenter's principal objection is the projected width 
of the aisle at heights more than 25 inches above the floor. The 
commenter notes that the special conditions require a 20 inches 
projected width at 43 inches above the floor, but expresses frustration 
at not knowing the projected width below that height. The commenter 
assumes that 43 inches represents the tops of the seat backs. This 
commenter also interprets the FAA's observations of the evacuation 
demonstration as indicating that there is a safety problem with the 
airplane.
    Regarding the projected aisle width, this varies essentially 
linearly from approximately 16 inches (at a height of 25 inches above 
the floor) to 20 inches (at a height of 43 inches above the floor). 
However, since the seat rows are longitudinally offset, there is never 
any point where the transverse measurement between seats is less than 
20 inches. As noted in the original final special conditions, the 
actual seat back height is almost 50 inches. Forty-three inches 
represents a typical seat back height for airplanes where the seats are 
mounted at the same level as the main aisle.
    As noted previously, an indication of some additional problems 
should not be inferred from the FAA's observations of the evacuation 
demonstration. They are simply the factual observations of the 
demonstrations.
    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 Amended Special Conditions

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the following amended special conditions are issued as 
part of the type certification basis for the Jetstream Model 4100 
series airplanes with an offset main cabin aisle.
    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 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 aisle 
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 November 8, 1994.
Stewart R. Miller,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 94-28286 Filed 11-29-94; 8:45 am]
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