[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]
[[Page Unknown]]
[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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