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

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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