[Federal Register Volume 62, Number 112 (Wednesday, June 11, 1997)]
[Rules and Regulations]
[Pages 31707-31708]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-15311]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM-131, Special Conditions No. 25-ANM-128]


Special Conditions: LET Aeronautical Works Model L610G Airplane

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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SUMMARY: These final special conditions are issued for the LET 
Aeronautical Works Model L610G airplane. This airplane will have a 
novel or unusual design feature associated with the use of the landing 
gear fairing as an assist means during an emergency evacuation. These 
special conditions contain the additional safety standards that the 
Administrator considers necessary to establish a level of safety 
equivalent to that established by the airworthiness standards of 14 CFR 
part 25.

EFFECTIVE DATE: July 11, 1997.

FOR FURTHER INFORMATION CONTACT:
Frank Tiangsing, Regulations Branch, ANM-114, Transport Airplane 
Directorate, Aircraft Certification Service, FAA 1601 Lind Avenue SW, 
Renton WA 98055-4056, (425) 227-121.

SUPPLEMENTARY INFORMATION: 

Background

    On April 25, 1990, LET Aeronautical Works applied for a type 
certificate for the Model L610G airplane. On March 28, 1995, they 
applied for an extension of the original application in accordance with 
14 CFR 21.17(d)(2). The L610G is a twin-engine, 40 passenger, high-wing 
airplane with a passenger emergency exit configuration consisting of 
one pair of Type I exits located at the aft end of the cabin and a pair 
of Type III exits under the wing near the middle of the cabin.
    Type III exits are typically installed over the wings of the 
airplane. The are allowed by part 25 to have a 27-inch step-down from 
the exit sill to the wing. Additionally, if the escape route on the 
wing terminates at a point more than six feet above the ground, means 
must be provided to assist evacuees to reach the ground. If the 
termination point is less than six feet above the ground, then the 
assist means is not required.
    Since this airplane is of a high-wing configuration, it is not 
practicable to incorporate overwing Type III exits. Part 25 permits 
non-overwing, non-floor level exits when certain conditions are 
satisfied. Included in these conditions is the requirement for an 
assist means for passengers and crew to egress from the airplane to the 
ground when the exit sill height is more than six feet. This assist 
means must be an automatically erected escape slide or equivalent, and 
must be self-supporting on the ground. The sill of the Type III exits 
on the L610G will be more than six feet above the ground; therefore, an 
assist means will be necessary.
    LET has positioned the Type III exits above the landing gear 
fairing such that the fairing will form a surface for evacuees to use 
in lieu of what would be provided by a wing. The evacuees would then 
slide or jump off the fairing to the ground in much the same manner as 
they would off a wing trailing edge.
    LET's use of the landing gear fairing as an assist means results in 
features which are characteristic of both escape slides and overwing 
evacuation routes; therefore, the requirements for either configuration 
are insufficient by themselves to assure that minimum standards are 
established.
    These special conditions include requirements pertinent to both 
overwing and non-overwing exits, as well as additional criteria for 
this specific exit.

Type Certification Basis

    Under the provisions of 14 CFR 21.17, LET must show the Model L610G 
meets the applicable provisions of part 25 as amended by Amendments 15-
1 through 25-70 thereon, except as follows:

Sec. 25.365  Amendment 25-71
Sec. 25.571(e)(2)  Amendment 25-72
Sec. 25.729  Amendment 25-75
Sec. 25.905(d)  Amendment 25-72

    If the Administrator finds that the applicable airworthiness 
regulations (i.e., part 25 as amended) do not contain adequate or 
appropriate safety standards for the Model 610G because of a novel or 
unusual design feature, special conditions are prescribed under the 
provisions of 14 CFR 21.16. In addition to the applicable airworthiness 
regulation and special conditions, the LET Aeronautical Works Model 
L610G must comply with the fuel vent and exhaust emission requirements 
of 14 CFR part 34 and the noise certification requirements of 14 CFR 
part 36.
    Special conditions, as appropriate, are issued in accordance with 
14 CFR 11.49 after public notice, as required by 14 CFR 11.28 and 
11.29(b), and become part of the type certification basis in accordance 
with 14 CFR 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, the special conditions would also apply to the 
other model under the provisions of 14 CFR 21.101(a)(1).

Novel or Unusual Design Features

    The Model L610G will incorporate the following novel or unusual 
design feature: a Type III exit will be located under each wing such 
that an evacuee using the exit would step out onto the main landing 
gear fairing. The evacuee would then slide or jump from the landing 
gear fairing to the ground.
    14 CFR 25.809(f) requires all non-overwing exits more than six feet 
above

[[Page 31708]]

the ground to be equipped with an approved means to assist occupants in 
descending to the ground.
    14 CFR 25.809(h) similarly requires all overwing exits having an 
escape route which terminates at a point more than six feet above the 
ground to be equipped with an assist means. The exit for the Model 
L610G will be more than six feet from the ground; however, the landing 
gear fairing surface will be within 27 inches of the lower exit sill. 
This distance corresponds to the allowable step-down for an overwing 
Typing III exit. The distance from the landing gear fairing to the 
ground is less than six feet.
    14 CFR 25.809(f) also requires that assist means be automatically 
erected during exit opening. Strictly speaking, the landing gear 
fairing does not satisfy this requirement since opening the exit is not 
correlated to the availability of the assist means; however, since the 
fairing is a fixed piece of airplane structure it is always available 
for use.
    The regulations also require that an assist means be self-
supporting on the ground. This requirement has been interpreted to mean 
that the assist means rests on the ground when in use such that an 
evacuee does not have to jump to the ground from the bottom of the 
assist means. In the case of an overwing exit where the terminating 
edge of the escape route is less than six feet from the ground, it is 
likely that evacuees might have to jump a short distance from the wing 
to the ground. The Model L610G incorporates aspects of both of these 
exit arrangements, which are addressed in these special conditions.
    Other features of the exit arrangement which involve both overwing 
and non-overwing exit considerations include marking, visibility, and 
width of the escape route. For the purposes of these special 
conditions, this exit will be treated as an overwing exit with respect 
to these requirements.
    Other areas which are of particular concern for this unusual exit 
arrangement are the effectiveness of the exit in the event of landing 
gear collapse and the proximity of the escape route to the engines and 
wheel wells. Since a collapse of the landing gear could result in some 
form of collapse of the landing gear fairing, the exit must be 
demonstrated to be usable and provide for safe evacuation, considering 
all conditions of landing gear collapse.
    Since the Type III exits are directly above the main landing gear, 
it is possible that a fire originating in the landing gear assembly 
could render such an exit unusable. Due to the design of the Model 
L610G, it is considered necessary to address the possibility that a 
fire on one side of the airplane could also render the opposite side 
unusable.
    These special conditions are intended to provided requirements 
which result in an evacuation system that is as effective and safe as 
those envisioned by the regulations. Where appropriate, requirements 
have been drawn from existing regulations. In other cases, new 
requirements have been developed to preserve the level of safety which 
is inherent in the design of more conventional exit arrangements or 
assist means.

Discussion of Comments

    Notice of Proposed Special Conditions No. SC-96-4-NM for the LET 
Aeronautical Works Model L610G airplane, was published in the Federal 
Register on August 16, 1996. No comments were received.

Applicability

    As discussed above, these special conditions are applicable to the 
LET Aeronautical Works Model L610G airplane. Should LET Aeronautical 
Works apply at a later date for a change to the type certificate to 
include another model incorporating the same novel or unusual design 
feature, the special conditions would apply to that model as well under 
the provisions of 14 CFR 21.101(a)(1).

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 applicant 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 authority citation for these proposed special conditions is as 
follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.

The Special Conditions

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the following special conditions are issued as part of 
the type certification basis for the LET Aeronautical Works L610G 
airplane.
    1. The landing gear fairing must be established as an escape route 
in accordance with the dimensional, reflectance, and slip resistant 
surface requirements of Sec. 25.803(e).
    2. The step-down distance from the exit sill to the surface of the 
landing gear fairing, where an evacuee would make first contact, shall 
not exceed 27 inches (ref. Sec. 25.807(a)(3)).
    3. The assist means must provide for safe evacuation of occupants, 
considering all conditions of landing gear collapse. In addition, safe 
evacuation must be afforded via the Type III exit in the event of main 
landing gear non-deployment.
    4. Exterior emergency lighting must be provided for the assist 
means and all areas of likely ground contact in accordance with 
Secs. 25.812(g)(1) (i) and (ii), and Sec. 25.812(h)(1), as amended 
through Amendment 25-58.
    5. The assist means must be demonstrated to provide an adequate 
egress rate for the number of passengers requested. The passenger 
capacity, as permitted by Sec. 25.807(c)(1), Table 1, may be reduced if 
satisfactory Type III exit performance cannot be demonstrated.
    6. It must be shown that a landing gear fire occurring on one side 
of the airplane is unlikely to render the opposite exit unusable.
    7. The assist means must be shown to be as reliable as an escape 
slide following exposure to the emergency landing conditions that may 
be encountered in service. In addition, safe evacuation from the 
airplane must be afforded following the crash conditions specified in 
Sec. 25.561(b).

    Issued in Renton, Washington, on June 3, 1997.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service, ANM-100.
[FR Doc. 97-15311 Filed 6-10-97; 8:45 am]
BILLING CODE 4910-13-M