title-14-part-27-sec27-563

508

14 CFR Ch. I (1–1–24 Edition)

§ 27.563

lateral roll, with the directions op-

tional, to account for possible floor
warp.

must be shown:

(1) The seating device system must

remain intact although it may experi-
ence separation intended as part of its
design.

(2) The attachment between the seat-

ing device and the airframe structure
must remain intact, although the
structure may have exceeded its limit
load.

(3) The ATD’s shoulder harness strap

or straps must remain on or in the im-
mediate vicinity of the ATD’s shoulder
during the impact.

(4) The safety belt must remain on

the ATD’s pelvis during the impact.

(5) The ATD’s head either does not

contact any portion of the crew or pas-
senger compartment, or if contact is
made, the head impact does not exceed
a head injury criteria (HIC) of 1,000 as
determined by this equation.

HIC

a(t)dt

2.5

−

(

)

−

(

)

⎡

⎣

⎢

⎤

⎦

⎥

∫

Where: a(t) is the resultant acceleration at

the center of gravity of the head form ex-
pressed as a multiple of g (the accelera-
tion of gravity) and t

is the time

duration, in seconds, of major head im-
pact, not to exceed 0.05 seconds.

(6) Loads in individual upper torso

harness straps must not exceed 1,750
pounds. If dual straps are used for re-
taining the upper torso, the total har-
ness strap loads must not exceed 2,000
pounds.

(7) The maximum compressive load

measured between the pelvis and the
lumbar column of the ATD must not
exceed 1,500 pounds.

(d) An alternate approach that

achieves an equivalent or greater level
of occupant protection, as required by
this section, must be substantiated on
a rational basis.

[Amdt. 27–25, 54 FR 47318, Nov. 13, 1989]

§ 27.563

Structural ditching provi-

sions.

If certification with ditching provi-

sions is requested, structural strength

for ditching must meet the require-
ments of this section and § 27.801(e).

(a)

Forward speed landing conditions.

The rotorcraft must initially contact
the most critical wave for reasonably
probable water conditions at forward
velocities from zero up to 30 knots in
likely pitch, roll, and yaw attitudes.
The rotorcraft limit vertical descent
velocity may not be less than 5 feet per
second relative to the mean water sur-
face. Rotor lift may be used to act
through the center of gravity through-
out the landing impact. This lift may
not exceed two-thirds of the design
maximum weight. A maximum forward
velocity of less than 30 knots may be
used in design if it can be dem-
onstrated that the forward velocity se-
lected would not be exceeded in a nor-
mal one-engine-out touchdown.

(b)

Auxiliary or emergency float condi-

tions—(1) Floats fixed or deployed before
initial water contact. In addition to the
landing loads in paragraph (a) of this
section, each auxiliary or emergency
float, of its support and attaching
structure in the airframe or fuselage,
must be designed for the load devel-
oped by a fully immersed float unless it
can be shown that full immersion is
unlikely. If full immersion is unlikely,
the highest likely float buoyancy load
must be applied. The highest likely
buoyancy load must include consider-
ation of a partially immersed float cre-
ating restoring moments to com-
pensate the upsetting moments caused
by side wind, unsymmetrical rotorcraft
loading, water wave action, rotorcraft
inertia, and probable structural dam-
age and leakage considered under
§ 27.801(d). Maximum roll and pitch an-
gles determined from compliance with
§ 27.801(d) may be used, if significant, to
determine the extent of immersion of
each float. If the floats are deployed in
flight, appropriate air loads derived
from the flight limitations with the
floats deployed shall be used in sub-
stantiation of the floats and their at-
tachment to the rotorcraft. For this
purpose, the design airspeed for limit
load is the float deployed airspeed op-
erating limit multiplied by 1.11.

(2)

Floats deployed after initial water

contact. Each float must be designed for
full or partial immersion perscribed in

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Federal Aviation Administration, DOT

§ 27.573

paragraph (b)(1) of this section. In addi-
tion, each float must be designed for
combined vertical and drag loads using
a relative limit speed of 20 knots be-
tween the rotorcraft and the water.
The vertical load may not be less than
the highest likely buoyancy load deter-
mined under paragraph (b)(1) of this
section.

[Amdt. 27–26, 55 FR 8000, Mar. 6, 1990]

ATIGUE

VALUATION

§ 27.571

Fatigue evaluation of flight

structure.

(a)

General. Each portion of the flight

structure (the flight structure includes
rotors, rotor drive systems between the
engines and the rotor hubs, controls,
fuselage, landing gear, and their re-
lated primary attachments), the failure
of which could be catastrophic, must be
identified and must be evaluated under
paragraph (b), (c), (d), or (e) of this sec-
tion. The following apply to each fa-
tigue evaluation:

(1) The procedure for the evaluation

must be approved.

(2) The locations of probable failure

must be determined.

(3) Inflight measurement must be in-

cluded in determining the following:

(i) Loads or stresses in all critical

conditions throughout the range of
limitations in § 27.309, except that ma-
neuvering load factors need not exceed
the maximum values expected in oper-
ation.

(ii) The effect of altitude upon these

loads or stresses.

(4) The loading spectra must be as se-

vere as those expected in operation in-
cluding, but not limited to, external
cargo operations, if applicable, and
ground-air-ground cycles. The loading
spectra must be based on loads or
stresses determined under paragraph
(a)(3) of this section.

(b)

Fatigue tolerance evaluation. It

must be shown that the fatigue toler-
ance of the structure ensures that the
probability of catastrophic fatigue fail-
ure is extremely remote without estab-
lishing replacement times, inspection
intervals or other procedures under
section A27.4 of appendix A.

(c)

Replacement time evaluation. it

must be shown that the probability of
catastrophic fatigue failure is ex-

tremely remote within a replacement
time furnished under section A27.4 of
appendix A.

(d)

Fail-safe evaluation. The following

apply to fail-safe evaluation:

(1) It must be shown that all partial

failures will become readily detectable
under inspection procedures furnished
under section A27.4 of appendix A.

(2) The interval between the time

when any partial failure becomes read-
ily detectable under paragraph (d)(1) of
this section, and the time when any
such failure is expected to reduce the
remaining strength of the structure to
limit or maximum attainable loads
(whichever is less), must be deter-
mined.

(3) It must be shown that the interval

determined under paragraph (d)(2) of
this section is long enough, in relation
to the inspection intervals and related
procedures furnished under section
A27.4 of appendix A, to provide a prob-
ability of detection great enough to en-
sure that the probability of cata-
strophic failure is extremely remote.

(e)

Combination of replacement time

and failsafe evaluations. A component
may be evaluated under a combination
of paragraphs (c) and (d) of this sec-
tion. For such component it must be
shown that the probability of cata-
strophic failure is extremely remote
with an approved combination of re-
placement time, inspection intervals,
and related procedures furnished under
section A27.4 of appendix A.

(Secs. 313(a), 601, 603, 604, and 605, 72 Stat. 752,
775, and 778, (49 U.S.C. 1354(a), 1421, 1423, 1424,
and 1425; sec. 6(c), 49 U.S.C. 1655(c)))

[Amdt. 27–3, 33 FR 14106, Sept. 18, 1968, as
amended by Amdt. 27–12, 42 FR 15044, Mar. 17,
1977; Amdt. 27–18, 45 FR 60177, Sept. 11, 1980;
Amdt. 27–26, 55 FR 8000, Mar. 6, 1990]

§ 27.573

Damage Tolerance and Fa-

tigue Evaluation of Composite
Rotorcraft Structures.

(a) Each applicant must evaluate the

composite rotorcraft structure under
the damage tolerance standards of
paragraph (d) of this section unless the
applicant establishes that a damage
tolerance evaluation is impractical
within the limits of geometry,
inspectability, and good design prac-
tice. If an applicant establishes that it