267
Federal Aviation Administration, DOT
§ 25.651
considered in showing compliance with
this section are:
(1) Any critical fuel loading condi-
tions, not shown to be extremely im-
probable, which may result from mis-
management of fuel.
(2) Any single failure in any flutter
damper system.
(3) For airplanes not approved for op-
eration in icing conditions, the max-
imum likely ice accumulation expected
as a result of an inadvertent encounter.
(4) Failure of any single element of
the structure supporting any engine,
independently mounted propeller shaft,
large auxiliary power unit, or large ex-
ternally mounted aerodynamic body
(such as an external fuel tank).
(5) For airplanes with engines that
have propellers or large rotating de-
vices capable of significant dynamic
forces, any single failure of the engine
structure that would reduce the rigid-
ity of the rotational axis.
(6) The absence of aerodynamic or gy-
roscopic forces resulting from the most
adverse combination of feathered pro-
pellers or other rotating devices capa-
ble of significant dynamic forces. In
addition, the effect of a single feath-
ered propeller or rotating device must
be coupled with the failures of para-
graphs (d)(4) and (d)(5) of this section.
(7) Any single propeller or rotating
device capable of significant dynamic
forces rotating at the highest likely
overspeed.
(8) Any damage or failure condition,
required or selected for investigation
by § 25.571. The single structural fail-
ures described in paragraphs (d)(4) and
(d)(5) of this section need not be consid-
ered in showing compliance with this
section if;
(i) The structural element could not
fail due to discrete source damage re-
sulting from the conditions described
in § 25.571(e), and
(ii) A damage tolerance investigation
in accordance with § 25.571(b) shows
that the maximum extent of damage
assumed for the purpose of residual
strength evaluation does not involve
complete failure of the structural ele-
ment.
(9) Any damage, failure, or malfunc-
tion considered under §§ 25.631, 25.671,
25.672, and 25.1309.
(10) Any other combination of fail-
ures, malfunctions, or adverse condi-
tions not shown to be extremely im-
probable.
(e)
Flight flutter testing. Full scale
flight flutter tests at speeds up to V
DF
/
M
DF
must be conducted for new type
designs and for modifications to a type
design unless the modifications have
been shown to have an insignificant ef-
fect on the aeroelastic stability. These
tests must demonstrate that the air-
plane has a proper margin of damping
at all speeds up to V
DF
/M
DF
, and that
there is no large and rapid reduction in
damping as V
DF
/M
DF
, is approached. If a
failure, malfunction, or adverse condi-
tion is simulated during flight test in
showing compliance with paragraph (d)
of this section, the maximum speed in-
vestigated need not exceed V
FC
/M
FC
if it
is shown, by correlation of the flight
test data with other test data or anal-
yses, that the airplane is free from any
aeroelastic instability at all speeds
within the altitude-airspeed envelope
described in paragraph (b)(2) of this
section.
[Doc. No. 26007, 57 FR 28949, June 29, 1992]
§ 25.631
Bird strike damage.
The empennage structure must be de-
signed to assure capability of contin-
ued safe flight and landing of the air-
plane after impact with an 8-pound bird
when the velocity of the airplane (rel-
ative to the bird along the airplane’s
flight path) is equal to
V
C
at sea level,
selected under § 25.335(a). Compliance
with this section by provision of redun-
dant structure and protected location
of control system elements or protec-
tive devices such as splitter plates or
energy absorbing material is accept-
able. Where compliance is shown by
analysis, tests, or both, use of data on
airplanes having similar structural de-
sign is acceptable.
[Amdt. 25–23, 35 FR 5674, Apr. 8, 1970]
C
ONTROL
S
URFACES
§ 25.651
Proof of strength.
(a) Limit load tests of control sur-
faces are required. These tests must in-
clude the horn or fitting to which the
control system is attached.
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