spaschal on DSK3GDR082PROD with CFR

Federal Aviation Administration, DOT

Section 25.629

from aeroelastic instability for all configurations and design conditions within the aeroelastic stability envelopes
as follows:
(1) For normal conditions without
failures, malfunctions, or adverse conditions, all combinations of altitudes
and speeds encompassed by the VD/MD
versus altitude envelope enlarged at all
points by an increase of 15 percent in
equivalent airspeed at both constant
Mach number and constant altitude. In
addition, a proper margin of stability
must exist at all speeds up to VD/MD
and, there must be no large and rapid
reduction in stability as VD/MD is approached. The enlarged envelope may
be limited to Mach 1.0 when MD is less
than 1.0 at all design altitudes, and
(2) For the conditions described in
Section 25.629(d) below, for all approved altitudes, any airspeed up to the greater
airspeed defined by;
(i) The VD/MD envelope determined by
Section 25.335(b); or,
(ii) An altitude-airspeed envelope defined by a 15 percent increase in equivalent airspeed above VC at constant altitude, from sea level to the altitude of
the intersection of 1.15 VC with the extension of the constant cruise Mach
number line, MC, then a linear variation in equivalent airspeed to MC + .05
at the altitude of the lowest VC/MC
intersection; then, at higher altitudes,
up to the maximum flight altitude, the
boundary defined by a .05 Mach increase in MC at constant altitude.
(c) Balance weights. If concentrated
balance weights are used, their effectiveness and strength, including supporting structure, must be substantiated.
(d) Failures, malfunctions, and adverse
conditions. The failures, malfunctions,
and adverse conditions which must be
considered in showing compliance with
this section are:
(1) Any critical fuel loading conditions, not shown to be extremely improbable, which may result from mismanagement of fuel.
(2) Any single failure in any flutter
damper system.
(3) For airplanes not approved for operation in icing conditions, the maximum 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 externally mounted aerodynamic body
(such as an external fuel tank).
(5) For airplanes with engines that
have propellers or large rotating devices capable of significant dynamic
forces, any single failure of the engine
structure that would reduce the rigidity of the rotational axis.
(6) The absence of aerodynamic or gyroscopic forces resulting from the most
adverse combination of feathered propellers or other rotating devices capable of significant dynamic forces. In
addition, the effect of a single feathered propeller or rotating device must
be coupled with the failures of paragraphs (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 Section 25.571. The single structural failures described in paragraphs (d)(4) and
(d)(5) of this section need not be considered in showing compliance with this
section if;
(i) The structural element could not
fail due to discrete source damage resulting from the conditions described
in Section 25.571(e), and
(ii) A damage tolerance investigation
in accordance with Section 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 element.
(9) Any damage, failure, or malfunction considered under SectionSection 25.631, 25.671,
25.672, and 25.1309.
(10) Any other combination of failures, malfunctions, or adverse conditions not shown to be extremely improbable.
(e) Flight flutter testing. Full scale
flight flutter tests at speeds up to VDF/
MDF must be conducted for new type
designs and for modifications to a type
design unless the modifications have
been shown to have an insignificant effect on the aeroelastic stability. These
tests must demonstrate that the airplane has a proper margin of damping

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