Code of Federal Regulations - Title 14

428

14 CFR Ch. I (1–1–14 Edition)

§ 25.629

(1) For normal conditions without

failures, malfunctions, or adverse con-
ditions, all combinations of altitudes
and speeds encompassed by the V

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 V

and, there must be no large and rapid
reduction in stability as V

is ap-

proached. The enlarged envelope may
be limited to Mach 1.0 when M

is less

than 1.0 at all design altitudes, and

(2) For the conditions described in

§ 25.629(d) below, for all approved alti-
tudes, any airspeed up to the greater
airspeed defined by;

(i) The V

envelope determined by

§ 25.335(b); or,

(ii) An altitude-airspeed envelope de-

fined by a 15 percent increase in equiv-
alent airspeed above V

at constant al-

titude, from sea level to the altitude of
the intersection of 1.15 V

with the ex-

tension of the constant cruise Mach
number line, M

, then a linear vari-

ation in equivalent airspeed to M

+.05

at the altitude of the lowest V

intersection; then, at higher altitudes,
up to the maximum flight altitude, the
boundary defined by a .05 Mach in-
crease in M

at constant altitude.

(c)

Balance weights. If concentrated

balance weights are used, their effec-
tiveness and strength, including sup-
porting structure, must be substan-
tiated.

(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 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

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

, and that

there is no large and rapid reduction in
damping as V

, is approached. If a

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