Federal Aviation Administration, DOT

Section 25.335

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-86, 61 FR 5220, Feb. 9, 1996]

Design airspeeds.

The selected design airspeeds are
equivalent airspeeds (EAS). Estimated
values of VS0 and VS1 must be conservative.
(a) Design cruising speed, VC. For VC,
the following apply:
(1) The minimum value of VC must be
sufficiently greater than VB to provide
for inadvertent speed increases likely
to occur as a result of severe atmospheric turbulence.
(2) Except as provided in Section 25.335(d)(2),
VC may not be less than VB + 1.32 U REF
(with
UREF
as
specified
in
Section 25.341(a)(5)(i)). However VC need not
exceed the maximum speed in level
flight at maximum continuous power
for the corresponding altitude.
(3) At altitudes where VD is limited
by Mach number, VC may be limited to
a selected Mach number.
(b) Design dive speed, VD. VD must be
selected so that VC/MC is not greater
than 0.8 VD/MD, or so that the minimum
speed margin between VC/MC and VD/MD
is the greater of the following values:

(1) From an initial condition of stabilized flight at VC/MC, the airplane is
upset, flown for 20 seconds along a
flight path 7.5Section below the initial path,
and then pulled up at a load factor of
1.5g (0.5g acceleration increment). The
speed increase occurring in this maneuver may be calculated if reliable or
conservative aerodynamic data is used.
Power as specified in Section 25.175(b)(1)(iv) is
assumed until the pullup is initiated,
at which time power reduction and the
use of pilot controlled drag devices
may be assumed;
(2) The minimum speed margin must
be enough to provide for atmospheric
variations (such as horizontal gusts,
and penetration of jet streams and cold
fronts) and for instrument errors and
airframe production variations. These
factors may be considered on a probability basis. The margin at altitude
where MC is limited by compressibility
effects must not less than 0.07M unless
a lower margin is determined using a
rational analysis that includes the effects of any automatic systems. In any

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Section 25.335