Don Hammer wrote

The FAA certification requirement for a fuel dump system is a takeoff
weight that is greater than 135% (I think) of the max landing weight.
They don't add the complexity and cost of a dump system unless it is
required for certification.

Don, the rules have changed since you and I flew those old Boeings. :-)

Section 25.1001: Fuel jettisoning system.
(a) A fuel jettisoning system must be installed on each airplane unless
it is shown that the airplane meets the climb requirements of §§25.119
and 25.121(d) at maximum takeoff weight, less the actual or computed
weight of fuel necessary for a 15-minute flight comprised of a takeoff,
go-around, and landing at the airport of departure with the airplane
configuration, speed, power, and thrust the same as that used in meeting
the applicable takeoff, approach, and landing climb performance
requirements of this part.

(b) If a fuel jettisoning system is required it must be capable of
jettisoning enough fuel within 15 minutes, starting with the weight
given in paragraph (a) of this section, to enable the airplane to meet
the climb requirements of §§25.119 and 25.121(d), assuming that the fuel
is jettisoned under the conditions, except weight, found least favorable
during the flight tests prescribed in paragraph (c) of this section.

(f) For turbine engine powered airplanes, means must be provided to
prevent jettisoning the fuel in the tanks used for takeoff and landing
below the level allowing climb from sea level to 10,000 feet and
thereafter allowing 45 minutes cruise at a speed for maximum range.
However, if there is an auxiliary control independent of the main
jettisoning control, the system may be designed to jettison the
remaining fuel by means of the auxiliary jettisoning control.


Bob Moore
ATP B-707 B-727
PanAm (retired)