CHAPTER 4 - DESIGN AND CONSTRUCTION
Section 1. GENERAL [RESERVED]
Section 2. CONTROL SURFACES [RESERVED]
Section 3. CONTROL SYSTEMS
34. GENERAL - § 25.671.
a. Explanation. This material deals with the all-engines out case of § 25.671(d). The intent of this rule is to
assure that in the event of failure of all engines, the airplane will be controllable and an approach and landing flare
possible. This may be done by analysis where the method is considered reliable.
b. Procedures. The airplane should be evaluated to determine that:
(1) It is controllable following the failure of all engines in the climb, cruise, descent, approach, and
holding configurations and can be flared to a landing attitude from a reasonable approach speed. The airplane must
be controllable when all engines fail in each of the specified configurations and in any specific configuration that is
to be selected and maintained following the failure of the engines in accordance with the AFM emergency operating
procedures.
(2) The effectiveness of the emergency power to drive the airplane control system, whether generated
from a windmilling engine or an auxiliary power supply, should be demonstrated in flight.
(3) For airplanes with fully powered or electronic flight control systems, the emergency procedures
section of the approved Airplane Flight Manual should contain the appropriate operating procedures and a statement
similar to the following:
"The airplane has a fully powered (or electronic) control system that is dependent upon engine windmill
RPM, or an auxiliary power supply, to provide the necessary source of control system power in the event
all engines fail in flight. A minimum airspeed of XXX knots IAS will provide adequate hydraulic or
electrical power for airplane controllability in this emergency condition."
Sounds reasonable. Is from the Advisory Circular referenced.