Situations Beyond the Scope of Non-Normal Checklists
It is rare to encounter in-flight events which are beyond the scope of the Boeing recommended NNCs. These events can arise as a result of unusual occurrences such as a midair collision, bomb explosion or other major malfunction. In these situations the flight crew may be required to accomplish multiple NNCs, selected elements of several different NNCs applied as necessary to fit the situation, or be faced with little or no specific guidance except their own judgement and experience. Because of the highly infrequent nature of these occurrences, it is not practical or possible to create definitive flight crew NNCs to cover all events.
The following guidelines may aid the flight crew in determining the proper course of action should an in-flight event of this type be encountered. Although these guidelines represent what might be called “conventional wisdom”, circumstances determine the course of action which the crew perceives will conclude the flight in the safest manner.
Basic Aerodynamics and Systems Knowledge
Knowledge of basic aerodynamic principles and airplane handling characteristics and a comprehensive understanding of airplane systems can be key factors in situations of this type.
Basic aerodynamic principles are known and understood by all pilots. Although not a complete and comprehensive list, following are a brief review of some basic aerodynamic principles and airplane systems information relevant to such situations:
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if aileron control is affected, rudder inputs can assist in countering
unwanted roll tendencies. The reverse is also true if rudder control is
affected
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if both aileron and rudder control are affected, the use of asymmetrical
engine thrust may aid roll and directional control
737 Flight Crew Training Manual
.
if elevator control is affected, stabilizer trim, bank angle and thrust can be
used to control pitch attitude. To do this effectively, engine thrust and
airspeed must be coordinated with stabilizer trim inputs. The airplane
continues to pitch up if thrust is increased and positive corrective action is
not taken by re-trimming the stabilizer. Flight crews should be aware of
the airplane’s natural tendency to oscillate in the pitch axis if the stable
pitch attitude is upset. These oscillations are normally self damping in
Boeing airplanes, but to ensure proper control, it may be desirable to use
thrust and/or stabilizer trim to hasten damping and return to a stable
condition. The airplane exhibits a pitch up when thrust is increased and a
pitch down when thrust is decreased. Use caution when attempting to
dampen pitch oscillations by use of engine thrust so that applications of
thrust are timed correctly, and diverging pitch oscillations do not develop
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a flight control break-out feature is designed into all Boeing airplanes. If a
jammed flight control exists, both pilots can apply force to either clear the
jam or activate the break-out feature. There should be no concern about
damaging the mechanism by applying too much force. In certain cases,
clearing the jam may permit one of the control columns to operate the
flight controls with portions of a control axis jammed. It may be necessary
to apply break-out forces for the remainder of the flight on the affected
control axis
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stall margin decreases with angle of bank and increasing load factors.
Therefore, it is prudent to limit bank angle to 15 degrees in the event
maneuvering capability is in question. Increasing the normal flap/speed
maneuvering schedule while staying within flap placard limits provides
extra stall margin where greater bank angles are necessary
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all Boeing airplanes have the capability to land using any flap position,
including flaps up. Use proper maneuvering and final approach speeds
and ensure adequate runway is available to stop the airplane after landing.
Flight Path Control
When encountering an event of the type described above, the flight crew’s first consideration should be to maintain or regain full control of the airplane and establish an acceptable flight path. This may require use of unusual techniques such as the application of full aileron or rudder or in an asymmetrical thrust situation, reduction of power on the operating engine(s) to regain lateral control. This may also require trading altitude for airspeed or vice versa. The objective is to take whatever action is necessary to control the airplane and maintain a safe flight path. Even in a worst case condition where it is not possible to keep the airplane flying and ground contact is imminent, a “controlled crash” is a far better alternative than uncontrolled flight into terrain.
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