Flying Handbook Menu > Transition to Multiengine Airplanes > Engine Inoperative Flight Principles
Best single-engine climb performance is obtained
at VYSE with maximum available power and minimum drag. After
the flaps and landing gear have been retracted and the propeller
of the failed engine feathered, a key element in best climb
performance is minimizing sideslip.
With a single-engine airplane or a multiengine
airplane with both engines operative, sideslip is eliminated
when the ball of the turn and bank instrument is centered. This
is a condition of zero sideslip, and the airplane is presenting
its smallest possible profile to the relative wind. As a result,
drag is at its minimum. Pilots know this as coordinated flight.
In a multiengine airplane with an inoperative
engine, the centered ball is no longer the indicator of zero
sideslip due to asymmetrical thrust. In fact, there is no instrument
at all that will directly tell the pilot the flight conditions
for zero sideslip. In the absence of a yaw string, minimizing
sideslip is a matter of placing the airplane at a predetermined
bank angle and ball position. The AFM/POH performance charts
for single- engine flight were determined at zero sideslip.
If this performance is even to be approximated, the zero sideslip
technique must be utilized.
Three different scenarios of airplane control
inputs are presented below. Neither of the first two is correct.
They are presented to illustrate the reasons for the zero sideslip
approach to best climb performance.
1. Engine inoperative flight with wings level
and ball centered requires large rudder input towards the operative
engine. [figure12-16] The result is a moderate sideslip towards
the inoperative engine. Climb performance will be reduced by
the moderate sideslip. With wings level, VMC will be significantly
higher than published as there is no horizontal component of
lift available to help the rudder combat asymmetrical thrust.
figure12-16. Wings level engine-out
2. Engine inoperative flight using ailerons
alone requires an 8 - 10° bank angle towards the operative
engine. [figure12-17] This assumes no rudder input. The ball
will be displaced well towards the operative engine. The result
is a large sideslip towards the operative engine. Climb performance
will be greatly reduced by the large sideslip.
figure12-17. Excessive bank engine-out
3. Rudder and ailerons used together in the
proper combination will result in a bank of approximately 2°
towards the operative engine. The ball will be displaced approximately
one-third to one-half towards the operative engine. The result
is zero sideslip and maximum climb performance. [figure12-18]
Any attitude other than zero sideslip increases drag, decreasing
performance. VMC under these circumstances will be higher than
published, as less than the 5° bank certification limit
figure12-18. Zero sideslip engine-out
The precise condition of zero sideslip (bank
angle and ball position) varies slightly from model to model,
and with available power and airspeed. If the airplane is not
equipped with counter-rotating propellers, it will also vary
slightly with the engine failed due to P-factor. The foregoing
zero sideslip recommendations apply to reciprocating engine
multiengine airplanes flown at VYSE with the inoperative engine
feathered. The zero sideslip ball position for straight flight
is also the zero sideslip position for turning flight.
When bank angle is plotted against climb performance
for a hypothetical twin, zero sideslip results in the best (however
marginal) climb performance or the least rate of descent. Zero
bank (all rudder to counteract yaw) degrades climb performance
as a result of moderate sideslip. Using bank angle alone (no
rudder) severely degrades climb performance as a result of a
The actual bank angle for zero sideslip varies
among airplanes from one and one-half to two and one-half degrees.
The position of the ball varies from one-third to one-half of
a ball width from instrument center.
For any multiengine airplane, zero sideslip
can be confirmed through the use of a yaw string. A yaw string
is a piece of string or yarn approximately 18 to 36 inches in
length, taped to the base of the windshield, or to the nose
near the windshield, along the airplane centerline. In two-engine
coordinated flight, the relative wind will cause the string
to align itself with the longitudinal axis of the airplane,
and it will position itself straight up the center of the windshield.
This is zero sideslip. Experimentation with slips and skids
will vividly display the location of the relative wind. Adequate
altitude and flying speed must be maintained while accomplishing
With an engine set to zero thrust (or feathered)
and the airplane slowed to VYSE, a climb with maximum power
on the remaining engine will reveal the precise bank angle and
ball deflection required for zero sideslip and best climb performance.
Zero sideslip will again be indicated by the yaw string when
it aligns itself vertically on the windshield. There will be
very minor changes from this attitude depending upon the engine
failed (with noncounter-rotating propellers), power available,
airspeed and weight; but without more sensitive testing equipment,
these changes are difficult to detect. The only significant
difference would be the pitch attitude required to maintain
VYSE under different density altitude, power available, and
If a yaw string is attached to the airplane
at the time of a VMC demonstration, it will be noted that VMC
occurs under conditions of sideslip. VMC was not determined
under conditions of zero sideslip during aircraft certification
and zero sideslip is not part of a VMC demonstration for pilot
To review, there are two different sets of
bank angles used in one-engine-inoperative flight.
• To maintain directional control of
a multiengine airplane suffering an engine failure at low speeds
(such as climb), momentarily bank at least 5°, and a maximum
of 10° towards the operative engine as the pitch attitude
for VYSE is set. This maneuver should be instinctive to the
proficient multiengine pilot and take only 1 to 2 seconds to
attain. It is held just long enough to assure directional control
as the pitch attitude for VYSE is assumed.
• To obtain the best climb performance,
the airplane must be flown at VYSE and zero sideslip, with the
failed engine feathered and maximum available power from the
operating engine. Zero sideslip is approximately 2° of bank
toward the operating engine and a one-third to one-half ball
deflection, also toward the operating engine. The precise bank
angle and ball position will vary somewhat with make and model
and power available. If above the airplane’s single-engine
ceiling, this attitude and configuration will result in the
minimum rate of sink.
In OEI flight at low altitudes and airspeeds
such as the initial climb after takeoff, pilots must operate
the airplane so as to guard against the three major accident
factors: (1) loss of directional control, (2) loss of performance,
and (3) loss of flying speed. All have equal potential to be
lethal. Loss of flying speed will not be a factor, however,
when the airplane is operated with due regard for directional
control and performance.