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one model to another. When transitioning to a new model, flight crews may not
realize that it does not respond to pitch input in exactly the same way as their
previous model.
October 31, 2006
777/787 Flight Crew Training Manual
Non-Normal Operations
Copyright © The Boeing Company. See title page for details.
FCT 777/787 Preliminary (TM) 8.25
Improper Use of the Flight Director
The flight director provides accurate pitch guidance only after the airplane is
airborne. With the proper rotation rate, the airplane reaches 35 feet with the
desired pitch attitude of about 15 degrees. However, an aggressive rotation into
the pitch bar at takeoff is not appropriate and can cause a tail strike.
Landing Risk Factors
A tail strike on landing tends to cause more serious damage than the same event
during takeoff and is usually more expensive and time consuming to repair. In the
worst case, the tail can strike the runway before the landing gear, thus absorbing
large amounts of energy for which it is not designed. The aft pressure bulkhead is
often damaged as a result.
Any one of the following landing risk factors may precede a tail strike:
Unstabilized Approach
An unstabilized approach is the biggest single cause of tail strike. Flight crews
should stabilize all approach variables - on centerline, on approach path, on speed,
and in the final landing configuration - by the time the airplane descends through
1,000 feet above ground level (AGL). This is not always possible. Under normal
conditions, if the airplane descends through 1,000 feet AGL (IMC), or 500 feet
AGL (VMC), with these approach variables not stabilized, a go-around should be
considered.
Flight recorder data show that flight crews who continue with an unstabilized
condition below 500 feet seldom stabilize the approach. When the airplane arrives
in the flare, it often has either excessive or insufficient airspeed. The result is a
tendency toward large power and pitch corrections in the flare, often culminating
in a vigorous pitch change at touchdown resulting in tail strike shortly thereafter.
If the pitch is increased rapidly when touchdown occurs as ground spoilers deploy,
the spoilers add additional nose up pitch force, reducing pitch authority, which
increases the possibility of tail strike. Conversely, if the airplane is slow,
increasing the pitch attitude in the flare does not effectively reduce the sink rate;
and in some cases, may increase it.
A firm touchdown on the main gear is often preferable to a soft touchdown with
the nose rising rapidly. In this case, the momentary addition of power may aid in
preventing the tail strike. In addition, unstabilized approaches can result in landing
long or a runway over run.
October 31, 2006
777/787 Flight Crew Training Manual
Non-Normal Operations
Copyright © The Boeing Company. See title page for details.
8.26 FCT 777/787 Preliminary (TM)
Holding Off in the Flare
The second most common cause of a landing tail strike is an extended flare, with
a loss in airspeed that results in a rapid loss of altitude, (a dropped-in touchdown).
This condition is often precipitated by a desire to achieve an extremely
smooth/soft landing. A very smooth/soft touchdown is not essential, nor even
desired, particularly if the runway is wet.
Trimming in the Flare
Trimming the stabilizer in the flare may contribute to a tail strike. The pilot flying
may easily lose the feel of the elevator while the trim is running. Too much trim
can raise the nose, even when this reaction is not desired. The pitch up can cause
a balloon, followed either by dropping in or pitching over and landing in a
three-point attitude. Flight crews should trim the airplane during the approach, but
not in the flare.
Mishandling of Crosswinds
When the airplane is placed in a forward slip attitude to compensate for the wind
effects, this cross-control maneuver reduces lift, increases drag, and may increase
the rate of descent. If the airplane then descends into a turbulent surface layer,
particularly if the wind is shifting toward the tail, the stage is set for tail strike.
The combined effects of high closure rate, shifting winds with the potential for a
quartering tail wind, can result in a sudden drop in wind velocity commonly found
below 100 feet. Combining this with turbulence can make the timing of the flare
very difficult. The pilot flying can best handle the situation by using additional
thrust, if needed, and by using an appropriate pitch change to keep the descent rate
stable until initiation of the flare. Flight crews should clearly understand the
criteria for initiating a go-around and plan to use this time-honored avoidance
　
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本文鏈接地址：787機(jī)組訓(xùn)練手冊(cè)Flight Crew Training Manual 787(134)