AOPA Pilot Magazine - July 2022 - 22

PROFICIENT PILOT
Flight control
failure
Rare, but worth your consideration
BY BARRY SCHIFF / AOPA Foundation Legacy Society chairman
MOST PILOTS HAVE seen the video of the United Airlines' DC-10
cartwheeling down Runway 22 at Sioux City, Iowa, in 1989. It is
a sight unlikely to be forgotten.
The accident was caused by the catastrophic loss of all hydraulic
power, which made it impossible to move any of the flight
controls. There are no backup cables with which to manually
control a widebody jetliner. Not even an Olympic weightlifter
could operate such massive control surfaces. The stabilator on a
Lockheed L-1011, for example, weighs 7,000 pounds.
Captain Al Haynes and his crew discovered that the only way
to control their crippled DC-10 was to vary the thrust of the two
underwing engines. (The uncontained failure of the center engine
in the tail caused the loss of fluid from all three hydraulic systems.)
Increasing and decreasing the thrust of both engines in unison
caused the jetliner to pitch nose up and nose down, respectively.
Applying power asymmetrically controlled the heading. When
more thrust was generated by the right engine, the aircraft
turned left, and vice versa. That the aircraft could be steered to a
runway in this manner was incredible. That 184 people survived
was a miracle.
This accident attracted the attention of Frank Burcham, chief
of the Propulsion and Performance Branch at NASA's Dryden
Flight Research Facility. He initiated a program to investigate the
handling qualities and effectiveness of controlling aircraft using
only engine power. His goal was to develop techniques and technology
to help those who might find themselves in similar peril.
Burcham invited me to participate in the research by flying a
visual simulator programmed to investigate the engine-only handling
qualities of several aircraft. He advised me that the primary
flight controls were inoperative and that I was to attempt landing
different aircraft using throttles only. This proved extremely challenging
and highlighted how difficult it had to have been for Haynes
to control his aircraft. Under the circumstances, he did a masterful
job. I prefer not to discuss my performance in the simulator except
to say that I am grateful that the results were simulated.
Burcham then offered me an opportunity to use a propulsion-enhanced
flight-control system. In this mode, control-wheel
inputs were converted into throttle commands. For example, pulling
the wheel aft increased the power of both engines, thus causing
the nose to rise, and vice versa. Turning the wheel right or left
22
AOPA PILOT / July 2022
operated the engines differentially, which induced a roll in the
desired direction.
It took considerable practice to adjust to the sluggish aircraft
response and the tendency to overcontrol. You had to make small
changes and wait for the results but operating the engines in this
mode did make it a bit less difficult to land.
Flight-control failure on a jetliner is rare. It also is unlikely
on general aviation aircraft. This is because the primary flight
controls of a lightplane are independent of one another and not
dependent on hydraulic power. Each flight control is operated by
its own cables or push rods. The only way for a lightplane pilot to
lose the use of all primary flight controls is to take off with the controls
locked. It is not so impossible, however, for one control to fail.
Loss of aileron or rudder control usually is not catastrophic
because one can be used in place of the other, but do not attempt
to land on a narrow runway or with a crosswind with such a handicap.
The most challenging problem is the loss of elevator control,
and the most likely cause of that would be the failure of a cable. Such
a failure, however, does not result in a total loss of pitch control.
An elevator control system consists of two cables. One raises
the elevator when back-pressure is applied to the control wheel;
the other lowers the elevator when forward pressure is applied.
Assume, for example, that the down-elevator cable fails. The
wheel can be moved forward but has no effect. At such a time,
nose-down pitch control can be restored by applying substantial
nose-down trim, enough to induce a significant nose-down
attitude. This essentially restores total pitch control. To raise
the nose, apply back pressure to the control wheel as you normally
would. To lower the nose, simply release some of the back
pressure necessitated by the nose-down trim. Landing in this
manner is not difficult. On the other hand, if the up-elevator
cable fails, pitch control can be restored by applying substantial
nose-up trim and varying forward pressure on the wheel to
control pitch attitude.
Such an emergency is thankfully rare and explains why many
might tend to discount the possibility.
Captain Haynes might
not have given it much
thought either.
BarrySchiff.com
BARRY SCHIFF was a
member of the Society of
Experimental Test Pilots.
http://www.BarrySchiff.com
AOPA Pilot Magazine - July 2022

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