Iron
Mike
Flying any aircraft is typically a hands-on endeavor for the
pilot.
He (or she) must interpret instruments, visual stimuli and
motion cues to place the aircraft in the attitude desired for the phase of
flight.
At times the pilot of an aircraft is very busy. Between
performing checklists, handling navigation charts, tuning radios and talking to
controllers, the pilot is sometimes as busy as the proverbial one-armed
paperhanger. In order to relieve the
pilot of the “hands-on” task of controlling the aircraft, Iron Mike was brought
into the cockpit as an aid to the pilot.
Iron Mike is not a copilot -- it is an electronic device
known as an autopilot.
In 1914, only 11 years after the Wright Brothers’ first
powered flight, Sperry Corporation demonstrated the first practical autopilot,
an aircraft control systems that enabled the pilot to command the aircraft’s
three axes -- roll, pitch, and yaw -- through an electronic autopilot. By
acting through an autopilot to control the aircraft in flight, the pilot can
manage essential systems and navigational duties without constantly monitoring
the attitude of the aircraft.
The most basic autopilot is known as a wing leveler. This autopilot will only keep the wings of
the aircraft level, acting through its ailerons. Although turbulent air can
upset the aircraft from level, the autopilot will cause the aircraft to return
to wings-level within a few seconds. This single-axis autopilot will allow the
pilot to fold charts or to perform other cockpit chores without having to
maintain a grip on the control wheel.
The next step up on the sophistication ladder is an
autopilot that allows the pilot to select a course for the aircraft to fly. By
using a heading “bug,” a small movable marker on the heading indicator, the
pilot can designate a heading for the aircraft’s autopilot to fly. If equipped,
the autopilot can also be directed to follow a course line from a ground-based
navigational station or from a space-based global positioning system.
An additional level of control is added if the autopilot is
equipped with yaw control. Yaw is the
movement of the aircraft around its vertical axis. In turbulence the rear of the aircraft may
not always follow the nose. This
constant “wagging of the tail” is not comfortable for passengers. A yaw damper, as part of the autopilot, will
monitor the yawing movement of the aircraft and apply appropriate rudder inputs
to lessen the amount of movement around the yaw axis.
An autopilot also can control the aircraft in the pitch
axis. This will allow the pilot to place
the aircraft in a climb or descent attitude or in level flight. Some advanced autopilots have altitude hold
modes that keep the aircraft at the same altitude without monitoring.
Highly sophisticated autopilots allow the programming of an
entire flight into memory. The pilot of
the aircraft would only need to engage the autopilot after takeoff and control
the throttles. The autopilot would then navigate the aircraft as programmed to
its destination. Just prior to landing
the pilot need only disconnect the autopilot and manually land the aircraft.
The most complex autopilots are known as flight management
systems. These FMS-equipped aircraft are
capable of Category III instrument approaches.
A CAT III approach may be conducted in weather conditions known as
zero-zero (zero visibility and zero ceiling). These autopilots not only fly the
aircraft but also control the throttles, and will even apply the brakes after
touchdown on the runway. The pilot only needs to drive the aircraft off the
runway, assuming the taxiway stripe can be seen.
Autopilots can fly an aircraft with greater precision than a
human pilot can. However an autopilot
cannot replace the pilot of an aircraft. The pilot is an essential element in
making the decisions necessary for a safe flight, something that the autopilot
is incapable of doing. The pilot must ensure that there is sufficient fuel for
the flight, make in-flight decisions regarding weather, and monitor the systems
of the aircraft -- including the proper operation of the autopilot.