|
 |
|
 |
|
If an airplane could be flown by
concentrating on only one instrument, flight on the
gauges would be easy. Normally,
constant reference must be made to six basic
flight instruments as well as the navigation and
engine instruments. This is accomplished through the
pilot's instrument scan; the instrument pilot's most
basic skill.
An important element of the instrument scan is
cross-checking the readings of each instrument with
other instruments to confirm an accurate
interpretation. Consequently, the pilot never fixes
his view on any single instrument for more than a
few seconds with the occassional exception of the
attitude indicator.
Pilots are taught specific procedures for each
phase of flight. For example, one manual's suggested
procedure for leveling off from a climb is: note the
altimeter; lower the nose on the attitude indicator;
check for increasing airspeed on the airspeed
indicator; check for constant heading on the heading
indicator (the heading often swings to the right on
level-off). Continue to monitor altitude, airspeed
and heading until the desired airspeed is reached,
then reduce power as required. Trim the aircraft's
controls for straight and level flight.
An aircraft can be flown remarkably accurately
with the six basic flight instruments, the basic
principles for which were developed in the early
1930's.
 Airspeed
Indicator
The airspeed indicator is one of the oldest and
most important of the flight instruments. It
measures the aircraft's speed through the air by
measuring the dynamic pressure of the airstream
rushing against the moving airplane.
During cruise, the aircraft may be flown within a
fairly broad speed range depending on whether fuel
economy, range or flight time is the primary
objective. However, in no case can the pilot allow
the aircraft to slow to stall speed - at which point
the wings can no longer sustain the aircraft - or
accelerate to "red line," above which structural
failure may result.
 Attitude
Indicator
In the middle of the top row of the panel is the
attitude indicator, or artificial horizon, the
central element of the pilot's instrument scan. In
instrument conditions, the attitude indicator
replaces the natural horizon, showing the
relationship of the nose and wings to the horizontal
plane.
The attitude indicator is the only instrument
that gives direct information about an
aircraft's attitude. Each movement of the aircraft's
controls is therefore made with reference to this
instrument.
 Altimeter
An altimeter is simply a barometer calibrated in
feet instead inches of mercury. With an increase in
altitude, since there is now less air above the
airplane, the pressure is less. The altimeter
measures this reduced atmospheric pressure and
displays it as the aircraft's altitude.
To compensate for barometric pressure changes,
the altimeter is frequently calibrated by the pilot
by setting the current barometric pressure in the
altimeter setting window using a small knob.
 Turn
Coordinator
This electrically-driven instrument not only
serves as a back-up to the attitude indicator in the
event of its failure, but also measures the rate and
quality of a turn.
In instrument flight turns are typically made at
a rate of three degrees per second or less; steeper
turns are considered dangerous. The quality of the
turn is measured by the ball in the curved glass
tube at the bottom of the instrument. A quality, or
coordinated, turn balances centrifugal and
gravitational forces keeping the ball centered.
 Direction
Indicator
The Direction Indicator (DI) , or directional gyro, uses
an internal gyroscope whose stability provides
accurate directional information once it is set to
the correct heading. The gyro-stabilized heading
indicator is required because of the errors that
occur in the magnetic compass during turns, speed
changes and even in turbulent air.
Because of drift errors, the instrument should be
checked against the magnetic compass during straight
and level flight at least once every 15 minutes.
Like the altimeter, a set knob is provided for
corrections.
 Vertical
Speed Indicator
The vertical speed indicator, or VSI, measures
the aircraft's rate of climb or descent as measured
by the change in the surrounding atmospheric
pressure.
Because of the instrument's inherent delay or
"lag," accurate climb or descent information is not
available for several seconds. For this reason, the
VSI is useful only as a back-up instrument in most
flight maneuvers.
During instrument flight, the pilot must guard
against spatial disorientation, or vertigo. This is
caused by the motion-sensing organs of the inner ear
becoming confused during instrument flight. This
requires that the pilot develop a total sense of
reliance on the flight instruments and disregard
other indications of motion. The pilot can also
minimize the possibility of vertigo by avoiding
sudden head movements and abrupt flight manoeuvres.
If the symptoms of vertigo appear and the
instruments confirm the aircraft is in
straight-and-level flight, the pilot should hold the
aircraft's attitude for a minute or two allowing the
disorientation to pass.
In addition to maintaining the aircraft's proper
orientation using the flight instruments, the pilot
also has navigation and communication
responsibilities. In instrument conditions,
responsibility for traffic avoidance lies solely
with the flight controller on the ground.
Is all of this as difficult as it sounds? No, not
really. The basic instrument flying skills can be
learned in a few hours by the careful student. Most
modern aircraft, unlike the Cessna 195, are equipped
with an auto-pilot, relieving the pilot of the need
to constantly monitor the flight instruments.
The key is to stay current and never, never take
anything about instrument flight for granted.
Sources:
|
Air Force Instrument Flying
Manual
The Instrument Flight Training
Manual by Peter Dogan
http://www.gruner.com
|
|
|
|
 |
|
