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Pilot's Handbook of Aeronautical Knowledge
Flight Instruments
Pitot-Static Flight Instruments

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Pilot's Handbook of Aeronautical Knowledge

Preface

Acknowledgements

Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making

Appendix

Glossary

Index

Just as in altitudes, there are multiple types of airspeeds.
Pilots need to be very familiar with each type.

• Indicated airspeed (IAS)—the direct instrument
reading obtained from the ASI, uncorrected for
variations in atmospheric density, installation error,
or instrument error. Manufacturers use this airspeed
as the basis for determining aircraft performance.
Takeoff, landing, and stall speeds listed in the AFM/
POH are IAS and do not normally vary with altitude
or temperature.

• Calibrated airspeed (CAS)—IAS corrected for
installation error and instrument error. Although
manufacturers attempt to keep airspeed errors to a
minimum, it is not possible to eliminate all errors
throughout the airspeed operating range. At certain
airspeeds and with certain flap settings, the installation
and instrument errors may total several knots. This
error is generally greatest at low airspeeds. In the
cruising and higher airspeed ranges, IAS and CAS
are approximately the same. Refer to the airspeed
calibration chart to correct for possible airspeed
errors.

• True airspeed (TAS)—CAS corrected for altitude
and nonstandard temperature. Because air density
decreases with an increase in altitude, an aircraft has
to be .own faster at higher altitudes to cause the same
pressure difference between pitot impact pressure
and static pressure. Therefore, for a given CAS, TAS
increases as altitude increases; or for a given TAS,
CAS decreases as altitude increases. A pilot can find
TAS by two methods. The most accurate method is
to use a flight computer. With this method, the CAS
is corrected for temperature and pressure variation by
using the airspeed correction scale on the computer.

Extremely accurate electronic flight computers are
also available. Just enter the CAS, pressure altitude,
and temperature, and the computer calculates the TAS.
A second method, which is a rule of thumb, provides
the approximate TAS. Simply add 2 percent to the
CAS for each 1,000 feet of altitude. The TAS is the
speed which is used for flight planning and is used
when .ling a flight plan.

• Groundspeed (GS)—the actual speed of the airplane
over the ground. It is TAS adjusted for wind. GS
decreases with a headwind, and increases with a
tailwind.

Airspeed Indicator Markings
Aircraft weighing 12,500 pounds or less, manufactured after
1945, and certificated by the FAA, are required to have ASIs
marked in accordance with a standard color-coded marking
system. This system of color-coded markings enables a pilot
to determine at a glance certain airspeed limitations that are
important to the safe operation of the aircraft. For example,
if during the execution of a maneuver, it is noted that the
airspeed needle is in the yellow arc and rapidly approaching
the red line, the immediate reaction should be to reduce
airspeed.

As shown in Figure 7-8, ASIs on single-engine small aircraft
include the following standard color-coded markings:
• White arc — commonly referred to as the flap operating
range since its lower limit represents the full flap stall
speed and its upper limit provides the maximum flap
speed. Approaches and landings are usually flown at
speeds within the white arc.
• Lower limit of white arc (VS0)—the stalling speed
or the minimum steady flight speed in the landing
configuration. In small aircraft, this is the power-off
stall speed at the maximum landing weight in the
landing configuration (gear and flaps down).
• Upper limit of the white arc (VFE)—the maximum
speed with the flaps extended.
• Green arc — the normal operating range of the aircraft.
Most flying occurs within this range.
• Lower limit of green arc (VS1)—the stalling speed
or the minimum steady flight speed obtained in a
specified configuration. For most aircraft, this is the
power-off stall speed at the maximum takeoff weight
in the clean configuration (gear up, if retractable, and
flaps up).
• Upper limit of green arc (VNO)—the maximum
structural cruising speed. Do not exceed this speed
except in smooth air.
• Yellow arc — caution range. Fly within this range only
in smooth air, and then, only with caution.
• Red line (VNE)—never exceed speed. Operating above
this speed is prohibited since it may result in damage
or structural failure.

Airspeed indicator (ASI).
Figure 7-8. Airspeed indicator (ASI).

 

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