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Instrument Flying Handbook
Flight Instruments
Pitot Static Instruments

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Instrument Flying


Table of Contents

Chapter 1. Human Factors
Chapter 2. Aerodynamic Factors
Chapter 3. Flight Instruments
Chapter 4. Section I
Airplane Attitude Instrument
Using Analog Instrumentation
Chapter 4. Section II
Airplane Attitude Instrument
Using an Electronic Flight

Chapter 5. Section I
Airplane Basic
Flight Maneuvers
Using Analog Instrumentation
Chapter 5. Section II
Airplane Basic
Flight Maneuvers
Using an Electronic Flight

Chapter 6. Helicopter
Attitude Instrument Flying

Chapter 7. Navigation Systems
Chapter 8. The National
Airspace System

Chapter 9. The Air Traffic
Control System

Chapter 10. IFR Flight
Chapter 11. Emergency

Effects of Nonstandard Pressure on an Altimeter.
Figure 3-8. Effects of Nonstandard Pressure on an Altimeter of an
Aircraft Flown into Air of Lower Than Standard Pressure (Air is
Less Dense).

Altimeter Enhancements (Encoding)
It is not sufficient in the airspace system for only the pilot
to have an indication of the aircraft's altitude; the air traffic
controller on the ground must also know the altitude of the
aircraft. To provide this information, the aircraft is typically
equipped with an encoding altimeter.

When the ATC transponder is set to Mode C, the encoding
altimeter supplies the transponder with a series of pulses
identifying the flight level (in increments of 100 feet) at
which the aircraft is flying. This series of pulses is transmitted
to the ground radar where they appear on the controller's
scope as an alphanumeric display around the return for the
aircraft. The transponder allows the ground controller to
identify the aircraft and determine the pressure altitude at
which it is flying.

A computer inside the encoding altimeter measures the
pressure referenced from 29.92" Hg and delivers this data to
the transponder. When the pilot adjusts the barometric scale
to the local altimeter setting, the data sent to the transponder
is not affected. This is to ensure that all Mode C aircraft are
transmitting data referenced to a common pressure level. ATC
equipment adjusts the displayed altitudes to compensate for
local pressure differences allowing display of targets at correct
altitudes. 14 CFR part 9 t requires the altitude transmitted by
the transponder to he within 125 feet of the altitude indicated
on the instrument used to maintain flight altitude.


Reduced Vertical Separation Minimum (RVSM)
Below 31,000 feet, a 1,000 foot separation is the minimum
required between usable flight levels. Flight levels (FLs)
generally start at 18,000 feet where the local pressure is
29.92" Hg or greater. All aircraft 18,000 feet and above use
a standard altimeter setting of 29.92" Hg, and the altitudes
are in reference to a standard hence termed FL. Between FL
180 and FL 290, the minimum altitude separation is 1,000
feet: between aircraft. However, for flight above FL 290
(primarily due to aircraft equipage and reporting capability;
potential error) ATC applied the requirement of 2,000 feet of
separation. FL 290, an altitude appropriate for an eastbound
aircraft, would be followed by FL 310 for a westbound
air craft, and so on to FL 410, or seven FLs available for flight.
With 1,000-foot separation, or a reduction of the vertical
separation between FL 290 and FL 410, an additional six
FLs become available. This results in normal flight level and
direction management being maintained from FL 180 through
FL 410. Hence the name is Reduced Vertical Separation
Minimum (RVSM). Because it is applied domestically, it is
called United States Domestic Reduced Vertical Separation
Minimum, or DRVSM.

However, there is a cost to participate in the DRVSM program
which relates to both aircraft equipage and pilot training. For
example, altimetry error must he reduced significantly and
operators using RVSM must receive authorization from the
appropriate civil aviation authority. RVSM aircraft must
meet required altitude-keeping performance standards.
Additionally, operators must operate in accordance with
RVSM policies/procedures applicable to the airspace where
they are flying.

The aircraft must he equipped with at least one automatic
altitude control:

  • Within a tolerance band of ±65 feet about an acquired
    altitude when the aircraft is operated in straight-and-
    level flight.
  • Within a tolerance band of ±130 feet under no
    turbulent, conditions for aircraft for which application
    for type certification occurred on or before April 9,
    1997 that are equipped with an automatic altitude
    control system with flight management/performance
    system inputs.