Analysis of Air Data Instrument Compensation and Integration

This report provides a comprehensive analysis of air data instruments used in modern aircraft. It begins with a comparison of how different air data instruments compensate for atmospheric changes, discussing true and indicated airspeed, pressure, altitude, and other parameters. The report then delves into the design considerations, construction, and operation of pitot-static systems, including error minimization and real-time responsiveness. A comparison between analog and digital air data computers is presented, highlighting their advantages and disadvantages. The construction and operation of a typical flight director system are examined, including its modes and components. The report also compares different types of electronic displays (LEDs, LCDs, and ELDs) and discusses their applications. Finally, the construction and integration of a typical flight instrument system are outlined, with a focus on instruments like the airspeed indicator, altimeter, and vertical speed indicator, and the role of ADAHRS. The report concludes by emphasizing the importance of these instruments in ensuring aircraft stability, navigation, and pilot control.

SOLUTIONS
1. Comparison of how 2 Air data instruments compensate for the principle changes in the
atmosphere.
Due to changes in barometric pressure, input errors would arise as aircraft maneuvers
in the air stream.
The air data has the true and indicated airspeed, pressure, altitude, ambient air
temperature, angles of attack and rate of climb among others
Now, the earth’s atmosphere is stratified into various zones; notably, the one in which
most aircrafts are flown is the troposphere. Other divisions include: chemosphere,
ionosphere, exosphere and ozonosphere. Temperature changes are fairly uniform in
the troposphere (Wiolland, 2005).).
The air data system mainly comprises the primary air data instruments, and pitot-static
tube; The primary air data instruments include : altimeter, vertical speed indicator and
air speed
Notably, the ground-based radar are normally used to establish the exact position and
velocity of the plane. However, the optical trackers can also be used in this case.
GPS receiver then determines the time, position and velocity minus drift errors.
Additionally, the euler angles are mostly measured using mutltiple GPS receiver.
The rate gyroscope is used in measuring angular acceleration rates and linear
accelerations. However, in steady flight, linear accelerators are used to measure pitch
and roll attitude.
Notaly, therefore, airdata instruments are useful in maintenance of the plane stability
hence contributing to safety, navigation and control by the pilot
Figure 1: Air speed indicator (courtesy of USA aerospace.com)

2. Selection of a Pitot-static system to be fitted into a modern aircraft (Provide the design
considerations, construction and operation that would influence the choice of the system)
Design considerations
Error-free: The system must be able to minimize the effects of error on the indicated
readings; too much exaggerated final readings may be risky as pilot receives wrong
information that could pose danger to aircraft maneuvers as the pilot is often informed
through the readings. Besides, factors such as resolution, accuracy, cost and maintenance
and size of aircraft requirements are critical in the integration of the system. The system
must be able to repeatedly give the same value in the same condition of performance
(FAA, no year).). However, practically, errors would often arise hence accuracy needs to
be within a small range that is allowable. Besides, it should be responsive in functionality
such that parameters like attitude and barometric pressure changes must be captured in
real-time and displayed for the pilot to make informed decision.
The construction and operation
The Pitot-static system is mainly composed of the pitot-static tube, airspeed indicator
altimeter and vertical speed are all connected to a static port such that air introduced into
the system via the port as the airplane climbs, the altitude changes so is air pressure. The
pressure changes are recorded by this system.
The air speed indicator measures speed of air by getting the static difference between the
static pressure and the ram air pressure. The display is usually done in a mach number in
knob units.
Notably, the air speed indicator is constituted with an expandable diaphragm such that air
rushes in, it is filled and expanded while ram air pressure is increased.
The altimeter measures air pressure; the calibration is normally in height. It indicates the
static pressure as altitude. The air speed indicator will indicate difference between pilot
static pressure and pitot pressure. The vertical speed gives an indication as to the rate at
which static pressure changes with either climbing or descending.
In the altimeter, the air pressure increases as airplane descends and decreases as the
airplane climbs.
The vertical speed indicator indicates the rate of climb or descends of the aircraft;
calibration is done in feet per minute.
There is a needle connected to the wafer such that it rotates as wafer expands and
contracts to indicate the rate of climb or descend of aircraft.

Figure 2: The Pitot-static tube (courtesy of NASA.gov)
3. Comparison of an analogue to digital air data computer and how they are integrated into
an aircraft. Discuss the advantages and disadvantages
Analogue air data computer Digital air data computer
This is the traditional air data computer that
was used. It mainly comprised of airspeed
indicator and altimeter in which primitive
pneumatically driven instruments was
performed and a nonlinear computation
done via a spring mechanism
The digital remote sensing is normally
separated from the display feature
Servo-driven cams would compute the
parameters like speed, altitude and mach
numbers.
Flat panel computer screens are used for
display of output information
The sensing and display functions are
driven in a single unit.
Special digital data buses are used to carry
information signals
Conveying of sensor information is done
via wires and pneumatic lines and cams
profiles. Numerous display gauges are
It normally maintains optimum
performance of aircraft

often used to show the output
Attitude capsule was the main airdata
sensing used ; it had a simple aneroid to
operate it
It provides additional information to the
aircrafts system
Varying accuracy at different altitudes It provides accurate and realtime sensing
and computation capabilities
It failed to maintain pressure rates hence
system failure was common
Has self-correcting mechanism which can
adjust as conditions and altitude change via
the static source error correction
4. Construction and Operation of a typical flight director system
This is normally an embedded system within the flight control system in which it
provides real-time guidance to the pilot or autopilot along a flight path by selection and
computation of various commands. It is linked with an ADC from which it receives the
input signal and flight data computer performs computation and supplies data such as
attitude, air speed, and flux and air temperature. These signals are then sent and displayed
in the altitude indicator (All Star Network, 2000). Notably, in the absence of the
autopilot, the FD should still be functional with manual maneuvers. In the manual mode,
the pilot directly instructs the FD to carry out the said functions and the system responds
by controlling the listed parameters.
The FD therefore provides a set of commands which are fed from the flight control
computer while in steering mode using a command bar located on the altitude director
indicator (Bombarider, no year). There are about three status modes, namely: vertical,
transfer and lateral modes which are selected accordingly.
The steering commands are in charge of providing visual guidance to pilot as she
manually operates the aircraft maneuvers. Therefore, in a nutshell, according to FAA (no
year) the FDS provides command options to perform selection of a desired altitude,
maintain altitude pressure and ensure aircraft stays at a vertical speed, holds a mach
number and ceases a preselected barometric altitude; a part from maintaining the trim
options and wing-level (All Star Network, 2000).
Construction
Now, the FD is composed of flight director indicator, horizontal situation indicator, mode
selector and a flight director computer. The flight director computer comprises features
such as altitude, indicator, glide slope, slip indicator, wearing flag for gyro, pitch and
bank command and fixed aircraft symbol. The HSI normally facilitates selection and
operation navigation aids while both outbound and inbound tracking is made possible.
The FDC receives input signals from the radar altimeter, sensors (barometric), and
compass and altitude gyro. Certainly, the FDC computes and provides steering

commands to enable pilot perform actions such as heading selection, ILS glide sloping
and flight track maintenance (Kayton & Fried, 1997).
Figure 3: The PFD system (Courtesy of UND aerospace.com)
5. Comparison of the 3 types of electronic displays explaining the operation. Advantages
and disadvantages of each
Basically, the following are the major electronic displays that are predominantly in use:
 LEDs

 LCDs

Figure 4: LCDs features (Courtesy of botskool.com)
 ELDs
The LED stands for Light emitting diodes where they do display arbitrary number of
digits and is based on injection luminescence mechanism. The LED has a wide range of
operating temperature; it is relatively inexpensive and can fully be integrated with the
digital logic units. Besides, its display quality guarantees a wide range of applications
where display quality is critical to system performance (The Airline Pilots, no year).
The ELDS stand for electroluminescent display which is similar in construction and
operation to ac plas ma display. However, in the place of gas-filled area, a thin film of
electroluminescent material is used. An AC voltage is normally applied between the rear
and front electrodes and light is emitted to facilitate display property. Normally, zinc
sulphide is often used for luminescence. It is mostly relevant in situations where a range
of display colors is required. Besides, it can be used in situations that require a wide angle
of vision (The Airline Pilots, no year).

The LCD stands for Liquid crystal displays. It occurs when solid surface molecules
interacts with a nematic liquid crystal (Kayton & Fried, 1997)
6. Construction and Operation of a typical flight instrument system. How instruments are
fully integrated
The system is comprised of display, controls and data processors. The display electronics
unit is the symbol generator where data is received from the pilot and signals from
sensors such that the data buses are used to ascertain the validity of these signals. There is
a graphics generator which undertakes the required computations.
The monitoring unit is comprised of the comparator where warnings for airspeeds, pitch
and altitude indications are facilitated. There is also an instrument display source which
would automatically reconfigure to catch up on the faults that arise in the system
(Bombarider, no year).
Construction
Basically, the system comprises the following instruments: airspeed indicator, altimeter,
gyro horizon, direction indicator and vertical speed indicator. The gyro horizon is
normally centralized such that it provides positive and direct indications of the altitude.
(i) The air speed indicator
This instrument that is often located in the cockpit deck displays real-time speed
of the airplane as it is airborne. Traditionally, the displays were analogue but with
the advancement in digital technology, the modern air speed indicator is a digital
readout
(ii) Aircraft heading and attitude
They are incorporated with sensors to measure both the attitude and heading with
a ground referencing as datum for airborne measurements. It has a self correcting
mechanism owing to the errors that it encounters while navigating the airspace.
However, this feature may be a challenge to effect in turbulent situations as
stability of flight becomes complex to maintain in real-time (Kayton & Fried,
1997). Therefore, pilots are called upon to remain conversant with the relevant
aircraft operating procedures. The sensors would relay critical information such as
attitude, static and dynamic barometric pressure. This is then integrated (as
mentioned earlier) in an air data computer system with processing capabilities to
calculate pressure, air speed (both true and vertical speeds). Therefore, air data
attitude heading reference system (ADAHRS) combines all of the instruments
into a single unit.

Figure 4: Altimeter instrument (courtesy of fly-by-me.com)
(iii) The altimeter
As mentioned earlier, this instrument measures the real-time altitude of the plane
as it ascends or descends. Mostly it is designated in feet.
Figure 5: The altimeter (courtesy of explainstuff.com)
(iv) The vertical speed indicator
The vertical speed is the rate of change in climb or descends of the airplane. This
is normally measured and indicated using the vertical speed indicator. However,

the error in the instrument is normally enlarged when the airplane flies in
turbulent regions (Houston, 2017).
(v) Turn coordinator
This instrument is normally used to measure the rate of turn or roll such that when
pilot maneuvers the plane by turning the plane, this is registered in the cockpit
and assists the pilot to undertake subsequent maneuvering actions accordingly
(Haering, 1995).
Figure 6: Turn coordinator (courtesy of cfinotebook.com)
(vi) The attitude indicator
This is a gyroscopic instrument which helps pilot to know whether the plane is
climbing or descending or even turning.

REFERENCE
All Star Network. (2000). Flight Director Systems. Available from:
www.dlielc.edu/olc/set/ANC/avdocs/index.php?dir...Flight+Director+Systems.pdf
Bombarider. (no year).Canadair Regional Jet 100/200 - Automatic Flight Control System.
Available from: www.smartcockpit.com/.../Bombardier_CRJ_200-Automatic_Flight_Control_System
FAA. (no year).Automated Flight Control. Available from:
https://www.faa.gov/regulations_policies/handbooks_manuals/.../aah_ch04.pdf
Kayton, M. & Fried, W.R. (1997). Avionics Navigation Systems. John Wiley and Sons
Publication. Available from: https://books.google.co.ke/books?
id=1KLTUWLz8jcC&pg=PA393&lpg=PA393&dq=Comparison+of+an+analogue+to+digital+ai
r+data+computer&source=bl&ots=6khHYhgk05&sig=jSyUbZXILQDriNRV_XjMaIK6wtA&hl
=en&sa=X&ved=0ahUKEwiJ3su46c_XAhUBLxQKHQxKDvMQ6AEIQjAI#v=onepage&q=Co
mparison%20of%20an%20analogue%20to%20digital%20air%20data%20computer&f=false
The Airline Pilots.(no year).Electronic Flight Instrument System (EFIS).
https://www.theairlinepilots.com/forumarchive/pilotslounge/efis.pdf
Wiolland,K. (2005). Air Data Computers. Porter-strait instrument co. inc. Available at:
www.aea.net/AvionicsNews/ANArchives/ADCJan05.pdf
Haering, E.A. (1995). Airdata Measurement and Calibration. National Aeronautics and Space
Administration. Available at: www.nasa.gov/centers/dryden/pdf/88377main_H-2
Houston, S. (2017).Traditional Flight Instruments Pilots Need to Know. Available at:
https://www.thebalance.com/aircraft-flight-instruments-the-basic-six-pack-282852