Air data systems

Question 1

Air data

Answer 1

The sensing of the medium through which the aircraft is flying

It is autonomous on based sensing method used to provide data for a range of systems

Critical for the safe operation of an aircraft

Question 2

Air data measurements

Answer 2

static pressure

total pressure

dynamic pressure(derived)

rate of change in static pressure

temperature

angle of incidence

Question 3

Sensors

Answer 3

static vent(port)

pitot probe/tube

pitot static probe/tube

Question 4

Static vent port

Answer 4

measure local static pressure relative to altitude

fitted facing perpendicular to the relative airflow

Question 5

Pitot probe/tube

Answer 5

measures total pressure

face into the relative airflow

Question 6

Pitot static probe/tube

Answer 6

• measures both static and total pressures
• 2 concentric tubes aligned with the relative airflow
  
  • inner tube brings the airflow to rest
    
    • kinetic energies converted into pressure thus total pressure for a frictionless and incompressible flow
  • the outer tube has pressure tapping to the freestream thus measures static pressure

Question 7

Total pressure equation

Answer 7

Question 8

Indicated airspeed equation

Answer 8

Question 9

What does an ADC compute?

Answer 9

calibrated airspeed

mach

altitude

Question 10

What happens when a pitot tube is sealed?

Answer 10

a pressure seal is applied

the total pressure is constant

Question 11

What happens when a pitot tube is blocked?

Answer 11

It acts as a static port

Question 12

What happens when a static port is sealed?

Answer 12

the altimeter becomes fixed

VSI becomes zero

ASI is only accurate for the altitude at which the static port became blocked

Question 13

ALT

Answer 13

barometric altitude relative to static air pressure

a pressure datum is set to measure the change in altitude

Question 14

VS

Answer 14

vertical speed

accurate indication of the rate of climb or descent

feet per min

Question 15

IAS

Answer 15

indicated air speed

inaccuracy due to sensor position and instrument error

Question 16

CAS = IAS, when corrected for?

Answer 16

pressure error

• misalignment of pitot with relative airflow
• corrected for each configuration

instrument error

• expansion of capsule diaphragm nonlinearly
  
  • nonlinearity compensated for by square law

Question 17

EAS = CAS, when corrected for?

Answer 17

compressibility

• above Mach 0.4, the air compresses
• total pressure is artificially high
  
  • higher AS than actual

Question 18

Airstream direction detector

Answer 18

measures direction of airflow relative to the aircraft

provides angle of incidence/attack data

Question 19

TAT

Answer 19

the temperature of the air at a stagnation point

indicator of leading-edge temperature for TAS calculation

Question 20

SAT

Answer 20

true temperature of ambient conditions

used in adverse weather to indicate icing potential

Question 21

TAT probe

Answer 21

placed away from the fuselage in the freestream

designed to decelerate airflow to rest relative to the aircraft

kinetic energy converted to thermal energy

the air is compressed and experiences an adiabatic increase in temperature

Question 22

Modern air data systems

Answer 22

• triplex systems
• standby must operate and be powered independently
  
  • air data modules convert air pressure into a digital signal
• use of relatively narrow bore tubing and pneumatic capsules
• ADM close to the sensors reduces errors
  
  • eliminates the chances of condensation and icing

Question 23

ADIRS

Answer 23

• integration of air data and inertial parameters in one multichannel unit
• supplies air data as well as altitude information to EFLS displays, navigation and autopilot
• each ADIRS linked to 3 A629 data busses to receive and distribute information
• ADIR has 2 main ADIRU
  
  • standby SAARU(secondary air data altitude reference unit) with separate power source may be used to provide primary air data and altitude information during an ADIRU failure