Chapter 2 - Pitot/static systems

Question 1

Why is a static system where there are static vents on either side of the fuselage not suitable for higher speeds?

Answer 1

Effect of shock waves can give false values

Question 2

When is an electrically heated combined or pitot head required?

Answer 2

Mandatory on all aircraft which has a Certificate of Airworthiness to fly in icing conditions

Question 3

How can pressure error caused by turbulent air be reduced?

Answer 3

Situating static pressure points on the aircraft structure less affected by turbulence

Question 4

Why are drain holes accurately calibrated on combined pitot static heads?

Answer 4

So that pressure leakage from pitot to static, and then static to atmosphere will not affect instrument readings

Question 5

What can cause incorrect pressures to be fed to the instruments giving false readings with regards to the pressure heads?

Answer 5

If they are bent or moved out of alignment with the airflow

Question 6

Why are non-standard dimensions used for pitot static pipelines?

Answer 6

Carry only low pressure

So prevents them being used in high-pressure systems

Question 7

Why are hose clips, if fitted, usually made from brass or stainless steel when fitted to pitot static pipelines at instruments?

Answer 7

Prevent them affecting direct reading magnetic compass systems which may be nearby

Question 8

What are used with special union nuts and at what value of pressure are these used for?

Answer 8

Rubber bushes

Up to a pressure of 1.7 bars (25 psi)

Question 9

How are pitot static pipelines identified?

Answer 9

Marked at each end and at intervals with adhesive tape marked INSTRUMENT AIR

• Colour coded orange/grey
• Standard symbol code black zigzag on white

Question 10

What must maintainers be aware of with regards to the rubber bushes used with union nuts in pitot static systems?

Answer 10

Can only be used once

Question 11

Where are moisture drain traps fitted?

Answer 11

At the lowest part of the system

Question 12

What problems can be caused with moisture in pitot static pipelines which don’t become frozen?

Answer 12

Acts as a piston, causing a fluctuation in pressure at the instruments

Question 13

What instruments are affected by water in the pitot pipeline?

Answer 13

ASI and machmeter

Question 14

What instruments are affected by water in the static pipeline?

Answer 14

All the instruments readings to fluctuate

Question 15

What precautions have to be taken with regards to blowing air through the pipelines to remove moisture?

Answer 15

• Use clean, dry warm air in the reverse direction
• Pressure must not exceed 1.7 bars