Pitot-Static Systems
Pitot-Static Systems
Lesduur is: 120 minOnderdelen in deze les
Pitot-Static Systems
Open with the big idea: aircraft do not measure speed or height directly with a ruler or speedometer on the ground. They infer them from air pressure.
Learning goal
I can explain how the pitot-static system uses pressure to show airspeed, altitude and rate of climb or descent.
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What words come to mind when you hear pitot-static system?
Use this to surface prior knowledge and misconceptions. Expect terms such as pressure, airspeed, altitude, pitot tube, static port and instruments.
The pitot-static system
The pitot-static system supplies pressure information to flight instruments.
It uses two sources:
Pitot pressure from air flowing towards the aircraft
Static pressure from the surrounding atmosphere
That pressure information is turned into instrument readings.
Keep the focus on function: this is a pressure-sensing system, not a separate engine or control system.
Where the pressure comes from
Pitot tube faces into the airflow
Static ports sample outside air pressure
These sources feed the air data instruments
Different instruments use the pressure in different ways
If useful, point out that the pitot tube and static ports are mounted where they can sample airflow and outside pressure as cleanly as possible.
Static pressure
Static pressure is the pressure of the surrounding atmosphere.
It exists whether the aircraft is moving or not. As the aircraft changes altitude, the surrounding atmospheric pressure changes too.
Remember: static = surrounding air.
Students often confuse static with 'not changing'. Here it means ambient atmospheric pressure.
Dynamic pressure
Dynamic pressure is linked to movement through the air.
When the aircraft moves faster, dynamic pressure increases. If the aircraft is not moving through the air, dynamic pressure is zero.
Remember: dynamic = movement through air.
You do not need the equation here unless your class already knows it. The key relationship is faster speed, greater dynamic pressure.
Pitot pressure
The pitot tube senses total pressure.
Static pressure + dynamic pressure → total pressure
The aircraft can compare pitot pressure with static pressure. That pressure difference is what allows the airspeed indicator to work.
Be precise with language: the pitot tube senses total pressure, while the ASI effectively uses the difference between pitot and static to infer dynamic pressure.
Which pressure exists even when the aircraft is not moving?
Total pressure
Static pressure
Dynamic pressure
Pitot pressure
Checks the contrast built across slides 4–6. A common misconception is choosing dynamic pressure because students link all pressure to motion.
Complete the pressure summary
The pitot-static system uses pitot pressure from air flowing towards the aircraft and static pressure from the surrounding atmosphere. The pitot tube senses total pressure, which combines static and dynamic pressure.
All three blanks are load-bearing terms already introduced in this block.
Three main instruments
Altimeter: uses static pressure to indicate altitude
Airspeed Indicator (ASI): uses pitot and static pressure to indicate airspeed
Vertical Speed Indicator (VSI): uses change in static pressure to indicate climb or descent
One pressure system supports three different readings.
This is the overview before taking each instrument one by one.
Altimeter
The altimeter uses static pressure.
As altitude increases, atmospheric pressure decreases. As altitude decreases, atmospheric pressure increases.
The instrument converts that pressure into an altitude indication.
Stress that the altimeter is indirect: it does not measure distance above the ground with a physical sensor in this basic system.
How the altimeter changes
Aircraft climbs → surrounding pressure decreases → altimeter indication increases
Aircraft descends → surrounding pressure increases → altimeter indication decreases
The key idea is that the instrument responds to changing atmospheric pressure.
If needed, mention that this is why pressure setting matters in real aviation, but keep this lesson centred on the basic mechanism.
What the altimeter is really measuring
It measures pressure, not height with a tape measure
Lower pressure is interpreted as higher altitude
Higher pressure is interpreted as lower altitude
This is a good misconception check: students may imagine the instrument directly senses distance from Earth.
As an aircraft climbs, what happens to surrounding pressure?
It decreases
It increases
It stops changing
It becomes dynamic
Targets the altimeter mechanism. Students who confuse height with speed may choose the wrong directional change.
Why does the altimeter rise when pressure falls?
Expected elements: the altimeter uses static pressure, pressure decreases with increasing altitude, and the instrument converts that pressure change into an altitude indication.
Airspeed Indicator (ASI)
The ASI compares:
Pitot pressure
Static pressure
The difference between them is related to dynamic pressure, which the instrument converts into an airspeed indication.
Use the exact labels pitot pressure and static pressure consistently.
Why the ASI needs both pressures
At the same altitude, a faster aircraft has greater dynamic pressure.
Greater speed → greater difference between pitot and static pressure → higher ASI indication
The ASI depends on a pressure difference, not on pitot pressure alone.
Students may assume 'more pressure in the pitot tube' is enough. Emphasise the comparison with static pressure.
ASI summary
Pitot tube senses total pressure
Static ports provide static pressure
ASI compares the two
Difference in pressure gives airspeed indication
You can summarise this verbally as: pitot minus static gives the part caused by motion through the air.
Vertical Speed Indicator (VSI)
The VSI uses changes in static pressure over time.
It shows whether the aircraft is:
climbing
descending
maintaining roughly constant altitude
It indicates rate of climb or descent, not altitude.
This is the main distinction from the altimeter: same pressure source, different information extracted from it.
Why the VSI responds
If static pressure is changing, the aircraft is changing altitude.
A rapid change in static pressure means a higher rate of climb or descent. Little or no change means the aircraft is maintaining approximately constant altitude.
You can phrase this as 'how fast the pressure is changing tells us how fast the altitude is changing'.
Comparing the instruments
Altimeter — static pressure → altitude
ASI — pitot pressure and static pressure → airspeed
VSI — change in static pressure over time → rate of climb or descent
This is the key comparison slide for retrieval and later failure analysis.
Which instrument uses changes in static pressure over time?
Altimeter
Compass
ASI
VSI
Tests the comparison among instruments after the full set has been taught.
Complete the instrument comparison
The altimeter uses static pressure to indicate altitude. The ASI compares pitot and static pressure to indicate airspeed. The VSI shows rate of climb or descent from changing static pressure.
Useful retrieval before moving into fault diagnosis.
Tracing the pressure paths
Pitot pressure goes to the ASI
Static pressure goes to the altimeter
Static pressure goes to the VSI
Static pressure also goes to the ASI
Use this as a bridge into fault diagnosis: if a source is blocked, whichever instruments depend on it may be affected.
When the pitot tube is blocked
A blocked pitot tube stops the ASI receiving correct pitot pressure.
Because the ASI depends on pitot pressure and static pressure, its airspeed indication can become unreliable.
The altimeter and VSI are not driven by pitot pressure.
Keep the failure effects simple and conceptual: pitot problem mainly affects airspeed.
When the static port is blocked
A blocked static port affects every instrument that depends on static pressure.
That means:
Altimeter may be affected
VSI may be affected
ASI may also be affected
One blockage can therefore affect more than one reading.
This is the most important systems-thinking point in the failure section.
Pitot icing
Ice around the pitot tube can stop correct pressure reaching the ASI.
If the pressure information is wrong, the ASI can show an unreliable airspeed indication.
That is dangerous because the pilot may be given incorrect information about aircraft speed.
Link this to real operating conditions without adding extra systems detail unless needed.
Failure summary
Pitot blockage → mainly affects the ASI
Pitot icing → can give unreliable airspeed information
Static blockage → may affect the altimeter, VSI and ASI
Remember:
Pitot is mainly linked to airspeed.
Static supports altitude, vertical speed and part of the airspeed measurement.
Use this slide to consolidate the system logic before moving to the practical model and summary.
A blocked static port may affect which instruments?
ASI only
Altimeter only
Altimeter, VSI and ASI
VSI only
The distractors reflect a common tendency to think in single-instrument faults rather than shared pressure sources.
Why can a static blockage affect more than one instrument?
Expected elements: static pressure feeds more than one instrument; altimeter and VSI depend on it directly; ASI also needs static pressure as part of its pressure comparison.
Pressure demonstration model
A simple classroom model can show how pressure-operated instruments respond.
Changing pressure in tubing or a syringe can move an indicator, showing the same basic idea as aircraft instruments: pressure changes can be turned into readable information.
Keep this conceptual. Do not turn it into an activity slide; just explain what the model demonstrates.
Safety for pressure models
Only low-pressure classroom demonstrations should be used.
No compressed gas
No excessive pressure or vacuum
Check tubing and equipment before use
Follow teacher instructions carefully
Briefly reinforce that the model demonstrates principles safely at classroom scale.
Lesson summary
Static pressure is the pressure of the surrounding atmosphere
Dynamic pressure is linked to movement through the air
Altimeter uses static pressure for altitude
ASI uses pitot and static pressure for airspeed
VSI uses changing static pressure for climb or descent
Blockages can produce unreliable indications
This resolves the central question: aircraft know speed, altitude and vertical motion by measuring and comparing pressures.
Which part of the lesson helped you understand the system best?
Pressure types
Instrument comparison
Failure scenarios
Model demonstration
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What is one idea from today that you will remember?
Invite brief reflection on the most secure takeaway, ideally linking it to a pressure source, an instrument, or a failure effect.
Which part still feels hardest to explain?
Use responses to identify misconceptions or steps to revisit, especially pressure differences, shared static supply, or instrument behaviour in failures.
Glossary
pitot tube - A forward-facing tube that senses total pressure from the airflow
static port - An opening that senses the pressure of the surrounding atmosphere
static pressure - The pressure of the surrounding air, whether the aircraft is moving or not
dynamic pressure - Pressure linked to the aircraft moving through the air
total pressure - The combined effect of static pressure and dynamic pressure
altimeter - An instrument that uses static pressure to indicate altitude
airspeed indicator (ASI) - An instrument that compares pitot and static pressure to indicate airspeed
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Glossary
vertical speed indicator (VSI) - An instrument that uses changes in static pressure over time to indicate climb or descent
airspeed - The speed shown by the ASI from pressure information
altitude - Height indicated from atmospheric pressure changes
rate of climb - How quickly the aircraft is gaining altitude
rate of descent - How quickly the aircraft is losing altitude
pitot blockage - A blockage that stops correct pitot pressure reaching the system
static blockage - A blockage that stops correct static pressure reaching the system
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