Type Rating Knowledge — Cessna 172S NAV III
Pitot-static system and flight instruments
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Two holes in the aeroplane
Everything in this module starts from two openings. Total pressure comes from a heated pitot head on the LOWER surface of the left wing — one head, with an electrical heating element built into its body, switched by PITOT HEAT on the panel below the lower left corner of the PFD. Static pressure comes from an external static port on the LEFT side of the forward fuselage. Plumbing connects both to the air data computer and to the conventional pitot-static instruments. That word "conventional" is doing real work: the standby airspeed indicator and standby altimeter on the lower centre panel are plumbed to the same two holes directly, with no computer in the path at all.
- PITOT HEAD — Heated total-pressure head on the LOWER surface of the left wing. It is the only source of total pressure on the aeroplane.
- OAT PROBE — Outside air temperature probe on top of the cabin, wired to the air data computer.
- STATIC PORT — External static port on the LEFT side of the forward fuselage — the normal static source.
- PITOT HEAT SW — Switch on the panel below the lower left corner of the PFD, feeding the heating element built into the body of the pitot head. Its breaker is on the lower left breaker panel.
- ALT STATIC AIR — Alternate static source valve beside the throttle. Pulled on, it takes static pressure from INSIDE the cabin.
- PITOT LINE — Plumbing carrying total pressure aft to the air data computer and to the standby airspeed indicator.
- STATIC LINE — Plumbing carrying static pressure to the air data computer and to both standby pressure instruments.
- AIR DATA COMPUTER (GDC) — Mounted behind the panel just forward of the MFD. It calculates pressure altitude, airspeed, true airspeed, vertical speed and outside air temperature.
- STANDBY ASI — Pneumatic standby airspeed indicator on the lower centre panel, driven straight off the pitot and static lines with no computer in between.
- STANDBY ALTIMETER — Aneroid sensitive standby altimeter on the lower centre panel, driven straight off the static line.
- PFD AIRSPEED TAPE — Vertical tape airspeed indication on the upper left of the PFD, computed by the air data computer.
- PFD ALTIMETER TAPE — Primary altitude tape right of the attitude indicator, computed by the air data computer. BARO is set with the knob on the GDU bezel.
- PFD VSI TAPE — Vertical speed tape right of the altimeter. Digits appear inside the pointer only above 100 feet per minute.