On simple aircraft, this may consist of a pitot-static system  head or pitot tube with impact and static air pressure ports  and leak-free tubing connecting these air pressure pick- up points to the instruments that require the air for their  indications. The altimeter, airspeed indicator, and vertical  speed indicator are the three most common pitot-static  instruments.  Figure 10-22  illustrates a simple pitot-static  system connected to these three instruments. A pitot tube is open and faces into the airstream to receive  the full force of the impact air pressure as the aircraft moves  forward. This air passes through a baffled plate designed  to protect the system from moisture and dirt entering the  tube. Below the baffle, a drain hole is provided, allowing  moisture to escape. The ram air is directed aft to a chamber  in the shark fin of the assembly. An upright tube, or riser,  leads this pressurized air out of the pitot assemble to the  airspeed indicator. The aft section of the pitot tube is equipped with small holes  on the top and bottom surfaces that are designed to collect  air pressure that is at atmospheric pressure in a static, or  still, condition. The static section also contains a riser tube  and the air is run out the pitot assembly through tubes and  Many pitot-static tube heads contain heating elements to  prevent icing during flight. The pilot can send electric current  is connected to the altimeter, the airspeed indicator, and the  vertical speed indicator.  [Figure 10-23] Pitot Tubes and Static Vents 10-13 $^{30.}$0 29.9 29.8 Pitot-static tube Pitot line Static line 30.0 29.9 29.8 Altimeter Heater (35 watts) Static port Vertical speed indicator (VSI) Airspeed indicator (ASI) Pitot heater switch Drain hole Pressure chamber Alternate static source Heater (100 watts) Pitot tube Baffle plate Static chamber Ram air Figure 10-23.  A typical pitot-static system head, or pitot tube, collects ram air and static pressure for use by the flight instruments.  Figure 10-22.  A simple pitot-static system is connected to the  primary flight instruments. 