How are the airspeed indicator, altimeter, and vertical speed indicator connected to the pitot-static system?

• A. Through tubes and diaphragms to sense pressure differences or static pressure.
• B. Wireless signals from sensors in the fuselage.
• C. Hydraulic lines feeding pressure actuators.
• D. Electric harnesses running to the instruments.

Answer: (A)

The airspeed indicator, altimeter, and vertical speed indicator all get their information from the pitot-static system through tubes that carry pressure signals to internal sensing elements. The pitot tube provides stagnation (pitot) pressure, while static ports supply ambient air pressure. Inside each instrument, these pressures act on diaphragms or aneroid capsules rather than on electrical components.

For the airspeed indicator, the instrument compares the pitot pressure with the static pressure to measure dynamic pressure. The resulting pressure difference moves a diaphragm, which translates into the airspeed reading on the dial. The altimeter relies on static pressure alone; as altitude increases, ambient pressure drops, causing the aneroid capsule to expand or contract and drive the altitude indication. The vertical speed indicator measures how quickly the static pressure is changing, using a calibrated mechanism that responds to the rate of pressure change to show climb or descent rate.

These readings depend on physical pressure signals transmitted through tubes, not on wireless, hydraulic, or electric connections, so keeping the pitot and static lines open and unobstructed is essential for accurate indications.