The Core of the Cockpit: The Six-Pack
Although advancements in aircraft technology are designed to create a more efficient and reliable flight experience, most aircraft still rely on six traditional instruments known as the “six-pack”. Like how the core of the human body is necessary for maintaining posture and balance, the “six-pack” is necessary for informing the pilot of vital information regarding the status of the aircraft.
These six instruments are classified into two separate categories based on their respective operating mechanisms: static instruments and gyroscopic instruments. And each classification has three instruments. Static instruments operate based on comparing the pressure of an enclosed capsule to fluctuating environmental pressure to indicate things like speed and altitude. Gyroscopic instruments are based on gyroscopes which indicate orientation and direction. Gyroscopic instruments can be found in vacuum or electric driven variations.
The static instruments include the altimeter, airspeed indicator, and vertical speed indicator (VSI). As the name suggests, the altimeter relays information on the altitude, or vertical distance of the aircraft. The altimeter works by comparing the static pressure of an enclosed capsule to the fluctuating pressure of the aircraft as it ascends or descends. This is then translated to a gauge display to indicate the vertical distance of the aircraft over the mean sea level. The airspeed indicator works in a similar fashion but differs by comparing ram air pressure to a constant air pressure in order to measure the speed of the aircraft. Temperature and density, which are components in measuring pressure, are both accounted for when measuring true airspeed— the actual speed of the aircraft. The VSI operates similarly to the previous two in order to measure the rate of ascent or descent of the aircraft, which is measured in feet per minute (fpm). However, the VSI differs from the other two in that it is more sensitive to changes in pressure, which makes it more sensitive to abrupt changes in pressure like in turbulence.
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