As a pilot, having accurate and reliable flight instruments is essential for safe and efficient flight. The six primary flight instruments in an airplane provide crucial information about the aircraft’s speed, altitude, attitude, heading, and rate of turn. These instruments are commonly referred to by their nickname, the “Six Pack”.
The Six Pack
- Airspeed Indicator
- Altimeter
- Attitude Indicator
- Heading Indicator
- Turn Coordinator
- Vertical Speed Indicator
Of these six instruments, three of them rely on the Pitot-Static system to gather information about the aircraft’s performance. These three are the Airspeed Indicator, Altimeter, and Vertical Speed Indicator. The other three – Attitude Indicator, Heading Indicator, and Turn Coordinator – use Gyroscopic Technology.
Let’s explore the functions and workings of each of these six primary flight instruments and how they work together to provide essential information to the pilot during flight. But before we dive into the Six Pack, let’s briefly discuss the basics of the Pitot Static system and Gyroscopic Technology.
What is the Pitot-Static system and how does it work?
The Pitot-Static system is a network of tubes and sensors that measure the pressure of the air surrounding an aircraft. The system is used to provide information to three of the flight instruments in the Six Pack. These are the aforementioned Airspeed Indicator, Altimeter, and Vertical Speed Indicator.
The system consists of two main components: the pitot tube and the static ports. The pitot tube is a pointed probe that faces forward and measures the total pressure of the air rushing past the aircraft. This pressure, known as pitot pressure, is used to determine the aircraft’s airspeed.
The static ports are small openings located on the sides of the aircraft that measure the static pressure of the air. This pressure is unaffected by the movement of the aircraft and is used to determine the aircraft’s altitude.
When the aircraft is in flight, the pitot tube and the static ports measure the differences in pressure between the pitot pressure and the static pressure. This information is then transmitted to the flight instruments. There it is used to calculate the aircraft’s airspeed, altitude, and rate of climb or descent.
What is Gyroscopic Technology?
In aviation, gyroscopic technology is used in several primary flight instruments, such as the Attitude Indicator, Heading Indicator, and Turn Coordinator. These instruments use a spinning wheel or rotor to detect changes in the aircraft’s orientation. This provides information to the pilot about the aircraft’s pitch, roll, and heading relative to the horizon.
The spinning wheel or rotor is usually powered by a small electric motor and is designed to remain stable and maintain its orientation, even as the aircraft moves and changes its orientation. This technology provides pilots with important information about the aircraft’s orientation and helps them maintain control and navigate the aircraft during flight.
Now that we’ve gotten that out of the way, let’s explore the instruments that make up the Six Pack.
Airspeed Indicator
The Airspeed Indicator, also known as the ASI, is a crucial instrument for pilots. It provides information about the aircraft’s speed, which is essential for maintaining the aircraft’s airspeed within safe operating limits.
The ASI works by measuring the pressure difference between the air entering the instrument and the air outside the aircraft. This pressure difference is proportional to the speed of the aircraft and is displayed on the ASI in units of knots, miles per hour, or kilometers per hour.
The ASI has several important markings that the pilot uses to monitor the aircraft’s speed. The white arc on the ASI represents the range of safe airspeeds for operating with the flaps down or extended. The green arc represents the range of speeds for normal operation of the aircraft. The yellow arc represents the “smooth air” range of speeds. This is the range in which the aircraft may be operated provided there is no significant turbulence. Finally, the red line indicates the maximum structural cruising speed, or “never exceed” speed.
Attitude Indicator
Also known as the Artificial Horizon, the Attitude Indicator is a flight instrument that displays the orientation of an aircraft relative to the earth’s horizon. It is an essential instrument for pilots, especially when flying in instrument meteorological conditions (IMC), where visibility is limited and the pilot must rely on instruments to maintain control of the aircraft.
The Attitude Indicator works by using a gyroscope to maintain a stable reference and display the aircraft’s orientation in roll and pitch. The instrument displays a representation of the horizon, typically with a blue half representing the sky and a brown half representing the ground. The ground marking always remains level with the earth’s horizon, regardless of the actual orientation of the aircraft, allowing the pilot to determine if the aircraft is level, climbing, or descending.
Read Also: What Are The Minimum Required Instruments For VFR Flight?
Altimeter
An Altimeter is a flight instrument that displays the altitude of an aircraft above sea level. It is an essential instrument for pilots, as it provides information for navigation and determining the aircraft’s height above the ground.
The Altimeter works by measuring atmospheric pressure and converting it into an altitude reading. The static port measures the pressure of the air outside of the aircraft. This pressure is then compared to the pressure, set by the pilot to the barometric pressure at their current location. The difference between the two is used to calculate the aircraft’s altitude.
The Altimeter has several important markings that the pilot uses to monitor the aircraft’s altitude. The face of the altimeter has a rotating drum with markings for hundreds and thousands of feet or meters, and a needle that indicates the aircraft’s current altitude. The pilot sets the barometric pressure using a knob on the instrument, which allows the altimeter to accurately display the aircraft’s altitude. The pressure setting is viewed through a small window on the Altimeter called the Kollsman window.
What is barometric pressure? What does 29.92 mean?
The barometric pressure setting for an altimeter is a reference pressure used to calibrate the instrument and determine the aircraft’s altitude. The barometric pressure setting is expressed in inches of mercury (inHg) and is set by the pilot using a knob on the altimeter.
The standard barometric pressure setting for the altimeter is 29.92 inHg. This value represents the average sea-level pressure at 15°C (59°F) and is used as a reference for calibrating the altimeter. When the altimeter is set to 29.92 inHg, the instrument will display the aircraft’s altitude above sea level.
It’s important to note that the actual barometric pressure can vary due to weather conditions and other factors. The pilot must periodically adjust the barometric pressure setting on the altimeter to ensure accurate altitude readings.
Turn Coordinator
The Turn Coordinator is a flight instrument that provides information about the aircraft’s rate and coordination of the turn. It is used to help the pilot maintain coordinated flight, which is crucial for stability and control. It is also used to ensure that turns are made smoothly and efficiently.
The Turn Coordinator works by measuring the rate of yaw and roll and displaying this information on the instrument. The instrument consists of a rotating ball that moves in response to the aircraft’s motion. The ball is mounted inside a circular scale, which has markings for rate-of-turn and slip/skid.
When the aircraft is turning, the ball moves off-center in the direction of the turn. The further the ball is from the center, the faster the aircraft is turning. The rate-of-turn markings on the scale provide the pilot with a visual indication of the aircraft’s rate of turn in degrees per second.
The Turn Coordinator also provides information about the coordination of the turn, which is the relationship between the rate of turn and the angle of bank. In a properly coordinated turn, the aircraft is banked at the correct angle to maintain level flight, with no slipping or skidding. If the aircraft is slipping or skidding, the ball will move to the side of the scale. This indicates the need for correction.
Okay, but wait a minute. What is a slip? What is a skid?
A slip and a skid are terms used to describe an aircraft’s deviation from a coordinated turn. A coordinated turn is a turn in which the aircraft is banked at the correct angle to maintain level flight, with no slipping or skidding.
A slip is a condition in which the aircraft’s nose is displaced from the intended flight path. This causes the aircraft to drift sideways through the air. This can occur when the aircraft is turning too slowly or not banking enough to maintain level flight. In a slip, the wing on the inside of the turn produces less lift than the wing on the outside of the turn, causing the aircraft to drift sideways.
A skid, on the other hand, is a condition in which the aircraft’s nose is pointing in the direction of the turn but the aircraft is not following the intended flight path. This can occur when the aircraft is turning too quickly or banking too much. In a skid, the wing on the outside of the turn produces more lift than the wing on the inside. The result is that the aircraft follows a curved flight path.
In both cases, the deviation from a coordinated turn can result in increased drag, reduced lift, and increased fuel consumption. More importantly, slips and skids can result in instability of the aircraft which can be dangerous. It is important for pilots to recognize and correct slips and skids to maintain efficient, safe flight. The Turn Coordinator instrument can provide information to the pilot about the aircraft’s deviation from a coordinated turn. This helps the pilot maintain proper control of the aircraft.
Heading Indicator
The Heading Indicator, also known as the Directional Gyro or simply the DG, is a flight instrument that provides information to the pilot about the aircraft’s heading. Specifically, it displays the direction in which the aircraft’s nose is pointed. Pilots use it to maintain proper orientation and navigate the aircraft.
The DG works by using a gyroscopically-stabilized platform that maintains its orientation in space, even as the aircraft turns. The instrument displays the aircraft’s heading relative to magnetic north, provided the pilot has set its orientation to align with the magnetic compass. The DG is marked with a compass rose, which allows the pilot to determine the aircraft’s heading in degrees.
The Heading Indicator is an essential instrument for navigation. It is used in conjunction with other navigation aids, such as a magnetic compass and GPS, to ensure that the aircraft stays on course. Pilots also use it to maintain proper heading during instrument flight when the pilot cannot see the horizon or other visual cues.
Vertical Speed Indicator
The Vertical Speed Indicator (VSI), also known as the rate-of-climb indicator, is a flight instrument that provides information to the pilot about the aircraft’s rate of climb or descent. Pilots use the VSI to control the altitude of the aircraft and maintain a stable flight profile.
The Vertical Speed Indicator works by measuring the rate of change in pressure inside the aircraft’s pitot-static system. The pitot-static system is a network of tubes and sensors that measure the pressure of the air surrounding the aircraft. The VSI uses this information to determine the rate of climb or descent. This information is usually displayed via a needle on the instrument in feet per minute.
When the aircraft is climbing, the VSI displays a positive value, indicating that the aircraft is ascending. When the aircraft is descending, the VSI displays a negative value, indicating that the aircraft is descending. The VSI is an important instrument for controlling altitude, as it provides the pilot with an accurate and continuous indication of the aircraft’s rate of climb or descent.
Conclusion
The six primary flight instruments in an airplane play a critical role in ensuring safe and efficient flight. Each instrument provides vital information about the aircraft’s speed, altitude, attitude, heading, and rate of turn. The Six Pack instruments work together to provide the pilot with the information necessary to make informed decisions during flight.
While the Six Pack instruments provide crucial information, the pilot is ultimately responsible for interpreting the information it provides. When pilots understand the functions and workings of these flight instruments, they are better equipped to make safe and informed decisions.