Why Planes Have Six Packs

Before the advent of the Glass Cockpit, every plane had a six pack. No I'm not talking about abs (that would certainly be a strange sight), I'm talking about the six pack of flight instruments that every pilot uses to fly. These include the Airspeed Indicator, Attitude Indicator, Altimeter, Vertical Speed Indicator, Heading Indicator, and Turn Coordinator. Now that sounds like a lot of instruments, but most of them are very self explanatory.

1. Airspeed Indicator

Just as the name implies, it tells you your airspeed. It uses the pressure that an instrument called the pitot reads along with the pressure the static air port reads in order to calculate how quickly the air is rushing past the plane and thus how fast the plane is moving through the air. This is usually given in Knots (Nautical miles per hour). One important thing to keep in mind is that this instrument does NOT tell a pilot their ground speed. It only tells them their airspeed, and their ground speed can be higher or lower based on whether they have a headwind or tailwind. The instrument also goes one step further on a lot of planes with different colored bands to indicate different operating ranges. The green band typically represents the range of normal operations, the yellow represents the speeds which should only be reached in very still air, and the red line marks the speed the aircraft should never exceed under any condition. There is also a small white band on the lower end of the instrument which marks the flaps operating range. This is the range of speeds at which the plane can fly with flaps down.

1. Attitude Indicator

The attitude indicator tells a pilot both the pitch angle of the plane with respect to the horizon, and the roll angle of the plane about its axis. The instrument uses an internal gyroscope to determine this information. The horizon is represented by the line where the blue and brown areas meet, and the horizontal lines each represent 5 degrees of pitch with the 10 degrees lines labelled as such. The lines going around the top of the instrument each represent various roll angles (Typically: 10, 20, 30, 45, 90). Using this instrument the pilot is able to tell whether the plane is pitching up or down, level, or if it's rolling.

1. Altimeter

Using a manually inputted altimeter setting and the air pressure at the static air port this instrument determines how high up in the air the aircraft is. This works because the air pressure decreases as the altitude increases. Because the density (and pressure) of the air varies with temperature and pressure fronts as well though, the altimeter setting can be manually adjusted by listening to nearby weather reports over the radio. This corrects for changes in local air pressure, and ensures a more accurate altimeter reading. One thing to note about altimeters is that they always show altitude above MSL (Mean Seal Level). This means they only show the plane's height relative to the sea level, not relative to the ground. As such the pilot always has to be aware of how high up the ground is where they are flying so that they know their altitude AGL (Above Ground Level). Reading altimeters is relatively simple. There are three hands: The longest hand - 10,000 ft The shortest hand - 1,000 ft The middle hand - 100 ft This altimeter, for example, reads ___.

1. Vertical Speed Indicator (VSI)

The vertical speed indicator shows how quickly the plane is climbing or descending in hundreds of feet per minute. It is connected to the static air port and uses the change in air pressure to calculate the rate of climb/descent. It is very useful for a pilot so that they can, at a glance, see how steep their climb or descent is in order to correct for it. If the hand is above the 0 ft/m mark then the plane is climbing, if it is beneath then the plane is descending.

1. Heading Indicator The heading indicator works much like a compass, showing the plane's heading in degrees. It uses a gyroscope to find the plane's heading meaning that unlike real magnetic compasses, the heading indicator is not affected by turns or changes in speed. However the heading indicator does have to be manually adjusted at times to account for errors. These include error caused by friction in the gyroscope's bearings, and error caused by the fact that the earth rotates at about 15 degrees per hour whereas the gyro is oriented in space (which does not rotate).

2. Turn Coordinator For anyone who doesn't fly, this might be the strangest of the six instruments in this post. In order to understand its function, it's best to first understand how planes turn in the first place. Planes turn by a combination of rolling and yawing. To turn right, for example, a pilot would bank right and apply right rudder in order to yaw in that direction. Without the added rudder, adverse yaw would try to turn the plane in the opposite direction to the intended turn. This is where the turn coordinator comes in. It helps the pilot double check their turn to make sure that they are coordinated (using the correct amount of yaw) throughout. The ball will always be in the center when the plane is coordinated, and will shift to the left or right when it isn't. In that situation pilots are often taught to "step on the ball". This basically means the pilot should step on the rudder pedal that is on the same side as the ball in order to correct for too much or too little yaw.