Introduction to the Cockpit

 The Basic Instruments

So far we have learnt what makes an aircraft fly and the regulations for flying around the countryside. We also have learnt about the controls that make the aircraft turn climb and descend. So what we are going to do know is describe the basic gauges in the cockpit that the pilot uses to make the aircraft fly at the required height speed and direction..

Some instruments are called pressure instruments. Others are gyro driven. We will start off the airspeed indicator. This gauge is a pressure instrument. On one side of a chamber on the gauge there is static air coming in from outside the aircraft away from the flow of air.. On the other side of the chamber dynamic air is pushed into a tube called the pitot head . This pushes onto a diaphragm and the pressure pushes a lever along like a piston which turns the needle on the gauge to indicate the airspeed. 

At high altitude the airspeed indicator should be ignored as it is inaccurate due to the air being too thin Pilots at High Altitude use a Mach meter for speed. It is essential that the pitot head is kept clear of ice otherwise the gauge will over read .the pilot could think he is safe and then the aircraft stalls. The pitot head has a heating element. The anti icing equipment should be turned if the temperature should fall below10 C especially if the air is humid or is in cloud. The gauge itself often are in different forms. The common gauge has markings on around the outside of the gauge. The white arc shows the area where stall speed is at the lower end and shows the maximum area where flaps can be deployed. The green arc is the normal operating speeds of the aircraft. The yellow arc indicates the speeds that the aircraft can only fly in when there is still air and no turbulence. At the top end of the gauge is a red line. This is the maximum this aircraft is permitted to fly at.. On some gauges at the top is a moveable gauge which the pilot can set his height to the temperature. This then has a slide rule around the outside the gauge and the pilot can convert indicated airspeed to true air speed instantly. At high altitude for example the gauge will under read. The gauge could show a speed of 200 knots yet the aircraft true airspeed could be 400 knots. Hence the use of the Mach meter. This over read or under read will vary with temperature and altitude.

The altimeter is a pressure instrument. The altimeter is really a barometer the pilot sets the altimeter by applying air pressure settings to the known barometer pressure for the area supplied by aerodromes and weather stations. Instead of the altimeter reading barometer pressure it reads altitude instead. As the aircraft climbs or descends the pressure changes and the altimeter needle moves up or down indicating what height the aircraft is at.

Pressure is measured at inches of mercury or millibars.. 1 millibar =30ft of height.. the standard pressure is 1013.2 millibars at sea level or 29.92 inches of mercury. So if an aircraft was parked at an airfield that is known to be 600 ft above sea level the altimeter if set correctly should read 600 ft even though the aircraft is still on the ground. The pilot would take off using this setting of the barometer at this height given by Air Traffic Control. 

Barometer Pressure for height above sea level is known as QNH

If the pilot sets the altimeter to zero ft at this 600ft airfield the reading would be a new barometer pressure called the QFE in this case the difference in millibars would be 20 millibars. 

As the pilot goes around the country the pressure of each airfield is passed to the pilot and he adjusts the altimeter setting so as to keep a safe height.

As the aircraft gets higher there is a height that all aircraft set their altimeters to the standard setting of 29.92 or 1013. this is known as transition level heights are then referred to as flight levels. More on that later. These heights vary from area to area.

The last of the pressure instruments is the vertical speed indicator. This measures how fast the aircraft is climbing or descending by detecting pressure changes. This instrument does lag behind a little bit so a pilot should give the instrument some time to settle before adjusting the aircraft. Otherwise the pilot would be constantly changing the height.

We now go onto the driven instruments either by vacuum or electric driven motors.

The Direction Indicator.

We have a magnetic compass in the aircraft which is affected in the turn making it unrealible . This is also affected when slowing down or accelerating as the compass needle swings. We therefore have a gauge called a direction indicator driven by a gyroscope that can detect the movement and turn a compass card on the pilots instrument panel. it looks just the same as a compass. This compass card is set to the compass heading by the pilot when the engines are started. This gives a better idea to the pilot when turning and flying on a heading than trying to judge the whisky compass. The pilot can then work out when to roll the aircraft level from a turn. This DI card will wonder off course gradually so the pilot must make regular checks on it and reset it to the same compass reading as the compass if it wonders off.. He must ensure when doing this the wings are level and the speed is stable.



The Whiskey Compass

The Whiskey Compass is there for general guidance should the DI fail and for setting the DI with.It is prone to swinging when accelerating and slowing down and lags behind in turns.If the aircraft gets hit by lightening the pilot should arrange on landing to have the compass realigned by an engineer as magnetic properties in the lightening could affect the needle.


The Turn and Balance Indicator and Slip indicator.

An aircraft in flight may slip or skid to indicate this to a pilot a spirit level type tube is attached to the turn indicator. The pilot should ensure the ball is in the centre at all times. if the ball is displaced to the left or right then the pilot should apply rudder in the direction of the ball until the ball centres.

The turn indicator is driven by a gyroscope. The gyroscope detects the amount of roll on the aircraft and displays it on the gauge. When the needle touches the bottom line the aircraft is said to be doing a rate one turn. You will learn more about this later in the course.This instrument is normally electrical driven so in the event of a vacuum failure which will cause loss of the direction indicator and DI the pilot still has a turn and level indicator.





The Artificial Horizon and Pitch Indicator

This is a Vacuum driven gyroscope which detects the pitch and roll of the aircraft and indicates on the pilots gauge exeactly what the aircraft is doing in both the horizontal and vertical axis of the aircraft. This gauge indicates whether the aircraft is level or turning and at what angle of bank. it also tells the pilot what angle the nose is in relation to the horizon.

You have a tachometer which will tell you engine RPM get to learn the settings for different phases of flight and speeds. This will make life easier for you.

A flap setting gauge is also in the cockpit and a vacuum gauge. Check the vacuum gauge every five to ten minutes as if it is not correct your instruments will give a false reading.

Radio Navigation is not part of the Private Pilots Licence Course so this will be explained later in the course.

The Gauges have now been described, its now the turn of the levers.


The throttle is self explanatory. On large jets the throttles are called thrust levers.


The Mixture Lever

The higher the aircraft flies the thinner the air is. Therefore you will not require as much fuel going into the engine. The mixture lever allows the pilot to control the amount of fuel entering the engine. The pilot should pull it out very slowly the engine splutters then gently push it in a fraction until the engine picks up again. This lever should always be fully in below 3000 ft. 


The Propeller Pitch Control Lever


Some propellers can be adjusted for better performance in the cruise. During take off climb and descent and landing phase the lever should be in. On a cruise the lever should be out. you will notice the revs drop. the aircraft will have greater range.

This completes the basic introduction to the cockpit levers and gauges in a light aircraft.
Now you will learn to fly it. The instrument relevance will be discussed further in the course. This is an introduction only so that you are aware of them.

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