Aircraft Instruments

Prior to World War II, few airplanes were equipped for flight without using ground reference navigation. Poor visibility or low cloud cover, therefore, required flying at dangerously low altitudes or not flying at all.

September 24, 1929:

• Jimmy Doolittle made a flight without outside visual references. The Consolidated NY-2 airplane he flew had an artificial horizon, sensitive altimeter and radio direction finder.

• Doolittle proved that blind flight indeed was possible

Aircraft instruments

• displays and dials in an aircraft

• allow them to understand where the plane is and what it is doing.

• rely on these instruments, especially when they're tens of thousands of feet in the air and might not be able to see anything because of the clouds.

1929 Cessna (panel)

• airspeed indicator and altimeter only

1940

• Zero Visibility

• Newly developed flight instrument

• keep the airplane straight and level with no outside reference

HISTORY

• Wright Brothers had very few instruments on their Wright Flyer: engine tachometer, wind meter and a stop watch

Flight Instrument exist for us to:

• Condition of the aircraft

• Engine Components

• Aircraft’s attitude in the sky

• Weather

• Navigation and communication

2 Types of Instrument System

Direct Sensing Instrument

• senses the situation and the other part displays it. In analog instruments, both of these functions often take place in a single unit or instrument

Remote Sensing Instrument

• requires the information to be sensed, or captured, and then sent to a separate display unit in the cockpit

3 Kinds of Basic Instruments

• FLIGHT INSTRUMENTS, ENGINE INSTRUMENTS, and NAVIGATION INSTRUMENTS. There are also miscellaneous gauges and indicators that provide information that do not fall into these classifications, especially on large complex aircraft.

Glass Cockpit

• features electronic (digital)

• typically large LCD screens

Conventional/Traditional Cockpit

• analog dials and gauges

• numerous mechanical gauges (nicknamed "steam gauges")

WHAT IS VFR? (Visual Flight Rules)

• a set of regulations under which a pilot operates an aircraft in weather conditions

• allow the pilot to see where the aircraft is going.

WHAT IS IFR? (Instrument Flight Rules)

• Rules and regulations established by the FAA to govern flight under conditions in which flight by outside visual reference is not safe.

• depends upon flying to instruments in the flight deck, and navigation is accomplished by electronic signals

Different Flight Instruments

• Altimeter • Airspeed Indicator

• Heading Indicator

• Artificial Horizon

• Turn Coordinator

• Vertical Speed Indicator

Altimeter

• displays the aircraft’s current height above sea level (not ground level)

• has three hands measuring hundreds, thousands, and ten thousands of feet.

• based on barometric pressure

• due to the constantly changing nature of barometric pressure the altimeter needs to be pre-set

Airspeed Indicator

• measurement is usually given in knots (Nautical Miles per Hour)

• it measures the speed of the aircraft as it moves through the air using air pressure differences (Pitot Tube)

Types of Airspeed

Indicated Airspeed (IAS)

• reading without any consideration for atmospheric conditions or potential installation and instrument errors.

Calibrated Airspeed (CAS)

• Indicated Airspeed corrected for installation error and instrument error. • More accurate than the IAS

True Airspeed (TAS)

• The Calibrated Airspeed corrected for altitude related atmospheric conditions such as temperature variations and air density

Groundspeed (GS)

• The aircraft’s actual speed over the ground, or the True Airspeed adjusted for wind resistance factors (headwind, tailwind etc.)

Vertical Airspeed Indicator

• sometimes called a variometer, or rate of climb indicator

• senses changing air pressure

• displays that information to the pilot as a rate of climb or descent in feet per minute, meters per second or knots.

• uses the aircraft pitot-static system to determine the vertical speed

Heading Indicator

• also known as the directional gyro

• displays the aircraft's heading with respect to magnetic north when set with a compass

• Bearing friction causes drift errors from precession, which must be periodically corrected by calibrating the instrument to the magnetic compass.

Turn Indicator

• include the Turn-and-Slip Indicator and the Turn Coordinator

• indicate rotation about the longitudinal axis

• include an inclinometer to indicate if the aircraft is in coordinated flight, or in a Slip or Skid

Navigation Instrument

• used to identify exact location by determining direction and distance from certain points.

• provides a general overview of several common navigation avionics systems that you, as the technician, will maintain

• Refers to the instruments used by nautical navigators and pilots as tools of their trade.

• to ascertain the present position and to determine the speed, direction etc. to arrive at the port or point of destination

VERY HIGH FREQUENCY OMNIRANGE (VOR)

• the standard radio navigation system for cross-country flying in the United States and most of the rest of the world for many years.

Advantages of VOR

• Provides an infinite number of radials or course indications

• Reduces the amount of indication errors from diverse atmospheric conditions.

AUTOMATIC DIRECTION FINDER (ADF)

• has been in use since the 1930s

• Many smaller airports that have no other radio aids for navigation provide transmitters called non-directional beacons (NDB) that can be used with ADF equipment

• used by even the largest transport aircraft.

• encompass both the ADF and NDB equipment since both the airborne and ground-based components are required to operate the system

Engine Instrument

• designed to measure operating parameters of the aircraft’s engine

• usually quantity, pressure, and temperature indications. They also include measuring engine speed

The most common engine instruments are the fuel and oil quantity and pressure gauges, tachometers, and temperature gauges

There are also several engine instruments that can be found in a reciprocating/piston engine such as the following:

• Cylinder head temperature

• Manifold pressure

most important instrument used by the pilot to perceive the health of an engine is the engine oil pressure gauge

• Oil pressure is usually indicated in psi.

• The normal operating range is typically represented by a green arc on the circular gauge.

Why is it important?

• Lubrication – to reduce friction and prevents heating of the engine

• Cooling – oil absorbs heat in the engine as it circulates in the system

• Cleaning – because of abrasion, the metal gets damaged and it will produce small metal particles inside the engine.

TACHOMETER

• measuring the rotation speed of a shaft or disk

• able to monitor revolution per minute (rpm)

EXHAUST GAS TEMPERATURE INDICATOR (EGT)

• used to monitor the exhaust gas temperature of an internal combustion engine

ENGINE OIL TEMPERATURE INDICATOR

• ability of the engine oil to lubricate and cool depends on the temperature of the oil

• show the temperature of the oil as it enters the oil pressure pump.

MANIFOLD PRESSURE GAUGE

• used in piston aircraft engines to measure the pressure inside the induction system of an engine

FUEL PRESSURE

• at which there is sufficient fuel entering the pump to maintain desired output pressure, is a condition that requires the pilot’s immediate attention