Aircraft/Instruments, Engines and Systems

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Aircraft Instrumentation

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There are two parts to any instrument system—the sensing mechanism and the display mechanism. Information is relayed from the sensors to the indicators via electricity, or direct pressure sensing via pneumatic or oil-filler tubes. [1]

There are three basic kinds of instruments classified by the job they perform:

  • flight instruments
  • engine instruments
  • navigation instruments

There are also miscellaneous gauges and indicators that provide information that do not fall into these classifications, especially on large or complex aircraft. such as Flight control position, cabin environmental systems, electrical power, and auxiliary power units (APUs) for example, are all monitored and controlled from the cockpit. All may be regarded as position/condition instruments since they usually report the position of a certain moveable component on the aircraft, or the condition of various aircraft components or systems not included in the first three groups.

Flight Instruments

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Basic 6 instruments
Basic flight instruments arranged in a T

There are six main flight instruments in an old-style analog cluster.

The most common arrangement is referred to as a T arrangement, with Airspeed, Artificial Horizon, and Altimeter across the top and heading indicator at the bottom. The other two instruments are the turn coordinator and vertical speed indicator.

Engine Instruments

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In a gas turbine engine, engine instruments generally indicate fuel flow and temperature indicators, as well as engine speed in percentage of normal shaft speed (N1 and/or N2). In a reciprocating engine, instruments generally indicate oil pressure and temperature, cylinder head temperature and exhaust gas temperature for one (usually the hottest-running) or sometimes all cylinders, and sometimes manifold absolute pressure, or MAP.

Engine Instruments in ATR 72 Cockpit
engine-indicating and crew-alerting system (EICAS)

On the right are a set of old fashioned analog gauges, and on the left is a modern Engine-Indicating and Crew-Alerting System (w:EICAS) found on a modern airliner or small jet, which only displays the information the pilot needs to see. This also replaces the w:Annunciator panel found on older planes, where a system failure triggers the corresponding annunciator to illuminate, as well as either the Master Caution if an amber-coloured annunciator is triggered, and the Master Warning light if a red-coloured (critical) system annunciator is triggered.

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Cessna 172 Instrument panel - Navigation
Cirrus Perspective Glass Panels

The navigation instruments include the basic 'wet' compass, Gyro Compass and Heading Indicator gauge, VOR w:Course Deviation Indicator(CDI) w:Radio direction finder(RDF) and w:Automatic Direction Finder (ADF) indicator combined with NAV/COM radios set to the frequencies of VOR and ADF stations.[2], w:Horizontal Situation Indicator(HSI) up to a w:Electronic Attitude Director Indicator (EADI), or w:Electronic Flight Instrument System (EFIS) The older navigation gauges to the right of the 'basic six' are the Dual VOR/ADF Course Deviation Indicator(CDI) (Nav1) which also serves as the w:Instrument Landing System(ILS) Localizer and Glidescope indicator, a single VOR CDI(Nav2) and an ADF Indicator. [3] with the VOR NAV1 and NAV2 radios, and ADF receiver which can be tuned to an ADF frequency or a non-directional (radio) beacon (NDB). The w:Instrument Landing System (ILS) is used to land the aircraft in poor visibility.

The same radio navigation is used in the Cirrus Perspective Glass Cockpit, but is presented in a more user-friendly manner, combined with modern GPS navigation. You can navigate a flight completely from runway to runway with GPS, but you still need to set up the NAV-COM radios for ILS landings.

Aircraft Powerplants

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Reciprocating Engines

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  • Normally Aspirated
  • Turbo Normalized
  • Ground Boosted
  • Turbo Supercharged

TurboProp Engines

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Turbine Engines

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Turbine engine sections are divided into cold section and hot section. Cold section is the fan and

Hot section is turbine.

Air sources are divided into:

  • Primary Air
  • Secondary Air

Primary air in a turbine engine is the air used directly for combustion. Secondary air, in the turbine section, is air used for cooling.


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The turbojet is an airbreathing jet engine, usually used in aircraft. It consists of a gas turbine with a propelling nozzle. The gas turbine has an air inlet, a compressor, a combustion chamber, and a turbine (that drives the compressor). The compressed air from the compressor is heated by the fuel in the combustion chamber and then allowed to expand through the turbine. The turbine exhaust is then expanded in the propelling nozzle where it is accelerated to high speed to provide thrust.[1] Two engineers, Frank Whittle in the United Kingdom and Hans von Ohain in Germany, developed the concept independently into practical engines during the late 1930s.

Turbojets have been replaced in slower aircraft by turboprops because they have better range-specific fuel consumption. At medium speeds, where the propeller is no longer efficient, turboprops have been replaced by turbofans. The turbofan is quieter and has better range-specific fuel consumption than the turbojet. Turbojets are still common in medium range cruise missiles, due to their high exhaust speed, small frontal area, and relative simplicity.

Turbojets have poor efficiency at low vehicle speeds, which limits their usefulness in vehicle other than aircraft. Turbojet engines have been used in isolated cases to power vehicles other than aircraft, typically for attempts on land speed records. Where vehicles are 'turbine powered' this is more commonly by use of a turboshaft engine, a development of the gas turbine engine where an additional turbine is used to drive a rotating output shaft. These are common in helicopters and hovercraft. Turbojets have also been used experimentally to clear snow from switches in railyards.


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Modern jet aircraft are low-bypass or high-bypass. The newer aircraft are usually high-bypass, more of the air that enters the front of the engine is used by the fan to provide thrust, while a smaller amount is used to drive the turbine and goes out the exhaust.

Aircraft Systems

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There are many systems to an aircraft

  • Landing Gear and struts
  • Hydraulic and Pneumatic
  • Controls
  • Navigation/Communication
  • Electrical/Lights
  • APU
  • Fuel Systems
  • Cabin Environmental Systems
  • Fire Protection
  • Ice and Rain Protection

See Also

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Introduction to aircraft components

Federal aviation regulations

Topic:Flight Instruments

Topic:Aircraft structures

Topic:Aerospace engineering


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Aviation Maintenance Resources for technicians and students

FAA-H-8083-15B, Instrument Flying Handbook

The FAA’s Regulatory & Guidance Library contains many aviation regulatory, certification, and safety information documents. This is the starting point for AMTs to do much of their research needed to do daily maintenance tasks, especially with General Aviation.

FARs or title 14 of the Code of Federal Regulations The portion of 14 CFR containing what was formerly known as the Federal Aviation Regulations can be found on the Web site. 14 CFR contains regulations designed to promote aviation safety, and govern all aviation activities in the United States.


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  1. AMT Airframe Handbook Chapter 10 - Aircraft Instrument Systems
  2. Instrument Flying Handbook ch9. Navigation Systems
  3. AMT Airframe Handbook pg 11-41 Radio Navigation