Dead reckoningreckoning noun navigation using calculations based on airspeed, course, heading, wind direction and speed, ground speed, and time o In the early stages of practical navigation, the student pilot navigates by using dead reckoning. Abbreviation DR (note: The term comes from ‘deduced’ reckoning or ‘ded’ reckoning.)
de-aeratornoun a device to remove gas from a liquid de-aerator traynoun a device in the lubrication system to remove air bubbles from oil dealnoun □ a great deal a large amount of, a lot of o A great deal of damage was done to the aircraft as a result of the fire. ■ verb to handle or manage o A computer can deal with the constant inputs required to control an unstable aircraft.
debrisnoun scattered broken pieces o Before running up the engine, check that the aircraft is on firm ground and that the area is free of stones and other debris. o The aircraft exploded in mid-air, spreading debris over a wide area of the countryside.
decalnoun picture, letters or digits printed on adhesive paper, which is transferred onto a surface and may be peeled away o A red decal with AVGAS 100LL in white letters indicates the type of fuel to be used.
decelerate‘ verb to slow down o Reverse thrust and brakes help to decelerate the aircraft after landing. Opposite accelerate decelerationnoun slowing down o Anti-skid braking systems units are designed to prevent the brakes locking the wheels during landing, thus reducing the possibility of wheel skid caused by the sudden deceleration of the wheel. Opposite acceleration
decimalnoun a decimal fraction ■ adjective □ decimal fraction a fraction as expressed in the decimal system o 0.50 is a decimal fraction that is equal to 1/2. □ correct to three places of decimal or to three decimal places correct to three figures after the decimal point o 2.754 is correct to three decimal places, 2.7 is correct to one decimal place.
decimal notationnoun the method of writing a number in the decimal system o The fraction 3/4 can be written as 0.75 in decimal notation. o Prices and number are normally written using decimal notation. o He finds it difficult to understand how the computer works because it uses binary not decimal notation.
Comment: The decimal point is used in the USA and Britain. In most European countries a comma (,) is used to show the decimal, so 4,75% in Germany is written 4.75% in Britain.
decision heightnoun the altitude at which, during an ILS landing approach, a pilot must decide whether to land or carry out a missed approach o The pilot waited until she was at decision height before initiating the missed approach procedure.
Comment: An ILS approach generally has a decision height of 200 ft (60 m) above ground level.
decknoun the floor of a ship or aircraft decodeverb to change coded information into readable form o Incorrectly spaced information pulses can result in failure by the ground station to decode the aircraft information.
decoder‘ noun a device used to decode signals from the air traffic control radar beacon system o The aircraft receiver is set to the required frequency and linked to a selective call system decoder which has a 4-letter code.
decrease nouna lessening or reduction o A decrease in power results in the aircraft descending. ■ verb to become less, to fall o Air density and pressure decrease with an increase in altitude. ► opposite (all senses) increase
deduceverb to work some thing out in the mind using information provided o Sometimes, it is possible to estimate the depth of the layer of mist or fog from the ground observations and hence to deduce the ground range from any height.
define‘ verb 1. to give an exact explanation, as in a dictionary □ it is not easy to define the word it is difficult to say exactly what the word means 2. to set the limits of something o Cloud tops are very difficult to define.
definitionnoun an exact explanation of what a word or expression means o The definition of a year is the time taken for a planet to describe one orbit around the sun. □ by definition understood by the use of the word itself o A sphere is, by definition, round.
deflateverb to allow air to escape from something, so that it becomes smaller or collapses. Opposite inflate □ to deflate a tyre to allow the air to escape from a tyre deflationnoun the act of allowing air to escape from something, so that it becomes smaller or collapses o Deflation of a tyre is done by depressing the valve.
deflectverb 1. to cause an object to move away from a neutral or central position o During an out-of-bal-ance turn, the ball in the slip indicator will be deflected to the left or right. 2. to move a moving object, gas or liquid away from its intended path o In an open-cockpit aircraft, the windshield deflects the airflow over the pilot’s head.
deflectionnoun 1.movement away from a central or neutral position o Full deflection of the ailerons is sometimes needed on takeoff to counteract a crosswind. 2. the movement of a moving object, gas or liquid away from its intended path o In the southern hemisphere the deflection of wind at the equator is to the left.
deformationnoun a change of the correct shape caused by stress o Deformation of wing panels may be an indication of serious structural damage. deg abbreviation degree degradationnoun a decrease in quality o Degradation of the radio signal sometimes makes it impossible to understand the message.
degreenoun 1. a level,amount or quantity □ the degree of compression the amount of compression □ a high degree of safety a high level of safety □ to a greater degree more than □ to a lesser degree less than 2. a unit of temperature o twenty degrees Celsius (20°C) o twenty degrees Centigrade (20°C) o seventy degrees Fahrenheit (70°F) 3. a unit of measurement of an angle equal to 1/360th of a circle – each degree is divided into 60 minutes and each minutes into 60 seconds o Make a turn to the right at a bank angle of 30°. □ an angle of 90° a right angle 4. a unit of direction as measured on a compass o east = 090° o west = 270° degrees truenoun degrees of direction measured from true north, not magnetic north. Also called true degrees. Symbol °T dehydrationnoun an unwanted and sometimes dangerous loss of water from the body o Dehydration can be avoided by drinking plenty of water.
The ground crew de-iced the aircraft prior to take-off.
delaynoun a period after the expected time that you have to wait before something happens, the length of time by which something is late o By day, the presence of cloud can cause a delay in clearance of fog. ■ verb 1. to make late, to cause to be late o Take-off was delayed because of fog. 2. to put something off until later o He delayed telling her the news until they had landed.
delayed-actionadjective in which there is an unusual passing of time between stimulus and response o The door is fitted with a delayed-action lock which operates one minute after the power has been switched off.
demandnoun 1. a need or use caused by necessity □ high current demand on a generator a situation requiring the generator to produce a lot of electricity 2. a request which is made firmly □ on demand when asked for or ordered o A computer will produce, on demand, a flight plan giving the optimum route, levels and fuel. ■ verb 1. to require as a necessity o Higher operating weights of modern aircraft demand an increase in the number of wheels fitted to the landing gear. 2. to ask firmly o He demanded an explanation.
demonstrateverb to show by clear example or explanation o Torricelli first demonstrated that the atmosphere has weight. o It will be demonstrated in chapter 12 that turbulence is associated with strong winds.
denseadjective 1. referring to a substance which is closely compacted □ dense fog thick fog 2. referring to the amount of mass of a substance for a given unit of volume o Air which contains water vapour is less dense than air which does not.
density altitudenoun the pressure altitude corrected for non-ISA temperature comment: Density altitude is a very important factor in calculating aircraft performance because of its effect on engine performance, time to reach takeoff speed (and therefore length of take-off run) and rate of climb.
departmentnoun a separate part of a complex whole, especially of an organisation departure‘ noun 1. the act of leaving □ departure time the time when an aircraft becomes airborne 2. the distance between two meridians at any given latitude departure lounge
noun a place on the map representing the place from which a flight begins departuresnoun the part of an airport that deals with passengers who are leaving dependverb 1. to be controlled or affected entirely by something o Whether or not an object can be seen by aircrew at a given distance will depend on factors such as size, shape and colour of the object. o If an aircraft ditches in the sea, early rescue depends on rapid location of survivors. 2. to rely on o Pilots depend on air traffic controllers to help them conduct a safe flight.