71 diffusion
dew /dju/ noun drops of condensed moisture left on the ground overnight in cool places
dew point /dju p..nt/ noun the
temperature at which air is saturated with water vapour and condensation begins
COMMENT: Weather reports usually include the air temperature and dew point temperature. When the difference between temperature and dew point is small, there is a strong possibility of fog, clouds, or precipitation.
DF abbreviation direction finding
DFDR abbreviation digital flight data recorder DFR abbreviation departure flow regu-
lation
DFTI abbreviation Distance from touchdown indicator DH abbreviation decision height DI abbreviation direction indicator diagonal /da..n(.)l/ adjective 1.
joining two opposite corners of a rec-tangle 2. sloping halfway between the vertical and horizontal . Early aircraft were of the wire braced type of con-struction, the wire being superseded by tubular diagonal struts. . noun a line joining two opposite corners of a rec-tangle
diagram /da..rm/ noun an often simplified drawing showing the struc-ture or workings of something . The diagram shows a simple open-circuit system.
diagrammatic /da..r.mt.k/
adjective referring to something which is shown as a drawing of a system or structure . diagrammatic format in the form of a diagram
dial /da..l/ noun the face of an instru-ment showing a scale . A cup anemom-eter is connected to an instrument with a dial showing wind speed in knots.
diameter /da.m.t./ noun the dis-tance from one side of a circle to the other, passing through the centre . equatorial diameter the distance from the equator, through the centre of the Earth to the equator on the opposite side of the globe
diaphragm /da..frm/ noun a thin sheet of material used to separate parts or chambers . Some switches are oper-ated by a diaphragm which flexes under fluid or air pressure.
differ /d.f./ verb to be unlike . Track
and heading differ by the amount of drift. . Because the chart time and the departure/arrival times differ, it is nec-essary to consider the movement of any weather system which might affect the route.
differential /d.f.ren..l/ adjective
referring to things which react differ-ently when measured against a norm or standard . differential heating of the atmosphere the heating of the atmos-phere to varying temperatures depend-ing on the relative warmth of the land at the equator and the poles

differential expansion switch
/d.f.ren..l .kspn.(.)n sw.t./ noun a switch which operates on the principle that the coefficients of expan-sion of dissimilar metals are different
differentiate /d.f.ren.ie.t/ verb to
recognise the difference between two things; to show two things to be differ-ent . Some types of colour blindness make the sufferer unable to differentiate between blue and red.