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lower octane rating or performance number than is specified for the engine.
The pressure rise inside the cylinder caused by the fast-moving flame front can heat and compress
the unburned fuel-air mixture enough for it to explode, or release its energy faster than the engine can
accept it. This causes a rapid rise in cylinder pressure, excessive cylinder head temperature, and a decrease
in engine power.
Detonation is often confused with preignition but is not the same. See preignition.
DETRESFA (distress phase) (ICAO). The code word used to designate an emergency phase wherein
there is reasonable certainty that an aircraft and its occupants are threatened by grave and imminent danger
or require immediate assistance.
deuterium. An isotope of hydrogen which has one proton and one neutron in the nucleus. A normal atom
of hydrogen has one proton, but no neutrons in its nucleus.
Deutsch rivet. A type of hollow-shank, high-strength blind rivet. The rivet is put into the hole in the
structure, and a tapered pin is driven into the hollow shank. The pin expands the rivet so serrations on the
outside of the shank press into the sides of the hole and hold the rivet firmly in place.
developed width of a part (sheet metal layout). The width of the sheet metal cut to form a part. If an
angle, with legs of one inch and two inches, is to be formed of sheet metal, the developed width of the
metal will be less than three inches. This is because the metal does not go to the mold lines of the angle, but
goes around the corner in the bend radius.
The developed width of the metal is the sum of the flats plus the bend allowance. This is less than
the sum of the mold line lengths (MLL).
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 185
developer (dye penetrant inspection). A powder used to pull a penetrating dye out of a defect in a part
being inspected by the dye-penetrant inspection method.
The part is soaked in the penetrant. Then, all the penetrant is washed from its surface and the
surface is covered with the developer. The developer pulls any penetrant that has seeped into a defect to the
surface where it shows up as a visible mark.
deviation (magnetic compass error). An error in the indication of a magnetic compass, caused by local
magnetic fields within the aircraft. Deviation error, which is different on each heading, is minimized by the
technician compensating, or swinging, the compass.
A compass must be compensated so the deviation error on any heading is no greater than 10
degrees.
dew. Water that condenses out of the air and forms on the ground and on objects that are cooler than the air.
Dew usually forms at night when the ground cools as heat leaves it by radiation.
Dewar flask. A special container used to store liquid oxygen and liquid nitrogen. A Dewar flask has an
inner and an outer container, with the space between them evacuated to form a vacuum. This serves as a
thermal insulator and minimizes the amount of heat allowed to enter the container. The two surfaces within
the evacuated area are silvered to reflect heat away from the container walls.
dewaxed oil. A petroleum oil from which some of the solid hydrocarbons, or waxes, have been removed in
the refining process.
DEWIZ (distant early warning identification zone). An air defense identification zone (ADIZ) over the
coastal waters of Alaska.
dew point. The temperature below which air can no longer hold water in its vapor state. At the dew point
temperature, the relative humidity is 100% and water vapor condenses out of the air and forms visible
water — dew.
DF (direction finder) (navigation system component). A radio receiver equipped with a
direction-sensing antenna used to take bearings on a radio transmitter.
Specialized radio direction finders are used in aircraft as navigation aids. Others are ground-based,
primarily to obtain a fix on a pilot requesting orientation assistance or to locate downed aircraft. A location
fix is established by the intersection of two or more bearing lines plotted on a navigational chart, using
either two separately located direction finders to obtain a fix on an aircraft or by a pilot plotting the bearing
indications of his DF on two separately located ground-based transmitters, both of which can be identified
on his chart.
UDFs receive signals in the ultrahigh frequency radio broadcast band, VDFs in the very high
frequency band, and UVDFs in both bands.
ATC provides DF service at those air traffic control towers and flight service stations listed in the
Airport/Facility Directory and the DOD/FLIP IFR En Route Supplement.
DF approach procedure (air traffic control). An emergency approach procedure used under conditions
　
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