D

Departure
Before an aircraft may take off, the control tower has to issue a departure clearance, which the pilot must confirm.

Decibel (dB)
Named after Alexander Graham Bell, the inventor of the telephone, the decibel (dB) is used to indicate the intensity of a sound.  It is measured on a logarithmic scale.  This means that a 20-dB sound is actually 100 times more powerful than a 10-dB sound. However, the human ear does not respond to all sounds in the same way. That is why devices for measuring sound are often fitted with a filter that acts more like the human ear.  If a so-called A-weighted filter is fitted, the sound pressure is given in units of dB(A). A-weighted sound pressure has proven its usefulness and has become the international standard. With respect to aircraft noise, a change by 4 dB(A) corresponds to a doubling or halving of the acoustic energy.

Directs
A "direct", or direct routing, can be requested by the pilot and/or assigned by the air traffic controller. A direct means that permission is given to leave the nominal departure route. As a rule, directs are only permitted above defined altitudes, depending on the time of the day and aircraft type. Directs imply that areas are overflown which are not located below departure routes and normally not affected by overflights.

Go-around
A go-around is an aborted landing of an aircraft on final approach. It is not an emergency procedure. It is a normal procedure which  can become necessary for very different reasons. The pilot decides whether to initiate  a go-around. For the missed approach procedure, he will use clearly defined routes. The air traffic controller will integrate the aircraft going around as quickly as possible into the normal traffic flow.