The aforementioned metal detector reacts only if it detects a metal object on the body of a person passing through the device. However, not only metal objects are a threat for aviation transport. There is an increasing commercially available materials that are equally durable as metal and replacing it in everyday household activities. For example, ceramic knives are equally effective as traditional metal knives and are undetectable using WTMD. Various types of plastic items are
also good replacements for objects listed in the current legal regulations as prohibited onboard an aircraft. Also, the 3D technology has become available, which allows for printing any object in plastic and such object may be brought onboard an aircraft to perform an act of unlawful interference.The same problem applies to explosive materials, which do not contain any metal elements and will not trigger the traditional WTMD, which may be detonated using generally available (even in the restricted area of the airport) items that may be carried onboard a plane.
Of course a terrorist attack conducted this way will in most cases become a suicide attack but given the experiences of the latest terrorist attacks this mode of operation must also be taken into consideration.
An effective method to detect dangerous prohibited items is security manual control. Undoubtedly the greatest effectiveness is achieved by performing a manual control of all passengers; however it is impossible due to the throughput of the airport. The legal regulations require the manual control to be performed randomly. Taking into consideration the operational needs as well as the risk analysis of the susceptibility of a country to acts of unlawful interference a set minimum frequency of security manual controls is established. Of course if there is a suspicion that the particular passenger may attempt to bring a prohibited item onboard a plane then a detailed manual control must be performed.
As part of this study a survey was conducted in June 2014 among the persons responsible for the security policy at airports. Based on this survey we established the Frequency of manual controllinguistic input variable as presented in Fig. 4.
As it has already been mentioned, the variable Frequency of manual control describes the total frequency of manual control that is the aggregate of WTMD triggering events and additional controls. The first value depends on the WTMD’s sensitivity that may be set for the WTMD. If the sensitivity is increased the number of triggering events which require manual control is also increased. The number of additional controls is established by the entity managing the process of security control at an airport.