0021: VFR squawk code for German airspace (5000 feet and below) - from 15 March 2007 replaced by the international 7000 code for VFR traffic.Shall not be used - is a non-discrete mode A code (Europe).Mode C or other SSR failure (in the UK).Military intercept code (in the U.S.).The use of the word "squawk" comes from the system's origin in the World War II Identification Friend or Foe (IFF) system, which was code-named "Parrot". Additionally, modern digital transponders are operated by buttons to avoid this problem. Pilots are instructed not to place the transponder in "standby mode" while changing the codes, as it causes the loss of target information on the ATC radar screen, but instead to carefully change codes to avoid inadvertently selecting an emergency code. This would momentarily have the transponder squawking a hijack code ( 7500), which might lead to more attention than one desires. For example, when changing from 1200 to 6501 (an assigned ATC squawk), one might turn the second wheel to a 5 (thus 1500), and then rotate the first wheel backwards in the sequence 1-0-7-6 to get to 6. Four octal digits can represent up to 4096 different codes, which is why such transponders are often called "4096 code transponders." Care must be taken not to squawk any emergency code during a code change. Thus the lowest possible squawk is 0000 and the highest is 7777. Squawk codes are four-digit octal numbers the dials on a transponder read from zero to seven, inclusive.
This allows easy identity of the aircraft on radar. A discrete transponder code (often called a squawk code) is assigned by air traffic controllers to uniquely identify an aircraft. Transponder codes are four digit numbers transmitted by the transponder in an aircraft in response to a secondary surveillance radar interrogation signal to assist air traffic controllers in traffic separation. Ident can also be used in case of a reported or suspected radio failure to determine if the failure is only one way and whether the pilot can still transmit or receive, but not both, e.g., "Cessna 123AB, if you read, squawk ident". This is often used by the controller to locate the aircraft amongst others by requesting the ident function from the pilot, e.g., "Cessna 123AB, squawk 0363 and ident". When radar equipment receives the IDENT bit, it results in the aircraft's blip "blossoming" on the radar scope. IdentĪll mode A, C, and S transponders include an "IDENT" button, which activates a special thirteenth bit on the mode A reply known as IDENT, short for "identify"".
Similarly, the Traffic Collision Avoidance System (TCAS) installed on large aircraft needs the altitude information supplied by transponder signals. Without the pressure altitude reporting, the air traffic controller has no display of accurate altitude information, and must rely on the altitude reported by the pilot via radio. Mode S transponders are compatible with transmitting the mode C signal, and have the capability to report in 25 foot increments. In the United States, this is known as a Mode C veil. Around busy airspace there is often a regulatory requirement that all aircraft be equipped with an altitude-reporting mode C or mode S transponders. Some lower-end altimeters do not normally have a built in encoder and so a modified Gray code, called a Gillham code, is used to pass altitude information to the transponder. īecause primary radar generally gives bearing and range position information, but lacks altitude information, mode C and mode S transponders also report pressure altitude. The pilot then selects the 0363 code on their transponder and the track on the radar screen of the air traffic controller will become correctly associated with their identity. * Note: The information on this list may change as new vehicle models and options come to the market.Main article: Aviation transponder interrogation modes OperationĪ pilot may be requested to squawk a given code by the air traffic controller via the radio, using a phrase such as "Cessna 123AB, squawk 0363". Half of the tag should be in the tinting, the other half out. Please contact the dealership where you purchased your car to see if your vehicle contains any of these features. Also, the following glass features may interfere with the E-ZPass signal and require alternative or exterior mounting: solar ray, solar tint, heated, heat reflected, insulated, Insta-Clear. In general, windshields that contain metal in the glass (metal oxide) and mirrors with compass or temperature readings may prevent the E-ZPass signal from being read properly.
The vehicles listed below have been identified as having special features that require an exterior License Plate Tag (LPT) or alternative placement as noted.