SSR EHS and ELS RNAV

Elementary Surveillance (ELSELS —Elementary Surveillance) and Enhanced Surveillance (EHSEHS —Enhanced Surveillance - which sends the Downlink Aircraft Parameters, or DAPDAP —Downlink Aircraft Parameters) are two of the most important components in the new Mode S system, allowing a whole wealth of data to be transmitted to ATCATC —Air Traffic Control units, allowing for much greater spatial awareness, and therefore improved safety. In terms of the components of each, these are simply facts to be learned, but the systems that send out this information will undoubtedly play a major part in commercial aviation for some time to come. The list of features are as follows:

Elementary Surveillance (ELSELS —Elementary Surveillance):

• Automatic reporting of aircraft identity
• Transponder capability report
• Altitude reporting +/- 25 ft
• Flight status: in the air or on the ground
• Datalink of 56 bit message

Enhanced Surveillance (EHSEHS —Enhanced Surveillance, DAPDAP —Downlink Aircraft Parameters):

• Magnetic Heading
• Indicated Airspeed
• Mach Number
• Vertical rate
• Roll Angle
• Track Angle Rate
• True Track Angle
• Groundspeed
• Selected Altitude