Date: Thu, 01 May 97 08:33:00 CDT From: Corkum D Capt 2OSS/OSTC <corkumd@oss2.barksdale.af.mil> Subject: Flying - A-10 follow-up Corkum D Capt 2OSS/OSTC <corkumd@oss2.barksdale.af.mil> "Both the A-10's transponder and the autopilot appeared to have been turned off. Perhaps there is a simple technical explanation why no one noticed anything at first." Let me try and fill in a few of the holes for non-flyers: When aircraft fly in close formation typically only the lead aircraft has a transponder turned on. This is due to limitations with Air Traffic Control (ATC) systems. These systems are designed to prevent two aircraft from getting too close together thereby preventing possible midair collisions. Unfortunately the computers can't distinguish between aircraft that are on a collision course and aircraft in formation that are intentionally close together. For this reason ATC operators often request wingmen to turn off their transponders. Once the A-10 dropped back he was not easily visible to the lead aircraft who would be concentrating on entering the bombing range, working coordination with ATC and the range controllers etc. Inside the range ATC no longer maintains operational control of the aircraft and would not be following any of the aircraft directly. The first indication of the aircraft missing would be a failure of the wingman to respond to a radio call. When this happened it would first be assumed that he was on the wrong frequency. The lead aircraft would try to find him on another frequency, then attempt to call him on the emergency frequency "Guard". When this failed the lead would likely assume that the wingman had radio problems and would attempt to locate him visually. Only after he failed to locate him visually would he begin to worry that something happened. His first thought would be that the aircraft had a major malfunction such as complete loss of electrical power, that forced the pilot to abort the mission and return to base, but also prevented him from calling to the lead aircraft. The other possibility would be that the aircraft was down due to pilot error or aircraft malfunction. The idea that the wingman simply took the aircraft would likely never occur to the lead pilot. The lead pilot at this point would abort his mission and attempt to ascertain what happened to his wingman. He would contact ATC and ask if they had transponder track on the aircraft or reports of an aircraft down. He would also perform a visual search of the area and attempt to call back to the home base to see if they knew what happened. By this time the rogue pilot may have been gone for at least 30 minutes and was actually 200 miles away. The reason ATC could not track him is a technical issue. Modern ATC radars rely primarily on the aircraft transponder to provide location and altitude information. The actual radar returns "know as raw data" are only used as a secondary means to track aircraft when their transponders have failed. This must be performed manually since the computer has no way to distinguish one radar return from another without the transponder. This method is only used when an ATC controller knows an aircraft transponder has failed and must be manually tracked. Since the A-10 was not supposed to have his transponder on, no-one would notice when he broke formation. Only after the fact when the FAA reviewed the taped radar returns were they able to piece together the likely course of the A-10. I hope this explained some of the more technical reasons for what happened. David Corkum PGP mail preferred Fingerprint: FE 90 1A 95 9D EA 8D 61 81 2E CC A9 A4 4A FB A9 Key available on BAL server, http://www-swiss.ai.mit.edu/~bal/pks-toplev.html --------------------------------------------------------------------- Steve Schear | tel: (702) 658-2654 CEO | fax: (702) 658-2673 First ECache Corporation | 7075 West Gowan Road | Suite 2148 | Las Vegas, NV 89129 | Internet: azur@netcom.com --------------------------------------------------------------------- "I know not what instruments others may use, but as for me, give me Ecache or give me debt."