{{Short description|Sonar location system}} 300px|thumb|right|How a towed pinger locator is deployed
A '''towed pinger locator''' is a water-borne device used to locate the sonar "ping" from the underwater locator beacon which is fitted to the Cockpit Voice Recorders and Flight Data Recorders installed in commercial airliners.<ref>{{cite web|title=Towed Pinger Locator 25 Specifications|url=http://timedotcom.files.wordpress.com/2014/03/tpl-25_specsheet.pdf|publisher=Phoenix International|access-date=2014-03-24|archive-date=2014-03-25|archive-url=https://web.archive.org/web/20140325041721/http://timedotcom.files.wordpress.com/2014/03/tpl-25_specsheet.pdf|url-status=dead}}</ref> They can locate pingers at depths of up to {{convert|20,000|ft|m}} underwater.<ref name="USN TPL 25 Fact File">{{cite web|title=Towed Pinger Locater 25 Fact File|url=http://www.navy.mil/navydata/fact_display.asp?cid=4300&tid=400&ct=4|archive-url=https://web.archive.org/web/20101205011341/http://www.navy.mil/navydata/fact_display.asp?cid=4300&tid=400&ct=4|url-status=dead|archive-date=December 5, 2010|work=US Navy Fact Files|publisher=United States Navy|accessdate=26 March 2014|date=22 November 2013}}</ref>
== Description == [[File:Navy Towed Pinger Locator.jpg|250px|thumb|right|United States Navy Towed Pinger Locator 25 system]]
The locator is mounted in a hydrodynamic shell, or "tow fish", connected by winch behind a surface vessel across the search area. The locator listens for the sound emanating from the beacon or "pinger". Once located, the beacon and its attached recorders can be retrieved by divers, submersibles or remotely operated vehicle (ROV), depending on depth. A model currently used by the United States Navy is the TPL-25, which has a weight of {{convert|70|lb|kg}} and a length of {{convert|30|in|mm}}; it is generally towed at {{convert|1-5|knot|km/h|0}}.<ref name="USN TPL 25 Fact File" />
Most beacons transmit a pulse once a second at 37.5 kHz.<ref>{{cite news|title=Navy prepares black box locator to search for missing Malaysia Airlines flight|url=http://wtkr.com/2014/03/24/navy-prepares-black-box-locator-to-search-for-missing-malaysia-airlines-flight/|last=Knight|first=Matt|newspaper=WTKR|date=March 24, 2014}}</ref><ref name="USN TPL 25 Fact File" />
The hydrophone must be positioned below the thermocline layer which reflects sounds, either back to the surface or back to the ocean floor. Since the pinger signal is relatively weak, the hydrophone must be within a nautical mile (about {{convert|6080|ft|m|-1}}) to detect it. The hydrophone is typically deployed about {{convert|1000|ft|m}} above the ocean floor, where it can scan a swath approximately {{convert|12000|ft|m}} wide, on a flat, level surface.<ref>{{cite web |url=http://www.wday.com/event/article/id/95224/group/News/ |title=Only days left before Malaysia airlines flight 370's black box dies | WDAY | Fargo, ND |publisher=WDAY |date=2014-03-30 |accessdate=2014-04-05 |url-status=dead |archiveurl=https://web.archive.org/web/20140407072117/http://www.wday.com/event/article/id/95224/group/News/ |archivedate=2014-04-07 }}</ref>
== See also == {{Portal|Aviation}} * Flight recorder * Emergency position-indicating radiobeacon station (ELTs) * Air France Flight 447 * Korean Air Lines Flight 007 * List of unrecovered flight recorders * Malaysia Airlines Flight 370 * Towed array sonar
== References == {{reflist}}
Category:Aircraft emergency systems Category:Beacons