View source for Joint precision approach and landing system

[[Image:LAAS Architecture.svg|thumb|300px|LAAS architecture, similar in concept to JPALS LDGPS fixed base category]]

In the [[United States Armed Forces]], the '''joint precision approach and landing system''' ('''JPALS''') is an all-weather system for precision guidance of landing aircraft. It is based on real-time differential correction of the [[Global Positioning System]] (GPS) signal, augmented with a local area correction message, and transmitted to the user via secure means. It is used on terrestrial airfields as well as the [[US Navy]]'s [[amphibious assault ship]]s and [[List_of_aircraft_carriers_of_the_United_States_Navy|aircraft carriers]] ([[Hull_classification_symbol|hull classifications]] LH and CVN, respectively).  

The onboard receiver compares the current GPS-derived position with the local correction signal, deriving a highly accurate three-dimensional position capable of being used for all-weather approaches via an [[Instrument Landing System]]-style display. While JPALS is similar to [[Local Area Augmentation System]], but intended primarily for use by the military, some elements of JPALS may eventually see their way into civilian use to help protect high-value civilian operations against unauthorized signal alteration.

==History==
[[Image:JPALS Tactical Prototype.jpg|250px|thumb|JPALS tactical prototype]]
The development of JPALS was the result of two main military requirements. First, the military needs an all-service, highly mobile all-weather precision approach system, tailorable to a wide range of environments, from shipboard use to rapid installation at makeshift airfields. Second, they need a robust system that can maintain a high level of reliability in combat operations, particularly in its ability to effectively resist jamming.

==Operation==
JPALS encompasses two main categories: SRGPS (shipboard relative [[GPS]]) and LDGPS (land/local differential GPS).  SRGPS provides highly accurate approach positioning for operations aboard ship, including aircraft carriers, helo and STO/VL carriers, and other shipboard operations, primarily helicopter operations.

LDGPS is further divided into three sub-categories: fixed base, tactical, and special missions. Fixed base is used for ongoing operations at military airfields around the world, while the tactical system is portable, designed for relatively short-term, austere airfield operations. The special missions system is a highly portable system capable of rapid installation and use by [[special forces]].

==Accuracy==
The accuracy of [[local area augmentation system]] (LAAS) is better than [[Instrument Landing System#ILS categories|CAT III ILS]] accuracy, and will provide horizontal and vertical resolutions of less than 1 m. Although the exact accuracy of JPALS will remain classified, it's estimated that JPALS will meet or exceed this accuracy for authorized users.

==Benefits==
The main benefit of JPALS is that it's a system that can be taken anywhere, anytime, providing a safe and effective way to conduct 24/7, all-weather, anti-jam instrument landing system capability to all authorized users, worldwide. A secondary benefit is a significant reduction in cost over current systems.

The naval version of JPALS transmits a signal that has a low probability of intercept; so it is unlikely that an enemy will detect the signal and trace it back to its source. The existing system, [[tactical air navigation]] (TACAN), is not encrypted or concealed in any way, which can reveal the location of the ship on which it is installed.  This is not acceptable in [[EMCON|emissions control]] (EMCON) or stealth conditions.

The increase in both accuracy and reliability will significantly enhance operations while reducing non-operational periods due to weather or adversarial efforts.

==See also==
*[[Local area augmentation system]] is a similar system for civilian usage.
*[[Wide area augmentation system]]
*[[Precision approach]]
*[[Instrument landing system]]
*[[Global Positioning System]]
*[[Differential GPS]]
*[[Microwave landing system]]
*[[Electronics_Technician_(United_States_Navy)|Electronics technician]]

==References==
* {{cite web
 |author=Federal Aviation Administration (FAA) 
 |date=February 27, 2004 
 |url=http://gps.faa.gov/Library/laas-f-text.htm 
 |title=Local Area Augmentation System (LAAS) Fact Sheet 
 |accessdate=November 20, 2005 
 |archiveurl=https://web.archive.org/web/20060118032723/http://gps.faa.gov/Library/laas-f-text.htm 
 |archivedate=January 18, 2006 
 |url-status=dead 
}}
* {{cite web
 | author=Department of Transportation and Department of Defense
 | date=March 25, 2002
 | url=http://www.navcen.uscg.gov/pdf/frp/frp2001/FRP2001.pdf
 | title=2001 Federal Radionavigation Plan
 | publisher=
 | accessdate=November 27, 2005
 }}

==External links==
* [http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/ FAA GPS Programs]
* [http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/laas/ FAA LAAS Fact Sheet]
* [http://waas.stanford.edu/research/jpals.htm Stanford JPALS Page] {{Webarchive|url=https://web.archive.org/web/20060427122246/http://waas.stanford.edu/research/jpals.htm |date=2006-04-27 }}
* [https://web.archive.org/web/20060311054600/http://www.raytheon.com/products/jpals/ Raytheon JPALS Product Page]
* [http://www.fas.org/man/dod-101/sys/ac/equip/jpals.htm FAS JPALS Page]
* [http://www.globalsecurity.org/military/systems/aircraft/systems/jpals.htm GlobalSecurity.org's JPALS Page]
* [https://web.archive.org/web/20140911053740/http://www.navair.navy.mil/index.cfm?fuseaction=home.displayPlatform&key=8559E3E9-42F1-4A08-876B-5F2E7FA6AAB2 US Navy information]
* [https://web.archive.org/web/20140911052320/http://www.navair.navy.mil/index.cfm?fuseaction=home.PhotoGalleryDetail&key=62593B59-C3A0-454F-8CA4-594D953A0005 US Navy images]

{{Satellite navigation systems}}

[[Category:Aircraft landing systems]]
[[Category:Military aviation]]
[[Category:Global Positioning System]]