On Glide Path, On Course

An air traffic controller is reflected in the precision approach radar scope as he directs an aircraft. (Photo courtesy of the National Archives)

 On Glide Path, On Course
Past, Present and Future

By Capt. Brett Easler and Cmdr. Bruce Herman, USN (Ret.)

“On glide path, on course” is a phrase from apprentice and journeyman controllers alike that most Naval Aviators hear time and time again. In many cases, those were reassuring words when the weather was obscured with zero visibility and fog, no other precision approach landing (PAL) aids were available, fuel was low or no suitable divert fields were within range.

Cutting a path through fog, rain and snow, the ground controlled approach (GCA) has long been the Navy and Marine Corps’ PAL system. Whether ashore, afloat or in the Marine’s austere expeditionary environment, the talk-down approach has been the standard by which we train, man and equip our controllers to meet the warfighter mission.


The naval air traffic control (ATC) community serves with great pride and a rich history. Since Naval Aviation’s earliest days, ATC has functioned as a critical element of the Naval Aviation mission. Invariably, the evolution of ATC parallels the evolution of the aircraft.

Sailors operate a ground controlled approach unit on Guam in 1946. (Photo courtesy of Cmdr. Bruce Herman, USN (Ret.))

On 22 December 1942, Ens. Bruce Griffin soaped over the windshield of an SNJ Texan Navy trainer so he was unable to see forward out of the windscreen. Griffin took off from NAS Quonset Point, R.I., and made the first blind landing using GCA MK-1. Lt. Evan Aurand was in the tower and brought Griffin in, making him the first true GCA controller. Nine days later on 1 January 1943, GCA was called into emergency use for the first time when a snowstorm closed Quonset Point approximately 30 minutes before the arrival of a flight of PBY Catalinas.

In May 1943, Navy operational personnel successfully field tested the laboratory model of the GCA system developed at the Massachusetts Institute of Technology’s Radiation Laboratory. Shortly thereafter, the Chief of Naval Operations (CNO) approved GCA as the Navy’s standard talk-down approach control system and field training of GCA crews commenced at NAS Gainesville, Ga.

Specialist yeoman, quartermaster and radarman ratings were trained in an eight-week course where each student controlled approximately 150 live approaches using the AN/MPN-1 radar and SNB aircraft. The specialist yeoman rating represented control tower operators and was used from 1943 through 1948.

When initially commissioned, GCA was a mobile system capable of deploying to support tactical operations, as well as remaining at fixed locations. Advantages of the system included its accuracy and the absence of a requirement for a dedicated avionics package in the aircraft. A trained pilot equipped with a functioning radio was able to make an approach and landing in adverse weather conditions. A number of locations had published GCA weather minimums of 100 foot ceiling and one-quarter mile visibility, with terrain and runway/approach lighting systems effecting published minimums. Disadvantages of the GCA system included its size and weight, which affected its transportation via airlift/sealift, and the increased number of personnel required to operate and maintain the system.

AN/MPN-1 mobile ground-controlled approach radar systems were integral precision landing equipment for air traffic controllers during World War II and into the 1950s. (Photo courtesy of Cmdr. Bruce Herman, USN (Ret.))

In March 1962, the Navy’s ATC schools and its 11 courses moved from Naval Air Technical Training Unit Olathe, Kan., to form the Air Traffic Control Schools Division of Naval Aviation Technical Training Center (NATTC) at NAS Glynco, Ga. The initial GCA course lasted 10 weeks and allowed each student to make 150 live runs using the AN/MPN-5 radar for synthetic training and the AN/CPN-4 radar for live training. The training was further refined to only six weeks, during which students made approximately 200 synthetic runs and 55 live runs using S-2 Tracker aircraft.

Students also received flight skins and flew in the right seat of the S-2 while listening and watching the pilot conduct GCA approaches. This approach to training provided the student controller with an appreciation of the pilot workload during a GCA. On 30 April 1974, the last S-2 live-run flights for GCA training took place in Glynco, ending a practice started in 1944. More than 290,000 approaches were made since training began at NATTC in 1962. ATC schools have resided at NATTC Pensacola, Fla., since April 1996 after a 20-year layover at NATTC Millington, Tenn.

In the early 1970s, GCA units merged with the air station ATC division into a single organization. The result of this transition was the air traffic control facility (ATCF). Before adoption of the ATCF concept, the staffing level for a GCA unit consisted of 15 controllers, three technicians, one engineman and two officers: an officer-in-charge and an approach controller.


An air traffic controller communicates with an aircraft at NAS Joint Reserve Base Willow Grove, Pa., 21 May 2004. (Photo by Journalist Third Class David P. Coleman.)

Navy and Marine Corps air traffic controllers now provide talk-down services at 31 air stations using the AN/FPN-63 precision approach radar (PAR); carriers use the AN/SPN-46 automatic carrier landing system for mode III approaches; and LHDs or LHAs use the AN/SPN-35 PAR. The nine Marine Corps ATC detachments also deploy the AN/TPN-31A air traffic navigation, integration and coordination system in support of humanitarian, disaster and contingency operations in every clime and place. Up to 160,000 talk-down approaches are conducted annually across the DoN. The number of GCAs have declined during the last 20 years, however, as a result of instrument landing system (ILS) installations, reduced flight operations and increased simulator time for the aircrew.

The DoN has installed 14 ILS (MK-1F and MK-20A) systems as site-specific operational requirements to support aircraft with ILS avionics. The first four systems went to NAS Adak, Alaska, (installed September 1989); NSF Diego Garcia, British Indian Ocean Territory (installed in August 1992); NAS Kingsville, Texas, (installed in September 1993); and Amchitka Island, Alaska. The ILS provides a PAL system compatible with shore-based multi-engine aircraft and a means to accomplish proficiency training at home stations and bases.

During the summer of 1994, both the CNO and the Chief of Staff of the Air Force approved a joint Mission Need Statement, which identified the requirement for a rapidly deployable, adverse weather and terrain, day/night, survivable and interoperable precision approach landing capability (PALC) system. The subsequent analysis of alternatives, updated in November 2005, recommended differential global positioning system technology as the preferred solution, which is now known as the Joint Precision Approach and Landing System (JPALS).

Until March 2013, JPALS was envisioned as the single solution for meeting the PALC requirement for all service branches in any operating environment, eliminating the requirement for multiple and/or varying PAL systems. JPALS Increment 1 was developed for sea-based application, and has completed initial sea-based testing while successfully conducting more than 70 auto-land approaches with pin-point accuracy using a modified F/A-18C Hornet. JPALS will become part of the ATC suite on aircraft carriers and amphibious assault ships in support of the F-35B/C Lightning II by the end of the decade.

Given the current fiscal environment, the Director, Air Warfare (OPNAV N98), ordered an extensive evaluation of the DoN PALC roadmap. The evaluation, performed by OPNAV N980A and the Naval Air Traffic Management Systems program office, reviewed multiple courses of action to ensure all-weather landing capability continues in support of Naval Aviation, while closing the interoperability gaps experienced under the current family of systems used to satisfy the DoN PALC requirement.

In June 2013, the Navy Resources and Requirements Review Board directed the continuing development of JPALS for aircraft carriers, amphibious assault ships and installation of ILS ashore through sundown of PAR by 2030, when ILS aircraft integration is scheduled for completion. As a part of the roadmap, existing AN/FPN-63 PAR systems ashore will receive upgrades to ensure service life until transition to the ILS is complete. A landing system upgrade program was also initiated to enhance the availability and sustainment of both the AN/SPN-46 and AN/SPN-35 sea-based precision radars.


We are at decision height and the PALC roadmap for Naval Aviation is “on glide path, on course” to replace PAR ashore with instrumented capability in the cockpit. The long-standing tradition of “Airman Timmy and Lance Corporal Jimmy” in the pilot’s headset giving course corrections and trend information will cross landing threshold one last time in the next decade.

So what’s the bottom line? Carriers will have AN/SPN-46 for currently configured aircraft and JPALS for the F-35C, while amphibious assault ships will have AN/SPN-35 for currently configured aircraft and JPALS for the F-35B. Both aircraft carriers and amphibious assault ships will continue to use AN/SPN-41 (Bullseye) as a backup and have the talk-down approach available if all else fails. Ashore, the AN/FPN-63 will sunset when the fielding plans for ILS air station installations and the aircraft avionics upgrades are complete. The introduction of JPALS and establishing ILS as the primary PALC will be the foundation for future aircraft avionics development and integration.

Until the PALC roadmap meets full operational capability, the GCA will be available until all aircraft within the Navy and Marine Corps inventory are capable of an unassisted instrument approach using a cockpit needles display.

This is an age of instant history when the startling innovations of yesterday become the anachronisms of today. Perhaps no place is this more apparent than in Naval Aviation. After more than 70 years of service with thousands of saves recorded in both civil and military records alike, it is time to bid farewell to a legend: a landing system that safely brought home Panthers, Banshees, Skyraiders, Cougars, Furies, Phantoms, Corsairs, Traders, Trackers, Tracers, Tomcats, Neptunes, Orions, Aries, Hawkeyes, Hornets, Seahawks, Vikings, Prowlers and Growlers in zero-zero conditions. As the era of GCA ashore concludes and the comforting phrases “approaching glidepath, begin descent” or “over landing threshold, on course” are no longer heard in headsets, the next-generation PALC systems will continue the Navy and Marine Corps ATC tradition of bringing our aircrew back safely.


Capt. Easler is retiring this fall after 36 years of active duty, serving his final tour on the staff of Director, Air Warfare (N98) as the Director, Naval Airspace and Air Traffic Control Standards and Evaluation Agency. Cmdr. Herman is also an air traffic control limited duty officer who retired in 2003 after 33 years of service.