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The Need For Improved Helicopter Navigation Systems

The Need For Improved Helicopter Navigation Systems


CSC 1992









Title: The Need For Improved Helicopter Navigation Systems



Author: Major C.W. D'Ambra, United States Marine Corps



Thesis: The navigation equipment on board Marine Corps

helicopters, tasked to fly in support of MEU(SOC) missions,

Is inadequate to meet the demanding mission requirements.

The Marine Corps must move aggressively to procure advanced

navigation systems for its helicopters, seeking both short

and long-term solutions.



Discussion: The Marine Expeditionary unit (Special

Operations Capable) (MEU[SOC]), forward deployed, is the most

responsive Marine Air-Ground Task Force (MAGTF) In the Marine

Corps. Missions of the MEU(SOC) include Noncombatant

Evacuation Operations (NEO), clandestine recovery operations,

Tactical Recovery of Aircraft and Personnel (TRAP),

in-extremis hostage rescue, airfield seizures, and the

seizure of static Gas/Oil Platforms (GOPLATS).


FMFPR 2-12 indicates that the most important capability

of the MEU is its ability to conduct quick reaction long-

range raids over-the-horizon during periods of darkness and

adverse weather conditions. Unfortunately, the majority of

aircraft tasked to fly on these missions still rely on the

same type equipment that was installed on the Navy RH-53Ds

used in the Iranian Rescue-Mission twelve years earlier. The

Holloway Report on that mission, referring to that navigation

equipment, indicates that the helicopters were "austerely



A review of recent history shows that the opportunities

to employ the MEU(SOC) are increasing, along with the risk,

but installed helicopter navigation systems are not keeping

pace. The system currently offering the greatest potential

for improved navigation capabilities is the Global Positioning

System (GPS). Although only available in limited quantities,

GPS receivers used during Operation Desert Shield/Desert

Storm received glowing reviews. In addition to advanced

navigation systems being developed for the military, several

commercial low-cost GPS's are currently available which could

provide an interim solution.


The Marine Corps cannot afford to needlessly jeopardize

the success of the demanding missions assigned to the

MEU(SOC) due to inadequate navigation equipment when the

technology exists to improve it today!









THESIS STATEMENT. The navigation equipment on board Marine

Corps helicopters, tasked to fly in support of MEU(SOC)

missions, is inadequate to meet the demanding mission

requirements. The Marine Corps must move aggressively to

procure advanced navigation systems for its helicopters,

seeking both short and long-term solutions.



I. Marine Expeditionary Unit (Special Operations Capable)

A. Background

B. Missions and Requirements


II. Current Helicopter Navigation Systems

A. Low-frequency/Automatic Direction Finding Set (LF/ADF)

B. Tactical Air Navigation (TACAN) System

C. Long-range Navigation (LORAN) System

D. Omega Navigation System (ONS)


III. Examples of Equipment Shortcomings

A. Beirut, Lebanon

B. Operation Eastern Exit

C. Operation Provide Comfort


IV. Advanced Navigation Systems

A. Global Positioning System (GPS)

1. System Overview

2. TRIMPACK -- An Immediate Solution

3. Civilian Options

B. Future Systems for the Military

1. Position, Location, Reporting System (PLRS)

2. Doppler Navigation System (APN-217)

3. Omega Navigation System Upgrade W/GPS

4. Miniature Airborne GPS Receiver (MAGR)


V. Procurement, Introduction and Training Considerations






The Marine Expeditionary Unit (Special Operations


Capable) (MEU(SOC)) embarked aboard Navy amphibious shipping,


is the smallest forward-deployed Marine Air-Ground Task Force


(MAGTF) and is considered to be the most responsive MAGTF in


the Marine Corps. The MEU(SOC) is the immediate response,


on-scene, sea-based Marine component of the fleet commander's


amphibious and power projection forces. The MEU is normally


composed of a reinforced infantry battalion -- Battalion


Landing Team (BLT) as the Ground Combat Element (GCE), a


composite helicopter squadron as the Aviation Combat Element


(ACE), and a MEU Service Support Group (MSSG) as the combat


Service Support Element (CSSE). Advanced training and the


addition of specialized equipment enhances the individual


skills and unit capabilities required for the performance


of MAGTF special operations, thus adding the "SOC"


designation.(11:31-36) In addition to being capable of


conducting amphibious operations of limited scope, the


MEU(SOC) is capable of conducting a variety of special


operations to include Noncombatant Evacuation Operations


(NEO), Clandestine recovery operations, Tactical Recovery of


Aircraft and Personnel (TRAP), in-extremis hostage rescue,


airfield seizures, and the seizure of static Gas/Oil


Platforms (GOPLATS). (13:25) FMFRP 2-12 states,


Most important is the MEUs capability to conduct

quick reaction long-range amphibious raids over-

the-horizon without electronic emissions, during

periods of darkness, and under adverse weather or

sea conditions with 6-hour notice. (11:33)


The primary means of transportation for many of these


missions is the embarked Marine Corps helicopters. Due to


the nature of these missions, they are most often conducted


under the cover of darkness and require pin-point accuracy


and split-second timing. Aircraft arriving early, late, or


not at all due to navigation problems could have dire


consequences for the forces on the ground and/or the


civilians/hostages that are the focus of a mission. In


addition to the potential loss of life from a failed or


aborted mission, the political implications must be


considered. Although not a direct result of navigation


problems, the Iranian hostage rescue mission in 1979 clearly


demonstrates the possible national and international


political ramifications from a failed mission. In the


Holloway Report on the Iranian Rescue Mission, investigators


indicated that the helicopters used were "austerely


prepared," referring to the fact that they were not equipped


with state-of-the-art equipment, although they did carry


precision inertial navigation systems (PINS) and Omega


navigation systems. (7:77) Twelve years later, our


helicopters are still flying with the same type equipment!


The navigation equipment on board Marine Corps helicopters,


tasked to fly in support of these MEU(SOC) missions, Is


inadequate to meet the demanding mission requirements. The


Marine Corps must move aggressively to procure advanced


navigation systems for its helicopters, seeking both short-


and long-term solutions.


The standard navigation equipment installed on all


Marine Corps helicopters consists of the low-frequency,


automatic direction finding (LF/ADF) set and the tactical air


navigation (TACAN) set. The LF/ADF provides relative


direction to a transmitting station, and the TACAN system


provides direction and range to the transmitting station.


Both systems were designed to give navigation information to


aircraft flying at minimum specified altitudes due to terrain


or obstacle clearance requirements while under instrument


conditions and to enable aircraft to safely conduct


standardized instrument approaches to airports. The systems


require land-or ship-based transmitters, and the accuracy of


the systems improve as aircraft approach the transmitter


sites. Unless one of these transmitters is located in the


mission objective area, neither system is of value within the


tactical environment. Although the Marine Air Control Group


(MACG) detachment of the ACE can deploy with the TPN-30


Ground Landing System (GLS), the system is only capable of


providing range information to helicopters. The Marine Corps


is currently pursuing a modification to the TPN-30 which


includes the addition of a TACAN, which will provide range


and azimuth information. (12) However, this system would


still be primarily used for expeditionary airfield or


shore-basing operations and of little value in short duration


special operations. Two additional systems with potential


for tactical use have been installed on some helicopters.


The CH-53 helicopter and a limited number of CH-46


helicopters have Omega Navigation Systems (ONS) installed


which receive and process Omega and very-low-frequency (VLF)


signals to provide worldwide navigation capability. The


system must be initialized (told where it is) upon start-up,


which can present some unique problems during shipboard


operations, as discussed later. Additionally, the operators


manual states that manual position updates should not be


accomplished unless the system error exceeds three nautical


miles; this would indicate an accuracy factor of several


miles, although the system may be capable of better


results.(10:4.2.1) Long Range Navigation (LORAN) systems


have also been installed on a limited number of aircraft.


This system, which is capable of self-initialization, uses


low-frequency (LF) radio signals from a series of master and


slave stations (called chains) divided into geographical


regions, to triangulate the aircraft's position, often with


accuracy within a couple hundred feet. Fortunately for the


U.S., there is a LORAN chain centered in Saudi Arabia, which


provided coverage for the Iraq/Kuwait battle areas of Desert


Shield/Desert Storm. Unfortunately, with the exception of


extensive coverage of the North American continent, global


coverage is limited. Although these two systems appear to


provide some of the needed capability, neither system


completely fills the requirements, as demonstrated by the


following examples.


During 1989, a MEU(SOC) was off the coast of Lebanon


preparing for the possible evacuation of the U.S. Embassy.


The mission was to be conducted at night. Helicopters were


to be launched from ships 15 to 20 miles off the coast,


proceed to the beach and locate a single stone jetty. The


jetty was the initial point to guide them to the embassy,


which was located a mile inland within a built-up area.


LORAN coverage did not exist in the area. The process of


initializing the ONS on a moving ship, vice a stationary land


point, can introduce errors of a mile or more into the system


before the aircraft takes-off. This factor, combined with


the indicated accuracy of the ONS and the fact that the


mission did not allow for a precision update over land prior


to reaching the Embassy, made the system unsuitable for the




Operation Eastern Exit, the NEO from the U.S. Embassy in


Mogadishu, Somalia, in January 1991, required two CH-53E


helicopters to launch at 0347 local time for a 466 nautical


mile flight with two in-flight refuelings in order to reach


the embassy. The Omega navigation system, which is the


CH-53E's primary long-range navigation system, failed to


provide navigation information in either aircraft shortly


after take-off. The Indian Ocean area, from which the


aircraft launched, is one of the areas not completely covered


by omega signals. Although one system did start providing


information later in the flight, it was used as a backup


system for the remainder of the flight. In their report on


Operation Eastern Exit, the Center for Naval Analysis states,


Thus, flying over water at night, the CH-53Es

relied on a combination of positive control from

Guam (to approximately 60 miles from the ship),

dead reckoning, and pathfinding by the KC-130s

[aerial refuelers] for their navigation. An

upgraded navigation system, whether an inertial

navigation system (INS) or one based on the global

positioning system (GPS), would be valuable if

CH-53Es are to be prepared to conduct other

long-range missions. (9:48)



During Operation Provide Comfort a section of


helicopters, returning from a refugee relief mission in the


mountains along the Turkey/Iraq border, became disoriented


trying to circumnavigate bad weather. Unsure of their


location and running low on fuel, they elected to land near a


small military outpost, which fortunately happened to be on


the Turkish side of the border! Again, LORAN coverage was


not available in the area and neither aircraft had the ONS


installed, due to limited system availability.


In the event of an in-extremis hostage rescue attempt,


the assault forces will normally make their way to the


objective area by clandestine means. The "take down" usually


commences at a prearranged time and helicopters must arrive


at the pick-up point within minutes to extract the forces


prior to enemy reinforcements arriving on scene. Errors in


navigation by the helicopter crews that cause them to arrive


early could compromise the mission and if they arrive late


they may find the assault forces dead or captured by the


enemy. Timing and accuracy is critical to mission success!


All of the systems mentioned previously fail to provide


the navigation coverage and accuracy required to optimize the


chances for success on the demanding missions assigned to the


MEU(SOC). However, a relatively new system called the Global


Positioning System or GPS, has demonstrated the potential to


meet the requirements. Unlike other navigation systems which


are land-based, GPS is a space-based system employing a


constellation of 21 satellites and 3 in-orbit spares which


continuously transmit their position and the time (based upon


an internal atomic clock). A GPS receiver uses this


information to triangulate its position with an accuracy of


approximately 10-15 meters, although the Department of


Defense can degrade the accuracy of GPS for military purposes


using an operational mode called "Selective Availability"


(S/A). The receiver must be able to "see" three satellites


in order to provide a 2-dimensional position and a minimum of


four satellites to provide a 3-dimensional (includes altitude)


position.(4) Although the GPS constellation is not yet


complete (currently there are 5 Block I test-phase model and


12 Block II operational model satellites in orbit), the Air


Force Space Command anticipates continuous worldwide


2-dimensional coverage by Spring of 1992, and worldwide


3-dimensional coverage by late Summer of 1992.(1:6; 6:60)


Until that time, there will be coverage gaps as the available


satellites move in their orbits and occasionally drop from


view. As was demonstrated during Operation Desert Shield/


Desert Storm though, this is not a problem as the satellite


orbits can be changed by Air Force control stations in order


to provide continuous coverage for selected areas.


One version of a GPS receiver already being used on a


limited number of Marine Corps helicopters is the Trimble


TRIMPACK. The Trimble TRIMPACK is a rugged, self-contained,


hand-held GPS receiver with a built-in antenna. While not


originally designed for aircraft use, its compact size (6.5"W


x 7.0"D x 2.0"H) and optional remote antenna make it easily


adaptable for helicopter use with minimum aircraft modifi-


cations. Although wiring the aircraft for the receiver


requires several hours, the receiver can be mounted in the


cockpit of a helicopter simply by using velcro to attach it


to the glareshield (dashboard) or console. Thus the unit can


remain portable for use in other similarly equipped aircraft


or for hand-held use in the field. The receiver operates


from a variety of battery types for flexibility and an


external power cable is available which enables the receiver


to operate off of aircraft power. Additionally, the


receiver's display is compatible with the night vision


devices currently used by pilots.


The Marine Corps originally purchased 250 TRIMPACK


units; these were disseminated throughout the Fleet Marine


Force (FMF) to both air and ground forces for testing and


evaluation. The units became highly sought after during


Desert Shield/Desert Storm and received high accolades from


all who had access to them during the war. Due to the lack


of identifiable terrain features and accurate maps of the


desert in Southwest Asia for navigation, the use of GPS was


instrumental not only for helicopter missions but also for


ground units to determine their location. At forward-based


sites, Marine AV-8B Harrier pilots would reinitialize their


Inertial Navigation Systems (INS) using position information


supplied by the GPS receivers from helicopter crews! The


receiver's ability to tell time from the satellite's atomic


clock eliminated the need for units to synchronize watches


for missions that required exact timing.(8:5)


Long range navigation routes have been flown with the


TRIMPACK at various altitudes and airspeeds with typical


error rates of less than 0.1 to 0.2 nautical miles. It has


been noted that the accuracy of the system is often better


than the pilot's ability to plot checkpoints off the typical


1:50,000 and 1:250,000 scale maps that are used for heli-


copter navigation. Checkpoints are normally plotted to six


digits when using the grid reference system and to tenths of


a minute or rarely whole seconds for the latitude/longitude


reference system. The TRIMPACK wild accept grid locations to


ten digits and latitude/longitude locations to tenths of a




Trimble Navigation has recently expanded its line of


civilian GPS receivers designed specifically for aircraft.


One of these receivers is the DZUS GPS Navigator which is


designed to be DZUS-rail configurable, the standard mounting


system for military and commercial aircraft. The Navigator


is available in a GPS only or GPS/LORAN combination. The


system includes a navigation database of worldwide aviation


information including airports, navigation aids, airspace


boundaries and much more. Trimble expects to have "military"


versions of these systems, which would include military grid


reference and "P code" capability, available this year. A "P


code" receiver's accuracy is not effected when DOD initiates


S/A mode operations for the GPS satellites. Additionally, a


half-dozen or more manufacturers are also currently producing


various versions of GPS receivers for aircraft use at this




The Marine Corps is currently conducting research and


development on the Position Location Reporting System (PLRS),


APN-217(V3) doppler navigation system and several GPS pro-


grams specifically designed for aircraft. These GPS pro-


grams include upgrading the APN-217(V5) and Omega systems


with embedded GPS receivers and the Miniaturized Airborne GPS


Receiver (MAGR) program.


While PLRS provide excellent accuracy and incorporates


several other useful functions, it should not be considered a


primary navigation system for helicopters because like the


TACAN, PLRS requires a "Master Station" to be located in the


operating area before it can be used. The system would be of


little or no value in long-range special operations. The


APN-217(V3) doppler navigation system has been under


development since 1985 for use in the CH-46 helicopter. The


system requires initialization upon start-up (like Omega);


then using precision measurements of movement, updates the


location based upon the units original starting point. After


seven years of development the system has yet to be installed


in fleet aircraft and during recent developmental testing had


difficulty meeting navigation accuracy requirements.


Additionally, sources at Headquarters, Marine Corps have indicated


that the manufacturer has been unable to integrate a GPS


receiver with the APN-217(V5) and that aspect of the program


has been discontinued. The case for the APN-217(V3) is still


pending; if it can meet requirements, it could be paired with a


"stand-alone" GPS receiver such as the MAGR as a viable


navigation aid. APN-217 installation is currently projected


to commence in 1994 and take several years to complete.


Currently the CH-46 is the only helicopter equipped


with the AN/ARN-148 (Trimble TNL-7880) Omega receiver, which


is capable of being upgraded with a GPS receiver. The Litton


211 Omega receiver in the CH-53E is an older system and will


not accept a GPS upgrade. The Marine Corps currently has 48


complete AN/ARN-148 mission kits and an additional 48 instal-


lation kits installed on the CH-46s so that the units can be


rotated among aircraft. This equates to an average of three


systems for each tactical squadron (containing twelve air-


craft), with four or five additional aircraft configured to


accept the system. Since this system was intended as an


interim solution until the AN/APN-217(V3) was available,


there are no plans at this time to purchase additional


systems for the CH-46 or other aircraft. The AN/ARN-148 with


the GPS upgrade has been evaluated by Marine Helicopter


Squadron One (HMX-1) and has been deemed a "significant


improvement" over the current system. (2:7)


The MAGR is considered a "non-developmental item," which


means it is a derivative of an off-the-shelf, commercial


product, the "3A". This reduces research and development


costs and time. The MAGR is currently undergoing testing and


if accepted, initial fleet installation of the MAGR or the


slightly larger 3A (for aircraft with larger avionics bays)


is scheduled to commence in 1994 and run for five years.


Unfortunately, programs still in the developmental stage


will not solve the navigation problems for the MEU(SOC)s


currently deployed worldwide. There exists an immediate need


to upgrade helicopter navigation capabilities before the next


mission is flown! Additionally, whichever system or systems


are decided upon must be procured in sufficient quantities to


provide pilots adequate training time over familiar terrain


to properly learn how to use them. The introduction of the


AN/ARN-148 OMEGA and LORAN systems into the CH-46 aircraft


are perfect examples of how not to add a new system. On


separate occasions, these systems were installed in a limited


number of aircraft-just prior to the squadrons (to which I


was attached) departure to the Mediterranean for six-month


deployments. Manuals were scarce and only a handful -of


pilots flew with the systems often enough to become profi-


cient with them. Most pilots viewed trying to use them as a


distraction when flying over unfamiliar terrain in foreign


countries and preferred to rely on terrain navigation,


leaving the systems turned-off. The Holloway Report,


referring to the navigation systems on the Navy RH-53Ds used


in the Iranian Rescue Mission, states the crews had "received


only limited training (in the systems) and expressed low


confidence in the equipment and their ability to employ


it." (7:78) Hence, their primary means of navigation was dead


reckoning with the map and compass.


Obviously, the procurement of any aircraft system is a


complex undertaking, often planned and budgeted for years in


advance. The APN-217 system has been planned for in con-


junction with the addition of a cockpit management system


(CMS); both the APN-217 and the MAGR require integration with


a CMS or some other type cockpit display system in order to


function. All the systems require some additional "acces-


sories" in order to work, adding to the planned costs.


Prices vary depending on the number of systems procured and


range from as low as 5000 dollars for a basic TRIMPACK to


over 100,000 dollars for the APN-217(V3) with a display unit.


The AN/ARN-148s in the CH-46 can be upgraded with GPS for


around 10,000 dollars per unit, a military version of the


DZUS GPS Navigator is expected to cost around 20,000 dollars


per unit when available, and the MAGR with a display unit is


projected to cost in the neighborhood of 50,000 dollars


per unit.


Political as well as economic considerations unfortunately


also play a role in the process of procuring aircraft systems.


should money be spent to upgrade the CH-46E when the Marine


Corps is pursuing a replacement for it? Will money spent now


on an interim system reduce the funding available for long-


term solutions? Would a GPS upgraded ARN-148 Omega threaten


the higher costing APN-217(V3) program which is already


funded and of which the Marine Corps already owns 65


uninstalled systems? If the APN-217(V3) is cancel led, what


impact would that decision have on the associated cockpit


management system-which is a separate system but funded as


part of the APN-217 package? while the impact of interim


fixes on the long-term goals must be evaluated, the impact of


inadequate navigation capabilities on the performance of


missions assigned to the MEU(SOC) must carry a greater weight


in the decision making process!


The Trimble TRIMPACK, although not designed for aircraft


use, is inexpensive (compared with most aircraft systems),


currently available, and has proven itself to be an excellent


system capable of delivering the navigation capabilities


needed until follow-on systems can be developed and delivered


to the FMF. Because it is portable, the receivers can be


easily rotated between antenna-equipped aircraft, reducing


the number of receivers necessary to equip the fleet's


helicopters. The AN/ARN-148 Omega systems in the CH-46


aircraft can be upgraded with GPS, to capitalize on the best


of both systems, for little more than the cost of the


TRIMPACKS. Within the year, the DZUS GPS Navigator may prove


to be an excellent low cost system for all the fleet's


helicopters. At least one of these systems or a combination


of these systems, such as TRIMPACKs and 148 upgrades, should


immediately be purchased in sufficient quantities to meet the


current needs of the helicopter community while development


continues on the more advanced and integrated systems for the


future. The Marine Corps cannot afford to needlessly


jeopardize the success of the demanding missions assigned to


the MEU(SOC) due to inadequate navigation equipment when the


technology exists-to improve it today!





1.            "DOD GPS Happenings." The Fighting Edge. San Diego:

ETA Technologies Corp., Oct-Dec 1991, p 5.


2.            Ferrell, Keith, Captain, USMC. "AN/ARN-148 GPS

Effectiveness Assessment." Nighthawk News, Marine

Helicopter Squadron One, Bulletin 1-91, Jan-Jun

1991. Quantico.


3.            Gabriel, Richard A. Military Incompetence: Why the

American Military Doesn't Win. New York: The

Noonday Press, 1985.


4.            "The Holloway Report: Iran Rescue Mission #3." Aviation

Week and Space Technology, Sept. 29, 1980, pp 84-85.


5.            Hurn, Jeff. GPS: A Guide to the Next Utility.

Sunnyvale, Ca.: Trimble Navigation Ltd., 1989.


6.            Kollcum, Edward H. "USAF Hopes Latest GPS Launch

Signals Return to Routine Schedule." Aviation Week

and Space Technology, March 2, 1992, p 60.


7.            Ryan, Paul B. The Iranian Rescue Mission: Why It

Failed. Annapolis: Naval Institute Press, 1985.


8.            "The Same Sheet of Music." The Fighting Edge. San

Diego: ETA Technologies Corp., Oct-Dec 1991, p 6.


9.            Siegel, Adam B. Eastern Exit: The Noncombatant

Evacuation Operation (NEO) from Mogadishu, Somalia,

in January 1991. Alexandria: Center for Naval

Analysis, Center Research Memorandum 91-191/Oct



10. TA 7880 Operators Manual. Austin: TRACOR Avionics, 1989


11. U.S. Marine Corps. Marine Corps Combat Development

Command. Marine Air-Ground Task Force: A Global

Capability, FMFRP 2-12. Quantico, 1991.


12. U.S. Marine Corps. Marine Corps Lessons Learned System,

Report number 71941-37553 (01363). Quantico, 1991.


13. U.S. Marine Corps. USMC Landing Force Training Command,

Atlantic. Marine Air-Ground Task Force Pocket

Guide, LFTCLANT 0305-3(3-90). Norfolk, 1990.

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