The Need For Improved Helicopter Navigation Systems
CSC 1992
SUBJECT AREA Aviation
EXECUTIVE SUMMARY
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
prepared.
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!
THE NEED FOR IMPROVED HELICOPTER
NAVIGATION SYSTEMS
OUTLINE
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 NEED FOR IMPROVED
HELICOPTER NAVIGATION SYSTEMS
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
mission.
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
second!
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
time.
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