ATM Modernization

Perspectives: eLORAN’s Shortcomings

By David Vacanti | March 1, 2007
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While I share the concern about possible backups to automatic dependent surveillance-broadcast (ADS-B) in the event of GPS local or larger outages, I don’t believe the entire story about Enhanced Loran (eLORAN) is being told. The whole story may help explain why it has not been met with wild enthusiasm.

To my knowledge, eLORAN does not provide vertical navigation capability. Assuming my statement is true, providing only lateral but not vertical information with good accuracy does not meet the needs of ADS-B, where altitude is a critical part of determining safe clearance. While baro nav is possible, it is not verifiable for all aircraft types.

Providing only non-precision approach capability with eLORAN is not sufficiently valuable across all airborne operations. Other technologies can be carried on aircraft to provide "coasting" between GPS outages that are short lived. Malicious jamming of GPS signals is only a threat when first initiated and operators are caught unaware. Once jamming is acknowledged, operations will be modified and flights reduced until the threat is eliminated. Coasting for minutes may be all that is necessary for aircraft to be made aware of the threat and begin the process of landing or otherwise taking refuge using other ground-based navaid support (primarily DME and VOR). The latter are universally available, commensurate with GA or non-air transport class operations.

eLORAN is only available over the United States and limited littoral regions. This is one very expensive WAAS-like (Wide-Area Active Surveillance) system that has regional limitations and is confined to primarily overland use. ADS-B continues to evolve as an international standard and as such, any backup system to GPS cannot be as regionally specific as eLORAN. That would not be economically viable for avionics suppliers.

Add to this the dilemma the required addition of a very large antenna to provide eLORAN coverage at a time when every effort is being made to wish automatic direction finding (ADF) off commercial transport aircraft. While small aircraft may be able to carry long wire antennas, high-speed transports and small jets cannot do this. They must carry 15 to 20 pounds of a wire-wound antenna over a ferrous metal core to provide required reception.

Moreover, it is dangerous to claim low-frequency eLORAN operation is virtually jam-proof. Just the creation of precipitation generated static electricity or lightning is enough to disrupt eLORAN operation locally on an aircraft. eLORAN is potentially threatened by EMI generated onboard an aircraft by local DC/AC power generation. Special paints and grounding techniques are required to preserve the operation of ADF receivers on transports to prevent large levels of noise caused by wind and rain on the antenna itself.

Any GPS backup system must be adaptable to more than just ADS-B operations, providing backup for lateral precision with vertical guidance, area navigation and required navigational performance and GPS landing system operations that continue to grow in importance. All of these systems require accurate vertical navigation.

In my mind, our taxes would be better spent on the more immediate upgrade of the Navstar GPS constellation to include the L5 aviation frequency. The second frequency dramatically improves availability and integrity and substantially improves vertical navigation. Addition of a second frequency significantly reduces the threat of malicious jamming of both operating frequencies at the same time because the modulation on each frequency is not identical and does not respond to a single jamming signal in the same way.

Non-precision approaches are nice for many GA and some commercial operations, but they do not address the more critical National Airspace System needs for better efficiency and safety as the volume of aircraft becomes more dense. ELORAN does nothing for high-accuracy navigation and perpetuates expensive regional solutions that require large infrastructures to be maintained yearly. Projects such as WAAS or eLORAN may benefit GA where the number of aircraft is large, but passenger numbers are low. The very large numbers of our fellow humans worldwide who fly in densely packed airline transports deserve better than eLORAN.

David Vacanti is Aerospace Fellow for RF navigation with Honeywell. The opinions expressed in this column are his personal views and do not represent Honeywell in any way.

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