Editorial

Will the effort to implement loran-based nonprecision instrument approaches follow the same tortuous, politically charged track that has characterized the microwave landing system? Let's hope not. Whereas MLS is of dubious value to general aviation — the cost of dumping ILS equipment and replacing it with MLS can't be justified on the basis of increased capability — loran approaches offer clear benefits. Chief among them is the prospect of issuing published approaches to hundreds of airports that now are VFR-only or have difficult or marginally useful nonprecision approaches because of the location of approach navaids.

The advocates of loran IFR approaches — state aeronautical agencies working through the National Association of State Aviation Officials, pilots as represented by AOPA and other user groups and associations, loran receiver manufacturers, and, most importantly, the FAA — have a six-year investment in meetings, technical papers, and research and development aimed at seeing loran approaches implemented. But recently, the effort appears to have hit a snag. Bendix/King, which makes the sophisticated and popular KLN 88 panel-mount loran, has waved a red flag.

Bendix/King has aggressively pursued certification of the KLN 88 for IFR approach use (the unit already is approved for enroute and terminal IFR operations). But after extensive flight tests and analysis, the company has reigned in its support of the certification program because of perceived shortcomings in the loran system. Bendix/King believes that loran signal availability is not reliable for approach use, that loran approach charts are inadequate, and that pilot work load during a loran approach is too high.

The company says it recognizes that the FAA is addressing the issues of charting and pilot work load and that those problems can be fixed. The show-stopper, in Bendix/King's view, is the loran signal itself: It may not be there when you need it most. Transmitter station outages and interference from thunderstorms, precipitation static, and other sources of high ambient electrical noise can cause a loran receiver to flag. In that case, a pilot would have to dead reckon on the approach while waiting for the loran to reacquire the signal, and a loran typically takes one to two minutes to reacquire.

That scenario indicates that loran simply does not ensure an acceptable level of safety for approach use, Bendix/ King argues. The company says it is pursuing technical solutions to signal problems, but it has made it clear that it will maintain a curmudgeonly attitude toward the loran approach certification effort until the issues it has raised are resolved.

Bendix/King is something of a lone dissenter among the parties involved in the certification effort. The company aired its concerns at a loran certification conference last October. Other avionics manufacturers working on loran approach certification who attended the session — Northstar, II Mor- row, and Arnav — acknowledge that problems exist, but each believes technological advances will provide the solutions. Significantly, FAA staffers involved in the loran approach effort are bullish about the prospects for overcoming technical challenges.

At that meeting, the FAA mapped out a four-pronged plan for research- ing certification problems. First, the FAA will fund an effort to determine how often momentary lapses in loran signal transmissions occur. A tougher challenge will be tracking — and reducing — signal outages due to precipitation static and electrical discharges from lightning.

Second, the FAA will work with the U.S. Coast Guard, which operates and maintains loran transmitting stations in this country, to determine how to reduce signal outages and what that might cost. The Coast Guard calculates that 7,000 outages of any type can be expected in one year. But that seemingly poor record includes very brief lapses in the signal that would not affect IFR approach guidance. The transmitter performance record should improve by 1995 when the last of six tube-type loran station transmitters will be replaced by solid-state equipment.

Third, the specifications governing IFR loran receivers will be examined for possible upgrade. One potential solution to loss of signal and flagging of the loran indicator is to allow a multi-chain or cross-chain receiver to also track stations outside the primary triad being used for the approach and provide for switching to enroute mode for guidance through a missed approach. Finally, the FAA will develop and provide loran training programs to pilots and FAA personnel.

No one thought the road to implementing loran IFR nonprecision ap- proaches was going to be short, straight, and smooth. The FAA was a reluctant partner initially but now is showing more enthusiasm. Bendix/ King has raised valid issues — certainly pilots should expect that a loran approach will be as safe and reliable as any other type of instrument approach. But too much work has been done and too much progress made toward extending the usefulness of general aviation airports and aircraft for the whole effort to now shift to idle or even die.