Letters

LAAS v. WAAS

I read William Reynish’s article "Happy Landing for LAAS?" (January 2007, page 30) with great interest. My main responses to the article are these:

Boeing, Airbus and the airlines are not interested in WAAS. It was developed for, at best, Category 1 approaches for business, regional and GA aircraft, where operations at levels higher than Cat I are not likely. WAAS was also developed to support LPV (Localizer Performance with Vertical Guidance) approaches — designed again for the same aircraft. WAAS has no migration path to any level above Cat I and, as a result, is a dead end to the transport world. Furthermore, RNP 0.15 or less operations for transport aircraft will provide nearly Cat I capability with even greater availability than WAAS, particularly if IRU/GPS coupling technology is employed. Check out WAAS availability for Cat I operations and discover that large regions of the coastal areas are not as well served as you might think.

Regarding LAAS, Boeing, Airbus and the airlines are very interested, specifically because LAAS is upgradeable to Cat II/ III. LAAS provides the potential for direct blending with RNP operations to provide simultaneous parallel approaches, required time of arrival operations, fully automatic landing and rollout and much more.

The combination of RNP and GLS Cat I/II/III operations provides the operational capabilities needed to actually implement new airspace improvements and throughput. WAAS has only marginal capability to provide some limited inputs to RNP operations leading up to final approach. The contribution of WAAS is greatest among GA users where a WAAS-based navigator can provide exceptional safety and accuracy with proper crew training. LAAS is the only means for transport aircraft to achieve better operational efficiencies in the National Airspace System and around the world. It also offers excellent potential for precision guidance in developing countries where modest investment in ground infrastructure (a LAAS ground station) can result in all runway ends at any airport site having better than ILS capabilities even at Cat I level.

David Vacanti

LAAS Clarified

Please pass my highest compliments to William Reynish for his article "Happy Landing for LAAS?" Mr. Reynish accomplished crystal clarity on a complex and confusing issue.

Sven Girsperger

Effretikon, Switzerland

SatNav Hype

All the hype that is being generated by the avionics industry about WAAS, LAAS, ADS-B and all the other acronyms is just so much buzz designed to create a much needed revenue stream without justification.

None of these systems have proven to be sufficiently marginally better than existing, ground-based systems and, in fact, some are worse. The example used by William Reynish, in which the vertical stabilizer of a landed 737 "deflected the ILS localizer beam" and disrupted the ILS approach of an MD-80, can also happen with LAAS and is nothing unique. In fact, LAAS or any other satellite-dependent system is far more vulnerable to human and atmospheric distortions than ground based systems.

Until satellite-based systems can demonstrate that their employment, particularly in high-traffic-density terminal areas, can significantly improve reliability, safety, security and cost effectiveness over existing, paid for, ground-based systems there is no justification for their implementation. None!

Karl Kettler