A recently releasedTransportation Safety Board investigation report detailing a mid-air collisionstated that “A number of international studies have addressed the overall issueof risk of collision effectiveness of the see-and-avoid principle. Allacknowledged the underlying physiological limitations at play and that, whenmid-air collisions occur, “failure to see-and-avoid is due almost entire to thefailure to see.” One study stated that “our data suggest that the relativelylow (though unacceptable) rate of mid-air collisionsin general aviation aircraft not equipped with TCAS is as much a function ofthe ‘big sky’ as it is of effective visual scanning.” 

The day after the release of thereport, the newswires surmised (as they’re prone to doing) that plane crashesinvolving GA aircraft were likely to increase, quoting an official stating “Theboard is concerned that the risk of collisions will remain . . . if we do nottake steps toward developing collision avoidance equipment which is usable in asmall, general aviation aircraft.”

Well, this technology DOES exist.Despite my efforts over the past couple of years to increase awareness of GAcollision avoidance technology, it seems evident that there’s still a long wayto go. A U.S. source estimates that merely 5% of American pilots are aware thatsome form of collision avoidance technology exists for general aviation. Inthis month’s Close Calls I will provide a short description of the varioustypes of collision avoidance systems on the market today.

In the interest of fulldisclosure, I’d like to remind readers that I do recommend and sell PCAS units now,but I a few years ago as a pilot-consumer I researched all technology availableat the time and chose PCAS (then known as TPAS, or Traffic Proximity AlertingSystem) to use in my aircraft to enhance flight safety for my family andfriends.

TCAS (Traffic alert and Collision Avoidance System) wasintroduced and mandated for larger commercial aircraft in response to seriousmid-air collisions that occurred in the 1970’s and 1980’s (along with theairspace definitions and the use of transponders).

TCAS systems actively interrogatethe transponders of targets and listen for interrogation responses to determinethe presence of conflicting traffic. The information is shown on a displayindicating the location of the target, its relative altitude, distance, andtrends. TCAS systems for general aviation fall in the $25,000 price rangewhereas more advanced TCAS systems for commercial use can be priced in thehundreds of thousands but also provide conflict resolution advisories.

TIS (Traffic Information Service) is a rebroadcasting systemrequiring a mode S transponder to provide the datalink. Ground stations broadcasttraffic information which can be displayed similarly to TCAS. TIS was neverintended to be an end-state solution but rather an intermediate one in wait ofADS-B. As a result, TIS was never really available in Canada and groundstations in the United States have been on a decommission schedule for sometime. Costs are similar to TCAS for general aviation and obsolescence is on thehorizon.

ADS-B (Automatic Dependent Surveillance – Broadcast) promises todeliver a great deal to the aviation community on the whole. On-board ADS-Bsystems will have the ability to receive not only traffic information but alsoweather and flight services data. ADS-B is in limited use in portions of theUnited States and has been met with rave reviews. Equipment costs for aircraftand the expansion of the ground infrastructure leave ADS-B out of the runningas a practical solution for (optimistically) 5 years, with many Canadianexperts believing that the time frame is more realistically 10 to 12 years.   

Zaon Flight Systems (known for PCAS, below) has patented asmall, portable, low cost passive ADS-B system capable of receiving both 1090ESand 978 MHz.  This system allowscurrent PCAS XRX users to utilize ADS-B in conjunction with their existing PCASwhich ensures consistent traffic awareness in and out of ADS-B service areas.Pricing is expected to be around 1/10^th that of available ADS-Bsystems (with discounts available for existing PCAS owners). Zaon expects tolaunch portable ADS-B at either Sun-n-Fun or Oshkosh in 2009.

FLARM (FLight alARM) is a system most commonly used in glidersin Europe. Each FLARM device transmits a signal that is received by other FLARMdevices. The system works best for soaring when all gliders are FLARM equippedand remain in the same approximate geographic area since gliders are seldomtransponder equipped. In a busy general aviation area, a FLARM equippedaircraft would only be able to detect other FLARM equipped aircraft. Thisseverely limits FLARM’s usefulness in general aviation or any practical useoutside of an organized implementation.

PCAS (Portable Collision Avoidance System) is similar to TCASin that it receives transponder responses and displays the relative altitudeand distance of the target aircraft. Some systems further indicate the quadrantbearing of the aircraft and have the ability to show this data graphically on aGPS display. These systems will also work with portable ADS-B receivers whenthey become available. Different from TCAS though, PCAS is passive meaning thatit does not emit the interrogation signal itself but instead relies on groundradar or overflying active systems to provide the initial interrogation. PCAScan also be useful for gliders – not to detect other gliders but rather todetect transponder equipped, powered aircraft breaching the soaring zone. PCASdevices are self-contained units that range in price between $500 and $1700.

More and more studies aresuggesting that see-and-avoid principle is simply not effective enough toassure the best possible chances of avoiding a mid-air collision or more likelya near mid-air collision (NMAC). Pilots should be aware that effective,practical, and affordable technology DOES EXIST to help pilots to spot nearbyaircraft.

Since most aircraft aretransponder equipped, TCAS (for premium accuracy) and PCAS (for costeffectiveness) are the best technological solutions for general aviation.Pilots should consider these aids as an addition to their repertoire untilADS-B becomes widely available in the next decade or so.

These devices aren’t intended toreplace any good practice however, but instead to add to a regimen ofmaintaining a thorough lookout, performing diligent radio work, and whenavailable, using flight following.

Fly safe(r).