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turns unless the approach procedure explicitly states otherwise. This has been upheld by prior FAA legal inter– pretations of § 91.126(b).
The AC goes on to describe radio communications and traffic pattern entries in detail. But it doesn’t provide any specific guidance for non-towered operations with inter– secting runways. In fact, even the Aeronautical Information Manual fails to mention this directly.
Technological Aids
There are several technological aids to collision avoidance, but they have their limitations. The first and by far most common aid is radio communication. The NTSB’s preliminary report, while subject to additional findings before it becomes final, states:
There were three witnesses to the accident, located in the airport lounge, within hearing distance of the UNICOM radio. Each witness reported seeing the Cessna 150 just airborne when it struck the empennage of the Cessna 525. Two of the witnesses stated that they heard the Cessna 150 pilot on runway 15 UNICOM frequency. The pilot of the Cessna 525 stated that he did not see the departing Cessna 150 while he was on a straight-in approach to runway 22, nor did he see the 150 during the landing roll. He stated that he did not recall making a radio call on UNICOM....
Landing at a non-towered airport under Instrument Flight Rules can be a high-workload event, even if weather is VMC and you are flying a visual approach. It’s easy to let vital tasks like making position and altitude calls on the CTAF when you are on Center or Approach and need to cancel your IFR flight plan. All too often, instrument pilots ignore these vital CTAF calls – making it less likely other pilots will see and avoid their aircraft. Of course, in most cases there is no requirement for aircraft at non-towered airports to have a radio at all, so looking outside is still the primary means of collision avoidance.
Most turbine aircraft have an onboard Traffic Collision Avoidance System (TCAS). TCAS calls out the
relative location of aircraft on a possible collision course and in some cases, suggests an avoidance strategy. According to the NTSB, the pilot of the Citation stated that while he did not make a radio call on CTAF, he did utilize his on-board Traffic Collision Avoidance System (TCAS) system while on approach. He stated that the TCAS did not show any traffic on the airport.
Unfortunately, this statement suggests a lack of familiarity about how TCAS works. TCAS relies upon receiving transponder information from other aircraft. Here’s why we can’t rely upon TCAS while landing at a non-towered airport:
1. Not all aircraft are transponder- equipped. There is not requirement for an airplane like a Cessna 150 to have a transponder at all.
2. Transponders emit replies to in– terrogations triggers when the transponder receiver is hit by an Air Traffic Control radar beam. An aircraft close to the ground, such as the Cessna 150 during its takeoff roll, is almost certainly too low to be in radar contact with ATC. Even if the aircraft had a transponder, the transponder would not have been emitting a signal to be picked up by the Citation’s TCAS.
3. Unless an aircraft has a TCAS or lower-technology TCAD (Traffic Collision Alerting Device, which warns of nearby aircraft but may not provide relative position information and does not give specific instructions for collision avoidance), transponder antennas are mounted on the bottom of the aircraft. This makes sense, because transponders rely on line-of-sight transmission, and they are designed to communicate with stations on the ground. Because transponder antennas are on the belly of the aircraft, however, that aircraft’s fuselage and wings blank out the transponder signal to nearby aircraft that are higher up. Even if a departing aircraft had a transponder and was somehow being interrogated by ATC radar, it’s almost certain that a nearby landing aircraft would not receive its transponder
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