Ventura, Calif.-based Dow-Key Microwave Corp. is well-known for its electro-mechanical and RF switches. But, what many do not know is that it has been a preferred supplier to the world’s largest aerospace company for nearly two decades. For roughly 20 years and still counting, no commercial airplane has left Boeing Corp.’s manufacturing facilities without Dow-Key Microwave RF switches, implemented within the aircraft manufacturer’s collision avoidance and landing systems.

Employed in aircraft’s traffic collision avoidance system (TCAS) and instrument landing system (ILS), Dow-Key provides its switches for all of Boeing’s current fleet of commercial airplanes, including the 777, 767, 747, and 737, as well as the forthcoming state-of-the-art 787 Dreamliner. The 787’s TCAS-II is equipped with the supplier’s advanced RF switching technology for mission-critical performance.

In the air, FAA mandated TCAS-II provides air traffic controllers with an aircraft’s identification and altitude, while terminal radar provides relative position and distance. In operation, if the system detects a possible in-flight collision with another airplane, it presents to the pilot on the flight deck a series of advisories that tells the pilot to pull up, dive, turn right or left, and so on.

“Safety is of key importance for Boeing, and has strict requirements therein,” says Carl Abendroth, president of Kirkland, Wash.-based Anzak Corp., an electronic components representative for Dow-Key. “Dow-Key provides Boeing with custom solutions to meet and surpass those safety requirements.”

Part of Boeing’s TCAS-II employs two antennas, one on the top of the fuselage and the other below. Internally, these antennas are connected either to one of two Mode-S transponders, which provide redundant support for a portion of the TCAS-II. In order to connect one or the other of the transponders to the two antennas, two Dow-Key 402-167 switches are used.

“While the FAA mandates the use of TCAS-II among all commercial airplanes,” explains Abendroth, “it allows for some options, one of which is a redundant Mode-S transponder. Not all aircraft manufacturers use a redundant system, but Boeing has done so for many years to ensure its customers solid reliability.”

On the ground. equally important is the aircraft’s ability to land safely. The ILS in the aircraft enables its pilots to acquire the specific RF signal that identifies the runway of choice. The ILS antenna acquires a glide scope signal, which can be described as an electronic highway with a decreasing angle that ends at the threshold of the runway. On all but the 787 Dreamliner, Dow-Key’s Model 402-188-1 switches actuate Boeing’s ILS equipment, allowing the pilots to choose from a variety of modes in which to land as they get closer to their destination. Depending on the size of the Boeing aircrafts, the complexity of the ILS could require as few as two or three switches or as many as six or eight.

“The pilot can fly the glide path manually,” he continues, “or choose one of the various categories of auto-land, which typically is found as an ILS option on fully equipped airplanes that do a lot of international travel.” Auto-land mode, which includes auto-pilot and auto-throttle modes, is triggered by an extra actuation switch inside Dow-Key’s 402-188-1 switch, when it acquires and is switched to that particular set-up antenna at the nose gear door.

According to Dow-Key, it also has been able to save Boeing much time during its qualification testing process for parts used on new airplane models, as per the Radio Technical Commission for Aeronautics document #D0-160C. Besides offering leading-edge switching technologies, the supplier is proud to deliver reliable solutions to its customers quickly and on time.