Lost from the Start
Thanks for your editorial and list of acronyms in the December 2002 Avionics Magazine (page 27). As a young engineer in 1967, I attended a meeting at The Boeing Co, in Wichita, Kan. I had just graduated from an engineering college. Engineering school had taught me many technical acronyms, but I was just about to enter a world that specialized in acronyms.
The Boeing engineer at that meeting stood and said, "The purpose of this meeting is to conduct an ATE TPS PMR for the B-52 EVS system." I was immediately lost, trying to understand the purpose of that meeting. The meaning of the acronyms, I now know, are the following:
ATE–automatic test equipment,
TPS–test program set,
PMR–preliminary design review,
B-52–Air Force bomber and
EVS–electroptical viewing system.
Ever since then I have been keeping lists of acronyms that reach back into the 1950s. I still dislike hearing people speak in acronyms and am still astonished at the many conversations in my world carried on without grammar or punctuation and laden with acronyms.
I thought your comments were clever, funny and informative. I thoroughly enjoy Avionics Magazine (AM) and have been a dedicated reader (DR) for many years.
Tinker Air Force Base, Okla.
Circuit Breaker Alert
I read with interest the December 2002 Avionics System Design column on circuit breakers ("Saving the Pilot: Part II, page 52). I have been working as a Flight Simulator engineer for the past 48 years and could not count how many times I have been called to the cockpit because of reports of inoperative systems, where all I had to do was tactfully push in a popped or pulled circuit breaker. Of course, the usual reply from the embarrassed trainee (or instructor) was, "I checked all the breakers."
Much training in simulators is done in subdued lighting, but a lot of real world flying also is done with subdued light in the cockpit. I doubt this scenario is limited to flight simulators.
About two years ago, I mentioned to an instructor that I didn’t think it would be very difficult to connect an infrared LED in series with a 2K resistor across each of the breakers on the 28-volt DC buses. The circuit current would be limited to about 15 milliamps, i.e., the load would not be totally isolated.
Infrared detectors mounted above or on the back of the pilot seats would alert the crew of an open breaker by a resettable flashing warning light. The dectectors would have to made to ignore changes in ambient light. (My TV set responds only to the light from my remote control). Wiring for this modification would be limited to the breaker panels themselves. The AC breakers would require other components.
Sounds cool to me. You also can use simple diode logic to detect open breakers and trip a master caution. The infrared emitter is not really required. You can also add a "blown fuse indicator" to a breaker by bridging across it with a visible red LED and resistor. This technology goes way back to World War II, when it was built right into the fuse-holder cap with light bulbs. All kinds of ways to improve the situation exist. I guess the real issue is generating enough interest to actually do something.
–Walter Shawlee 2
Only When Flight Essential
Since the TWA 800 and Swissair 111 accidents, we have been very focused on all the wiring issues. Therefore the Safety in Avionics column in the November 2002 issue ("Breaking the Electrical Arcing Cycle," page 48), written by David Evans was interesting to read.
However I want to make you aware that, today, a tripped circuit breaker must not be reset in flight, except when the system linked to the circuit breaker is essential for the safe continuation of flight. This recommendation would be in contradiction to the procedure described in the column, which mentions, "...the pilot will have the ability to reset the device a certain amount of times. On a flight critical system, the SSPC (solid state power contoller) might be programmed to allow just one reset in flight..."
The pilot in command must be able to reset a tripped circuit breaker for flight essential systems; otherwise he could induce flight critical situations by depowering systems.
Team Leader-Electronics & Avionics