28 June 2010
These two articles describe the transponder interrogation/response protocol in a little more detail than my course materials. I'd always wondered how the transponder worked and had been under the mistaken belief that the primary air traffic control (ATC) radar pulses triggered the transponder to reply. Not so. It turns out that separate directional and omni-directional antennas transmit groups of three interrogation pulses on 1030 MHz. If an aircraft transponder receives these pulses with proper relative amplitudes, it will transmit the encoded squawk code and altitude on 1090 MHz after a 3 microsecond delay. The three interrogation pulses ensure that transponders will only be triggered by the main lobe of the rotating ATC antenna. The system can compute the distance of the aircraft from the ground antenna by measuring the time difference between the interrogation transmission and reception of the aircraft's reply. It is interesting that the transponder squawk codes use the octal number system. So there are 8^4 = 4096 possible 4-digit octal squawk codes. This makes efficient use of the log2(4096) = 12 bits that are needed to represent the squawk code in the response. If the codes were instead represented using 4 decimal digits, ceil(log2(10^4)) = 14 bits would be required and not all of the possible bit combinations would be usable.
27 June 2010
Per my usual pattern, I have gotten a little bit ahead of myself. I asked around about the gear that I'll need for flight training so that I can buy some of it now, while working through the ground school material, to spread some of the costs around. On the list was a headset. After some research, I bought a David Clark H10-13 S passive (non-noise-cancelling) headset. This is the H10-13.4 headset, except with a stereo phono plug and mono/stereo switch on the yoke. The stereo version cost $10 more, but it should permit stereo music listening with an iPod and proper adapter module. I've read that this can be a good thing on the long cross-country flights. The foam microphone covers look like they might be easy to tear up. I picked up a spare cover just in case. We'll see how it goes....
I have resolved to earn an FAA Private Pilot Certificate (PP-ASEL) so that I can legally rent and fly a single-engine airplane, such as a Cessna 172. This is something that I have always wanted to do, but for whatever reason, I had deemed impractical. Now that I am in my early 30's, I have concluded that life is too short to put this off any longer. I created this web log to document my progress and experiences along the way. Right now, I am at the very beginning of the process. The milestones are roughly:
- Visit an FAA Aviation Medical Examiner and take a physical to receive a 3rd class medical certificate. This needs to be done before flying solo, but in my case, it is good for 5 years and I want to get it out of the way. A pilot friend of mine recommended a local physician, and I plan to make an appointment soon.
- Find a Certificated Flight Instructor (CFI). My local GA airports are KHEF, KJYO, and possibly KHWY. I need to do some research here. I have read that the airspace in the Washington DC area is complex to negotiate due to the Special Flight Rules Area (SFRA) and the fact that most of the nearby airports are in Class B airspace thanks to busy Dulles and DCA. Warrenton/Faquier Airport is outside the SFRA and the Dulles Class B airspace, but it might be too far to drive 2-3 times per week for lessons.
- Pass the FAA Knowledge Test. This doesn't need to be done until just before the checkride, but I have begun to study the material. Based on many recommendations, I opted to use the King Schools course to prepare for the test in lieu of a formal ground school. I am about 1/3 through the course now--it is corn-ball city, but good. I have also been reading Stick and Rudder--a great text from 1944--in the hope that it will help me intuitively understand the flight dynamics when I first experience them in a real airplane.
- Learn to physically fly an airplane
- Solo Flights
- Cross-Country Flights
- Night Flights
- Instrument Flights
- Practical Test Preparation
- Pass the FAA Practical Test (checkride)