trying to get ahead of the learning curve

Over the last couple months, I have been behind the learning curve in a big way. I started a new job in a new domain, and I decided to get my instructors rating. Since I haven't flown for a couple years, I decided to concentrate on my ground instructor rating, then I can go look at flight instructor another time. Two big domains of information cramming stuff into my little brain has been a challenge finding time to explain stuff. (nevermind the holidays and family issues, and all).

The FAA is changing the testing for everyone, and that could be a good thing, but it may not be. As part of the advanced ground instruction (AGI) rating I completed recently, there were two distinct parts. There was the flying instruction, and the fundamentals of instruction (FOI) part. The flying part was relatively easy, since I feel pretty confident in my understanding of the fundamentals of flight. The ground instruction test was pretty easy, and the questions and answers mostly matched the test prep I used.

The FOI was a real challenge. The FOI test is the one the FAA has changed significantly in the last couple of years. The main book for the test is the Aviation Instructors Handbook (FAA-H-8083-9A). It looks a little more colorful than most of the other FAA documents, and seems to have some really good information in it. Lots of learning theory, and psychology presented in a way to help the reader understand how people in general, and pilots in particular learn. Things that may offer help in overcoming difficulty when instructing different individuals.

The FOI test took a left turn from there. There are plenty of really informative good ideas in the book, but the test rather than focusing on those items, decided to test on nuances that may not be applicable. One example of the test, it asked the details of Bloom's Taxonomy of the Cognitive Domain, and not why they matter, or how to apply them. Like in a flight while teaching, I will consider Knowledge, Comprehension, Application, Analysis, Synthesis, and Evaluation, when  dealing with a student about to cross control an aircraft in a base to final turn. As we are spinning into the ground, I will think more about the application of control inputs, and how I should have emphasized them more, without considering the students comprehension.

Other places in the FOI test, they put in three perfectly good answers. I know at least twice in the test, I said to myself, "all of the above". Other places, there were three answers that contradicted the book. A question about the PTS asked what they are for. They are for testing, but the answer choices where all over the place, were they teaching aids (well the book says introduce them in the last three hours, sounds like a teaching aid to me).

I felt like I worked really hard preparing for this test. None of my practice tests since Christmas (when I re-read the book) did I get less than an 82. When I got done with the real test, I knew I didn't do that well and felt my score, if I passed, was just above 70. It was above 70, but not by much.

I guess end of the day, in 3 years when teaching a class no one will ask me if I got a 99 on the test or a 71, I passed, and I will continue to learn, and part of being a professional includes research (that was another question on the test). I shall be a professional.

What will I do with my new knowledge, and skill? I hope to introduce people to the concepts of flying. I want my classes to be broad enough that it will answer peoples questions about how aircraft work, with enough detail to allow the students to pass the private pilot ground school at the end, and give them the tools to do something with their knowledge. I am considering another blog around teaching people to fly.

What do you all want to know?

FMS FMC and how airplanes know where to go.

Flight Management, how does the airplane know where it is, and where it ought to go. The pilot may want to be in charge, but his job is to manage the systems. There are many systems in an aircraft, and many come together in a single computer called the Flight Management Computer (or Flight Management System). The pilot can use the FMS/FMC on the airplane to help manage these systems.

The heart of the navigation system are the gyroscopes and accelerometers. The gyros are known as the Inertial Reference System (IRS). The IRS will be used to measure changes in flight orientation. The IRS will output heading, attitude and change being imparted. Gyroscopes will measure current conditions, accelerometers will measure the change being imparted on the current conditions.

Gyroscopes are great tools for use in aircraft. The horizon gyroscope will hold true through many oscillations of the aircraft, climbs, turns and dives it will usually show the blue side up. The bank gyro will also handle climbs, turns and dives. The directional gyro will maintain heading for hours.

Accelerometers will measure the forces acting on the aircraft in the various directions. As you were taught in instrument training, or perhaps in private pilot ground school, the seat of your pants isn't accurate at measuring change in coordinated flight. Accelerometers are like the seat of your pants, measuring g forces in three directions (forward/rearward, left/right bank and pitch). They will inform the pilot, or flight management system if the aircraft isn't in coordinated flight, or the increase or decrease of thrust is having and effect.

Integrating the accelerometers and the gyros is how the aircraft can measure where it is relative to where it started. When the aircraft is initialized by the pilot, the current latitude and longitude are entered or received from the GPS system. As the aircraft changes position, the accelerometers will measure the forces acting on the aircraft from the TUG as it pushes the aircraft back from the gate. When the aircraft is in flight, turns can be measured by combining the angle of  bank, and the "vertical" acceleration to measure the horizontal component of lift (HCL), and compare it to centripetal force, to measure the rate of a turn.

A couple posts ago, I was going to talk about Kalman filters. This is where the Kalman filter pays dividends. The Kalman filter will take data that isn't perfect, and make some sense out of it. Sometimes gyros or accelerometers will measure unreasonable values, some large, some small. The Kalman filter will make a best effort to use that information in a way that is reasonable (it may throw the data away, or it may smooth it, such that it looks like a normal reading).

The gyros precess. Since bearings and motors are not perfect, the gyro won't always hold the proper heading for the entire trip. A certified IRS should be accurate to about 650 meters in 1 hour. That means that the aircraft know where it is in the world with a 650meter sphere around it. Most modern aircraft will update the FMS with GPS information, allowing the IRS and the GPS to argue about who is more accurate.

The IRS will output all this information, and the FMS will work together to let the pilot know where the aircraft thinks it is. The FMS will talk to the autopilot, and allow it to make corrections to insure the aircraft gets to it's destination.

The FMS will display what it knows to the pilot through various displays. The primary flight display (PFD) will show the pilot the location it thinks it is, along with what is around the aircraft. The control display unit (CDU) will be the user interface where a pilot can enter flight plan, and other information. The ailerons, rudder and elevator will adjust to make the aircraft head to the programmed direction.

When the aircraft is initialized, the pilot will enter a flight plan. The plan will include airports and other waypoints that the aircraft will be flying to. The FMS will also contain the navigation database. The nav database is where all the waypoints are defined, and any important information about them. The nav database is how the FMS uses the IRS data to know if the aircraft is heading to the proper place in space or not.

 About here is where I need to talk about autopilots, and I am running out of space. I'll talk about autopilots in another post.

Keep me up on your thoughts.

UAT or 1090ES?

If you are considering ADS/B, there is a choice to make. Do you install a Universal Access Transceiver (UAT) or the Mode S transponder that has an extended squitter (1090-ES)? It all depends...

What country are you in? If you aren't in the USA, then the choice is pretty much made. The USA offers the option of a UAT. The rest of the world needs Mode S transponders for ADS/B installations.

If you are in the USA, and you mostly fly above FL180, then the choice is pretty much made again. The FAA doesn't allow aircraft flying above 18,000ft to use the UAT. It just makes sense to get the 1090-ES transponder that will do Mode S if you want take advantage of ADS/B and fly about FL180.

The UAT transmits and receives on 978MHz, the 1090-ES transmits and receives on 1090MHz. The ADS/B system will allow all participating aircraft to see each other. If the two devices work on different frequencies, how does a 1090MHz transceiver see a 978MHz transceiver? The ground stations will repeat the 978MHz messages on 1090MHz, as well as repeat the 1090MHz message on 978MHz. The ground station will also show both messages on the "RADAR" scope, so the air traffic controller knows where everyone is.

The FAA separated the two systems for a couple reasons. The 978MHz devices can handle more data (has more bandwidth), so more aircraft in a concentrated area will work without overloading ground stations or other aircraft. The 1090 Mode S transponders are already on the larger faster aircraft that are flying higher, so the expense should be minimized (I am repeating the FAA here, in reality, most operators will need to replace the transponders they have to get the extended squitter feature).

The UAT's are even more useful, since the FAA will broadcast extra information. The two extra messages that the FAA is broadcasting are the TIS/B and FIS/B. The 1090-ES system will get TIS/B, but not FIS/B.

TIS/B is Traffic Information Service-Broadcast, where non-ADS/B equipped aircraft will show up on the aircraft display, similar to ADS/B equipped aircraft. The ground station will broadcast the position of aircraft that are only visible on RADAR. As a pilot, you will be able to see more of what the controller sees.

FIS/B is Flight Information Service-Broadcast. Flight information includes weather, and aeronautical products. While XM provides some weather, that you must subscribe to, the FIS/B is free to everyone. The XM product may have additional information, or be more timely. The FIS/B data is what the FAA will be looking at, including potentially air traffic control. The aeronautical products appear to be weather like items, such as NOTAMs and SUA status.

Exactly what device to get will depend on the capability of the chosen display. Many of the MFD manufacturers will take either device for input, the displayed information may help make the choice. Some will show the weather RADAR information in great detail, others will show it blocky or not at all. Over the next couple years, the MFDs are sure to get better.

Should you wait, or should you buy today? Today the ADS/B MFD technology is being developed. Over the next 5 years, the technology will surely mature. Having ADS/B in on a tablet computer will allow a pilot to get their feet wet, sooner. By 2020, most aircraft will be required to have ADS/B out, which probably means, unless someone builds an under $1000 solution to ADS/B out only, most aircraft will be equipped with ADS/B in and out.

Can you get rid of your transponder once you have ADS/B? No, the Mode/C component will still be needed for RADAR service and TCAS for non-ADS/B equipped aircraft.

It'll be an interesting couple years going forward. What do you think?

Transponders

Surveillance RADAR is very useful, and can be augmented like GPS. RADAR alone can only tell range and azimuth. If the transponder is added, the range and azimuth can be augmented with altitude and identification.

Transponders are transceivers, like DME. When the RADAR interrogation is received, the transponder transmits a specific response. For most GA aircraft, the response will be the identification (mode A), and the altitude (Mode C). The transponder concept comes from a technology developed around WWII, used for positively identifying friend or foe targets (IFF). Early targeting RADAR on aircraft could identify targets, but not who they were. Occasionally people will still call a transponder  an IFF box.

If the transponder is Mode S, the response will include quite a bit more information. The mode  S transponder has a payload capable of holding identification, altitude, and various other information, depending on mode. The message can be 56 or 112 (extended squitter or ES) bytes and include a 24 digit ICAO identifier assigned to each unique aircraft. Location and speed can also be encoded in the response. There are various modes the Mode S transponder will work in. (For a good article that covers much of the ModeS modes, see this EETimes article)

Usually aircraft transponders will transmit on 1090MHz. TCAS receivers and RADAR antennas will all be expecting to receive messages on 1090MHz. The transponder is mostly listening, but can be quite busy in class B airspace, with several TCAS units pinging traffic in the area. 

The code that is entered in the transponder is asigned by ATC. There are only 4096 unique codes, and some are reserved (IE 1200, 0000, etc). The numbers are limited to 0-7 or octal digits (octal = 8, and 0-7 are 8 distinct values). Octal is a throwback to early computers that were used for Air Traffic Control, and numbers were represented in octal values. On a busy day, there may be more than 4000 aircraft in the air at once, how does air traffic control keep conflicts out? Certain ranges of transponder (squawk) codes are reserved for local traffic (staying in the area, like training, or ferry flights). Other ranges are for long distance flying, some east, some west, depending on origin and destination. Occasionally, something unexpected happens, and two aircraft with the same transponder code appear in the same area, and the RADAR display will alert the controller to that.

The altitude that all the transponders send is pressure altitude. Pilots will set the altimeter on the ground to local barometric pressure. The altitude encoder attached to the transponder is not adjusted to local barometer. ATC will set their scope to the local pressure. Having ATC consistently reading the same uncompensated pressure will allow more consistent readings aircraft to aircraft. Sometimes pilots will forget to change their altimeter, or set it wrong, and this would cause trouble for ATC trying to figure out what everyone's altitude is. If ATC is saying the aircraft reporting altitude is significantly different than the pilot thinks they are flying, ATC may ask the pilot to stop reporting altitude, and the pilot will switch to Mode A.

Most Mode S transponders are capable or working in Mode A/C or just Mode A as well. Mode S transponders, with their large payloads can be used for ADS/B as well. ADS/B will require other  transponders in the area to be sending specific payloads, in order to plot the position on the receiving aircraft's display.

Transponders add a great deal to RADAR. Transponders will stay on aircraft even after the aircraft are switched to ADS/B. Eventually, the need for a transponder will be replaced by the ADS/B system, but that may be many years. 

Whats wrong with RADAR?

Ever see the news reports about the "World War II RADAR technology"? The headlines are usually provided by the FAA or other vendors when talking about NextGen technologies. RADAR has significantly improved since World War II. It is much more reliable, more consistent, and more accurate. The output now is mostly digital, and requires little adjusting.

All RADAR systems work by sending out a radio signal, and listening for that signal to bounce off a target, and timing the round trip of the signal. A passive RADAR signal is one where dish sends out a signal, and listens for the return. The passive RADAR message can only measure distance from the dish. Knowing the orientation of the antenna when the target distance was measured will allow the operator to know the range and azimuth of the target relative to the antenna.

The radio signal goes about the speed of light through the air, or about one foot per nanosecond, or about 5ms per mile, and remembering to double that for the round trip, will allow the RADAR system to determine the distance.

The RADAR dish is used to focus the transmitted signal, as well as the return signal. The pointy part near the bottom of the dish is the antenna for both the transmitter and receiver. The dish is a parabolic reflector, with the antenna at the focus point. The antennas are aimed at the dish. While the antenna does a good job of focusing the signal, it still goes out in a cone shape.

RADAR will detect various targets. The metal targets reflect the radio signals well. Other material will reflect at different levels. Most aircraft have metal somewhere, including tube and fabric, composite and wooden aircraft. Water also reflects radio signals. A large blob of moisture will show up on RADAR as a target. The processor on the RADAR unit will separate the blobs of moisture from the metal things. The blobs of moisture will be called weather, and the other metal objects will be considered primary targets.  

Many dishes have a secondary surveillance antenna on them as well. Secondary surveillance is used to listen for the transponder that is on many aircraft. The transponder on the aircraft will transmit the aircraft altitude, and some other data. The transponders will automatically transmit when they hear the RADAR interrogation signal.

Mostly there are two types of RADAR in use for civil aviation in the US, enroute and tracon. Enroute RADAR, or ARSR covers a radius of about 250 miles, and the dish rotates in about 12 seconds. Tracon RADAR covers about 60 miles, and the dish rotates in about 4.7 seconds. Both RADAR types can feed computers, that allow different people to see different views of the same data.

Since the RADAR signal go goes out in a cone shape, the exact position of the aircraft is less accurate the farther the target is from the RADAR antenna. The tracon RADAR will be more accurate than the ARSR RADAR since it is turning faster, and only is looking at shorter distances.

The RADAR signal can be blocked by buildings and terrain. Buildings and terrain can also reflect signals. Reflected signals can make the targets appear to be farther away. If an aircraft is opposite terrain relative to the antenna, it won't be picked up by the RADAR. Enroute charts will have a MSA altitude indicating the lowest altitude the RADAR can allow the controllers to see the aircraft.  

The RADAR units will output various channels, weather, secondary, and primary target data.  This data will be collected by computers, and be correlated to determine a track. Correlating the secondary target with the primary data will allow a track to know an aircraft speed, altitude and location. Correlating the signals will also need to remove bogus signals, like reflections, or smallish blobs of weather.

Newer technologies called multilateration is another way to find an aircraft. The multilateration will rely on the transponder on the aircraft. The ground station will have multiple receivers in known locations. A transmitter in the area will send out a signal, the transponder will detect the signal, and respond. The ground stations will measure the time it took to receive the signal,and the difference will tell the range and azimuth of the signal. The signal will contain the altitude.

Building RADAR sites can be expensive, building multilateration sites can be significantly less. If some acreage is available, the multilateral station can be a good choice to cover mountainous terrain, rather than building new RADAR sites in the mountains. The output of the multilateration system can feed the same computer systems that are used for RADAR displays.

Modern RADAR systems are quite flexible. Much different than the "World War II technology" the newscasters present. RADAR also has the advantage of not requiring any technology on the aircraft to work. Should an aircraft have a system failure, or an operator turn off a transponder. The FAA would like to decommission RADAR, but I believe long term, they won't completely. DOD and other organizations will require their existence. 

Is that helpful?