Tuesday, April 30, 2013

Next Gen

This is the first part of at least a 3 part post. I could write one giant novel of a post, but then I don't think as many people would read it, and this way I can break things into logical chunks, so people who understand one subject (IE WAAS) don't have to read that.

GNSS Basics

GNSS stands for Global Navigation Satellite Systems. That means there are signals coming from satellites that help you know where you are. In the USA there is the GPS system, Russia provides GLONASS, China is building Beidou and the EU is building Galileo. While they all generally do the same thing, they all do it slightly differently, and on a slightly different radio frequency. All the systems do is tell you what time the satellites think it is, very accurately.

I'll say GPS, when I mean any of the GNSS systems, just to make things consistent and short.

All the GPS systems do, is tell you where the satellites are at the moment they sent the time. Since all they do is tell you what time it was when the signal was transmitted. When the GPS receiver hears the message containing the time, and the location, it can calculate how far away the satellite was when the signal was transmitted. Knowing how far away the receiver is from 3 points will give a pretty good idea of where the receiver is. Knowing how far away from 4 or 5 satellites will give even more accuracy, indicating elevation, as well as position on the surface of the earth.

Since the receiver doesn't really know where it was when it was turned on, it needs a couple minutes to figure out all the possible positions it could be based on the number of receivers it can hear, and how far away from them it is.

Radio signals are pretty reliable, but sometimes they are interrupted, or bounce around. Ever have some ghosting images on a TV from signals being delayed to the TV receiver? The same thing can happen with GPS receivers. Various atmospheric conditions can delay or accelerate signals. Close to the ground in an urban setting can be the worst, since the signals will bounce off of buildings and vehicles making the receiver work extra hard to figure out where it is. If a signal just doesn't make any sense to the receiver, it can reject that signal.

The satellites are moving at around 17000mph, the earth is turning at about 650 mph and the receiver may also be moving. The earth is not round, it is egg shaped (average). The math gets quite complicated. There are some handy mostly simple formulas to get latitude/longitude math at http://williams.best.vwh.net/avform.htm. Add in some other math to calculate the movement, and now things get all kinds of fun.

Since everything is moving, sometimes several satellites will not be in optimum positions to let the receiver hear them. Some be very close together, straight up, or some may be close to the horizon. If they are all bunched up in the sky, their time will all be the same, and it will be hard to differentiate between the signals. Likewise when the satellites are close to the horizon, they will subject to more interference, either through buildings or mountains.

The GPS constellation has about 32 active satellites. That means 16 are on this side of the earth and 16 are on the other side. Actually it will be maybe 12, since probably 4 of the 16 are too low on the horizon just rising, or just setting. Sometimes too, the satellites are having maintenance done on them, with software upgrades, or other tests. Hearing 8 satellites in any day is a really good place to be.

Because of the dynamic nature of the satellite constellation and the earth, and the vehicle we may be in, sometimes we don't get a good signal. The quality of the signal can be predicted. The FAA provides a web site that will show the current and future signal quality for the USA. If you use java in the browser the tool is very dynamic: http://www.raimprediction.net/applet.php Looking at the top of the page, there are also summaries. When they show a red area, that means the accuracy quality worst case is not able to be met for that time period. The 3 levels they show are enroute = 2miles, terminall=1mile, NPA=0.3 miles.

GPS is giving the position of the receiver in 3 dimensions. GPS can calculate latitude, and longitude as well as altitude. If the latitude is off by 0.3 miles, that means the altitude is also off by around 0.3 miles, or 1500 feet. Vertical guidance by GPS seems a huge challenge. Many aircraft receivers have an option for barometric aiding. The altimeter in the aircraft works by measuring changes in barometric pressure. The same concept can be used with the GPS receiver. By feeding the receiver with a know barometric pressure, it can more accurately calculate altitude.

Various GPS receivers are available in the aviation market that are built to various standards. Most of the early GPS receivers installed in aircraft were certified to a TSO C-129 standard. Some aircraft may have TSO C-196 standard receivers as well. The C-129 and C-196 receivers are able to receive GPS signals and may be enhanced with some kind of barometric aiding. The more popular standard these days are the TSO C-145/146 standard receivers. The C-145/146 receivers are able to receive WAAS signals.

WAAS is a Satellite Based Augmenation System (SBAS). WAAS stands for Wide Area Augmentation System. WAAS is another satellite or constellation that broadcasts correction values to GPS receivers. The WAAS system has a few ground based systems at known locations measuring the difference from the GPS broadcast position and where the location really is. Receivers listening to the WAAS signal can adjust the calculated GPS position using the known difference to be more accurate.

Any aircraft flying relying completely on GPS navigation is required to make a pre-flight check. If the receiver is using the C-129 or C-196 standards, then a full RAIM prediction must be made. The above map at http://www.raimprediction.net is sufficient. For aircraft using the C-145/146 standard receivers, then a check for GPS NOTAMs is required.

GPS Receiver Systems

A typical aviation GPS receiver is really a system. The GPS receiver can only tell you where it is. Typically the GPS receivers are connected to computers that are watching where they have been, and projecting where they are going. There is a function that can be used to smooth out the path, and predict where everyone is going called a Kalman Filter. There is some mapping software that holds the location of most of the waypoints for the region. The computer is also connected to a display to the pilot can see where they are, and enter a flight plan.

Next time I will talk more about augmentation systems. The third part will be about RNP and ADS/B.

Thanks for reading, and I look forward to some feedback.

Monday, April 29, 2013

Batteries in Airplanes

Batteries seem to be a popular subject these days. Certainly the 787 has had it's share of trouble. Even a couple years ago, batteries in phones and laptops were catching fire, seemingly randomly. Mostly the fires have been harmless to people, but the equipment hasn't come out so well. During 2007 there were several laptops that spontaneously combusted Here is one (warning coarse language) http://www.youtube.com/watch?v=mlZggVrF9VI. Several manufacturers had recalls, and since then, there haven't been too many laptops that caught fire..

About the time everyone figures the trouble is over, people start getting burned with cell phones in their pocket. I have a couple batteries from my previous phone that are slightly bulged. The bulges signify something bad happening on the inside of the case. Bulging is a mechanical function, charging is normally a simple exchange of electrons.

I don't know the details of the 787 exactly, just what I have read, and the pictures I've seen. It seemed the original design had multiple cells packed together inside of the blue box. The new design has insulation between cells, and the cells are isolated. Lithium batteries are more likely to fail when heated. If one cell is misbehaving and getting warm, and touching another cell, the non-warm cell is more likely to do something bad, even though everything about it is normal. The misbehaving cell will inspire the adjacent cell to enjoy its company. Their friends may joint in, being neighborly, and things are getting quite hot now. The heat seems to multiply, especially being in a box, and suddenly there is smoke coming out.

There is a theory that all electronics run on smoke. When the smoke gets out, they quit working. Batteries tend to be the source of smoke for many electronics, so when the smoke gets out of them, things really don't work.

Why would anyone put something that dangerous in their airplane? As Collin Chapman used to say about building race cars, "Simplify, then add lightness", or Burt Rutan used to say, "Throw it up, if it comes down, it doesn't belong on your airplane". Basically what these people are saying, that making things light is the proper way to build airplanes, and cars. Why lithium? Look at this table:

      Fuel        |             Watts / Kilogram
    Lead Acid     |            0.05
    Lithium       |            0.224
    Gasoline      |           12.88

Lithium batteries are much lighter per unit of work (watts).

Wow, that does seem dangerous, or does it. Well, it is significantly more dense than a lead acid (the traditional airplane battery, although some airplanes are now ni-cad powered), and quite a bit less dense than gasoline. No one carries gasoline in their pocket.

How much battery does an airplane need. I built and airplane once, and was told I only need enough battery to start the engine. Once the engine is started, then the Alternator should take over powering all the accessories. All the radios, gear retracting motors, and lights all run off the alternator. A bigger battery might be handy in case the alternator quits, but then you are hauling around a battery for every flight that you may never need. A second "back-up" battery is just extra weight that you haul around.

Airplanes should be designed so failures are an inconvenience, not a catastrophe.  If your alternator fails, you know the battery will be dead eventually. Once it fails, you can continue without radios and such, or you need to land before it gets dark. With a backup battery, you may continue farther, but you will still need to land soon.

In a modern jet airliner, there are alternators on each engine. Two seems like a good idea. There are actually 3, since the aircraft actually has a third turbine engine called the auxiliary power unit (APU). The APU is hidden in the tail of the aircraft, and connected to a generator capable of starting both engines, and running the majority of everything electric in the aircraft.

The 787 is unique, in that there is no hydraulic system to help the pilots fly the airplane. The items normally controlled by hydraulic fluid are run by servo motors, including control surfaces and brakes. The electrical system is quite important.

The batteries will help start the airplane. On the ground, there will usually be a device called a ground power unit (GPU) that will allow the aircraft to be started. The GPU can also be used to charge the batteries.  If the aircraft is operated away from the GPU, the battery will usually start the APU since that is a smaller turbine. Once the APU is started, it will be used to start the other engines.

Will the new battery solution help prevent a catastrophic failure on the 787. Probably, since the misbehaving battery cell will be isolated from its neighbor. Will there be cell failures? Probably, but the new monitor system will alert the pilots, and isolate the bad cell when needed.

If someone wants to have a wanna be engineer to ride around on the 787 during test flights, I'll volunteer. Give me a call, we'll set something up.


Saturday, April 27, 2013

Sequestration Ha!

I was going to write something about the furloughs and why they would cause the delays that they do, but I think everyone has heard enough. Now that they are over, it may not matter, but then again, how are they going to end...

So in a contract position, a fraction of the workforce was forced to reduce their work by 10%. Everyone is supposed be treated equal, so how can this be, not everyone had their work cut by 10%? How are they going to make it fair? The whole mess will take over a month to resolve, unless there is an emergency order, causing the folks who got the time off to be paid for the time they took off anyway (such a deal!).

I don't know if the whole deal was worked out yet. Sure congress got beat up, and something happened, but has the President signed off on it (does he need to, I am thinking he will eventually). The whole deal is a rob Peter to pay Paul anyway. No one authorized the FAA to spend what they used to spend, just that they can use some other money to pay the controllers. That money is still ready to be used for the projects it was originally intended to be used for, and someone else will be screaming if they don't get theirs.

Why do to furloughs cause delays? In a air traffic control center, there are various geographical regions that are covered, broken into sectors. Not all controllers are certified to work all sectors. The midnight shift will combine multiple sectors and work them together, where during the day, a single controller or team (RADAR (R) and Data (D) side) will work a single sector. If you don't have enough staffing, the number of controllers certified to work the sectors will be reduced.

One day the guy certified to work sectors 1,2 and 3 will have the day off, and the next day the guy certified to work sectors 2,4,6,8 will have the day off. Scheduling becomes a challenge. Then throw in vacations, and sick days, and some days you may only have one guy on a shift qualified to work sector 5 or something. For one guy to handle the sector, then only maybe 12 aircraft can be in the sector at a time. Maybe it is a gateway sector, and he is doing his best but that means that sectors 6 and 4 have to hold or slow down aircraft. Slowing aircraft has a ripple effect, and sectors 3 and 7 have to manage the aircraft coming into sectors 6 and 4 smartly (and so on).

Equipment went from same day repair to next day repair. It wasn't just the controllers on furlough, but tech support as well. If the only person who normally would be on staff certified to repair some piece of equipment was off that day, the equipment was out of commission. Maybe it was not terribly critical, but caused more inconvenience to the controller, they will have to slow even more.

So traffic backs up all day, and the airlines are taking delays. (travelers still bought tickets, and they want to get where they are going). There ends up being higher volumes of traffic at some airports until well into the midnight shift. The midnight shift that is short staffed with overlapping sectors. All the FAA can do is ask some of the night shift controllers to stay late (and pay them overtime) since the sectors will be impossibly full until even later. So everyone is taking a 10% paycut, but to make that work, the FAA has to pay overtime to some of the staff. 

Since the first week required one third to half the staff to take a day off, how is it that the other folks are going to balance that out? Again, with vacation and sick days, to make it fair, it'll probably take a month for everyone to have the same hours. I know it says that they will "fix" it by Monday, but how can that be? There were controllers who decided the whole government employment situation is silly, and took their retirement, or just quit once they got threatened with the furlough.

It kind of begs the question, who is in charge? Congress tells the FAA to cut spending, and the FAA says we can cut this or that expense, and congress says no, not that one. Why have any administrators if congress is just going to override their decisions. Tower closures were overridden. For many years the FAA has been trying to consolidate TRACONs and such to save money, but it seems someone in congress forces the FAA to not do it. Congress talks the big talk, cut, cut, cut, but when they do, they say "not that way".

Thursday, April 18, 2013

Routes to Nowhere

Even professionals do silly things sometimes. Take a look at this approach plate for Nashville Tennessee.
Click to Zoom
The other day I saw a route from MDW to this airport that was something like


It seemed ok, pretty simple. I remember a controller telling me once, you don't want a clearance to an airport, you want a clearance to your approach, especially in the radar environment.

Look at the plate again, BNA! that is a VOR on the airport, but it isn't an initial approach fix (IAF). The FIDDS intersection is the IAF for this approach. Even from the North to the 20's runways, BNA isn't an IAF. 

So this poor pilot was cleared to a VOR. What should the pilot do if he looses communication? Assuming this was a ICAO flight plan, the destination airport was in field 16, no big deal. ATC should know where you want to end up. But what should this pilot do when they get to the BNA VOR in the soup? (assuming they have ILS or VOR receivers but no COM, it could happen).

Even if the pilot had good radios, and was planning on the ILS 2L, what should the controller tell this poor pilot? Well he has to figure out a way to this approach. Using the 2's, no big deal, since BNA is mostly on the way to FIDDY. Imagine though, the pilot wanted to go to the 20's. The IAF for the ILS 20R is HIKRY. HIKRY is 20 miles to the north. The pilot still gets to fly 40 miles more than needed to plus two huge turns. It isn't that far, but the pilot is still in the airport traffic area and has the controller guessing what to  do with this aircraft, to keep the pilot out of the way of all the other aircraft.

If the flight plan were filed to the IAF, or better yet, to a transition point on a STAR, so the sequencing can be done easier. The controllers like to know where you are going as far out as practical. The controllers like more time to think, and plan ahead, knowing what is planned, things go smoother.

Probably the proper route would be (ICAO format):

Getting off of J73 at PXV is safe and about as direct as you can get. It is 128 miles and gets the aircraft on the ILS 2L without any questions. The controller can assume the aircraft is going on the ILS, assuming ATIS says ILS 2L approach is in use.

I am hoping this helps. Any other thoughts?

Tuesday, April 16, 2013

Drones In Airspace

There seems to be a huge "land grab" trying to happen these days. Drone builders are wanting their products to be sold at all cost. I don't blame them, who doesn't want their product to sell. There are a couple issues to work out before we have our sky's filled with buzzing aircraft.

1. Safety
The airspace already has many aircraft in it. People fly their personal airplanes everyday, and there are airliners flying others even more. How are we going to insure these different aircraft don't come in contact with each other. To keep the "little guys" out of the way of the "big guys", there are specific rules. There is positive controlled airspace (the airspace between 18,000ft and 60,000ft) where anyone flying there is required to have altitude reporting transponders, and IFR flight plans and ATC is responsible for separating aircraft.

Below 18,000ft, the rules are different. Pilots are to see and avoid each other as the first line of defense. Aircraft flying easterly are to use odd thousand altitudes (IE 7000ft, 9500ft, etc), and flying westerly even thousand feet (IE 6500ft, 10,000ft). That helps separate aircraft, and mostly avoids head on collisions. The pilots are responsible for their own separation, when flying on visual flight rules (VFR). Pilots flying on  instrument flight rules (IFR) with a flight plan have ATC keeping an eye on them, as long as they are above the altitude that the RADAR can see them.

Piloted aircraft have great visibility, usually. The windows allow a wide field of view, and the pilots can rely on peripheral vision to see what is happening around them. Pilots are taught to scan the sky, and can usually pick out another aircraft well before most of the passengers even know it is there. If there is more than one pilot, the second pilot is also scanning, and the two pilots will be able to keep each other aware of any hazards.

While it sounds pretty fool proof, there are still mid-air collisions. Transitioning altitude accidents are the most common. Climbing from the departing airport to 10,000ft an aircraft will transition several even and odd thousand altitudes. If one of the pilots in that altitude, or the climbing aircraft isn't scanning, they may miss the climbing aircraft. Similar with descending from cruise altitude to the arriving airport, there may be conflicts. There are differing speeds of aircraft as well, and this can cause issues. If a 200mph aircraft is converging on a 120mph aircraft, at a 90 degree angle, even if both aircraft are going westerly, for instance, they may be in conflict, and have to avoid each other.

Drones whether remotely piloted or autonomous may pose a greater risk. They may fly following all the same rules as piloted aircraft (even/odd altitudes,see and avoid, flight plans, and ATC separation) they don't have the same capabilities. There are limitations of cameras if so equipped, communication latency, and other sensors are lacking.

The field of vision for most cameras isn't anywhere near the 180 degrees most people have of peripheral vision, and that is the biggest trouble. What the pilot can't see, they cannot avoid.  Radio waves can only go at the speed of light, maximum (roughly 1 foot per nano-second, 5280 feet in a mile = 5280 nano-seconds or about 5 micro seconds, then a thousand miles would be 5 milliseconds). What the pilot sees will have to be send via some radio from the aircraft to the pilot.

Being thousands of miles away from the actual aircraft that the pilot is flying will cause latency to the controls, that is basic physics.  It doesn't sound like much, but it matters, since what the pilot sees is from say 5 milliseconds ago, and what the pilot does takes another 5 milliseconds to start the affect. If the aircraft is satellite linked, start making that seconds, since satellites are thousands of miles up and the radio signal is not going straight up and straight down.

Communication links fail. They just do, it may be something completely random, like a backhoe taking out a ground based link. An antenna may break or fail due to ice or other cause, and sometimes radios just quit. Who controls the drone then? Maybe the drone should stop or fly in a circle until control comes back, it isn't on a flight plan at that point so what should ATC do about it? What happens when it runs out of gas, or battery? Can a drone call mayday?

There is lots of talk about aircraft broadcasting satellite based location information. The technology is there to do it, and many aircraft will in the future do that, but not all aircraft will ever. It is still legal to fly an aircraft without an electrical system. The systems to broadcast satellite based location are still thousands of dollars ($5000-10000), and this can sometimes represent more than half the cost of a whole aircraft (yes, you can buy an airplane for under $20,000), not everyone flies a multimillion dollar jet. How will the drones ever see one of these non-GPS equipped aircraft? (how about if the drone manufacturers develop a small, battery powered  $500 ADS-B in/out system that they can give to the general aviation community?)

In the current situation, a collision scenario is not an if but a when. Will it be a 747 with 300 people and a drone, or will it be a commuter jet with 50 people? Does it matter? Who will get the blame, the people who pushed the bad legislation through, or the poor pilot of the drone (could you live with yourself?)

2. Privacy
What are people wanting to do with all these drones. The manufacturers have all kind of ideas, like launching weapons, and surveillance. I don't think we need some municipality having armed drones, and the local sheriff deciding they need to get the drone out to control the crowds. 

Who will be buying and operating these drones. The manufacturers want nearly everyone to have one. More users mean more money. So maybe the local newspaper will use them to help get to a newsworthy site quickly, that seems good. What about the gossip paper, who might be nosey, or someone fishing for something to report, should they be able to go look for stuff to report?

You say, you don't have anything to hide, so it shouldn't bother you. I normally don't have anything to hide, but I don't really want free reign on people just looking! Not that anyone would want to see me naked, but do I need to close all the shades every time I am changing clothes in my bathroom with only a window well above me? Say I do something that may look shady to someone who flies over at the wrong time, might they report that?

Imagine the drones are connected with surveillance devices besides video cameras? Listening devices and radio scanning devices come to mind. Maybe someone wants to listing to what is happening below. Never mind bugging cell phones, that is too complicated. Detect things from the source. Think it can't happen?

3. Noise
The folks who don't like airports in their back yard should be all up in arms about dozens of these drones taking off and landing in their neighborhood. Many of the bigger drones will need real airports, and make real airplane noises. Smaller drones may may buzzing noises, that may not be as loud as real airplanes, but could still be annoying.

Remember the plan is to have more drones than current piloted aircraft. Lots of quiet things make a noise, anyway. What will people do about that problem. More make more noise, it all adds up.

Thoughts about solutions.

I am not totally against drones. They will have their purpose. Mostly in combat situations, not spying on the general citizens. The test areas should be out over completely unpopulated areas, like the ocean, or wide open desert areas where people don't typically fly.

If the drone builders can come up with a workable solution for the see and avoid problem, that doesn't cost the people in the civilian airspace then I could see limited mixing. It doesn't seem reasonable to make people who have nothing to do with this technology pay to make them work. (the old change the laws until your business plan works model, shouldn't apply in this situation)

Armed drones should never be allowed over civilian population, in the US or any other country. Armed drones should only be allowed in front line combat. This bit of common sense will be ignored, and people will get hurt, but it will be justified to most people.

Aviation is expensive. There are limited exceptions, but to play with the big boys, it will take real money. 

Friday, April 12, 2013

Hijacking With Android

Nope! not gonna happen. Well, not without a lot of other technology.

CNN as they are wont to do, posted a sensational article about some dude using an Android phone app to take over an airplane. That is all it is, sensational. There are some bits that could be true, but lets look at things from a more technical point of view.

Hugo Teso used a simulator to 'demonstrate' this 'hack'. It wasn't on a real airplane. The hardware he chose was not flight certified, so most of his claims are completely dubious.

First, lets get some terminology right. Hackers are getting a bad rap by this Hugo. Malicious people are crackers or criminals. Hackers are are people who repurpose technology. Think of a car customizer, someone who takes perfectly good cars and makes them better or different, they might be considered a hacker. In the pre-computer days, hackers were the folks who could do amazing things with very little. They were the folks you went to, to get things done. Places like Hack A Day is an example of a group of these folks, or the Maker movement.

An Android cellphone only work in frequencies maybe at the low end 700MHz, and if you include Bluetooth and WiFi there are radios that talk in the 2.5GHz or 5GHz frequencies. There are actually several radios covering the various modes, including Voice and the various data modes, like 3 and 4G, HSPA+, LTE, etc. They are all between about 700MHz up to about 5GHz.

ACARS is a ground to air digital messaging system. Think of it like instant messaging ( IM) from the airline operations center to the airplane. ACARs allows the airtraffic Controller Pilot Data Link Commands (CPDLC). The ACARS radios are in the 110-130Mhz frequencies. The Cell phone can't talk on frequencies that low. He would need a radio that will talk on those frequencies to talk to the ACARs device to inject some CPDLC commands. The CPDLC commands are like "turn right heading 230", the pilot must acknowledge or reject that 'command' before the aircraft will react.

ADS-B is a technology that allows the airplanes to tell each other where they are using GPS location, and a transceiver that are in the participating aircraft. The ADS-B signals are either on Universal Access Transceiver (UAT) on 976MHZ or on 1090Mhz mode-s transponder frequencies. Since UATs are US only, the dude might have gotten his cellphone to talk on the 1090Mhz frequency (although that is highly unlikely, but I don't know what brand phone he had or what radios the european version of that phone contains, it may be possible). Most of the radios in the phones aren't that programmable, and the FCC pretty much gives the 1090MHz frequency and surrounding frequencies to aircraft and not cell phones.

The Flight Management System (FMS or FMC) are the 'brains' of the aircraft. It manages the auto pilot, connects to the ACARs radio, and the initertial reference system (IRS) some of the other navigation systems. The FMS talks to the airplane. The FMS doesn't talk WiFi, so you can't just use the WiFi on the airplane to talk to the FMS or any of the displays in the cockpit (unless they have an iPad or other tablet, but those aren't connected to the airplane anyway). The FMS usually talks something like ARINC-429 and has a giant plug on it with each device having a separate wire.

FMSs can be reprogrammed, but not over the air (at least that I know of, there may be some new brand or version that can be, but if that were allowed, I am pretty sure it wouldn't allow being reprogrammed while controlling the airplane). They are finicky, and the ones in version X of the 737 can't be programmed the same way as version Y of another 737. If you want to know if Airbus and Boeing share anything, it is unlikely any of those FMSs would even share one line of code.

There is no one technology that can get this guys app to hijack a plane. You aren't going to find terrorists lining up at the T-Mobile stores to buy Android phones and downloading the app so they can take over the airplanes. Actually some might, it might be good for the stores selling phones, but folks are gonna be disappointed, and return the phones, and go buy and iPhone to be like all the cool kids until Apple comes out with that app.

We can all relax, sit back and enjoy the ride. Airplanes won't be hijacked by cell phone.