Over the last couple years, I have written about many bits of technology that aircraft use. I really haven't discussed too much what bits are used when, and for what. This post, I will try and tie all the items and their use into a comprehensive post. I'll use a commercial airliner (Part 121) for the discussion, both because they typically use more technology, and because that is what my background is. I will also base most of this on flights in the US, to keep it simpler.
We can start a few hours before the flight actually leaves. As the flight approaches it's scheduled time to leave, a group of folks have started planning for the flight. Sure, there is network planning, they set up the schedules and try to be sure the flight will make money, and provide continuity, and such, but that is usually done months in advance. There are also the simulators that the pilots use for proficiency checks, and training, but that is on going and not related to a particular flight, but important none the less.
Dispatchers and meteorologists are considering the situation between the origin and the destination of the flight. The meteorologists are generalists, looking at the weather over the country, where dispatchers are more concerned with the weather along the route between the cities. The dispatcher needs to consider the situation at the specific airports, for runway closures, and other challenges unrelated to weather. There is a tool called Collaborative Decision Making (CDM), where the dispatchers work with the other airlines so everyone can utilize the airports and airspace as optimally as possible.
The dispatchers can use CDM to look for areas to avoid when selecting a route between the two cities. If there is a bad thunderstorm along the optimum route and all the other airlines are avoiding it to the south, the dispatcher may pick a northern route to stay out of everyone elses way. Once the dispatcher selects a route, they need to build the rest of the flight plan. The dispatcher will build a flight plan using many tools. The dispatcher may allow the flight planning engine to select routes, or the amount of fuel. Depending on aircraft maintenance situation, and MEL deferrals and such the flight planning engine can accurately predict the fuel burn based on weather and route.
Once the dispatchers are happy with route and fuel selected, they will file a flight plan. The flight plan will be filed with the Air Navigation Service Provider (ANSP) for both the origin and the destination. For the US the ANSP is the FAA, in Canada is is NavCanada, and in the UK it is NATS. The ANSP handles all the RADAR and air traffic control (ATC) functions. The flight plan will give the ATC controllers a heads up on what the aircraft was planning on doing once in the air.
As the pilots get to the aircraft, one will typically do a walk around of the outside of the aircraft making sure the aircraft looks safe and no damage is visible. The other pilot will typically go to the cockpit and begin setting things up. There may be a the initialization of the FMS, maybe a RAIM check of the GPS, and entering the flight plan prepared by the dispatcher into the FMS. The dispatcher provided flight plan will usually include weather information for the route, and any other non weather realted information for the route (IE ATC changes, etc), The flight plan will also contain fuel and time information that the pilot can double check, insuring the dispatcher hasn't made any mistakes.
When the pilot know the fuel situation, they may confer with the fueler to adjust any fuel amounts to be put on board. The pilot will also need to know how many bags and passengers are on the flight, so they may make proper weight and balance calculations. Some airlines have a load planner who takes care of the weight and balance, others still let the pilot take care of this. Depending on the aircraft, it may be necessary to have a person dedicated to making the load calculations.
As all the passengers are seated, and the pilot is about to move the aircraft, they will ask for permission to move. There may be a ground controller dedicated to the gate area, and there will need to be taxi clearances and such needed from them. Other airports everything is controlled from the tower, and any movement must be cleared through the tower controllers. An ACARs message may be sent requesting the Pre Departure Clearance (PDC), that will be a version of the flight plan sent to the ATC with any ATCneeded changes to the plan. The PDC will also contain the code the pilot needs to enter into the transponder. The pilot must acknowledge receipt of the message.
After the aircraft is taxied to the runway, the pilot will ask the tower for the final airport clearance, by announcing "ready for takeoff". Once the ATC controller gives the pilot final instructions the pilot can access the runway and start the takeoff. The ATC instructions will be the route the pilot should take to get from the runway to the beginning of the flight plan route. Every bit of the instructions and plans for the takeoff are there in case there is a failure. If there is a radio failure either from ATC or the Aircraft, the instructions given are good enough for the pilot to take off, fly the planned route, and approach the destination. It is a safety situation, should the plan be the safest and most expeditious way to fly the route.
Once the aircraft is above about 300 ft, depending on the airport, the aircraft will appear on RADAR. The first RADAR that will show the aircraft is the TRACON, who will control the aircraft after tower hands off the aircraft. The TRACON controller will control the aircraft until it is more than 30-50 miles from the airport. The TRACON will hand the aircraft off the enroute controllers who will control the flight until it is 30-60 miles from the destination airport. The RADAR data will be collected and sent to the FAA command center for others to view, and use the ADSI information. As we move into NextGen, there may be more ADS/B position reporting, instead of RADAR.
Once the aircraft is on the route, the pilots will typically engage the autopilot. The autopilot will help maintain the route of flight, altitude and throttle settings to insure the aircraft flies the route planned, and uses the fuel planned. The pilot must monitor the autopilot to be sure it is engaged, and doing the right thing the whole flight. Occasionally pilots will hand fly the aircraft, for practice. Once in a while the autopilot will fail, and the pilots must had fly the aircraft. The systems in the aircraft are designed for certain reliability levels.
During the enroute portion of the flight, there may be messages the pilots need to send to the company operations center. The pilots will usually send a text message over ACARS if they don't have a lot of urgency to the message. The pilots also have an option for voice communication using company assigned frequencies. If there were to be a medical emergency, the voice communications will be used, if a pilot is looking for a weather report for 400 miles ahead, they will use ACARS.
As the aircraft gets closer to the destination, ATC will typically begin having the aircraft start to descend. Newer approaches follow a continuous descent profile, where the pilots set the throttles to idle at altitude, and basically use the potential energy to glide the aircraft to the runway, reducing noise, fuel burn and pollution.
Current approaches typically are designed for the aircraft to provide it's own guidance. That is there are airs on the ground (or satellite) to provide the aircraft the information it needs to know where it is, and fly to the runway. Features like DME and ILS radions are on the ground, and GPS satellites are in the air.
The enroute controller will hand the flight off to the TRACON controller about 50 miles from the airport, where the aircraft will be below about 10,000ft. The TRACON controller will clear the flight for the approach that it will use to get to the airport. At about 5 miles out, the pilot will be told to contact the tower, and the tower and the pilot will make the final checks and be cleared for the runway to land on. Once on the ground, the pilot will talk to the ground controllers to get to the proper parking area, and maybe a gate controller for certain airports. Once the wheels are chocked, and the engines shutdown, the pilots are mostly done with the flight.
Yes, there is a bit of technology going on between each gate, and a little before. Ever think about that before.
Showing posts with label FMS. Show all posts
Showing posts with label FMS. Show all posts
Sunday, January 4, 2015
Thursday, December 5, 2013
Air Data and FMS
I missed a bit in my last post about FMS's. (I am shortening everything to FMS,
it is mostly the same thing, a system). Air data, what is that...
Air data is usually known as the pitot static system on smaller aircraft. Getting the pressure information into the aircraft involves a analog to digital (A to D) conversion.
All aircraft have pitot tubes to measure air pressure because of speed. Pitot tubes are closed tubes, and the airspeed indicator, or air data computer only can measure the pressure of the air trying to get into them. Larger aircraft may have multiple pitot tubes on them, for redundancy mostly. The airspeed indication is made by comparing the difference in pressure from the ambient air, and the pressure forced in the pitot tube.
The ambient air pressure is entered to the system through static ports. There are multiple static ports on most aircraft. The static ports also help measure altitude and rate of altitude change (vertical speed indication). Again the static system measures change in pressure, from ground level to altitude.
There is a relativly simple formula (thanks to wikipedia) for incompressible fluids pt is total pressure, ps is static pressure, p is density. V becomes the fluid velocity, or airspeed for us.
Air is easily compressible, and that makes the formula a little more complicated, since you have to integrate pressure and stagnation values.
Static pressure is a little easier. The air pressure doesn't change at a constant rate as the aircraft flies at a higher altitude, but the curve is relatively constant. Thanks to engineering toolbox we can use:
p = 101325 (1 - 2.25577 10-5 h)5.25588
p is air pressure (millibars) and h is height above a fixed point in meters. To get the whole formula, you need to include temperature, and humidity as well, see the wikipedia entry if absolute MSL needs to be measured.
A small transducer can measure the different pressures, and provide a voltage that the computer can read. Computers are good at math, even complex math, allowing us to have usable information on heads up displays, tapes and other graphical presentations.
The air data computer reads these transducers, and puts the data into a usable format that the FMS can use.
The FMS allows setting marks called bugs on the instruments. If the pilot wants to fly at 250kt indicated airspeed, they may enter a command on the CDU keyboard, it will display on the airspeed indicator. The FMS also allows setting heading bugs, and feeds the flight director when flying on a flight plan.
There are more things in the FMS as well, and as I have time, I'll keep adding to the blog.
Write, and let me know what you think
it is mostly the same thing, a system). Air data, what is that...
Air data is usually known as the pitot static system on smaller aircraft. Getting the pressure information into the aircraft involves a analog to digital (A to D) conversion.
All aircraft have pitot tubes to measure air pressure because of speed. Pitot tubes are closed tubes, and the airspeed indicator, or air data computer only can measure the pressure of the air trying to get into them. Larger aircraft may have multiple pitot tubes on them, for redundancy mostly. The airspeed indication is made by comparing the difference in pressure from the ambient air, and the pressure forced in the pitot tube.
The ambient air pressure is entered to the system through static ports. There are multiple static ports on most aircraft. The static ports also help measure altitude and rate of altitude change (vertical speed indication). Again the static system measures change in pressure, from ground level to altitude.
There is a relativly simple formula (thanks to wikipedia) for incompressible fluids pt is total pressure, ps is static pressure, p is density. V becomes the fluid velocity, or airspeed for us.
Air is easily compressible, and that makes the formula a little more complicated, since you have to integrate pressure and stagnation values.Static pressure is a little easier. The air pressure doesn't change at a constant rate as the aircraft flies at a higher altitude, but the curve is relatively constant. Thanks to engineering toolbox we can use:
p = 101325 (1 - 2.25577 10-5 h)5.25588
p is air pressure (millibars) and h is height above a fixed point in meters. To get the whole formula, you need to include temperature, and humidity as well, see the wikipedia entry if absolute MSL needs to be measured.
A small transducer can measure the different pressures, and provide a voltage that the computer can read. Computers are good at math, even complex math, allowing us to have usable information on heads up displays, tapes and other graphical presentations.
The air data computer reads these transducers, and puts the data into a usable format that the FMS can use.
The FMS allows setting marks called bugs on the instruments. If the pilot wants to fly at 250kt indicated airspeed, they may enter a command on the CDU keyboard, it will display on the airspeed indicator. The FMS also allows setting heading bugs, and feeds the flight director when flying on a flight plan.
There are more things in the FMS as well, and as I have time, I'll keep adding to the blog.
Write, and let me know what you think
Sunday, December 1, 2013
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.
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.
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.
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.
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