Like mentioned earlier that after the retrieval of the passengers after an incident the second most important priority is the location and the retrieval of the black box. To make that the flight data recorders survive the crash and that the CSMU can adequately and sufficiently protect the Flight Data Recorder and the Cockpit Voice Recorder inside the CSMU manufactures thoroughly test the CSMU's through a number or rigorous tests to make sure they are up for there task.
The tests done by the manufacturers to test the CMSU's crash survival rate are:
Crash Impact Test: the Crash impact test is done applying equal or more pressure then the pressure a CSMU might experience during a crash. The current regulations ask that the CMSU should be able to withstand a impact force of 3400 g's for the time of 6.5 milliseconds. The deceleration caused by an impact of 3400 g's is equal to that of stopping from a speed of 310miles/h or 500 km/h to a complete zero in the only a distance of 45 cm. Test is carried out by placing the CSMU in a air cannon and firing it to make sure that it can with stand at least 3400 times its own weight.
Pin Drop Test:
A pin drop test is a test done to check penetration level of the CSMU and this test is carried out by dropping a steel pin from a height of 10 feet or 3 meters with a force of 500 pounds or 2225 N onto the part of the CSMU that is most susceptible to penetration.
Static Crush Test:
The static crush test is done to make sure that all the sides of the CSMU can withstand a minimum pressure of 5000 pounds per square inch for the least amount of time of 5 minutes.
Figure 08 - Inside the Black Box by Julian Edgar
In a fire test the CSMU is tested to see how much fire resistant it is to fire or high temperatures. To do that it is tested with a Propane source fire using three fire burners to see if it can withstand a minimum of 1100 degrees Celsius for at least 60 minutes. The CSMU also has to be tested at temperatures of 260 degrees Celsius for about the time of 10 hours.
Deep-sea submersion - in this test the CSMU tested to see if it could handle the sea depths of at least 20000 feet for a minimum of 24 hours.
Salt-water submersion - in this test the CSMU is placed in salt water for a minimum of 30 days to test its survivability but also
Fluid immersion test - in this test the CSMU is tested by placing it different types of fluids to check whether it can resist or withstand the corrosive properties of those chemicals. The chemicals the CSMU might be tested different types of fluids such as fire extinguishing fluids and Jet fuel etc.
When the tests are completed the last stage is to dissemble the CSMU and then try to read the pre-recorded data on the memory so as to make sure that the data stored on the memory prior to the tests is still intact.
Flight Data Sources
As mentioned earlier that the information recorded in the FDR are received from the various sensors that are located at different positions across the aircraft. The data from the sensors is carried to the FDR through a digital bus and the rate at which this data is produced by the sensors can be varied from continuously producing data to once per second or even longer but most of the data that is more important to the investigators is not sampled at very high speed so to provide sufficient amount of information to the investigators about that certain parameter.
Broad range of categories from which data gets sampled are:
Flight situation: this is a range of information about the parameters of flying or aeronautical situations of the aircraft, which include parameters such as angle of attack, altitude, vertical speed, heading and airspeed.
Engine conditions: this is information regarding the conditions of the engine of the aircraft and they include parameters such as, oil temperature, engine pressure ratio and the RPM of the propellers.
Flight control Situation: This information involves the data on how the flight control services are acting and the parameters for these would include aileron deflection, elevator deflection, trim tab position, flap direction and rudder deflection.
Flight control inputs: this information is regarding the data of what the flight crew is trying to do the flight control surfaces through the use of there flight control inputs so basically this is related to the flight control inputs. The parameters this category would include would be aileron control deflection, elevator control pressure, flap lever position and rudder pedal position.
Environmental situation: the information in this category is related to the environment in which the aircraft is flying and the parameters under this category would be presence of ice, type of precipitation experienced by the aircraft, direction, wind speed and the temperature outside the aircraft.
The minimum of parameters that need to be recorded in the new digital Solid-State FDR's or also know as the digital recorders is minimum 88 parameters which must include these parameters as shown in the list below:
Heading -- primary flight crew reference (if selectable, record â€¨discrete, true or magnetic)
Normal acceleration (Vertical)
Manual radio transmitter keying, or CVR/DFDR synchronization â€¨reference
Thrust/power of each engine -- primary flight crew reference
Autopilot engagement status
Pitch control input â€¨24
Lateral control input
Rudder pedal input
Primary pitch control surface position
Primary lateral control surface position
Primary yaw control surface position
Pitch trim surface position or parameters of paragraph (a)(82) of â€¨this section if currently recorded
Trailing edge flap or cockpit flap control selection (except when â€¨parameters of paragraph (a)(85) of this section apply)
Leading edge flap or cockpit flap control selection (except when â€¨parameters of paragraph (a)(86) of this section apply)
Each Thrust reverser position (or equivalent for propeller airplane)
Ground spoiler position or speed brake selection (except when â€¨parameters of paragraph (a)(87) of this section apply)
Outside or total air temperature
Automatic Flight Control System (AFCS) modes and engagement â€¨status, including auto-throttle
Radio altitude (when an information source is installed)
Localizer deviation, MLS Azimuth
Glideslope deviation, MLS Elevation
Marker beacon passage
Air/ground sensor (primary airplane system reference nose or â€¨main gear)
Angle of attack (when information source is installed)
Hydraulic pressure low (each system)
Ground speed (when an information source is installed)
Ground proximity warning system
Landing gear position or landing gear cockpit control selection
Drift angle (when an information source is installed)
Wind speed and direction (when an information source is installed)
Latitude and longitude (when an information source is installed)
Stick shaker/pusher (when an information source is installed)
Wind shear (when an information source is installed)
Throttle/power lever position
Additional engine parameters (as designated in Appendix M of this â€¨part)
Traffic alert and collision avoidance system
DME 1 and 2 distances
Nav1 and 2 selected frequency â€¨25
Selected barometric setting (when an information source is installed)
Selected altitude (when an information source is installed)
Selected speed (when an information source is installed)
Selected Mach (when an information source is installed)
Selected vertical speed (when an information source is installed)
Selected heading (when an information source is installed)
Selected flight path (when an information source is installed)
Selected decision height (when an information source is installed)
EFIS display format
Multi-function/engine/alerts display format
Thrust command (when an information source is installed)
Thrust target (when an information source is installed)
Fuel quantity in CG trim tank (when an information source is â€¨installed)
Primary Navigation System Reference
Icing (when an information source is installed)
Engine warning each engine vibration (when an information source â€¨is installed)
Engine warning each engine over temp. (when an information â€¨source is installed)
Engine warning each engine oil pressure low (when an information â€¨source is installed)
Engine warning each engine over speed (when an information â€¨source is installed)
Y aw trim surface position
Roll trim surface position
Brake pressure (selected system)
Brake pedal application (left and right)
Yaw or sideslip angle (when an information source is installed)
Engine bleed valve position (when an information source is â€¨installed)
De-icing or anti-icing system selection (when an information source â€¨is installed)
Computed center of gravity (when an information source is â€¨installed)
AC electrical bus status
DC electrical bus status
APU bleed valve position (when an information source is installed)
Hydraulic pressure (each system)
Loss of cabin pressure
Computer failure â€¨26
Heads-up display (when an information source is installed)
Para-visual display (when an information source is installed)
Cockpit trim control input position -- pitch
Cockpit trim control input position -- roll
Cockpit trim control input position -- yaw
Trailing edge flap and cockpit flap control position
Leading edge flap and cockpit flap control position
Ground spoiler position and speed brake selection
All cockpit flight control input forces (control wheel, control â€¨column, rudder pedal)
Retrieving the "black Box"
As mentioned earlier the so called "black box" is actually a brightly orange coloured box and the reason for that would to increase its visibility while trying to search for in it in the debris of the aircraft crash. Apart from that paint helping to locate the FDR after a crash the FDR's are also equipped with something know as the ULB which is the underwater locator beacon. The picture below of the FDR shows a white handle cylinder that not only can be used as a handle to the carry the CMSU but also is a beacon. The beacon contains submergence sensor on its side which when coming in contact with water gets activated thus sending out ultrasonic signals which might be heard by naked human ears but can be easily picked up by the sonar or acoustical locating system.
The beacon as mentioned earlier during the testing of the CSMU's part of this dissertation can transmit the signals up to a depth of 14000 feet at 37.5 kilohertz and once the process of signaling starts the CSMU can signal one signal per second for 30 days. The battery that is used to power the beacon has a shelf life 6 years.
After the black box has been recovered from the scene of the accident the next step is to extract the data from the black box and since there can be damages this task can be difficult and meticulous. The reading mechanism and software are usually provided by the manufacturers and in the case where the flight data recorder isn't damaged the process of extracting the data is as simple as plugging the recorder to a system to read it and play back the data recorded and with the new Solid-State FDR's also know as the digital recorders this information can be extracted in minutes.
In instances when the recorder recovered from the accident site is damaged the by being burnt or dented the CSMU is disassembled and the memory boards inside that have the recorded information are removed, cleaned and attached to a new interface cable. After those steps are carried out the memory boards are attached to new recorder that has special software that allows the data stored on the memory boards to read easily without overwriting the existing data.
Future Developments of FDR Units
As mentioned earlier that regardless of the CSMU's being built to survive crashed but sometimes the accident can be so devastating that either the CSMU's are damaged very badly or also can be lost in deep water so there new units that are being thought of that would self-eject out of the plane on the point of impact by utilizing the kinetic energy of the aircraft at the point of impact to dislodge themselves from the aircraft.
A bill in America was introduced in 19th of July 2005 known as Safe Aviation and Flight enhancement act of 2005 and the act required that all the aircraft that were legally obligated to carry flight data recorder and Cockpit voice recorder would have to carry to carry another or additional set of digital flight data recorder, voice recorder and a locating beacon which have the use of the self ejecting technology so in a circumstance where a accident would happen the recorder data would eject out of the aircraft allowing the data to be protected from damage. The bill that was introduced to Committee of transportation hasn't been passed yet but maybe in the future with more adjustments it might be looked into but the problem with this process being utulised in the military is that the data that gets ejected might not be safe and might get into the wrong hands.
Air France Flight 447
Figure 09 - Airbus A330-203 aircraft. Photographed by Vincent Edlinger.
Air France 447 commercial and scheduled flight traveling from Rio de Janeiro, Brazil to Paris, France, 1st June 2009 had disappeared off the radar, crashing into the Atlantic Ocean due to a succession of events, according to France's Bureau of Investigation and Analysis (BEA). The aircraft has fallen the vertical distance of 38,000 ft in the recorded time of 3 minutes and 30 seconds, killing on impact the total of 216 passengers and 12 aircrew members.
The investigation to determine what happened to the aircraft carried on for three years after the accident as evidence was not clearly presented; poor eyewitness and radar tracks, but most importantly is the difficulty in obtaining the aircraft's black boxes due to its submergence in the bottom of the ocean. It took two years into the investigation and 25 million pounds to finally find the black box in May 2011 that provided the aviation industry and the rest of the world with reliable information to the succession of events leading to the fatal accident.
The Air France 447 flight aircraft was the Airbus A330-203, one of the safest and most technologically advanced types of commercial aircrafts. It is powered with two general electric engines with the takeoff thrust of maximum 68,530 lb. giving it the speed range of 871 km/h to 913 km/h. The Airbus A330 is an automated aircraft, the autopilot is usually only turned off for manual takeoff or landing, which amounts to 4 minutes of total flight time.
On the 31stof May 2009, the flight 447 departure at 22:29 UTC time for its 11 hour journey from Rio de Janeiro Galeo airport to Paris Charles de Gaulle airport, with 30 minutes delays but nothing to worry about. The plane has three pilots on duty, one captain, Dubois (apx. 11,000 flying hours) and two co-pilots, Robert (apx. 6,500 flying hours) and Bonin (apx. 3,000 flying hours).
01:35 UTC, the flight makes last radio contact with Brazilian air traffic control as they leave Brazilian air space, heading towards a radar dark spot in the middle of the Atlantic ocean. Until it becomes in range of Belize air traffic control, the aircraft would be out of radar contact. At 03:45 UTC, flight 447 still has not appeared into the radar screens of EL taco, Sentagol, which headed off the alarm for the missing aircraft. Few hours later when the search party found no traces, no witnesses and no sign of wreckage as it was in an area of no radar (17,000 km2), Air France publically makes an announcement that flight 447 is missing.
On June the 6th, 5 days after the accident, first signs of wreckage and bodies emerged which narrowed down the search area. Finding the black boxes was vital in order to determine the cause of the crash and use it to inform better future safety procedures. In the first 30 days of the black boxes hitting the water, ultrasonic signals are emitted which can be picked up by the French nuclear submarine that has enlisted to help. With 30 days passing and no avail, mini-submarines, the American team who found the titanic and many other marine search resources, costing 25 million pounds and taking two years time after the crash, the black boxes were finally found, May 2011, 13,000 ft. down on the seabed. The black boxes would provide the necessary explanations to the series of events of the crash.
During the Air France flight 447, 2 hours into the flight, they pass the equator entering an area of inter-tropical convergence site that creates a lot of convective weather (icing, hail, etc.) and thunderstorms. In such bad weather conditions, the pilot could either maneuver around the storms or stay on route passing the storms. Captain Dubois decided to stay on route course disregarding the snow and the thunder in front of them. Anticipating turbulence ahead, Captain Dubois leaves for his scheduled rest assigning Bonin, the least experienced co-pilot in charge.
The weather deteriorates soon afterwards as the plane enters an area of turbulence. At 02:06 UTC, pilot Bonin steers the plane 12 degrees to the left. At 02:10 UTC, ice crystals hit the aircraft which at the same time, the autopilot and the auto-thrust have shutdown, sounding the alarm informing the pilots to manually fly the plane. The ice crystals cause three vital sensors called Pitos (detects the speed of the air against the speed of the aircraft) to temporarily stop working. Theoretically, the Pitos will resume working after the ice melts which practically enforces the usual drill stating that the pilot does no action but keep the plane level with the same engine power till the Pitos resume working.
As Pilot Bonin carries on with no speed information, he made the situation worse by taking immediate and hasty action of pulling back on the side stick, making the plane climb with the nose-up. The thought behind the pilot pulling the nose up could be justified as the reading on the aircraft instruments showed that the plane lost 400 ft in altitude which the pilot aimed to recover. The aircraft's reading of speed and altitude was incorrect at the time due to the frozen Pitos. Due to the continuous nose-up action of the side stick by the Pilot Bonin, the plane kept rising with the speed of 7,000 ft/minute into thin air that does not support the aircraft causing it to slow down. Soon afterwards the aircraft's speed dropped from 275 knots to 60 knots, unsurprisingly, the stall warning sounded. A stall is when an aircraft travels too slowly for the wings to produce the appropriate amount of lift that subsequently the aircraft starts to fall instead of fly. Although due to the false information the pilot was following, this made the situation even more confusing for him. The way to fix the situation was to move the side stick forward and acceleration which gives the aircraft the speed it requires and reducing the angle of attack. Bonin keeps the stick back resulting in the aircraft gaining more altitude and losing more speed. At this time, the Pitos sensors defrost and go back into function, providing accurate readings which change the previous inaccurate readings dramatically causing pilot Bonin to doubt them more. The angle of attack increased on the aircraft causing the airspeed to have a sharp rise to 215 knots, which was displayed a minute behind by the Integrated Standby Instrumental System (ISIS). The Trimmable Horizontal Stabilizer (THS) rapidly moved in one minute from three degrees to thirteen degrees nose-up, which was the position it remained in till the rest of the flight.
At 02:11 UTC, approximately 38,000 ft high in the air, with an angle of attack on 16 degrees and thrust levers were fully forward (TO/GA detent), the aircraft flight 447 has reached its maximum altitude. At 02:11:15 UTC the pitch altitude was 16 degrees and decreasing, while the angle of attack increased rapidly to 30 degrees. At this point the aircraft started to fall as the wings have lost their lift and the aircraft was stalled. At 02:11:40 UTC the captain returned to the cockpit from his break after numerous calls from co-pilot Robert. The Pilot Robert takes over without verbal consent to Bonin, focusing on getting the wings of the aircraft straight, not knowing that Bonin still had the side stick pulling the aircraft's nose upwards. By then, the angle of attack has reached 40 degrees and with the engines running at 100% N1, the aircraft had descended to 35,000 ft. N1 delivers the most of a turbofan engine's thrust as it is the rotational speed of the front intake fan. At this point the aircraft is falling 10,000 ft/minute creating a tremendous amount of noise due to the turbulence caused by the wings. The stall warnings had stopped, as the aircraft's computer did not consider airspeeds as low as 60 knots and an increasingly high angle of attack, treating those readings as invalid. The aircraft was falling with its nose upwards.
At 02:12 UTC, the pilot lowered the aircraft's pitch in a small amount which made the airspeed readings more valid resounding the stall warning, which constantly carried on till the pilot increased the aircrafts nose-up pitch again in order to try to save the situation. The angle of attack remained at a constant 35 degrees with the engines responding to commands; developing at either N1 100% or at a TO/GA thrust. At 02:14:28 UTC, the aircraft Air France flight 447 hit the Atlantic Ocean, breaking on impart and killing all of the 228 passengers on board. This was the last reading that was recoded by the black boxes flight data recordings. Showing the aircrafts ground speed at the time of impact to be 151 knots and descending at 10,912 ft/minute with a nose up of 16.2 degrees. The aircraft fell 38,000 ft into the Ocean in 3 minutes and 30 seconds; being stalled the whole duration and turning more than 180 degrees to the right (to a 270 degrees compass heading). This was the analysis due to the information provided in the FDR (Flight Data Recorder) black boxes.
The final report to the investigation came out on the 5th July 2012 stating the unfortunate events leading to the crash. It was clear to the aviation industry and the world that the pilots were not able to handle the situation appropriately. There were many occasions during those 3 minutes and 30 seconds for the aircraft problem to be salvaged. The plane needed some manual run by the pilots that could anticipate what is happening around them and understanding the clear warnings of the plane's stall. Unfortunately the pilots were not trained to handle stalls of aircrafts at such high altitude and how to recover from such situations. Their inability to handle the situation, which is not their fault but the fault of the training faculty, lead to the wrong decision making of the pilot leading to an unrecoverable aerodynamic stall. This lack of manual training is technically acceptable at the time in the aviation industry but has clearly shown otherwise in the Air France 447 tragedy.
Due to the findings of the succession of events from the black boxes, the BEA has addressed DGAC, EASA, FAA, ICAO, the Brazilian and the Senegalese local authorities on 41 safety recommendations making sure the Air France flight 447 unfortunate accident would not repeat itself. The Safety recommendations extended from manual training of pilots, specific-situation training of pilots, flight recorders recommendations, certification, SAR and ATC, cockpit ergonomics, flight simulators and operational feedback.
Streaming Flight Data via Satellite
After we have understood what and how the flight data is recorded on an aircraft and how it is protected and can be recovered then we discuss how to secure this vital information better instead of having to rely on just the physical FDR data that can only be extracted when it is recovered from a crash site.
To understand the need of such a system we need to realize that in many aircraft accidents the most vital information about the even could be lost due to not being able to retrieve the FDR or the FDR being severely damaged to the point where the data becomes unreadable. The process of retrieving the FDR sometimes is not only time and effort consuming but also in a number of aircraft disasters in the recent decade many times the investigation teams despite their efforts were not able to recover the FDR. The investigation teams have a particular difficulty in retrieving the FDR's when the accident takes place in the middle of the ocean as we saw in the case study of the Air France flight 447 which crashed in the Atlantic Ocean on the 1st of June 2009 and unfortunately took the lives of all the 228 people on board the aircraft.
When we look at the technology of today's commercial aircrafts in comparison to those of 2 or 3 decades ago we realise how far we have really progressed but unfortunately the two most vital components of the aircraft that hold all the vital data such as the FDR and CVR haven't made so much progress. The problem is that we still can only rely on data that is collected in the FDR and CVR only and when these components can be retrieved from a crash site so the idea here is that apart from having the two systems on board it would be greatly useful if the vital information from those two components could be transmitted to servers on the ground thus allowing us to not fully depend on the recovery of the FDR and CVR of the aircraft to analyse what went wrong.
The general perspective of the people is that when in flight the flight crew is almost always in contact with the ground but that is not the case as there are several areas of the world whether they be a large ocean, desert, forest etc. where the pilot cannot get in contact with the ground communications due to lack of radio signals and when the aircraft is being maneuvered through these radio black out zones there is no contact between the aircraft and the ground except the short messages that are send through a systems called ACARS - Aircraft Communication Addressing and Reporting System. This system basically send short intermittent signals through a satellite but these messages do not have that much information and only send very limited amount of data which does not help that much. As in the scenario of the Air France flight 447 the little information that the investigators initially got was from these ACARS messages like when the Air France flight 447's pilot reported going into a storm, communications stopped and at this point there were 24 ACARS messages sent from the aircraft to the ground, an example of that would be "221002006AUTO FLT AP OFF"; this message indicated that the flight had been disengaged from autopilot. Apart from this very limited information carrying few messages the transmitting of data through the satellite is very expensive and if large amount of data had to be transferred it is thought that the ACARS just does not have enough of radio bandwidth to transmit such large information in real time.
As mentioned the Air France along with a couple of other tragedies such as the accident of the Yemenia Airlines in June 2009 that tragically took the lives of 152 people raised the necessity to find alternative methods of transferring information as in these events there were big problems faced by the investigators in the recovery of the flight data recorders and as mentioned in the case study of the Air France flight 447 the flight data recorder was recovered after two years of the aircrafts crash and also the amount of money that was spent during that recovery was a approximately 25 million pounds.
When we think about the real time transmission of data we need to know that the technology is available to transmit information through a satellite and specially in this day and age when satellites are being used for the most mundane of things we would think that it would important for airline companies to take advantage of this technology to safe guard the thousands of passengers that travel through there aircrafts but the problem with this scenario is that like other things such as mobile communication or such for which satellites are being used the information on an FDR is different, the process highly expensive and not to mention the shear amount of information coming through from the thousands of aircrafts flying at a time would be chaotic.
In a report that was done the L3 Aviation recorders which is one the largest companies for producing aircraft flight recorder it was shown that if a airline company had to adapt the real time transmission through a satellite the approximate cost to a typical airline would be around 300 million dollars annually. So for this purpose better alternatives have to be found and certain companies have been working on this for sometime. One of the most effective ways to tackle this problem might be by using a system which would either manually or automatically be programmed in such a way that on detection of a problem it would start transmitting the data of the aircraft to the ground.
There is one such system made by the Western Avionics know as the CommuniCube or also as the C3. This system has been around for a few years and has already been used on aircraft for the purpose of EMS that is Emergency Medical Service in which the emergency details of the patients are sent to the hospitals before they can arrive so the hospital staff is ready for them. The C3 might have been engineered to transmit operational data similarly to that of the ACARS system but in the recent years it has been advanced enough to produce Real time data transfer from an FDR if required. Like mentioned earlier these systems would not be to replace an FDR or CVR but to provide additional advantage in data retrieval and it could be used as either manually to transmit data by the push of a button on signs of problems or it could be used to send data automatically by using EDAT (Emergency Data Automated Transfer) mode when sensors detect certain problems in the aircraft by detecting certain changes in the parameters of the flight.
This technology of C3 is currently being tested on a number of commercial aircrafts for the purposes of FOQA which is Flight Operations Quality Assurance and had this system been installed in the Air France flight 447 then maybe the millions of dollars that were spent in the retrieval of the FDR with no result could have been saved but more importantly the investigators would have more information to pinpoint the areas of problems in that flight and maybe provide recommendation which could help other aircrafts be safer and thus avoid the same tragic fate.
Other then the C3 a Canadian company know as the AeroMechanical Services has come up with a system know as AFIRS 220 (Aircraft Flight Information Reporting System) branded as FLYHT is capable of transmitting information via satellite (in specific the Iridium global satellite system) to multiple ground or other recipients simultaneously.
As we I explained earlier when transmitting the data in real time one of the problems is that since the data is of high amount the bandwidth required to send this data needs to be very high but the AMS personnel have dealt with this problem by using the same band width as available but instead compressing the flight data information so that it can be transmitted using the already available band width. Another advantage of the AFIRS 220 would be that it has been designed to have a two way voice communication through satellite thus allowing flight crew to communicate even when the aircraft is in an area without any radio communication (also know as the radio blackout zones) as the Iridium Satellite network that the AFIRS 220 uses has a global coverage. Apart from that similar to the C3 the AFIRS 220 can also either be activated manually to transmit data and also be programmed to be self-activated in the situation where any fault or problem is detected.
Other then those two devices if we even take the existing technology of the ACARS it can be changes or upgraded to perform the data transfers during critical or emergency situations. This changes need to be made to the ACARS system wont be a lot and in turn would allow the ACARS system to act in a similar fashion as the C3. A professor from the University of North Texas Named Krishna Kavi has proposed the idea of altering the ACARS system to make it transmit data in emergency situations in 2001 has stated that when optimised the ACARS system would be able to transmit data at low speed of 4 to 8 kilobytes per second.
ACARS is already being used in commercial aircrafts for different functions such as alerting the ground technicians of aircraft issues and performance before the aircraft lands so that if need be any maintenance can be carried out and personnel can be ready to clear the problems as soon as the aircraft has landed and can also inform ground crew if the aircraft is going to delayed for a period of time. Since it is already in use on the aircraft it has an advantage that it would only need to be optimized to be used that way instead of having to install a complete new mechanism on the aircraft and as we know every new thing added to the aircraft could affect space and weight which are crucial to the aircrafts.
During the investigation of Air France 447 It was found that a Lufthansa international aircraft being used as a weather station by the use of this updated ACARS technology had passed the same area where the Air France flight 447 experienced turbulence only 20 minutes before and had not noticed any dangerous or unusual weather conditions which could have caused the aircraft to crash thus showing that there might have been a sudden change in the weather that could have caused the ill fated tragedy to take place.
Currently there are approximately 8000 aircrafts that are using the ACARS system to transmit information through satellite and as mentioned with a little tweaking of the system can allow it to be used for transmitting vital information during periods of emergencies for example as mentioned before that before the last cut off the Air France flight 447 was able to send out 24 messages through ACARS such as the depressurization and failure of electrical equipment after which soon the aircraft went down. Now as mentioned earlier these little messages provide a little information but not enough to draw a precise conclusion and if the ACARS system was programmed to transmit a few more pieces of vital information it might have helped pinpoint the cause instead of having hypothetical scenarios.
Apart from the Air France flight 447 there were many such instances where the FDR wasn't able to be retrieved thus leaving the investigations of those events incomplete. Even in cases such as the Yemenia Airbus A310 crash in the indian ocean which immediately followed the Air France crash the FDR was discovered but with a lot of hardship, so for this we need to employ some of the methods as mentioned earlier to try to have more chances of recovering data incase a tragedy or accident takes place.
Real-Time Flight Data Transmission System
When considering a real-time flight data transmission system we need to establish what kind of standards it might have and know that the requirements of a real-time transmission would different to the requirements of flight data recorders on board the aircrafts. In order for a real-time transmission to be effective we need for it to transmit information on a flight by flight basis so that the information being sent on the ground can only be stored for that said flight and would be erased or written over when the aircraft flies again. The standards that should apply to a real-time flight data transmission system would obviously be less then those that apply to on-board flight recorders because those have to be able to withstand high pressure impacts, underwater pressure and etc., so the proposed standards that should set on a real-time flight data transmission should be the time recorded on it, number of channels used and the number of parameters.
The table below shows an example of what the proposed standards should be:
25 hours FDR
2 hours audio CVR
Number of Parameters
5 to 300+
Number of Voice Channels
Transmission of Flight Data off Aircraft
In this section of the dissertation I will discus the 5 different mediums that can be used to transfer flight data of an aircraft and the qualities those medium posses and how we can use either one or multiple mediums together at a time to transfer the data in the most reliable way.
First we need to understand what things to consider when selecting one of the five mediums so that we can see the characteristics of each medium and asses which medium would be best to transmit data in different types of situations.
Things to consider:
Frequency: when considering mediums we need to keep in mind that frequency would have an effect on the bandwidth thus having an effect of how much information that set medium can transmit
Geographic coverage: this factor deals with how much of the world geographically is covered by the set medium so that we can make sure that we sure right medium for transmission in the rite places.
Cost: how much would it cost to transmit from the particular medium
Along with the characteristics mentioned above there are other factors that also need to be kept in mind when evaluating which medium to use when.
The table illustrating is on the following page.
The table below shows the factors and there description:
Range of frequencies on the radio spectrum in which the medium operates.
The volume of data that can be transmitted using the medium.
For digital signals its is usually expressed in bits per second transmission rate.
Degree of confidence that the medium can be reliably transmit the flight data
Features of the medium that mite limits its use.
Geographic Coverage Area
The areas of the word where the medium can be used to transmit the flight data.
Qualities or certain features that make the medium better for use.
Qualities or certain features that makes the medium not good for use.
The cost of using set medium which also includes cost of bandwidth, maintenance and equipment
The five mediums that could be used either singularly or in combination depending on there characteristics and the situation are:
The tables illustrating those 5 are on the following pages.
C-band (6 GHz transmit, 4 GHz receive), L-band (950-1535 MHz), Ka-band (30 GHz transmit, 20 GHz receive), Ku-band (14 GHz transmit, 12 GHz receive)
Almost any bandwidth that the real-time transmission system would require.
If there is good signal acquisition the reliability of this medium of data transmission is high. (Mobile transceiver systems for aircrafts maintain the system acquisition)
Satellite acquisition must be maintained and can easily be lost.
The number of available satellite communication channels and total available bandwidth is limited; satellite capacity may be an issue.
Geographic Coverage Area
Worldwide coverage of signal, high reliability and enough bandwidth for large amounts of data transfer
High Cost for bandwidth and equipment and the could lose satellite acquisition at unusual flight altitudes which could be expected in a crash sequence
High for equipment and bandwidth
Data rates up to 31.5 kbps
Very Reliable when properly used
Line-of-sight propagation. Useful range 100-120NM.
Geographic Coverage Area
Coverage Not available in Remote areas
Low cost. Reliable.
Uses commonly available equipment, both airborne and ground.
Receiver network already exists in much (most) of the world.
All aircraft have VHF radios installed, including antennae systems. Using existing radios or adding a dedicated one for flight data transmission is relatively easy.
Can suffer signal drop out.
Coverage not available in remote areas or over oceans and in polar regions.
Not directional.â€¨Limited channel capacity.
300 Mhz to 3 GHz
Data rates up to 115.2 kbps
More sensitive towards obstructions in signal path than VHF.
Useful range 100-120NM.
Geographic Coverage Area
Within relatively short distance of receiver; remote area and oceanic coverage not available.
Not commonly used.
Adds another radio and antenna system to most (if not all) civil aircraft.
Limited channel capacity
Slightly higher then VHF
3 MHz to 30 MHz
Relatively low due to the low frequency of the carrier.
Highly susceptible to atmospheric interference
Signal routinely drops out with changing ionosphere conditions.
Lots of noise even on a "clear" signal making digital transmission questionable if not nearly impossible.
Not suitable for data transmission use in bad weather due to disruption of signal by electrical discharge (lightning).
Geographic Coverage Area
Wide. Oceanic and remote area coverage is available.
Good signal coverage. HF is used for transoceanic communication and was the standard before the advent of satellite communications. It is still in widespread use and is required equipment for transoceanic flights.
Reliability and bandwidth are low.
Medium and it would require installation on the aircraft because most civilian aircrafts travelling through domestic routes do not have HF equipment
L-band (950-1535 MHz).
Expect >115.2 kbps data rate.
Exceptionally line-of-sight coverage.
One frequency per radar system split between all aircraft served at any given time significantly limits data bandwidth available to each aircraft.
Exceptionally line-of-sight coverage.
One frequency per radar system split between all aircraft served at any given time significantly limits data bandwidth available to each aircraft.
Geographic Coverage Area
Not so good. Oceans are not covered
Good signal quality.
Burst transmissions required.
Can only transmit when the radar antenna sweeps through the position of the aircraft.
If the transponders installed on the aircraft are used to transmit the data then the cost is relatively low
Data Transmission Methods
In this part of my dissertation I would like to discuss the different types of ways in which the data can be transmitted of an aircraft and some of the ways of transmitting that data include:
Broadcast when in trouble
Transmission to nearby aircraft
To understand why need to look at such systems we need to considers the facts of transmitting data in real-time and the facts would be that when having to transmit data in real time we need to realize that a normal or general flight usually does not need all its flight data analysed and transmitted to the ground in real-time since the aircrafts are maintained and properly checked before every routine flight.
The data on flight data recorders becomes most important in the event of an accident of the aircraft where the investigators need to piece together the information to conclude on what happened in the accident thus allowing us to make future improvements to avoid those situations. Then if we consider that amount of data that would have to be transmitted of every single aircraft in air and the amount of systems required to store that information on the ground it all seems unnecessary and costly, as these large amounts of information would most probably go unused.
We need to consider those factors so that we can design a real-time data transmission system that would be practical and possible and so for that we need to examine those four methods of transmitting the flight data of the aircraft.
This method of transmitting data of an aircraft as the name suggests is a method in which the flight data would be continuously transmitted of the aircraft that would include all the data being stored in the FDR and all the audio from the CVR.
According to Frank Doran who is a senior executive for L3 communications which is one the largest manufactures of Flight Data Recorders the minimum amount of bandwidth that would be required for audio CVR transmission continuously would be 120kbps (Kilo Bytes per second), 3kbps for flight data of FDR and if cockpit video would be in future use that would require a further bandwidth of 1.6Mbps (Mega Bytes per second) bringing the total required bandwidth without the video to off 123Kbps and if video included to a total of 1.723Mbps.
Now as we looked at the data transmission mediums discussed earlier we realise that VHF and UHF data links barely provide enough bandwidth for even the audio and flight data alone, as they would allow a maximum of bandwidth of about 115kbps. For us to be able to transmit data, voice and video of the cockpit we would require either the use of SATCOM data link or we would need to utilize multiple VHF/UHF links at a time and the problem with using multiple VHF/UHF links at a time would be that the data would be required to split and then combined again on the ground and this process could become problematic.
Broadcast when in trouble
Like mentioned earlier that the usual flight data collected during routine flight do not require any accident investigation so for that reason only transmitting vital data of the aircraft when in a problematic situation would makes sense as it would bring down the amount of data needed to stored on ground.
Now this method or system would require us to have knowledge of what the normal processes or parameters of the flight are and if we have a system onboard the aircraft the would constantly compare flight data being collected to the normal conditions of a flight it would be able to detect any anomalies in flight. Once if it would detect any problems while monitoring the flight parameters then the computer would activate the real-time system and the system would start transmitting the information of the aircraft immediately and would not transmitting data until the flight has safely landed.
The advantages of this system as mentioned earlier would be that in this system having to only transmit data when needed would reduce the amount of data being transmitted and stored on ground, help reduce cost and use of bandwidth.
The disadvantages of this system could possibly be that if the system does recognize any anomaly and right then the flight starts to crash then the system might not have enough time to transmit all the amount of vital information.
Transmission To Nearby Aircraft
When we look at the options of the mediums of transmitting the data SATCOM seems the most to be the best option as it has good signal qualities such as high bandwidth and has a global coverage but as discussed earlier this medium of transmission can get costly and also the signal acquisition of this medium can also be a problem when the aircraft is trying to maneuver through unusual altitudes as the one that we could expect during an aircraft crash. So for this reason a more economical way of transmitting data could be to a nearby aircraft by using VHF/UHF data links since there are always at least one aircraft close enough for this to be a possibility. In this situation the aircraft would either continuously send the data or it could send in the Broadcast when in trouble way. After the data could be transferred it could either be stored on board the nearby aircraft and the data could be retrieved from it when that aircraft landed or it could be re-transferred to the ground directly from the nearby aircraft.
The biggest problem with this complex structure would be to identify and tag the information coming in from a different aircraft and when it would be eventually extracted on ground or re-transmitted to ground would be that it would have to be put together and assembled with the rest of the data collected from the crashed aircraft.
In this method of transmission we would have to save the data when gathered and at the same time compress the recorded data and then during regular intervals transmit the compressed data all at once. This method would require a system or computer which could store and the data and at the same time compress the data and transmit it because at the moment the current flight data recorders do not have the feature of simultaneously reading and writing data.
This system would be made up of a system on board the aircraft that would also receive the flight data that is going towards the flight recorders and compressing and transmitting it either at predetermined regular intervals or like the broadcast in trouble mechanism could be activated by some problem and then would transmit the data but in which ever method chosen the key to this is to compress the data recorded and when the data would only be transmitted in short compressed forms between long intervals the problems of frequency congestion and inadequate channel capacity can be reduced.
The only negative of this procedure could be that in a scenario where the aircraft goes into an accident or crash in between these long intervals the last and probably the most vital parts of the information which show of what went wrong could be lost.
In this part I would like to discuss what sort of technical consideration would have to be made in order for the data to be able to be transmitted using those methods. The technical consideration needed to be made for that purpose would involve:
Necessary equipment's required for that process of transmission
In this part I would like to discuss the equipment's that would be necessary to collect flight and to transmit it from the aircraft.
The Solid-State flight data recorders or the digital recorders that are being used at the moment have digital memories that can store up to 25 hours of flight data and 2 hours of audio of the cockpit voice recorder. The memory recorder on these Solid-State flight data recorders gets recorded in loop fashion which mean once it gets full it starts writing on the old memory and since these recorders are continuously recording flight data it is not possible to read off of them at the same time thus it is not possible for them to be used to take the recorded data from while using burst transmission method.
For this reason we need to take the flight data off the sensors but the problem with that is then when taking information of the sensors the information taken is not in a transmittable format. The audio data being picked up from the cockpit is in a analog format and also the data coming from the flight sensors is not in transmissible format thus we require a dedicated computer system which would pick up the audio signals heading toward the CVR and the flight data heading from the sensors and then either digitize the collected data or turn then in to a format which can be transmitted. After that this reformatted data would be sent to the radio systems of the aircraft where they could be transmitted of the aircraft. Like I mentioned during the burst transmission method this computer system could programmed in such a way so that it can either send the information out in burst of compressed information with regular intervals or also could be programmed to be triggered in the event of any problem.
Figure below shows of how this would process would look like.
Figure 10 - On-Board real-time transmission system components
Transmission and Antenna Systems:
When trying to install real-time data transmission system we need to realise that a usual commercial aircraft might have transmitter on board that could be used or shared by this real-time data transmission system and for that reason we might need to install new transmitters and also the antenna systems for those transmitters.
2.Signal Acquisition and Availability
In this section I would like to discuss the technical consideration we would have to make in regard with acquisition of the signals and there availability.
When we look at SATCOM the signal acquisition means the method of linking the satellite to aircraft for which would need the aircraft antenna to be aligned with the satellite and as mentioned before if the aircraft stays in normal maneuvering patterns then signal will stay but the problem with that is if the aircraft does go in a crash or stall it would cause unusual altitude which would therefore lead to a loss of signal and the thus the data will not be able to be transmitted. An example of situation like this would be Alaska Airlines flight 261 that on January 1st 2000 was crashed in to the Pacific Ocean. When the accident was being investigated it was found through CVR transcripts that the aircraft during the crash was inverted and was also going through other irregular patterns and this would show that in a situation such as the one mentioned or any crash situation where the aircraft goes through unusual patterns the acquisition of signal through satellite could be questionable and specially since the last moments of flight data recorded are so crucial towards investigation.
Even though VHF and UHF have line of sight properties they are regardless not hard to acquire but because they have the line of sight issue there could be problems in keeping the signals if there are objects in between the antenna and the receiver. Also if the flight experiences unusual altitudes it causes interference with the signals thus making the signal strength weak enough to stop the transmission of data for a short or long periods of time.
Obstructions such as mountains and buildings and such have know to cause problems with the signals strength as the can come in between the line of sight. It is important for us to recognize these patterns of reception in the VHF and UHF receivers so that we can engineer special patterns for signals that the system can use to most effectively and reliably transmit data off the aircraft.
When for this system we need a transmitter on board to transmit the data and a require a receiver on the ground or another aircraft that the data could be passed on to but the important thing when using VHF/UHF we need to a free radio frequency so that we can transmit the data.
When bringing up the fact about having a clear radio frequency for transmission I need to explain why that would be important and its because in the aviation communications usually there is basically only line or frequency that has to be used by all the aircrafts to contact the ground and only one at a time can transmit or communicate, so for this purpose generally the pilots are trained to notice if there is silence on the radio before they contact or transmit to the ground so that they can avoid the unfortunate and common problem which is of two pilots contacting or transmitting at the same time which could lead to the data being not transmitted.
This idea which has been used for several years for voice communication is one which the ways as that each pilot use the frequency for short time so that it can be left open for use for another pilot but in the case real-time data transmission systems we would continuous transmission of data.
Since there is are only limited amount of data that the channels can carry in a aircraft VHF and UHF allocating these channels to stream the flight data off the aircraft continuously would cause exhaustion of available data link channels so therefore to illuminate or reduce this problem we can use a number of different strategies such as compressing the data before transmission, sending the data off in short burst and also put regular intervals between transmission so that frequency is clear for other aircrafts to do so as well but like mentioned earlier there is a possibility where before the data can be transmitted off using burst transmission if the aircraft crashed in between those intervals the vital data specially off the last few minutes which are so important could be lost.
In this dissertation I have looked at the working of the flight data recorders and seen how they work so I can suggest ways off transferring data off the aircraft and also discussed all the different methods and different mediums that could be involved in such a process; talked about case studies of unfortunate events such as of Air France flight 447 and discussed some new technologies that were being looked at and were being tried and tested so that we can improve upon our capability to ensure flight data safety by having other systems along with the current flight data recording systems. After all that it is very clear that we do have to have alternative methods and as discussed that those methods might have some problems but with more engineering into them we can make them more effective, reliable and at the same time more cost friendly so that we can implement them in todays economically challenged aviation industry.
Since the disaster of Air France flight 447 the European Union has been showing a lot of interest to idea of transmitting information off an aircraft during times of emergency to supplement the flight data recorded in FDR and CVR. This allows more safety and chances for the vital data to be received so that we can investigate it and offer improvements to whether our training procedures of the flight crew and engineers as seen in the scenario of Air France flight 447 or to allow us to improve upon our equipment's to make them more reliable and saferfor future use.
For the purposes of making the real-time data transfers of vital data via satellites the European Union representatives in a global aviation summit held in Montreal 2010 made strong points towards the implementation of this idea and also tried to get the representative of other countries on board as well. They presented the summit with a report made by a group of international experts in this area and also a French team as well to show the summit that the idea of data streaming via satellites during emergencies was a feasible one and could be cost-effective if it the data transfer method of transferring flight data off an aircraft was used only when an aircraft went into a state of emergency. The other countries in this summit such as United States and also ICAO (international Civil Aviation Organisation) put there support behind this idea but even then like I mentioned there would be some technical and economic issues to resolve before this idea to be implemented on commercial aircrafts.
This show that this necessity cannot be dismissed so easily anymore; we are in need of such systems and as mentioned in the this dissertation earlier it is feasible and there are systems to make this happen even if they do require a little bit more engineering to make this idea a more cost-effective and reliable possibility.
The United States in March 2010 came out with the plans for changing the nature of the currently used ground system to a more satellite based system and has named this system as "NextGen" which is planned to be in working order till 2018.
List of Figures
Figure 01- Inside the black box by Julian Edgar
Figure 02- Inside the black box by Julian Edgar
Figure 03 - The magnetic tape inside the flight data recorder from EgyptAir Flight 990, which crashed on October 31, 1999.National Transportation Safety Board (NTSB)
Figure 04 - A Solid State Recorder. L-3 Communication Aviation Recorders.
Figure 05 - Sample data recovered from a Flight Data Recorder.
Figure 06 - Diagram of data flow to aircraft black boxes.
Figure 07 - Inside the black box by Julian Edgar
Figure 08 - Inside the black box by Julian Edgar
Figure 09 - Airbus A330-203 aircraft. Photographer by Vincent Edlinger
Figure 10 - On-Board real-time transmission system components