In light of the tragedy of Flight MH370 and the aftermath of being unable to find the plane, we not only sympathize with family and friends of the passengers and crew, but there is an urgent need to know what happened in order to avoid this situation in the future and how electronics technology is being improved to better locate a missing aircraft or sea-going vessel.
Aircraft monitoring and communications possible shortcomings
Was it an aircraft-related malfunction? A terrorist act? First, we must discount any cost-related or procedure-related issues such as the expense or difficulty of continuously monitoring all aircraft or the procedure of pilots to turn off a transponder or other communications gear. Crews are always in communication with air traffic control (ATC) as well as aircraft personnel on the ground. Transponders are not used in non-radar areas, but there are other means of communications such as SATCOM, CPDLC, HF radio, FMC datalink, and more to be used depending upon which ATC facility with which you are working in a particular region of the globe.
So either all this equipment stopped working by being switched off intentionally or it all failed. This hinders any tracking capability. Transponders can be turned off for three reasons. First, to avoid clutter on ATC radar when parked at the gate. Second, in case of safety concerns of a fire or protection of the electrical system. And third, a malfunction where the transponder begins to transmit erroneous or incomplete data. In this case the crew will reset or cycle the device or swap out with a replacement unit. There are usually two transponders on board.
Once an aircraft is beyond a distance from the coastline, transponders are no longer used for tracking because they only work in areas of ATC coverage. However, the units are kept on because of the TCAS anti-collision system which is transponder-based. But this isolated region is where SATCOM, ACARS, FMS datalink, or other systems are used for communications and position reporting.
It is possible that we may never truly know if it was an act of terrorism or an accident.
Equipment used to locate “downed” aircraft at sea
In this age of advanced electronics, we obviously do not have the systems in place find the aircraft in a reasonable amount of time and at a reasonable cost. Let's look at what we have in the way of electronics today and then determine what we still need for an adequate solution. I will especially go into detail regarding two of the most promising technologies to help solve this problem: Deep-sea drones/ROVs (the wreck of the RMS Titanic was discovered by an innovative remotely controlled deep-sea vehicle called Argo, which could be towed above the sea bed while its cameras transmitted pictures back to a mother ship) and satellite imaging technology.
Let's first assume that the aircraft was somehow lost at sea. Of course the possibility exists that it is somehow on land, but that is a whole other scenario for locating it as well as a very remote possibility.
Let's assume that the aircraft somehow crashed into the ocean. Now we can look at the electronics for locating the plane and/or wreckage.
The “black box”
Please see this brief explanation of the inside of an aircraft’s black box on EDN.
Early on in April, the search team, looking for the “black box”, stopped using the Towed Pinger Locator, a device towed behind a ship. Because the U.S. Navy's pinger locator can pick up signals to a depth of 6,100 meters (20,000 feet), it should be able to hear the plane's data recorders even if they are in the deepest part of the search zone — about 5,800 meters (19,000 feet). But that's only if the locator gets within range of the black boxes — a tough task, given the size of the search area and the fact that the pinger locator must be dragged slowly through the water at just 1 to 5 knots (1 to 6 mph).
Bluefin 21 (Artemis)
The search team then began to use the Artemis, the Bluefin 21 Autonomous Underwater Vehicle (AUV), at 14,800 feet, the depth at which the possible pings from Flight 370 were thought to be heard. Artemis programmed to conduct a side-scan sonar search, looking for a debris field. If it found one, the search team would exchange Artemis's sonar module for a camera and have Artemis run a tight grid pattern over the area, taking photos. These photos would then be converted into a detailed mosaic. See Figure 1.
The Bluefin has sensor integration with more than 70 different sensors. Here is a summary of the systems and sensors:
- Side scan sonar (SSS)
- Synthetic aperture sonar (SAS)
- Multibeam echosounders (MBES)
- Imaging sonar
- Sub-Bottom Profiler (SBP)
- Video Camera
- Still Camera
- USBL system
- LBL system
- Doppler Velocity Logger (DVL)
- Pressure sensor
- Inertial Navigation Sensor (INS)
- Inertial Measurement Unit (IMU)
- Acoustic tracking transponder
- GPS (SAASM, P-code, L-band)
- CTD, CT sensor
- Turbidity sensor
- Sound velocity sensor
- Beam attenuation meter
- Scattering meter
- Acoustic modem
- RF modem
- Acoustic modem
- RF modem
Figure 2 shows an internal view of another type of AUV, the Deep 1 Explorer.5
Because is unlikely that the voice and data recorders will be identified in the photo mosaic, an ROV was deployed to conduct a methodical visual search for the recorders. This is a slow, deliberate process. It can take more than two hours for the ROV just to reach the bottom, and four hours or more to bring debris to the surface. The Bluefin has sensor integration with more than 70 different sensors. See Figure 3.
Another possible solution: ROSUB6000
One of the more obvious possible solutions, however costly, is the Submarine or Deep Sea Drone. The ROSUB60002 can function at a depth of 6,000 meters. It was developed by the National Institute of Ocean Technology (NIOT) in India. Salvage support operations are one of its functions.
The ROSUB system is comprised of a Remotely Operable Vehicle (ROV), Tether Management System (TMS), Launching and Recovery Systems (LARS), Ship Systems, and Control console. See Figure 4.
Obviously a robust camera and lighting system is a key part of this type of vehicle. The power supply is also an important consideration in performance of the imaging capabilities.
Ship power and control
The ship’s power of 415 V at 50 Hz is converted to 6,600 V at 460 Hz using a standard frequency converter and a step-up transformer. There are subsea power converters in the TMS and ROV that convert the 6,600 V at 460 Hz to the power levels needed in the subsystems. The 6,600 V level was selected as a tradeoff between the size of the tether and umbilical cables, the voltage drop in the 6000 meter transmission cable and the power requirements of the system. The 460 Hz frequency was selected to reduce the size and weight of the power conversion equipment in the ROV and TMS.
Voltage management system in ship side
The 6,600 V at 460 Hz is stepped down and rectified to get 300 V and 24 V DC to operate the propulsion thruster and control systems.
Thrusters and pumps in the ROV and TMS use brushless DC (BLDC) motors controlled by power electronic controllers. A BLDC motor produces back-EMF voltage spikes when in operation with significant energy through the low-resistance motor winding. This will have a potentially damaging effect on all power electronics controllers connected to the 300 V DC network. To solve this problem, capacitor banks of 82 mF and 23 mF are connected across DC buses in the ROV and TMS.
The ROV consumes a power of nearly 60 kW at near unity power factor for propulsion and control systems. To have selective fault discrimination and isolate the faulty portion of the network, remotely operable switchgear is required in the TMS that can handle 10 A at 6,600 V. The ROV-TMS isolation switchgear experiences large arcs when the contactor opens.
To avoid the above this, a possible solution would be to delay opening of the switchgear by a few seconds. Within this time the electrical load on the switchgear shall be reduced. Thus the switch-gear is ensured to operate at almost no-load condition and hence termed as Medium Voltage (MV) switch. This requires an independent energy source located in TMS.
Even though batteries could be attractive in terms of size, they are not so attractive in terms of reliability and safety. Super capacitors are found to be the best trade-off. They are electrochemical double layer capacitors which are much preferable because they offer high power and energy densities.
A super capacitor-aided, pressure compensated switchgear is designed and implemented to achieve compactness and robustness. Based on these parameters the requirements of energy and minimum capacitance are calculated. Twelve super capacitors are connected in series to get the effective capacitance of 0.833 Farads so that it can hold the MV switch up to 60 seconds. See Figure 5.
There are cameras and lamps in the system. The cameras outputs in the ROV are multiplexed to the multiplexer and converted to an optical signal of 1310 nm wavelength. At the ship end the optical signal is converted back to electrical and de-multiplexed and distributed to display and recording systems.
There were many improvements that contributed to improved video quality. One was to improve the quality of the input power supply to the video processing electronics. EMC studies showed a range of frequencies in the band from 150 kHz to 30 MHz. Specially designed EMI filters were deployed with a current rating of 250 A between the HF converter and the HF step-up transformer. See Figure 6.
Ground loops were detected originally between the video signal and the operating power supply. To correct this, Ground Loop Galvanic Isolators were inserted between the cameras and the multiplexer. In addition, the power supply module energizing the multiplexer electronics was replaced by an isolated power supply.
Another area of improvement was increasing the luminous output of the ROV from 26,200 lumens to 57,760 lumens. This in turn increased the power supply from 400 W to 1 kW.
Optical communication was selected to take into account the cable lengths.
A super-capacitor-aided, pressure-compensated switchgear is designed and implemented to achieve compactness and robustness. The switchgear operating coil energizes with 24VDC supply and requires a coil holding current of 0.2 A. The design criteria involve ensuring a minimum voltage of 12V for continuous holding of the coil for duration of 60 seconds. When the voltage falls below 12V, the contactor de-energizes and relieves the supercapacitor system from load resulting in re-building up of the capacitor voltage. This results in re-closing of the contactor coil. This process continues until the voltage permanently below 12 V. This phenomenon creates chatter in the contactor. The chatter protection circuit is used to prevent these undesired phenomena. See Figure 8.
Based on these parameters the requirements of energy and minimum capacitance are calculated. Twelve super capacitors are connected in series to get the effective capacitance of 0.833 Farads so that it can hold the MV switch up to 60 seconds.
Satellite imaging using crowdsourcing
Satellite imaging is an obvious technique to locate life rafts, survivors, or wreckage debris from an aircraft accident at sea. What has not been tried before is crowdsourcing that will allow anyone to access and scrutinize satellite images of the search area. See Figure 9.
DigitalGlobe, a US commercial remote-sensing-services provider, based in Colorado, used its Tomnod crowdsourcing platform to enable the public to help in the search for the missing Flight MH370. This company has sub-meter resolution satellites to capture images in the search area. The archived and new images are uploaded to their site for amateur data analysts to examine and tag possible signs of wreckage on the ocean surface. The WorldView-2 is their satellite of choice. See Figures 10 and 11.
A similar company, Blackridge in Germany, is doing the same with five of its RapidEye synthetic aperture radar (SAR) satellites loaded into a MapBox Platform.
Airbus Defense and Space is using the French high-resolution Pleiades satellites and medium resolution Spot 5 and 6 optical imaging spacecraft, and also the German SAR satellite TerraSAR-X, which will all capture images of the search area.
The space and Earth observation at Paris-based Euroconsult used radar and optical imaging satellites with 5-meter resolution or better. This kind of resolution can detect if a plane has landed on the ground, where a satellite with 15-meter resolution could find it, but it just look like a large dot. With 5-meter resolution you will be able to see the fuselage and the wings and possibly the shape of the engines. At 2.5 meters you can definitely see it is a jet plane, and of course at 1 meter, experts could tell you it is a 777.
How can we improve on this technology?3
The paper in Reference 3 explains:
- The area accessible from satellite imaging radar, such as a synthetic aperture radar (SAR), generally increases with the elevation of the satellite while the map coverage rate is a more complicated function of platform velocity and beam agility.
The imaging coverage of a low Earth orbit (LEO) satellite is fairly limited by the ground velocity times the relatively narrow swath width. The instantaneously accessible area will be limited to some hundreds of kilometers away from the sub-satellite point.
In the other extreme, the sub-satellite point of a SAR in geosynchronous orbit will move relatively slowly. The area which can be accessed at any given time is very large, reaching thousands of kilometers from the subsatellite point. To effectively use the accessibility provided by a high vantage point, very large antennas with electronically steered beams are required. (See Figure 12.)
[Editor’s note: The key component here in a phased-array radar system is the Transmit/receive module comprised of a power amplifier, low noise amplifier, phase shifter and programmable attenuator. Reference 3 explains that these electronics modules must have a small footprint and be lightweight so that they can be mounted on the thin membrane design which must be able to fold and unfold. Present design of LEO systems with rigid honeycombs, will not be able to meet the needed weight goals here.]
- Medium Earth orbits (MEO) will enable powerful observational systems which provide large instantaneous reach and high mapping rates, while pushing technology less than alternative systems at higher altitudes. Using interferometric SAR techniques which can reveal centimeter-level (potentially sub-centimeter) surface displacements, frequent and targeted observations might be key to developing better imaging from space.
[Editor’s note: A MEO SAR antenna will have a smaller antenna and be lower power than the geosynchronous SAR design.]
So going into the future, there are so many possibilities and plans to greatly improve satellite imaging that will help in situations like the loss of Flight MH370. See Table 1 and Figure 13, the technology roadmap for membrane-based SAR antennas.
Table 1. SAR technology assessment for LEO, MEO, GEO systems. (Courtesy of Reference 3)
CR (cost reducing technology), E (enabling technology), NR (not required for mission)
This is a viable technique as well. Sonar technology was used to search for Air France flight 447 in June 2009. The main section of the plane was found in April 2011 four km or 2.5 miles beneath the ocean. It is used in the ROV’s, Bluefin21 and ROSUB6000.
Latest reports have search teams investigating an underwater low-frequency sound signal picked up by underwater sound recorders off Rottnest Island just after 1:30 AM UTC on March 8th , which could have been the result of Flight MH370 crashing into the Indian Ocean. (Although a natural event like a small earth tremor could have caused the signal as well.)
Curtin University's Centre of Marine Science has deployed these underwater sound recorders (USR), devices capable of autonomously collecting large amounts of acoustic data under a range of sampling schemes. The USR can be deployed for up to two years and is particularly suited to long term monitoring of man-made and natural underwater sound. See Figure 14.
The device specifications are:
- Integral Pre-Amplifier (20dB gain, user selectable lower frequency cutoff filter – 8Hz or 160Hz).
- Integral Anti-Aliasing Filter (0-20db pre filter gain, 6th order Butterworth filter, high frequency cut off from 1kHz to 15kHz, additionally 0-20dB of post filter gain is available on a secondary output).
- 16 bit Analog to Digital Conversion (RMS noise of A/D – 3 quantization levels) (Note: total recorded noise level depends on hydrophone capacitance, pre-amplifier used, amplifier gain, cut-off frequency, etc).
- Power Supply, GPS and Terminal Interface Card.
- IDE Hard disk drive interface card.
- Processor card with onboard sea noise recorder firmware and Compact Flash interface; User configurable via RS232 interface (sampling rate (up to 26k samples/sec), bandwidth, gain, sampling durations, record intervals) (support for two user configured sampling schedules).
- Data Storage — one 2.5″ hard disk drives (size determined by availability, generally in the region of 60GB to 160GB) and Type 1 Compact Flash Card (256MB) (The hard drives use FAT32 file structure and can be read with a standard Windows PC – individual files for each recording event)
P8A Poseidon aircraft
The US Navy used one of its newest and most advanced assets, the P-8A Poseidon, which only began flying operational missions in 2013. See Figure 15.
The P-8 Poseidon is outfitted with infrared and night-vision sensors, on-board radar to detect ships and small vessels and an advanced magnetic anomaly detection (MAD) system which can detect submarines underwater. Aircraft like this can cover huge areas and direct ships in the area to possible crash sites.
Please click to see a FlightGlobal cutaway revealing all of the electronics on-board this amazing aircraft.
I sincerely hope and pray that technology will lead us to find out what actually happened to Flight MH370. In addition, I am excited about the future of electronics solutions in this critical area of search and rescue under extreme conditions. We have heard repeatedly that the surface of the moon is more explored and mapped than the depths of our vast oceans on Earth. We surely are heading towards development of more advanced systems that will help us both explore and to aid search, salvage and discovery in our deep blue seas.
Please do give me your thoughts, experiences and ideas about these technological efforts and their future advancement.
- Ask the Pilot, a website authored by Patrick Smith, active airline pilot.
- Challenges in realizing robust systems for deep water submersible ROSUB6000, N Vedachalam, R Ramesh, S Ramesh, D Sathianarayanan, A N Subramaniam, G Harikrishnan.
- SB Pranesh, VBN Jyothi, Tamshuk Chowdhury, GA Ramadass, MA Atmanand, National Institute of Ocean Technology, Chennai, India
- Concepts and Technologies for Synthetic Aperture Radar from MEO and Geosynchronous orbits, Wendy Edelstein, Soren Madsen, Alina Moussessian, and Curtis Chen, Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena CA 91109, USA.
- 5 Customizing an Autonomous Underwater Vehicle and Developing a Launch and Recovery System, E. Hayashi, H. Kimura, Christina Tam, James Ferguson, Jean-Marc Laframboise, Gina Miller, Chris Kaminski, Alex Johnson, Fukada Salvage & Marine Works Co. Ltd. And International Submarine Engineering Ltd.