The loss of Malaysia Airlines MH370, a Boeing 777-200ER en-route from Kuala Lumpur to Beijing remains a mystery.

It is still very hard to understand how quite a large commercial aircraft could have disappeared without trace. Speculation continues as to what occurred on board the Malaysia Airlines flight MH370 in March 2014.

Much attention has since been focused on how technology and GPS position acquired from satellites, can be better utilized to locate Flight Data Recorders easily, quickly and effectively in the event of an aircraft accident or disappearance.

Even back in 2014, smart phone technology could theoretically locate a lost phone anywhere on the earth's surface through the Internet; yet the remains of a multi-million dollar commercial airliner with many people on board is lost.

How a modern Boeing 777 aircraft flying commercially at high altitude could lose all contact with Air Traffic Control (ATC) for a sustained period and then subsequently vanish is a mystery.

Today some airlines allow their passengers to connect to the Internet in flight through an aircraft's in-flight WiFi system; so it is even possible to locate your own smartphone in flight. The technology is certainly out there; but whether these capabilities are being maximized in terms of flight safety, is a question that has been under the spotlight since MH370 disappeared.

It's important to understand the types of communication equipment that are typically used in-flight on a modern airliner. Pilots communicate with Air Traffic Control by voice over VHF & HF radios. They also communicate through on-board systems like Automatic Dependent Surveillance Broadcast (ADS B) and Controller Pilot Data Link Communications (CPDLC). It is mandatory for most aircraft to be fitted with a Transponder that electronically relays information about a particular flight (e.g. a basic of flight number, altitude and speed) to ground radar stations that are within receiving range of the aircraft. Transponder information is displayed on the screen of an Air Traffic Controller as an alpha-numeric identification readout.

The flight crew of a Boeing aircraft routinely communicate with Air Traffic Control and with their own airline through discrete VHF & HF radio channels. Satellite Communication (SATCOM) and Aircraft Communications Addressing and Reporting System (ACARS) are also used. Transponders may be used to send signals that indicate specific problems with an aircraft (for example a discrete code for distress, hijacking or radio failure) to a radar station that is within receiving range.

In 2014, a B777 customer option (at extra cost) was available to an Airline purchasing an aircraft to have extra monitoring technology fitted on board. This technology automatically relays in-flight real time engineering data at frequent intervals to their HQ. Many airlines purchased the system; but some did not. It is not clear from public reports whether the B777 that was MH370 had this technology fitted.

This technology is called ACM by Boeing and it normally reports data back to the purchasing airline maintenance offices. It enables monitoring of component parts of the aircraft, such as engines and aircraft systems and it allows in-flight troubleshooting and aircraft performance data to be collected. It can alert an airline engineering office of any abnormalities.

Aircraft Condition Monitoring (ACM) uses the ACARS system to send the real time maintenance and flight data; especially if on-board parameters are exceeded. Of course, the system has to be functioning on the day and all airlines have specific Minimum Equipment listed through their MEL for every flight. The detail given in this list can be specific as to which geographical area on the surface of the earth that an aircraft will be operating in.

If all communication from an aircraft in-flight were to cease suddenly (without a distress signal or Mayday call being made), it might indicate a sudden catastrophic failure. Such a failure may not allow time for the crew to communicate either by radio or through the aircraft transponder, because of the nature of the distress. However this is only one possibility in the case of MH 370.

Even if a B777 aircraft had a substantial engine power loss on both engines or a severe electrical failure, the aircraft could continue to fly safely and have limited communication capacity provided one engine could be restarted. If that aircraft was out of radar range when the failure occurred then it could safely navigate and fly to an area with radar coverage and be identified by Air Traffic Control radar.

A complete in-flight electrical failure in isolation, could theoretically prevent communication momentarily from a Boeing airliner in distress; but it is unlikely to be a long term communication issue; because of redundancies in the aircraft systems. For example, the B777 Ram Air Turbine (RAT) deploys and uses the power of the wind generated by the motion of the aircraft in flight, if both engines and electrical generators were to fail simultaneously. In this case there would only be a momentary interruption in the electrical supply; but enough electrical power to power critical navigation and communication systems would be available. Essential Hydraulic power for flight controls is immediately provided by the RAT. During this dual engine failure process, the Auxiliary Power Unit (APU) would auto-start even though the APU start selector switch normally rests in the OFF position. Thus, Electrical power is provided and takes over from the RAT in less than 60 seconds at high altitude. Air Conditioning and re-Pressurisation would be provided by the APU below 22,000 feet altitude in this case.

Flight Recorders and ELTs.

Broadly speaking, if a catastrophic failure occurs, then the continuously updated flight history until the moment of the catastrophe is held in the aircraft Flight Recorders. The Flight Recorder comprises the Flight Data Recorder (FDR) and the Cockpit Voice Recorder (CVR). These black boxes are usually orange in colour; and of course they have to be located in order to retrieve the flight information.

Regulations state that Flight Recorders must be fitted with a locating device capable of operating under water (ULD - known as a Pinger); that can generate an ultra-sonic rescue signal for around 30 days, so as to help rescuers locate a plane and/or the aircraft Flight Recorders.

Additionally, Emergency Locator Transmitters (ELTs) are carried on aircraft. They are devices that transmit an electronic distress signal in the event of an aircraft loss. They are separate emergency beacons that could be damaged by impact. For example, if an antenna is sheared the ELT would be rendering inoperative.

Some older ELTs have to be activated by anyone who survives a crash landing on land or at sea; but a key factor is that they must be activated by someone in order to function. Newer generation ELTs can be G-force activated during an impact. As with most modern electronics, ELT technology has been vastly improved over the years. A crash impact may activate an ELT beacon, but if a damaged plane sinks in water in less than 50 seconds (the time necessary for it to transmit its first emergency signal) the ELT will not work well under water, because of the natural laws that govern radio waves.

A modern activated ELT will send a signal to one or more Satellites and this information will be disseminated to a Search and Rescue Centre(s) so as to fix the geographical position of the transmitting ELT.

To re-cap the fine details about ELTs.

A B777-200 like MH370 typically has four ELTs. Two of the ELTs are stored with an airplane life raft, to be activated by hand or by contact with the water, if the life rafts are deployed. A third ELT is stowed in the cabin. But the ELT of greatest interest is the remaining fixed ELT that is mounted to the aircraft frame. The fixed ELT like a Honeywell RESCU 406 AFN is positioned near the rear door and connected to an antenna on top of the aircraft. It could be activated, either manually by a pilot in the cockpit, or automatically upon impact, by the inertial G-switch.

The RESCU 406 AFN is designed to provide emergency transmission for aircraft flying over land, according to published specifications. According to Honeywell, They are not mandated or designed to work under water but experts say any impact; whether on land or at sea is likely to have activated the transmitter. Once activated, the device simultaneously transmits bursts of short, digitally coded signals on three frequencies. Two of the frequencies, namely 243 MHz and 121.5 MHz are VHF frequencies and can help search planes hone in on a target. The third frequency is 406 MHz. That is the one that Satellites can detect.

In 1979, the United States, Canada, France and the former Soviet Union teamed up to provide a global, satellite-based system known as the International Cospas-Sarsat Programme. This system detects emergency beacons activated by planes, ships and also other alerts such as those from country hikers. The system distributes those alerts to rescuers. Cospas-Sarsat relies on six low-altitude, Earth-orbiting satellites and six high-altitude geostationary satellites, each with advantages and disadvantages.

The six low-altitude satellites, whose main function is to provide meteorological information, orbit the poles and give complete but non-continuous coverage of the surface of the Earth. They can only view a portion of the Earth at any given time; so the satellite may need to store geographic information from an emergency beacon and rebroadcast it when it comes within view of a ground facility. The six geostationary satellites, parked in spots more than 22,000 miles above the equator, cover most of the Earth's surface but cannot determine the location of the beacon unless the location is encoded in the signal. All of the satellites listen for a beacon signal on 406 MHz. Together can identify the location of a beacon to within approximately 3 kilometers, or just under 2 miles.

If an ELT on MH370 had transmitted a 406 MHz signal, it almost certainly would have been picked up by one of the geostationary satellites. Two satellites, India's Insat-3A and Russia's Electro-L1, are both parked over the Indian Ocean. A signal should have also been picked up by an orbiting low-altitude satellite. Australia, Singapore, Indonesia and China all have antennas that can monitor for emergency transmitter via a satellite. Some or all of them would likely would have received the distress signal. The authorities say no satellite signals were sent.

Assuming that the device was working correctly, the crash could have broken the antenna or cut the connection with the ELT, rendering it useless. Another possibility is that the aircraft could have sunk before the ELT began transmitting. It takes 50 seconds for the ELT to establish the necessary connection. It only takes one half-second data burst to indicate there is an emergency. But it can take a half-dozen bursts at the rate of one every 50 seconds, to provide information that will allow Cospas-Sarsat to triangulate the beacon's position.

In the case of Malaysian 370, there was not even one burst, according to the reports. If the plane crashed in the southern Indian Ocean, as Investigators believe, the lack of a distress call could indicate that the plane plunged into the water, or sank quickly, because once underwater, the beacon is ineffective. Likewise, the water-triggered ELTs in the life rafts would be ineffective if they became submerged, according to published Honeywell manuals for the devices.

Cospas-Sarsat notes that beacons must have a relatively unobstructed view of the sky to work properly. A submerged beacon, or one with its antenna blocked by the body of an aircraft or vessel, is unlikely to be received by the satellites - the organization said.