Terrain masking explained
Flying low enough allows a plane to avoid detection because of the way radar beams work, says aviation expert Professor Jason MiddletonPT1M18S http://www.canberratimes.com.au/action/externalEmbeddedPlayer?id=d-34xv5 620 349 March 17, 2014
- Missing flight MH370 likely to be near Australia, says analyst
- Australia agrees to lead search in Indian Ocean
- Missing Malaysia Airlines jet may have flown under radar
In the light of the latest evidence that Malaysia Airlines flight MH370 flew for eight hours and may have been hijacked, a host of new questions arise. We try to answer a few of them.
1. Why two arcs for the search?
A woman walks past a board reading "Pray for MH370" for passengers aboard a missing Malaysia Airlines plane. Photo: AP
The arcs represent the possible locations from where the last ping, which are also known as electronic handshakes, was sent from the engine monitoring system on the jet to an Inmarsat satellite. This was at 8.11am, Malaysian time. The arcs are not flight paths, just possible locations for the last ping, and the aircraft could have been anywhere along these arcs. The arcs are calculated by measuring the angle of the signal to the satellite.
The pings are sent every hour, so the question remains: where were the earlier pings sent from? This would potentially give a better clue on flight path. Authorities in Kuala Lumpur have calculated the plane sent out six pings after its communications equipment was deliberately disabled by someone on board.
The seventh ping never came, indicating the plane either landed and the engine was shut off or it crashed.
A Malaysian Maritime Enforcement Agency pilot studies a map on board a Japanese aircraft. Photo: Reuters
2. Why didn’t anyone spot MH370 on civilian or military radar?
This is the $64 million question and adds to the likelihood that the plane went out over the Indian Ocean, rather than north-west over Asia.
If it went north-west, it would have been over Indian and Pakistani airspace, which is heavily monitored and also in airspace monitored by the US military out of Afghanistan.
A picture of the missing Malaysia Airlines Boeing 777 jetliner taken on December 26, 2011.
Primary radar, which bounces off the skin of the plane, requires line of sight. Malaysian authorities have suggested MH370 flew at very low altitudes - as low as 5000 feet- which could have masked its flight path, particularly in hilly terrain, so a north-west path cannot be ruled out entirely.
If it went south-west towards Australia and the Indian Ocean, it might have been picked up by Australia's Jindalee over-the-horizon military radar. But there is no civilian radar in the area, except at Paraburdoo in the Pilbara.
Jets using Australia's north-western airspace above 29,000 feet are required to have a secondary system that uses GPS to send a code, which then allows air traffic control to cross reference with their flight plan. But without a flight plan, the plane would be invisible.
3. Why no mobile phone calls from the plane?
During the hijackings of 9/11 there were calls from passengers to loved ones even at relatively high altitudes. But the aircraft needs to be within reach of a mobile phone tower. In the case of GSM, the system used by most Australians, the maximum reach is generally 25 kilometres, although a weak signal can sometimes be picked up as far away as 35 kilometres.
CDMA has a longer reach of about 62 kilometres. That said, there are lots of variables, such as obstacles, cloud cover and the number of calls on the network that can affect a connection. Over populated land it is possible to get a signal. But once off the coast or over the jungle of Malaysia, the signal would be rapidly lost.
The other possibility is that the passengers were unconscious or dead early into the flight due to a deliberate decompression of the cabin.
4. Could the plane be on the ground at an airport?
Barry Jackson, a former pilot, told the Herald a Boeing 777 needs a runway length of at least 1500 metres and MH370 is said to have had enough fuel to travel about 4000 kilometres from its last known posisition over the Gulf of Thailand.
There are approximately 634 runways that meet these criteria, spread across 26 countries, including such far-flung places as the Maldives, Mongolia, Western China and north-west Australia. But would no one have spotted it in over a week?
5. Could whoever was in control of the plane have subdued more than 200 people?
Sadly, the answer to this is yes. If the plane was travelling at 45,000 feet - which the Malaysian authorities have said it may have been briefly - then an accidental or deliberate decompression of the cabin would have rendered the passengers unconscious within minutes.
Even if the oxygen masks had fallen from the roof, the emergency oxygen lasts for only 15 minutes to enable the pilot to take the plane to a safe lower altitude.
The pilots have a separate emergency tank, but it, too, does not last long.