Yesterday morning, the Malaysian prime minister confirmed that Malaysia Airlines flight 370 crashed in the south Indian Ocean, killing all 239 people on board. Curiously, though, despite the PM’s confidence, this conclusion is based entirely on second-hand information provided by UK satellite company Inmarsat. There is still no sign of debris from MH370, and investigators still have absolutely no idea what happened after the final “All right, good night” message from the cockpit. If you’ve been following the news, you probably have two questions: How did Inmarsat narrow down MH370′s location from two very broad swaths across central Asia and the Indian Ocean, and furthermore, if we know where the plane crashed into the ocean, why haven’t we found it yet?
How Inmarsat tracked down flight MH370
After flight MH370′s communication systems were disabled (it’s still believed that they were disabled manually by the pilots, but we don’t know why), the only contact made by the plane was a series of pings to Inmarsat 4-F1, a communications satellite that orbits about 22,000 miles above the Indian Ocean.
The initial Inmarsat report, which placed MH370 along two possible arcs, was based on a fairly rudimentary analysis of ping latency. Inmarsat 4-F1 sits almost perfectly stationary above the equator, at 64 degrees east longitude. By calculating the latency of MH370′s hourly satellite pings, Inmarsat could work out how far away the plane was from the satellite — but it couldn’t say whether the plane went north or south.
To work out which direction was taken by flight MH370, Inmarsat, working with the UK’s Air Accidents Investigation Branch (AAIB), says it used some clever analysis of the Doppler effect. The Doppler effect describes the change in frequency (the Doppler shift) as a sound/light/radio source travels towards the listener, and then again as it moves away. The most common example is the change in frequency of a police or fire truck siren as it passes you. Radio waves, such as the pings transmitted by flight MH370, are also subject to the Doppler effect.
Basically, Inmarsat 4-F1′s longitude wobbles slightly during its orbit. This wobble, if you know what you’re looking for, creates enough variation in the Doppler shift that objects moving and north and south have slightly different frequencies. (If it didn’t wobble, the Doppler shift would be identical for both routes.) Inmarsat says that it looked at the satellite pings of other flights that have taken similar paths, and confirmed that the Doppler shift measurements for MH370′s pings show an “extraordinary matching” for the southern projected arc over the Indian Ocean. ”By yesterday [we] were able to definitively say that the plane had undoubtedly taken the southern route,” said Inmarsat’s Chris McLaughlin.
So, where is flight MH370?
At this point, if we assume that Inmarsat knows what it’s doing, we know with some certainty that flight MH370′s last satellite ping originated from around 2,500 kilometers (1,500 miles) off the west coast of Australia. Because we know how much fuel the Boeing 777 was carrying, we know that it probably ran out of fuel sometime after that last ping, crashing into the Indian Ocean. Assuming the plane was flying at around 450 knots (517 mph, 833 kph), the potential crash zone is huge.
The southern Indian Ocean is one of the most inhospitable and remote places on Earth. Its distance from major air and navy bases make it one of the worst possible places to carry out a search and rescue mission. Even if satellite imagery purports to show debris from flight 370, waves, weather, and ocean currents mean that the debris will be constantly moving. ”We’re not searching for a needle in a haystack,” said Mark Binskin, vice chief of the Australian Defence Force. “We’re still trying to define where the haystack is.”
Multiple nations are sending search-and-rescue aircraft and ships to the region to look for flight 370, and the US is deploying its Towed Pinger Locator — a device that can locate black boxes up to a depth of 20,000 feet (6,100 meters). The flight data recorder (FDR) or cockpit voice recorder (CVR) generally only have enough battery power to ping for a month or two, so time is of the essence.
