What debris and the Indian Ocean told drift modellers about MH370 search area
It started with the discovery of a piece of wing, the flaperon, found in Réunion Island in July 2015.
The long search in the Indian Ocean for missing Flight MH370 has since been punctuated by the arrival of debris along African coastlines.
New drift testing research using a flaperon from another Boeing 777 has shown how that first piece of debris might have travelled so quickly from the presumed southern flight path of the missing plane west across the Indian Ocean.
The findings in the CSIRO’s latest, and final, report to the Australian Transport Safety Bureau made public today give increased confidence in the drift modelling and in what is now identified as the most likely search area of missing Malaysian Airlines Flight MH370.
The ATSB’s First Principles Review committee of experts working on the Australian-led search for the plane in the Indian Ocean met last November. As a result of oceanographic studies done by CSIRO and presented to the meeting, a new search area near 35 degrees south was recommended.
The CSIRO’s report confirms those recommendations, based on new testing of a real flaperon.
“Our final recommendation is way more precise than I dreamed we would be able to achieve,” says CSIRO’s Dr David Griffin, team leader of the oceanographic study.
“When we started on this I thought we would be basing our conclusion on backtracking across the ocean. But that is doomed because of the distances involved. We stumbled upon something that gave much more certainty about the whereabouts of the plane than we anticipated.”
UNDERSTANDING THE PHYSICS OF THE INDIAN OCEAN
Dr Griffin’s work with oceanographic satellite data and how that information could be used to examine ocean currents started in 1996, studying the life cycle of rock lobsters of western Australia
Oceanography has come a long way since it was applied in the two-year search for Air France Flight 447 which crashed in June 2009, he says.
“We have a much more detailed model of the global oceans, a much greater ability to analyse the satellite data measuring sea levels, and a clearer picture of ocean surfaces.
“It’s the ability of those models to get value out of the data which has improved so much in the past 10-20 years.”
To understand the mystery of missing Flight MH370, you need to understand some of the peculiarities of the Indian Ocean.
Down south, around 40-50 degrees latitude, ocean currents go from west to east in the Sub-Antarctic Current, with the band of westerly winds.
Up around the 20 degree south mark, the wind and South Equatorial Current are going to the west.
In between is the intermediate zone – no great movement east or west.
Then there are the forces at play as the ocean fringes approach coastline.
On the Australian side of the Indian Ocean there’s a slow, generally northward movement , apart from the southward Leeuwin Current near Australia. On the African side there are fast boundary currents, southward in the southern region, and northward in the northern region.
APPLYING OCEANOGRAPHY TO THE MH370 SEARCH
The Boeing 777-200ER aircraft registered as Malaysia Airlines 9M-MRO and operating as Flight MH370 disappeared from air traffic control radar after taking off from Kuala Lumpur on March 7, 2014.
The flight was a scheduled passenger service to Beijing, China with 227 passengers and 12 crew on board.
Satellite analysts relied on a series of ‘handshakes’ between Flight MH370’s Boeing 777 engines and the Inmarsat satellite made on March 7 and 8 to determine the likely trajectory of the plane through the air after it disappeared from radar control.
They identified the southern corridor flight path, with a terminal point somewhere along a curved line known as the 7th Arc.
The Australian Government took the lead in the initial search and rescue operation and then in the extensive sea floor search and recovery operation in the southern Indian Ocean, in support of the Malaysian accident investigation.
CSIRO was commissioned by the Australian Transport Safety Bureau in 2016 to conduct surface current modelling.
DRIFTERS TRACKING THE CURRENTS
After the initial search and rescue operation, the hope was to find debris which would provide vital clues to the fate of the plane and its passengers.
The initial challenge for oceanographers was, if the splash point of the plane was in the intermediate zone – how could they predict the likely trajectory of debris?
“We had to work out what the ocean currents were doing every day for more than two years,” Dr Griffin says.
Hundreds of buoys deployed by the United States National Oceanic and Atmospheric Administration Global Drifter Program were important indicators of likely trajectories.
“Buoys give you the temperature of the surface of the ocean and often atmospheric pressure, for input into the world’s weather forecasting,” he explains.
“For me, they give you a trajectory of something drifting in the ocean. For MH370, it’s the later half of the buoys’ lives which are interesting to us because, when they’ve lost their drogue (anchor) they become an item floating on the surface just like a piece of aircraft.”
Initially, the team thought ocean eddies would confuse those trajectories, instead they found that initial trajectories had a lasting impact.
What the satellite data told them and the report said was that there were “two prominent ~150km-wide bands of westward flowing surface current crossing the 7th Arc in March 2014 – one near the 35 degree south and one near 30 degree south”.
“A ridge of high sea level cut across the 7th Arc on March 8th, so flow was initially to the west, changing the long-term destiny of potential debris, offering an explanation for non-arrival of debris off Australia,” the report concludes.
DEBRIS CONFIRMS THE MODELS
Once debris was found on the African side of the Indian Ocean, clearer conclusions could be made using those models. The piece of debris which has received the most attention is the flaperon, the first piece of debris to be found, on Réunion Island in July 2015.
“For our work, the value was knowing that many things are drifting,” says Dr Griffin.
What mattered was that a debris field existed and that items were being found exclusively on the African side of the Indian Ocean and not along the West Australian coastline.
It was the absence of debris to the east of the Indian Ocean which narrowed the latitude span for the likely search area.
“The `penny drop’ moment is described in Section 3.3 of the first report.
“There was only one place that explains the absence of findings on the West Australia coast while being consistent with other factors. It was the only chance of precision. It leapt out of the page.”
REPLICA FLAPERONS REFINE THE MECHANICS
The remaining question was how to convincingly explain the arrival on Réunion Island of the flaperon in July 2015.
The oceanographic map of currents and likely trajectories of the water is only half the story. The mechanics of wind and wave forces on a floating object in those conditions is also critical to understanding the passage of floating objects over such a wide expanse.
“The details of how drifting items sail through the water is important,” says Dr Griffin.
“To get to the bottom of that, we built some replicas of the plane parts using Boeing diagrams and information gathered by the French authorities. We put them into the water next to oceanographic buoys and compared how quickly they moved. And that came up with same fascinating results.
“The flaperon moved faster than the drifting buoys whereas other plane parts moved more slowly or at a similar speed. Once we had that information we could use the thousands of buoys that are out there in the ocean now and over the past 20 years to calibrate our model and then change that slightly so that it can simulate a flaperon.”
It was this information which led to the December 2016 report to the ATSB; “The search for MH370 and ocean surface drift”, and which provided the basis for the First Principles Review committee’s recommendation of 35 degrees south as the most likely search site.
A REAL BOEING 777 FLAPERON VALIDATES THE PREDICTIONS
Transport ministers of Australia, Malaysia and China jointly announced in January 2017 that the 120,000 square-kilometre search was suspended.
It was a month later, in February, that an actual Being 777 flaperon was sourced by the ATSB from the US and shipped to Hobart where it was cut down to resemble the recovered Flight MH370 flaperon.
The flaperon was tank tested to compare its buoyancy to the French Direction Générale de l’Armement (DGA) results for the recovered flaperon.
Dr Griffin and his team then conducted 13 days of field tests in North West Bay and Storm Bay off Hobart, comparing the real Boeing 777 flaperon to the replicas and to the buoys.
“This last bit of work has made one slightly uncomfortable cog fall into place,” says Dr Griffin.
“The surface current model said most debris went north of Réunion Island.
“The model also said that arriving on Réunion in July is too early but possible for the flaperon. I was prepared to accept that but I was always nagged by it. I suspected the real flaperon would go faster because it floated higher in the water and the French modelling said it would go left.
“We did the field testing and I saw straight away on our boat that it was going to the left. I knew this would explain the arrival at Réunion.”
The genuine flaperon goes about 20 degrees to the left, and faster than the replicas, as expected.
“The arrival at La Réunion in July 2015 now makes perfect sense.”
THE VALUE OF SCIENCE
Internet memory will peak over this period with speculation on the fate of Flight MH370, expert and otherwise.
What lasting impression will the search itself leave?
“It is causing a lot of grief for the families of the 239 people on the flight and it has captured the imagination, perhaps ghoulish curiosity, we have for these disasters. We don’t like mysteries,” says Dr Griffin.
“I don’t think I’ve ever been so completely consumed by a scientific question, applying to a mystery that so many people are so desperately wanting to solve.”
Read the full report at the ATSB website.