How MH370 Got Away

annotated-radar-chart-2

One minute after MH370’s flight crew said “Good Night” to Malaysia air traffic controls, and five seconds after the plane passed waypoint IGARI at 1720:31 UTC, the plane’s Mode S signal disappeared from air traffic control screens. As it reached the border of the Ho Chi Minh Flight Information Region (FIR) approximately 50 seconds after that, the plane made an abrupt 180 degree turn. The radius of this turn was so small, and the ground speed so low, that it appears to have been effected via a semi-aerobatic maneuver called a “chandelle.” Similar to a “box canyon turn,” this involves climbing under power while also banking steeply. The maneuver offered WWI pilots a way to reverse their direction of flight quickly in a dogfight.

Chandelles are not a normal part of commercial 777 operation. They would not be used by pilots responding to in-flight fire.

The fact that such an aggressive maneuver was flown suggests that whoever was at the controls was highly motivated to change their direction of flight. Specifically, instead of going east, they wanted to go west.

At the completion of the left-hand U-turn the plane found itself back in Malaysia-controlled airspace close to the Thai border. It flew at high speed (likely having increased engine thrust and dived from the top of its chandelle climb) toward Kota Bharu and then along the zig-zaggy border between peninsular Malaysia and Thailand (briefly passing through the outer fringe of Thai airspace) before making a right-hand turn south of Penang. We know this “based mostly on the analysis of primary radar recordings from the civilian ATC radars at the Kuala Lumpur (KUL) Area Control Centre (ACC) and at Kota Bahru on the east coast of Malaysia; plus (apparently) the air defense radars operated by the RMAF south of Kota Bahru at Jerteh, and on Penang Island off the west coast,” according to AIN Online.

At 18:02, while over the small island of Pulau Perak, the plane disappeared from primary radar, presumable because it had exceeded the range of the radar at Penang, which at that point lay 83 nautical miles directly behind the plane. Then, at 18:22:12, another blip was recorded, 160 miles to the northwest.

The most-asked question about the 18:22 blip is: why did the plane disappear then? But a more pressing question is: why did it reappear? If the plane was already too faint to be discerned by Penang when it was at Pulau Perak, then how on earth could it have been detected when it was three times further away?

One possibility is that it was picked up not by Malaysian radar, but by the Thai radar installation at Phuket. An AFP report from March 2014 quoted Thailand’s Air Marshal Monthon Suchookorn as saying that Thai radar detected the plane “swinging north and disappearing over the Andaman Sea,” although “the signal was sporadic.”

At 18:22, the plane was approximately 150 miles from Phuket. This is well beyond the range at which Penang had ceased being able to detect the plane. What’s more, when the plane had passed VAMPI it had been only about 120 miles from Phuket. If it hadn’t seen the plane when it was at VAMPI, how was it able to detect it when it was 30 miles further? And why just for a momentary blip?

I don’t believe that, as some have suggested, the plane climbed, was detected, and then dived again. As Victor Iannello has earlier pointed out, the plane was flying at around 500 knots, which is very fast, and suggests a high level of motivation to be somewhere else, not bleeding off speed through needless altitude changes.

I propose that what happened at 18:22 was that the plane was turning. Entering into a right bank, the plane would turn its wings temporarily toward the Phuket radar station, temporarily presenting a larger cross section. Then,  when the plane leveled its wings to straighten out, the cross section would shrink, potentially causing the plane to disappear.

Why a right bank? The diagram at top is an annotated version of one presented in the DSTG’s “Bayesian Methods” book. The vertical white line is the 18:25:27 ping arc. The orange line represents the path from the 18:22:12 radar detection to the first ping arc. It is 13 miles long. To travel 13 miles in 3.25 minutes requires a ground speed of 240 knots. Prior to final radar return, MH370 was traveling at approximately 490 knots. A plane can’t slow down that quickly without a radical climbing maneuver, which can be dangerous at cruise altitude (cf Air France 447.)

If it had continued at its previous pace, the plane would have traveled 26.5 miles in that time — enough to carry it to the unlabeled yellow thumbtack. Or, to turn to the right and take the path shown in green.

I don’t mean this path to seem so precise and deterministic; there are errors associated with both the position of the ping arc and the radar return. The ping arc, for instance, is generally understood to have an error bar of about 10 km. If the ping arc radius is 10 km larger, and the radar hit location stays the same, then the heading will be be 336 degrees instead of 326 degrees; if the ping radius is 10 km smaller, the angle will be 310 degrees, representing just a 20 degree right turn from a straight-ahead path.

It does not, however, seem possible that the combined radar and ping-arc errors will allow a scenario in which the plane continued on its VAMPI-to-MEKAR heading and speed. As the “Bayesian Methods” book puts it, “the filtered speed at the output of the Kalman filter is not consistent with the 18.25 measurement, and predictions based purely on primary radar data on this will have a likelihood very close to zero.” Neil Gordon confirmed to me in our conversation that something must have changed.

Dr Bobby Ulich, in his recent work examing different flight-path scenarios, has also concluded that the plane turned north at this time. He looked at a southern turn, too, but observed that “the left-hand turn… needs a turning rate higher than the auto-pilot bank limit allows.”

Looking at the over picture of MH370’s first hour post-abduction, we note that:

  • The timing of the silencing of the electronics was coordinated to within several seconds to the optimum time to evade detection.
  • The 180-degree turnaround maneuver was highly aggressive.
  • The plane’s course allowed it to remain in Malaysian airspace. After Penang it stayed closer to the Indonesian FIR (lower black line) than the Thai FIR (upper black line).
  • Post diversion, the plane was traveling at high speed, faster than normal cruise flight. This suggests that whoever was flying it was motivated to escape primary radar surveillance–they wanted to get away.
  • When last observed, MH370 was likely making a turn to the northwest, in the general direction of Port Blair in the Andaman islands. This is consistent with Air Marshal Monthon Suchookorn’s assertion that Thai radar detected the plane “swinging north and disappearing over the Andaman Sea.”

The overall shape of the flight path from IGARI to 18:25 is U-shaped, curving around Thai airspace. In the Malacca Strait it remained closer to the Indonesian side than the the Thai side. It is possible that the turn at 18:22 resulted from a compromise between two goals: to stay beyond the detection range of the radar station at Phuket, and to travel in a northwesterly direction.

It is widely believed that, since the plane presumable ended up in the southern Indian Ocean, the flight up the Malacca Strait was undertaken in order to avoid penetrating Indonesian airspace en route to the southern ocean. If this were goal, and the person flying the plane should have turned to the left at 18:22, onto a westerly or west-southwesterly heading.

The fact that they did not suggests that, whatever ultimately transpired aboard the plane, the goal prior to the “final major turn” was a destination to the northwest, and that the reason the plane flew southwest from IGARI before turning northwest was to avoid Thai airspace and radar surveillance.