The Hendra sighting and the right-left flame-out sequence

01 Feb 2019, 08 Feb 2019

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Upfront: The early press reports about this sighting state it was on the morning of Sunday 9th March WIB, on which date it would be completely impossible to see the missing plane. Some readers may choose to reject the sighting for that reason. This author however believes that the date stated in early press reports is likely to be incorrect, and that this sighting should be taken seriously.

Indonesian fishermen Hendra, Fadli, Agus, and Sahroni, on their small fishing boat in the northern Malacca Strait, saw a plane circling lower and lower, emitting smoke, and descending towards the ocean.

This article compares their observations of the plane, and the final descent sequence predicted by the official investigation.

Hendra sighting

The official investigation has predicted this flame-out sequence:
First the right engine stops working due to fuel exhaustion.
Some minutes later, the left engine stops working due to fuel exhaustion.

The following details about the Hendra sighting are from source [1].

(A) "mereka ada melihat ... pesawat tersebut berputar-putar semakin rendah"
"they saw ... the plane circling lower and lower"

Interpretation: This is consistent with the period after the right engine had already stopped working. The plane is flying with thrust from the left engine only. The ATC (Asymmetric Thrust Compensation) system would attempt to correct for this. If that system managed to achieve only partial correction, the plane would circle. The news reports do not state whether the plane was circling clockwise or anticlockwise during this first part of the sighting. If the interpretation here is correct, the circling would be clockwise on a map.

(B) "Saat putaran kedua, pesawat ... terbang dalam kondisi miring ke kiri."
"On the second circling, the plane ... flew away in a tilted state to the left"

Interpretation: this is consistent with the moment the left engine stops working. There is now zero thrust, which is symmetrical thrust. However the rudder is still in the state previously set by the ATC system when the plane had left thrust only. Therefore when the left engine stops, this causes a roll/turn to the left.

Next comes the most intriguing observation of this sighting: the words in bold below.

(C) "Saat putaran kedua, pesawat mengeluarkan asap di bagian kanan belakang dan terbang dalam kondisi miring ke kiri"
"On the second circling, the plane emitted smoke from its right rear part and flew away in a tilted state to the left"

Interpretation: There appears at first to be no possible way for flame-out of the left engine to cause the observed smoke from the right rear of the plane. However in fact there is one system which is automatically activated when the second engine stops, is located near the rear of the plane, and is capable of of emitting smoke if it fails or malfunctions: The APU (Auxiliary Power Unit) system.

The sequence predicted by the official investigation includes this further detail: that upon flame-out of the left engine, there would be an automatic attempted start of the APU.

The APU is located at the rear of the plane, and some of its components are located in the right rear part of the plane, for example its fuel drain mast, and its battery. Is it possible that malfunctioning of various other systems during the flight may have adversely affected the APU and the APU battery? Might this have caused the APU system to malfunction when it was started, and emit the observed smoke from the right rear? These questions will be examined in a later addition to this article.

This article has shown that the observed path of the plane in the Hendra sighting is consistent with the predicted right-left flame-out sequence.
Also it has conjectured that the witnesses may also have seen a malfunctioning of the predicted automatic APU start.

To be continued ...


[1] https://www.merdeka.com/peristiwa/sekelompok-nelayan-sumut-lihat-pesawat-jatuh-di-selat-malaka.html

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