It will not be long before accident investigators reveal the reasons why the Jeju Air Boeing 737-800 crew felt they had to commit to a flapless, gearless landing on runway 19 at Muan, South Korea. But the reason so many people died was not the landing as such, but the fact that the aircraft (HL8088) collided with a very hard obstruction just beyond the runway end.

That collision broke up the hull and caused a conflagration. What was the obstruction, and why was it positioned on the runway extended centreline only about 200m beyond the runway threshold?

It looks as if it was a concrete anchorage for the Instrument Landing System (ILS) antenna array. ILS antennae are often just beyond runway ends, but they are normally designed to be frangible so any aircraft that collides with them suffers only minor damage. This was hard. Very, very hard.

The sequence of events that led to this accident began with the aircraft approaching runway 01, cleared to land, but the crew elected to go around just after ATC had warned them of a potential birdstrike. It looks as if a birdstrike did, indeed, take place, and the crew declared a Mayday emergency shortly after that.

The crew then elected to land on the same runway but in the opposite direction – on runway 19. This was not much of an issue because the wind was very slight and the visibility was excellent.

But when they returned for the fatal landing on 19 they touched down with no flaps and no landing gear. Why? Perhaps because the birdstrike caused the right engine to fail, and all or some of the hydraulics with it. And the gear and flaps are hydraulically powered.

We don’t know yet, but we will know soon.

Meanwhile the touchdown was as good as a flapless/gearless touchdown could be: wings level, nose not too high to avoid breaking the tail. But being flapless, the airspeed was very high – probably around 200kt.

Look at the video of the landing run. The aircraft slid the full length of the runway with the fuselage, wings and engines substantially intact, and with no fire. It slid over the end still going fast – maybe 70kt or so, but still with no further substantial damage to the structure and no fire.

Then the aircraft hit the obstruction about 150m beyond the hard runway overrun, but until impact it remained substantially undamaged and fire-free. At impact, the hull buckled and broke up, the wing fuel tanks were ruptured and instantly exploded into flames. The wreckage came to rest just beyond the obstruction, near the wire perimeter fence.

If the obstruction had not been there, the aircraft would have slid through the antenna array, across the level ground beyond it, and through the wire perimeter fence. It would have come to rest with most – possibly all – those on board still alive.

We will soon find out the whole truth about why the landing took place as it did. But because the accident killed all on board except two of the cabin crew, those answers will be almost academic. The question to answer is: what was that obstruction, and why it was there?